International Journal of Oil, Gas and Coal Technology (132 papers in press)
Production Decline Analysis of Oil and Gas Resources with Robust Fit and Time Series Analysis
by Huazhou Li, Di Niu, Octavianus Wiliantoro
Abstract: Production decline analysis is widely used in petroleum industry for many purposes such as reserve estimation, well/field life span prediction, and economic analysis. In this paper, a comprehensive study is conducted to evaluate, enhance and compare the performance of both parametric (i.e., the Arps exponential decline model and Duongs model) and nonparametric (ARIMA) models in terms of their application in production decline analysis. Instead of using ordinary least-squares fit, we propose to apply robust fit to train the parameters in Duongs model (2011) and Arps exponential decline model (1945), which improves the accuracy of these two popular decline models. We also propose to apply time series analysis, in particular, an ARIMA model with novel preprocessing techniques to obtain probability distributions for the predicted production rates. Based on the production data collected from 11 wells, we demonstrate that robust fit can create more accurate linearization and better model the trend of production data than the conventional ordinary least-squares fit in Duongs model (2011), although it gives comparable performance as the ordinary least-squares in Arps exponential decline model (1945). We further show that the proposed ARIMA model can easily yield the 90% confidence interval as well as the P50 prediction at a lower cost, as compared to the Monte Carlo method that is normally needed to generate probabilistic results in Duongs and Arps exponential decline models. Compared to the original Duongs model (2011) and the enhanced Duongs model (2011) with robust fit, our proposed ARIMA model is able to provide significantly higher accuracy in terms of P50 predictions.
Keywords: Production decline analysis; robust fit; reservoir engineering; ARIMA model.
The Novel Use of Malonic Acid based Deep Eutectic Solvents for Enhancing Heavy Oil Recovery
by Yahya Al-Wahaibi, Iman Al-Wahaibi, Rashid Al-Hajri, Baba Jibril, Suleiman Shuwa
Abstract: This study investigates the potential of deep eutectic solvents (DES) to recover the residual oil left after waterflooding. For the first time to our knowledge, the effectiveness of two DESs - choline chloride-malonic acid of molar ratios 1:1 and 1:0.5 - in enhancing oil recovery was investigated. The solvents were characterized by measuring density, viscosity, conductivity and pH at different temperatures. Also, measurements of interfacial tension, wettability alteration, spontaneous water imbibition, emulsification, core flood and formation damage tests were conducted at different temperatures. The core flood tests were carried out at reservoir condition using Berea sandstone cores and fluids from the field of interest. Results showed the solvents produced 7-14% of the residual heavy oil after brine flooding as tertiary recovery stage and without causing any formation damage. Both DESs showed better performance at higher temperatures. Wettability alteration was found to be the dominant mechanism for the oil recovery enhancement.
Keywords: residual heavy oil; deep eutectic solvents; interfacial tension; wettability alteration.
Colloidal stability and hot filtration test of residual fuel oils based on visbreaking and ebullated bed residue H-Oil hydrocracking
by Dicho Stratiev, Ivelina Shishkova, Natalia Vanova, Anife Veli, Radoslava Nikolova, Magdalena Mitkova, Kiril Stanulov, Georgi Argirov, Dobromir Yordanov
Abstract: Six H-Oil based residual fuel oils, two H-Oil atmospheric tower bottom products, two H-Oil vacuum tower bottom products, one visbreaker based residual fuel oil, and three different straight run vacuum residual oils were studied in this work. The colloidal stability parameters S-value (ASTM D 7157), and separability number (ASTM D 7061), along with SARA based colloidal instability index, and the solubility parameters of asphaltene and maltene fractions of the studied residual oils were tested to correlate with the residual oil sediment content. It was found that none of the colloidal stability parameters correlated with the residual oil sediment content, while correlations were found between the different colloidal stability parameters. This study has shown that only the residual oil samples whose S-value has been at minimum of 1.375 kept their sediment contents without change with the course of time.
Keywords: residue colloidal stability; S-value; separability number; solubility parameters; hot filtration test; SARA; colloidal instability index.
A New Sorption-corrected Deconvolution Method for Production Data Analysis in a Shale Gas Reservoir Containing Adsorbed Gas
by Joohyung Kim, Youngho Jang, Hyeok Seomoon, Wonmo Sung
Abstract: When characterizing a reservoir with the production data acquired from a shale gas well, the rate-normalized pressure (RNP) method is widely used due to its simplicity. However, for sharply varying production data, such as production and shut-in of a well, the RNP method yields erroneous reservoir characteristics. On the other hand, the deconvolution method can overcome these limitations, but it is only applicable for linear pressure-rate relationships. That is, it is not appropriate for production data acquired from a reservoir containing adsorbed gas. This production data shows nonlinear pressure-rate relationship due to the compressibility of desorbed gas, which strongly influenced by the pressure. In this study, in order to utilize the deconvolution method to analyze sharply varying production data containing adsorbed gas in a shale gas reservoir, we propose the linearized relationship of the sorption-corrected pseudopressure and production rate by using a variable substitution method such that it can be correctly implemented for deconvolution. From the results of sorption-corrected deconvolution method, we conduct pressure transient analysis for obtaining shale gas reservoir characteristics.
Keywords: sorption-corrected pseudopressure; deconvolution; desorption; shale gas; production data analysis; variable production rate.
CFD SIMULATION OF AN OIL - WATER SKIMMER TANK
by Jean Coll, Antonio Bula, Luis Arias, Nestor Durango
Abstract: Water recovery from oil wells is an environmental necessity. In order to achieve this goal, an air bubble technique is used to separate water from oil. This technique is being developed for usage in oil fields, and Computational Fluid Dynamic, CFD, simulation is helping to improve the cleaning efficiency of the process. In this paper, the separation of an oil-water mixture using an air bubble stream in an open tank, Skimmer Tank, is implemented. The simulation was performed using a commercial computational fluid dynamics software, CFD, Star CCM
Keywords: Skimmer tank; CFD simulation; Multiphase modelling.
Investigation of semi-interpenetrated networks gel for water production control in a mature offshore oilfield
by Qin Yu, Xiangguo Lu
Abstract: Water flooding as the dominant method to improve oil recovery has been widely applied to most oilfields in the world; however, excess water production has become a major problem for reservoirs that have been flooded by water for many years. The objective of this paper is to prepare and evaluate a novel strong gel that can be used to significantly reduce the permeability of the fluid channels resulting from water flooding. We developed a novel fluid diversion agent called CPP gel, which is a semi-interpenetrated networks gel cross-linked by acrylamide grafting onto sodium carboxymethyl cellulose / polyglycol. The paper investigated its applicability with the Bohai offshore oilfield reservoir conditions. The gel properties, including the rheological performance and blocking efficiency, as well as its influencing factors were investigated. The results showed that the CPP had less injection pressure but higher blocking efficiency than conventional polymer gels, and its blocking efficiency was dependent on the gel components, temperature, water salinity, rock permeability and rheological properties. The decrease in the network chain length, the increase in the interactions among molecules and the increase in the uniformity of the overall network structure could contribute to the enhanced blocking mechanisms.
Keywords: semi-interpenetrated network; blocking efficiency; rheological property; influence factors; blocking mechanism.
Prediction of production performance by comprehensive methodology for hydraulically fractured well in coalbed methane reservoirs
by Hochang Jang, Jinyoung Park, Jeonghwan Lee
Abstract: Production data from hydraulically fractured well in coalbed methane (CBM) reservoirs was analyzed using decline curve analysis (DCA), flow regime analysis, and flowing material balance to forecast the production performance and to determine estimated ultimate recovery (EUR) and timing for applying the DCA. To generate synthetic production data, reservoir models were built based on the CBM properties of the San Juan Basin and Appalachian Basin. Production data analysis shows that the transient flow (TF) occurs for 1~3 years in the vertical well and 6~16 years in the horizontal well and then the boundary dominated flow (BDF) was reached. In the TF period, it is impossible to forecast the production performance. In case of vertical well, if the production data are available for more than 3 years after the BDF has been reached, the production rate and EUR can be predicted with EUR error of approximately 5%. In the case of a horizontal well, the prediction can be conducted using the production data of more than a year after reached BDF with EUR error of approximately 5%.
Keywords: Coalbed methane; Production decline curve analysis; Flow regime analysis; Hydraulic fracturing.
Imaging of Pipeline Irregularities Using a PIG System Based on Reflection Mode Ultrasonic Sensors
by Zainal Zakaria
Abstract: Natural gas transmission pipelines age after a certain duration and are prone to internal anomalies due to the presence of carbon dioxide (CO2) and hydrogen sulphide (H2S) in the natural gas constituents. An Intelligent Pipeline Inspection Gauge (PIG) is one method that is used to evaluate pipeline integrity, particularly damage resulting from corrosion threats. In this paper, an Ultrasonic Prototype PIG was developed that incorporates reflection mode ultrasonic sensors to measure anomalies on the internal surfaces of pipelines. The ultrasonic PIG instrumentation system consists of ultrasonic sensor modules, conditioning circuits and a Data Acquisition System (DAS). Sixty ultrasonic sensors were used based on a transceiver mode at a frequency of 390 kHz. Surface anomalies were simulated at different locations on the internal surface of the pipeline to simulate changes in the pipe wall thickness. The ultrasonic wave was transmitted from the ultrasonic sensor, and the wave was propagated toward the internal wall of the pipeline before it was reflected back to the ultrasonic sensor. The output signal of the ultrasonic sensor was recorded by the DAS in the form of DC voltage, which indicated the distance between the ultrasonic sensor and the internal wall of the pipeline. Variation in the measured distances implied the existence of surface anomalies. The results showed that the percentage error was less than
Keywords: Pipeline; PIG; Ultrasonic; Reflection; Corrosion.
Study on the productivity of the multi-stage fractured horizontal wells in tight oil reservoirs
by Linjing Xu, Shicheng Zhang, Fei Wang, Xinfang Ma
Abstract: Production in a multi-stage fractured horizontal well in tight oil reservoirs is a complex process involving multiple pore/fluid transports and interactions. Because of the limited understanding of the underlying flow mechanisms in fractured tight oil reservoirs, the well production performance has not been modeled comprehensively with existing simulators. In this paper, a comprehensive dual-porosity and dual-permeability oil/water flow model that uses experimentally determined reservoir properties to simulate the well performance of hydraulically fractured tight oil wells was established. A numerical simulator was then developed based on the proposed flow model, which has been validated by the commercial simulator Eclipse and field production data. A numerical simulation of the well productivity in fractured tight oil reservoirs with the effect of threshold pressure gradient, stress-sensitive matrix permeability, stress-sensitive fracture conductivity, and capillary pressure was conducted, revealing that those factors affect the well productivity in different degrees. Thus, sensitivity analysis of those factors was conducted. The results indicate that the presence of threshold pressure gradient can significantly reduce the well productivity. The impact of stress-sensitive matrix permeability coefficient should be significant to cumulative oil production in high stress-sensitive tight oil reservoirs. The maintaining of the fracture conductivity is vital for the economic development of tight oil reservoirs. Besides, the capillary pressure has non-negligible impact on oil production. This study provides a basis for long-term tight oil production analysis, oil/water flow simulation and post-treatment productivity prediction of hydraulically fractured tight oil wells.
Keywords: tight oil reservoir; multi-stage hydraulic fracturing; well productivity; multiphase flow simulation; horizontal well.
Prediction of Two-Phase Compressibility Factor in Gas Condensate Reservoirs Using Genetic Algorithm Approach
by Ehsan Kamari, Saber Mohammadi, Mohammad Mahdi Mohammadi, Mohsen Masihi
Abstract: As experimental determination of two-phase compressibility factor in gas condensate reservoirs is expensive/time-consuming, developing a reliable theoretical-based method is vital for this purpose. Here, based on data of constant-volume-depletion experiments, genetic algorithm method was used to develop a correlation for estimating the two-phase compressibility factor in gas condensate reservoirs. The proposed correlation was validated with experimental data of five gas condensate reservoirs, and also compared with most reliable correlation presented in the literature by Rayes et al. (1992). It was found that the proposed correlation by genetic algorithm predicts the experimental values of two-phase compressibility factor with a good accuracy and better than the Rayes et al.'s (1992) correlation.
Keywords: Gas Condensate; Two-Phase Compressibility Factor; Genetic Algorithm; Correlation; Experimental.
Wongawilli roadway backfilling coal mining method - a case study in wangtaipu coalmine
by Liqiang Ma, Zhiyuan Jin, Wenpeng Liu, Dongsheng Zhang, Yao Zhang
Abstract: The current backfilling coal mining methods still have many limitations, such as lack of filling time and filling space and poor coordination between filling time and filling space. On the basis, this paper proposed the Wongawilli roadway backfilling coal mining method (WRBCM). As a pattern of backfilling while mining, WRBCM gives fully play to the advantages of the Wongawilli mining method and the backfilling mining method. The research results have been put into practice in Wangtaipu coal mine. As the recovery ratio of coal resources in the panel reached 96.8%, the values of surface deformation were smaller than the indicators for building damage grade I in China. WRBCM also implements the safe and efficient coal mining deposited under buildings, railways and water bodies.
Keywords: Wongawilli Roadway Backfilling Coal Mining Method (WRBCM); Mining roadway(MR); Mining phase; Backfilling while mining.
Oil Price Prediction Using a Supervised Neural Network
by Adnan Khashman, Claudia Georgeta Carstea
Abstract: Many attempts have been made at designing efficient prediction systems for oil price due to the impact of oil on the worlds economy. In this paper we present an efficient oil price prediction system based on using a supervised neural network. The neural model receives at its input novel key economic and seasonal indicators, which we extract from the West Texas Intermediate (WTI) dataset of crude oil prices over 24 years. The model predicts at its output weekly oil prices within five dollars/barrel accuracy. The experimental results reveal that the obtained correct prediction rate of 88% is higher than rates reported in other related works, thus indicating that neural networks can be effectively used for predicting oil prices.
Keywords: crude oil; price prediction; forecasting; neural networks; intelligent data modelling; artificial intelligence.
A New Model for Fracturing Fluid Leak-off in a Single Natural Fracture
by Cong Lu, Xinghao Gou, Jianchun Guo
Abstract: Hydraulic fractures can open or penetrate natural fractures when naturally fractured oil and gas reservoirs are hydraulically fractured. Meanwhile, fracturing fluids enter the natural fractures, significantly increasing the leak-off volume. This paper proposes a new model of fracturing fluid leak-off in a single activated natural fracture, taking the deposition of solid-phase residues into account. The impact of leak-off on the viscosity of the fracturing fluids, volume concentration of the solid-phase residues, and critical natural fracture width were analysed using example calculations. The leak-off in a natural fracture mainly occurred in the beginning when the fracturing fluids enter the fracture. Within a few minutes, the viscosity of the fracturing fluids, the particle size, and dosage of solid-phase residues reached an optimal value range. The model calculation results provide guidance for the control of fracturing fluid leak-off in a natural fracture.
Keywords: natural fracture; hydraulic fracturing; leak-off; numerical model; filling zone.
Optimisation of Steam and Gas Push to Prevent Water Influx from a Top-Water-Bearing Area into a Vapor Chamber
by Sunghoon Chung, Joe M. Kang, Changhyup Park, Baehyun Min, Ilsik Jang
Abstract: This paper presents a strategic operation to mitigate the groundwater influx from a top-water-bearing zone into an oil sands reservoir. The impact of naturally occurring and/or co-injected non-condensable gas on bitumen production was investigated using numerical studies. Non-condensable gas can improve energy efficiency in two ways: reduction of dynamic vacuum effect and blockage of direct contact of steam chamber and top water layer. An optimisation scheme based on an Artificial Neural Network (ANN) model was suggested to alleviate the detrimental effect from the top water layer. The ANN model adjusts both pressures of steam and non-condensable gas injected as well as the amount of non-condensable gas, which maintain the adequate pressure within the steam chamber enough to prevent excessive water influx. The results show the proposed optimization scheme can improve the energy efficiency of thermal recovery for bitumen production by maintaining the pressure within steam chamber. Increasing the injection pressure of steam and gas and the amount of gas co-injected with steam were recommended when the growing Steam Assisted Gravity Drainage (SAGD) vapor chamber reaches the top-water-bearing stratum. At the end of the production stage, the amount of non-condensable gas should be maintained at a high mole fraction to prevent water influx from the thief zone, while the injection pressure decreases gradually to utilise the latent heat in the chamber.
Keywords: steam and gas push; oil sands; top-water-bearing zone; steam chamber; energy efficiency.
Petroleum Geochemistry, Burial History and Shale Gas potential of the Goldwyer Formation (Canning Basin, Western Australia)
by Amir Karimian Torghabeh, Reza Rezaee, Nuno Pimentel, Lukman Johnson, Munther Alshakhs
Abstract: Global natural gas consumption is rapidly growing worldwide, therefore it is becoming increasingly difficult to satisfy this increasing demands by conventional resources. Shale gas is considered as an unconventional resource for natural gas production. There are several organic-rich shale horizons in the Canning Basin, Western Australia, which serve as source rocks for conventional oil and gas fields. The aim of this study is to investigate the Goldwyer Formation in the Canning Basin as a potential shale gas play. The Goldwyer Shale is Ordovician in age, the same as the Utica Shale in Ohio and Pennsylvania, USA. Geochemical analysis, such as Rock-Eval pyrolysis, total organic carbon (TOC) estimation, as well as thermal and burial history modeling were used in this study. A trend of increasing maturity in the west central part of the basin can be seen on thermal maturity data. The total organic carbon (TOC) content varies between 0.16 and 4.8 wt%. The studied interval has reached thermal maturity between 0.71 1.3 Ro%, therefore in main oil to wet and dry thermogenic gas zones, depending on the location. The organic matter is mixed Type II/III kerogen, the measured Tmax ranges from 335 oC to 471 oC. The results of our study show that the Goldwyer shale may be considered as potential shale-gas play.
Keywords: Shale-gas; Burial history; Thermal modeling; Canning Basin; Goldwyer Formation.
Mechanistic Study of Steam Assisted Gravity Drainage in Heavy Oil Naturally Fractured Reservoirs
by Ali Fattahi, Hamed Akhondzadeh, Mohd Nawi Derahman
Abstract: While SAGD has been applied in tar sands for years and its mechanism is well understood, the SAGD process mechanism in heavy oil Naturally Fractured Reservoir (NFR) has not been studied yet. In this paper, the mechanism of SAGD in NFRs was studied numerically through sensitivity analysis of some influential reservoir parameters. According to the results of this study, initial fracture water saturation plays a conspicuous role in production from such reservoirs, and consequently SAGD process can be initiated without preheating in NFRs. The presence of initial fracture water saturation causes large amount of water production providing voidge for large amounts of steam injection possibility, hence fast steam chamber creation. Based on simulation results, in oil-wet reservoirs, oil drainage takes place inside the steam chamber. In water-wet media, however, capillary imbibition contributes to oil recovery behind the steam chamber in hot water zone. The index Km/Lm was introduced which combines matrix permeability and size to propose a determining factor for matrix oil drainage rate. The controlling term of Kf Sfw/
Keywords: Fractured reservoirs; Heavy oil; SAGD Mechanism; Enhanced Oil Recovery.
Weak interaction between water molecules and different rank coals: A DFT-D3 study
by Yongjin Liao, Zhengyang Gao, Weijie Yang, Jun Zhong, Yi Ding
Abstract: Weak interaction between water molecules with different rank coals was studied by density functional theory with dispersion correction (DFT-D3) in quantum chemistry method. In order to fully discuss microscopic mechanism, anthracite, bituminous, subbituminous and lignite were selected as the typical rank coals. The equilibrium configurations of water molecular on the surface of coal molecules were optimized, analysis of electrostatic potential on the surface of coal molecule was conducted, and interaction energy between coal molecular surface and water molecular was calculated, as well as interaction types of water on the different rank coals molecular surface were confirmed by calculating the reduced density gradient function (RDG). Research indicates that the adsorption process of water molecular on coal molecule surface belongs to physical adsorption. Lignite is more likely to interact with polar water molecules owing to its largest molecular surface area with large electrostatic potential. Rich functional groups on the surface of lignite are the main reason why lignite surface contains large electrostatic potential. The electrostatic potential of coal surface determines whether coal is easy to adsorb water molecules. The maximum adsorption interaction energy of four different rank coals adsorbed water molecular can be in the order of lignite > subbituminous > bituminous > anthracite, rivaling that water molecules adsorption on the surface of lignite is the most stable. Adsorption interaction energy is related to interaction type, while there is no obvious relationship between the deformation of adsorption process and adsorption interaction energy. Interaction type between coal and water molecular can be obtain clearly from RDG color contour map and adsorption interaction energy can be compared and explained from RDG scatter plot.
Keywords: coal; adsorption water; interaction type; electrostatic potential; RDG analysis.
Development of a Fully Implicit Simulator for Surfactant-polymer Flooding by Applying the Variable Substitution Method
by Zhichun Jia, Daolun Li, Zhenggang Xue, Detang Lu
Abstract: A PEBI (Perpendicular Bisection) gridding based two-phase five-component fully implicit simulator for polymer-surfactant flooding is proposed which utilizes the substitution of variable method in the numerical calculation procedure. The substitution of variable method utilizes two sets of primary variables based on the phase equilibrium states. When an oil-microemulsion system exists, the primary variables to be solved are the oil phase pressure po and the volume concentrations of oil, polymer, surfactant and salt in the microemulsion i.e., Com, Cpm, Csm and Cbm. When a single microemulsion is formed, the primary variables are po, Sm, Cpm, Csm and Cbm. A fully implicit iterative scheme is established based on the substitution of variable formulation in which separate forms of linearized equations are derived according to oil phase disappearance or appearance during a time step which reduces the number of primary variables. The calculation speed of the new simulator is compared to a conventional fully implicit simulator. Results show that by utilizing the substitution of variable method the calculation speed is significantly improved compared with the fully implicit simulator without using substitution of variable method.
Keywords: fluid mechanics in porous medium; enhanced oil recovery; reservoir simulation; phase behavior.
Study of Novel Self-initiated Aggregating Proppant for Channel Fracturing
by Kaili Liao, Jijiang Ge
Abstract: Channel fracturing is a promising technique for unconventional reservoir stimulations. Fibers bonded proppants and resin coated proppants are the two common technologies used for heterogeneous proppant placement. This paper discusses a new kind of surface modified proppant with the unique performance of self-initiated aggregating property in distilled water and guar gum fracturing fluid, which is suitable for keeping proppant cluster together during transportation in the wellbore and fracture. The changes of the zeta potential of the proppant grains and the intertwining effect of the polymer coating account for the self-initiated aggregating property. An evaluation method for measuring the self-initiated aggregating strength of the proppant column was introduced, with which the aggregating speed and the aggregating perdurability were evaluated. Due to the re-aggregating property, the fracture conductivity was significantly improved, and the higher the closure stress, the more obvious the advantages. The findings of this study provide a new alternative for channel fracturing.
Keywords: self-initiated aggregating proppant; channel fracturing; surface modification; evaluation method; fracture conductivity; heterogeneous proppant placement.
Colloidal stability tests on vacuum residue hydrocracked products obtained at increasing severity
by Kirtika Kohli, Ravindra Prajapati, Nivedita Singh, Samir K. Maity
Abstract: Stability of the thermally hydrocracked products has been investigated by measuring different parameters such as colloidal instability index (CII), Stankiewicz plot (SP), qualitative-quantitative analysis (QQA), stability cross plots (SCP), spot tests, merit number, and separability number (SN). Each parameter is measured in the products obtained from two vacuum residues having different asphaltene content. The stability of the hydrocracked product is different for the different parameters. But in general, the products obtained at lower and higher temperature are stable by most of the parameters. Spot test and separability number gives the similar results. Interestingly, it is found that the product obtained at 420OC from low asphaltene content feed is unstable by all above said stability parameters whereas the product (at 420OC) from high asphaltene content feed is stable, indicating that the stability of a hydrocracked product depends not only on the asphaltene content of a feed but also the nature of other components such as aromatic and resin. It is also observed that CII and SP parameters which are calculated from SARA fractions also predict colloidal stability with good agreement.
Keywords: colloidal instability index; stability cross plot; separability number; asphaltene.
Water/Oil Cresting in Horizontal wells, A Sensitivity Study
by Hector Akangbou, Martin Burby, Ghasem Nasr
Abstract: This work presents a rigorous sensitivity analysis on cresting using a physical model, to investigate the effects of varying oil viscosity, inclined section and lateral insertion lengths of a horizontal well. This was investigated in both thick- and thin-oil rim homogeneous reservoirs faced with strong bottom aquifer and considerable gas cap.
From the results, it was observed that the geometry of the horizontal well and location of the bottom water injection points significantly influence the cumulative liquid produced, particularly in thin-oil rim reservoirs. The cumulative water produced and cumulative Water Cut were found to increase with an increase in oil viscosity. The oil recovered from the thin-oil rim reservoir, were as high as 17.84% and 24.92% for oil viscosity of 50 cP and 100 cP respectively, whereas water cuts of 19.15% and 13.93% were observed for cumulative water produced in thick-oil rim reservoir at 50 cP and 100 cP respectively.
Keywords: Cresting; oil recovery; Water Cut; reservoir homogeneity; horizontal wells; Gas-Oil- Contact; Water-Oil-Contact; strong bottom aquifer; pressure drawdown; optimization.
Optimization of Well Rates under Production Constraints
by MARCIO AUGUSTO SAMPAIO PINTO, Ana Teresa Ferreira Da Silva Gaspar, Denis José Schiozer
Abstract: The optimization of well rates of an oil field can increase oil recovery and reduce water production, maximizing production life-cycle economic gains. A way to improve the oil field management involves designing optimal production strategies by dynamically adjusting the production wells flow rates under production constraints of platform. A major difficulty occurs in establishing the rules for optimizing production of wells, according to constraint for the long term production of a field. The optimal controls are often difficult to obtain, in practice, due to the large number of control variables to be adjusted during the optimization process, requiring a large amount of computational infrastructure. Therefore, we have tested some options of well control available in a commercial simulator. These controls employ parameters of production in real time to calculate the well rates under production constraints (platform capacity). These assessments were made in two ways: (1) with default parameters in the formulas used in these controls and (2) with hybrid optimization in each type of control. This hybrid optimization corresponding to a higher level, a fast genetic algorithm (FGA), which is a robust and an indicated method for sweeping the solution space with many variables. However, due to its low efficiency in finding the local maximum, a lower level optimization in our framework was employed through a non-linear conjugate gradient (NCG). This approach was applied to UNISIM-I-D benchmark case with production strategy previously optimized by Gaspar et. al. 2015, testing the process of adjusting flow rates of wells in a complex reservoir with several production and injection wells. We tested different types of controls to perform an apportionment of wells under constraints, comparing the advantages and disadvantages of each type of control in the optimization process. The results showed an improvement in reservoir management by additional gains of NPV for the entire time production and through the proposed robust optimization algorithm, showing advantages of the better well operations without additional investments.
Keywords: Optimization; Apportionment of Well Rates; Reservoir Management; Hybrid Optimization.
Numerical Simulation of Transport Behaviour of Small Cuttings in Extended Reach Wells
by Titus Ofei, Sulaiman Yaaqob
Abstract: In the drilling of extended reach wells, cuttings transport becomes a challenging phenomenon to carry out due to the accumulation of cuttings to form cuttings bed in the narrow gap of eccentric annuli. Therefore, efficient hole cleaning is essential in the design of the hydraulic program. Several parameters govern cuttings transport which include fluid rheology, drillpipe rotation, cuttings size, flow rate, and hole inclination. While many extensive researches have been conducted in the past decades on individual parameters accountable for cuttings transport, a key problem persists, in that, hole cleaning collectively depends on a combination of parameters. The purpose of this study is to examine the effect of drillpipe rotation and cuttings size on hole cleaning efficiency in a horizontal annulus flowing with a non-Newtonian fluid. It adopts computational fluid dynamics (CFD) simulation to predict annular pressure losses, cuttings concentration profiles, and cuttings velocity profiles. An experimental benchmark case study was identified in literature and the numerical model was validated against such that it replicates the behavior of the experiment. The study showed that the combination of Wen-Yu drag force model and k-epsilon turbulence model closely predicted the experimental data. The impact of non-drag forces was however negligible. The results indicated that drillpipe rotation improves the transport efficiency of small cuttings of size 0.5 mm better than larger cuttings size of 5 mm. Annular pressure losses increased with increasing drillpipe rotation but decreased with increasing cuttings size. This study is very unique as it reveals various flow patterns that may occur during drilling operation with different cuttings size and drill pipe rotation speeds. It also serves as a guide to optimize drilling hydraulics for efficient hole cleaning in extended reach wells.
Keywords: Cuttings transport; hole cleaning; extended reach drilling; Computational Fluid Dynamics (CFD); pressure loss; drillpipe rotation; cuttings concentration.
Accurate prediction of some properties of petroleum fuels and coal liquids
by Tareq Albahri
Abstract: New correlations are developed to calculate the molecular weight, the carbon to hydrogen weight ratio, and the aniline point temperature for petroleum fractions and coal liquids over a wide range (70 < MW < 1685 g/mol, 5.4 < C/H< 15.1, and 45.5 < AP < 106.4 ⁰C), using the average boiling point and the standard specific gravity as input parameters. The developed correlations are more accurate than similar ones in the literature with squared correlation coefficients of 0.9853, 0.95 and 0.9452 for MW, C/H and AP, respectively. The proposed correlations have the advantage of combined accuracy, simplicity and convenience compared to similar methods. They cover a wider property range and apply to petroleum fuels and coal liquids as well. In addition, examples are provided to utilize the predictions of the developed correlations to calculate the average molecular formula for fuels and coal liquids.
Keywords: Aniline point; C/H ratio; Coal Liquids; Molecular weight; Petroleum Fuels.
Oscillation Impacter Improves the Rate of Penetration
by Dawei Qin, Jiyou Xiong, Guohua Wang, Xuecheng Dong
Abstract: In order to improve the rate of penetration and drilling performance, a tool named oscillation impacter is designed, which enables hydraulic energy to transform into mechanic one and generate static-and-dynamic loading on the bit and local instantaneous low pressure at the bottom. This paper attempts to analyze the structure and working principle of oscillation impacter, study the rock breaking mechanism of local instantaneous low pressure through theoretical analysis and the rock breaking mechanism of static-and-dynamic loading by the method of numerical simulation. Reasonable working parameters are recommended after analyzing the influence that frequency and the maximum amplitude of dynamic loading act on rock breaking. According to the simulation results, corresponding drilling technology is established and field tests are conducted in Huabei oilfield. The statistical results manifest that the performance of oscillation impacter is favorable in different formations and the ROP is improved significantly.
Keywords: oscillation impacter; rate of penetration; static-and-dynamic loading; local instantaneous low pressure; rock breaking; numerical simulation; chip hold down effect; bottom hole rock; drilling technology ; Huabei oilfield.
Experimental investigations of Vanadium and Nickel distribution while firing petcoke in a Circulating Fluidized Bed test facility
by Jaygopal Jayamohan, Ganesh Palappan K, Lakshminarasimhan M, Rajavel M, Suresh S
Abstract: Petcoke was fired as independent fuel in CFB test facility and the distribution of vanadium and nickel throughout the boiler and its deposition rate was assessed. It was found out that during combustion, 7-8% of the total vanadium is in bottom zone of furnace, 31-33% is in circulating zone, nearly half of total V (47-49%) is in second pass and the rest 11-15% got deposited in the boiler or escaped through the stack. Meanwhile in the case of nickel, 26-29% is in primary loop and rest 66-68% is in second pass. Vanadium deposits were found as inclusions in lime based deposits. XRF and XRD analysis of loose deposits found in back pass confirms the presence of vanadium. It was noticed that although petcoke contains high amount of vanadium and nickel, most of them were absorbed in situ limestone and turned to stable solid form.
Keywords: Petcoke; Vanadium; Nickel; CFB; Primary loop; Second pass.
Upgadation of Mianwali Coal using Froth Flotation and Nitric Acid Leaching
by Qurat Ul Ain Rana, Rubab Arif, Khurram Shahzad, Javaid Akhtar, Shahid Munir
Abstract: Mainwali coal was upgraded using flotation process followed by acid leaching. For flotation tests parameters such as pH (7, 8, 9, 10, 11), impeller speed (1000, 1100, 1200, 1300, 1400 rpm), solids in pulp (15, 20, 25, 30, 35 %) and particle size [(-105, +127
Keywords: Beneficiation; Froth Flotation; Pakistani Coal; Nitric acid leaching.
Mobility of elements released from coal during CO2 sequestration
by Changjiang Liu, Geoff Wang, Shunxun Sang, Huihu Liu
Abstract: A key greenhouse emission reduction strategy is to sequestrate CO2 in the subsurface by injecting it into coal seams. We investigated the injection of CO2 into coal seams using static batch experiments conducted under similar temperature and pressure conditions to that of the formation from which the coal samples were originally obtained, in an effort to understand the mobilization of elements released from the coal. Anthracite and high volatile bituminous coal samples (4-8 mm in size) were exposed to a solution of supercritical CO2 (ScCO2) and water at a temperature of approximately 40℃ and a pressure of 9.8 MPa. The results obtained indicate that elements show different mobilities after exposure to the ScCO2-H2O solution. Their mobilities are mainly influenced by the occurrence of the elements in the coal minerals. It was found that the mobilization of elements associated with carbonate minerals was greater than that of elements associated with sulfide and sulfate minerals; which was in turn greater than that of elements associated with silicate minerals. The results also show that close attention should be paid to the potential environmental hazards that might arise if the elements are released into groundwater systems during the CO2 sequestration process.
Keywords: coal; elements mobility; CO2 sequestration; environmental hazard.
Comparison of Combustion Characteristics of an Automotive CRDI Engine with Conventional HCV Engine
by Saravanan Subramani
Abstract: In this present work, combustion parameters of an automotive CRDI diesel engine was investigated. A 3 cylinder CRDI passenger car engine employed with split injection pattern was tested at two different operating conditions namely, operating the engine at different speeds by maintaining a constant engine torque and also at different torques by maintaining a constant engine speed. Variation of combustion parameters of the engine was presented as function of BMEP, speed and torque. The variation of cylinder pressure and heat release rate of the CRDI engine was compared with a four stroke, 6 cylinder, Heavy Commercial Vehicle (HCV) direct injection automotive engine employed with mechanical fuel injection system and significant variation was observed between the two. In the CRDI engine the magnitude of the cylinder pressure varied marginally during the combustion period when compared with mechanical fuel injection engine and the effect of split injection was observed in the heat release curve of the CRDI engine. Variation of start of combustion, peak pressure, maximum rate of pressure rise, maximum heat release rate and combustion duration with respect to speed and torque was presented for CRDI engine.
Keywords: Diesel engine; CRDI; combustion; torque; speed.
An Experimental Study on the Gas and Soot Formation in Ethanol Pyrolysis
by Qi Zhao, Jingyu Ran, Changlei Qin, Lin Yang, Mingchu Ran
Abstract: Ethanol is an alternative fuel to oil with high oxygen content, and its utilization is helpful in solving the issues of petroleum shortage. Pyrolysis is always existed in the process of Ethanol utilization so it is very important to understand the process of gas production and soot formation during Ethanol pyrolysis. Also, excessive soot will affect the effective use of Ethanol, so the analysis of soot production at various conditions is significant, and soot rate is a key factor to predict and control soot yield. In the paper, pyrolysis experiments have been carried out in a quartz tube reactor in the temperature range of 700
Keywords: Ethanol pyrolysis; gas production characteristics; soot formation characteristics.
Thermodynamic Modeling of Wax Precipitation Using PC-SAFT in a Multi-Solid Framework
by Reza Bagherinia, Mehdi Assareh, Farzaneh Feyzi
Abstract: In this work, a multi-solid approach is used for Wax precipitation modeling with PC-SAFT. A Vapor/liquid/solids calculation is performed for determination of Wax precipitation weight percent. Beside this, the proposed model is applied to predict the Wax appearance temperature (WAT) for the published oil samples experimental precipitation data. The PC-SAFT parameters for petroleum plus fractions are estimated with reliable correlations. Finally, the results of modeling are compared with the results of Lira-Galeana et al. (Lira-Galeana et al., 1996) , Pedersen et al. (Schou Pedersen et al., 1991) and Dalirsefat and Feyzi (Dalirsefat and Feyzi, 2007) models and a recent work of the authors using a solid solution approach with PC-SAFT plus UNIQUAC activity coefficients (Bagherinia et al., 2016). The results demonstrate progress in accuracy and propose the model as an acceptable predictive tool. The average absolute deviations percent for WAT estimation over all fluid samples is 0.20 in comparison with 0.55 for the recently published modeling approach (Bagherinia et al., 2016).
Keywords: PC-SAFT; Wax precipitation; Multi-Solid; VLSE; Petroleum Fluids.
Valve Nozzle Shape Effect on Gas Lift System Performance
by Zainal Zakaria
Abstract: One of the important components in designing an efficient continuous flow gas lift system is a gas lift valve. Therefore the objective of this paper is to study the effect of gas lift valve nozzle shape on the continuous flow gas lift system efficiency. Experiments were carried out using four gas lift valve nozzle shapes which are conical, bevelled entrance, bullet and orifice with port diameter of 5 to 12 mm. A nitrogen-glycerin with nitrogen injection rate of 0.033 to 0.167 l/s flow through a transparent vertical pipe of 50 mm diameter and 3 m height to simulate a continuous flow gas lift system. Taylor bubble length and liquid produced mass were measured to investigate the effect of the gas lift valve nozzle shape on the continuous flow gas lift system efficiency. The flow pattern was observed along the process and the image was recorded using Digital Single-lens Reflex camera. It was found that only slug flow occurred along the process and the conical nozzle shape has the highest efficiency. The gradual enlargement shape in conical nozzle reduced the energy loss within the valve. The overall results show that the conical nozzle produced the highest efficiency of the gas lift system due to the less energy losses within the valve nozzle and the most stable gas flow achieved in the fluid column pipe.
Keywords: gas lift; valve; shape; bubble; stimulate; continuous flow.
Experimental study on the influence of oil on spontaneous combustion characteristics of coal
by Hu Wen, Duo Zhang, Yang Xiao, Xuezhao Zheng
Abstract: Generally, the coexistence of coal and oil is a frequently occurrence state of coal seam in Huangling-Longdong mining area in China. The presence of crude oil should cause a certain impact on coal spontaneous combustion. For studying the effect of crude oil on coal spontaneous combustion tendency, this study collect the coal and the crude oil in rock from the existence of coal and oil symbiosis in Huangling mine No. 410 working surface, and mix the coal sample(YM) with crude oil (SY) at different mass ratio (YM: SY = 1: 0, 1: 0.05, 1: 0.1, 1: 0.15) to proceed the programmed temperature oxidation experiment, which revealed that the variation rule of gas composition in the outlet of coal sample tank, the oxygen consumption rate, the gas production rate , the exothermic intensity of the coal samples with different oil content vary with the temperature and the index gas of coal spontaneous combustion prediction can be obtained during the low temperature oxidation process. This study result indicate that Oil-bearing coal samples and coal samples are easy causing spontaneous combustion, and the rate of gas production of three kinds of oil samples got the similar effect in the process of low temperature oxidation. Under the same conditions, the higher the oil content, the oxygen consumption rate of coal, the amount of oxidizing gas produced, the smaller the exothermic intensity, which Indicated that coal is not easy to cause the spontaneous combustion, that is, crude oil has a blocking effect on the coal spontaneous combustion.
Keywords: Spontaneous combustion of coal; Coal and oil symbiosis; Programmed heating; Oxygen consumption rate; Heat release intensity; Indicator gas.
Quantitative well placement optimization of five-spot patterns in an anisotropic oil reservoir
by Yingfang Zhou, Weiwei Xie, Chen Li, Xiaodong Wang
Abstract: This article describes the influence of anisotropic permeability on the development effects of five-spot patterns. Existing research on five-spot patterns in anisotropic reservoirs has mainly focused on two types of flooding pattern orientation: one type is that the producer-producer direction is parallel to the direction of principal permeability, and another type is that the injector-producer direction is parallel to the direction of principal permeability. This paper extends the previous research to any flooding pattern orientation. To calculate the seepage problem in anisotropic reservoirs, a coordinate conversion method is used to transform the anisotropic reservoir into an equivalent isotropic reservoir; and the streamline model is used to analyze the reservoir development effect. The results indicate that the anisotropic permeability has destruction and reconstruction effects on general well patterns. The initially designed injection-production relationships are broken up; and new injection-production relationships are developed. The relative angle between the direction of maximum principal permeability and the well line direction is a key factor for the occurrence of the destruction and reconstruction effects. The deformation process of a flooding unit is shown in detail for square five-spot patterns, and the variation ranges of the anisotropy ratio and the flooding pattern orientation, in which the destruction and reconstruction effects occur, are given. Further research shows that a small change in the flooding pattern orientation can lead to an entirely different result for the development of the five-spot patterns, especially, when the degree of anisotropy is high. To prevent the destruction of well patterns, the common five-spot patterns must be modified based on the reservoir anisotropy. A general analytical solution for the well placements of five-spot patterns is provided to optimize the development effects of anisotropic oil reservoirs. The results of this paper provide an easy method for designing the well placement in planar anisotropic reservoirs; and can provide theoretical guidance for the reasonable construction of five-spot patterns in oil fields.
Keywords: Anisotropy; direction; deformation; streamline; quantitative; well placement optimization.
Analysis of adsorption kinetics and thermodynamics of methane in shale based on the volume filling theory of micropores
by Shuai Yin, Runcheng Xie, Jingzhou Zhao
Abstract: Volume filling of micropores is an adsorption behavior of adsorbates at higher equilibrium pressures. In this paper, the meaning of the parameters defined in the volume filling theory of micropores is discussed, and the adsorption performance of methane in shale is analyzed. Research indicates that it is most appropriate to use the characteristic index curve n = 1 to describe the adsorption behavior of methane in shale. As adsorption capacity increases, the differential adsorption work (A) will decrease. As the temperature increases, the characteristic energy (E) tends to decrease gradually, and for the case of n = 1, the values of E for shale samples ranged from 4.14 to 5.63 kJmol-1. As the filling rate θ increases, the absolute values of the thermodynamic parameters (Q, ΔH and ΔS) decrease gradually. Under experimental P-T conditions, the values of the thermodynamic parameters change very regularly and do not have mutation characteristics. This indicates that the adsorption energy can be extrapolated under much wider supercritical conditions. We believe that the thermodynamic parameters actually represent the complementarity and comprehensive effects of the TOC and Ro parameters.
Keywords: Micropores; volume filling; shale; methane; thermodynamic parameter.
A Study of a Pressure Analysis Model for SRV Fractured Vertical Wells in Tight Oil Reservoir
by Langtao Zhu, Xinwei Liao, Xiaoliang Zhao, Lingyu Mu
Abstract: Tight matrix blocks and fractures normally have high stress-sensitivity. In addition, due to the tightness, unsteady cross flow (UCF) often occurs between matrix and fractures. Those two factors can affect the shapes and characteristics of bottom hole pressure (BHP) and thereby the reliability of well test interpretation. In this study, a physical model of a fractured vertical well with stimulated reservoir volume (SRV) was developed for the purpose of pressure propagation simulation, based on micro-seismic data monitored at SRV fractured vertical wells in different typical tight oil reservoirs. Then a mathematical model was presented to describe BHP of SRV fractured vertical wells by considering stress sensitivity and UCF.
Later, the proposed BHP analysis model was applied to a typical SRV fractured vertical well. The results reveal that compared to models without stress sensitivity and UCF, the proposed model can provide more accurate estimates of the inner fractured zones radius and other relevant reservoir parameters.
Keywords: Tight oil reservoir; SRV fracturing; Pressure analysis model; Stress sensitivity; Numerical inversion.
Experimental investigation and field pilot testing of air assisted cyclic steam stimulation technique for enhanced heavy oil recovery
by Yanyong Wang, Shaoran Ren, Liang Zhang, Junyu Deng, Zhiwu Gong, Changhao Hu
Abstract: Air assisted cyclic steam stimulation (AACSS) process is a novel technique for enhanced heavy oil recovery, which is efficient and economically attractive compared with other non-condensable gases and solvents injection based techniques. In this study, the performance of AACSS process for an ultra heavy oil reservoir was investigated via laboratory experiments and field data analysis. The results indicate that air injection based on steam stimulation can effectively increase oil recovery in comparison with the conventional cyclic steam stimulation (CSS) process. The injected air can significantly increase and maintain the reservoir pressure, and reduce oil viscosity via flue gas dissolution and the thermal effect of low temperature oxidation (LTO) of the crude oil. The field pilot testing results of the AACSS technique in Liaohe Oilfield (Northeast China) demonstrate that AACSS can significantly increase oil production, prolong the effective production period of time, reduce water cut and the steam to oil ratio. A scoping economic study shows that the AACSS process can be more economically attractive than CSS process in terms of net present value. The AACSS technique has been effectively applied in mature heavy oil reservoirs developed by the conventional CSS, and it is also a feasible option to deep and offshore heavy oil reservoirs.
Keywords: heavy oil; air injection; low temperature oxidation; cyclic steam stimulation; economic evaluation.
Application of GIS-based Decision Making Model to Evaluate Safety of Underground Mining under Neogene Aquifers
by Binbin Yang, Wanghua Sui, Jiawei Liu
Abstract: This paper presents a decision-making model to evaluate the safety of underground coal mining under the Neogene aquifers which are composed of sand based on geographic information system and entropy values. An evaluation index system which contains the main factors that determine the safety of underground mining under the Neogene aquifers is first proposed by considering the geological and hydrogeological conditions. The values of these factors are collected by using the 3D analysis module of ArcGIS for further quantitative analysis. Then, the thematic maps of the factors are used to analyze the complex spatial characteristics of mining safety under the Neogene aquifers. In order to measure all these thematic maps of the factors in dimensionless units, these thematic maps are normalized. An extensive model is proposed based on a mathematical model of entropy, which is used to describe the complex nonlinear relationships between the index system and mining safety under the Neogene aquifers. Additionally, the weight of the main factors that determine the safety of mining is calculated. As a result, a comprehensive decision for mining under the Neogene aquifers is also shown by thematic mapping. The decision model is demonstrated by using data from the Taiping coalmine in Shandong Province, China. The new method is effective and advantageous, since the influence of multiple factors has been quantitatively considered in accordance with the geological and mining conditions.
Keywords: Underground mining; Decision-making model; Geographic information system (GIS); Entropy values; Neogene aquifers.
Custard Apple Seed Oil as Promising Biodiesel Feedstock using Advanced Techniques and Experimental Investigation on Diesel Engine
by Ashok Kumar Yadav
Abstract: In this present work, biodiesel is produced from a new feedstock; Custard Apple seed oil using hydrodynamic cavitation (HC), ultrasonic cavitation (UC) and conventional mechanical stirring (MS) methods via transesterification under optimized conditions. Production conditions are: oil to methanol ratio at 1:6 in the presence of 0.75 wt.% potassium hydroxide as catalyst and at 60
Keywords: Ultrasonic method (US); Hydrodynamic Cavitation (HC); Mechanical Stirring (MS); Custard Apple oil methyl ester (CAME); Diesel Engine.
A Semianalytical Solution for Hydraulically Fractured Vertical Wells in Tight Gas Reservoirs with Fracture Networks
by Shuyong Hu, Bo Li, Liehui Zhang, Bin Tang
Abstract: Massive hydraulic fracturing technology is a key technology for efficient development of tight gas reservoirs. During the fracturing process, a complicated stimulated reservoir volume (SRV) is created around the wellbore and the major fracture. The existence of fractures is essential to the recovery and performance of tight reservoirs wells. In this paper, a rectangular composite model of a tight gas reservoir was established to describe a fractured well with an SRV. In the model, the SRV is characterized by the WarrenRoot dual-porosity model. The solution of the model is then obtained by Greens and source functions. The well testing type curves are obtained by Stehfests numerical inversion method. In addition, the transient gas flow regime and the sensitivity of variable parameters are analyzed. Based on the results, the transient production rate and cumulative production curves with different parameters of well-produced constant bottomhole pressure are plotted, and the corresponding parameters sensitive analyses are done. The results show that the seepage resistance was significantly decreased due to the existence of SRV, and the higher the SRV permeability was, the smaller the seepage resistance would be.
Keywords: production performance; semi-analytical method; SRV; tight gas reservoir; well testing.
Development of a stress-based approach for achieving the risk assessment of fault-related coal and gas outburst
by Qinglong Zhou, Juan Herrera-Herbert, Arturo Hidalgo
Abstract: In underground mining, gas accumulation or gas content anomaly caused by geological structures often results in catastrophic coal and gas outburst accidents, this kind of outburst has already been reported for decades and caused thousands of casualties. However, so far there have been very few studies about how to conduct risk assessment for this kind of geological-structure-related outburst.
In this study, our aim is to develop an approach to evaluate the risk of fault-related outburst. The approach developed in this study is a stress-based approach and it considers the associated factors including the gas pressure, the fault attitude and the tectonic stresses. The fault-related outburst index proposed in this work not only can be used for evaluating the fault sealing capability but also can be used for quantitatively assessing the risk degree of fault-related outburst. It is a practical approach and can be recommended to apply in more underground engineering.
Keywords: Gas outburst; Fault sealing; Fault plane; Seal capability; Mine disaster.
Laboratory scale characterization of brittleness and permeability enhancement due to rock failure.
by Jihoon Wang, Peter Valko, Ahmad Ghassemi
Abstract: In this study, the multi-stage triaxial compression testing method is adopted to obtain geomechanical parameters without heterogeneity effect. Using the geomechanical characterization we calculate various brittleness indices previously suggested in the literature. Before the compression test and after the ultimate rock failure, we also measure the permeability enhancement ratio caused by rock failure with characteristic time obtained from pulse decay permeameter. Analyzing the relationship between the various brittleness indices and the permeability enhancement, we assess the ability of the former to predict the latter. The results show that no unique brittleness index can explain completely the permeability enhancement, but those indices perform better which contain information on post-peak behavior in direct or indirect manner. We conclude that at least three aspects of the failure behavior are important and hence at least two indices are required to characterize the potential of permeability enhancement.
Keywords: brittleness index; permeability enhancement; pulse decay permeameter; characteristic time; multistage triaxial test.
CO2 EMISSIONS and MILITARIZATION in G20 COUNTRIES: PANEL COINTEGRATRION and CAUSALITY APPROACHES
by Melike Bildirici
Abstract: This paper aims to test the relation among militarization, CO2 emission, economic growth, and energy consumption in G20 countries from 1965 to 2016 via panel methods. Long and short-run coefficients and the causal relationship between the variables showed the importance of energy policy and strategy for G20 countries. Due to the importance of energy policy and strategy for G20 countries, the results were not obtained by one testing approach; instead, several tests were compared. The cointegration among CO2 emissions, militarization, energy consumption, and economic growth was determined by using Pedroni, Kao, and PARDL methods. Further, Pairwise Stacked Common Coefficient Panel Causality test and Dumitrescu-Hurlin causality test were applied and unidirectional causalities from militarization to CO2 emissions and from energy consumption to CO2 emissions were determined. Furthermore, it was determined there is the evidence of bi-directional causal relationship between per capita GDP and militarization, between per capita GDP and energy consumption, and unidirectional causality from militarization to energy consumption. This paper recommends that environmental and energy policies must recognize the differences in the relation among militarization, energy consumption, and economic growth in order to maintain sustainable economic growth in the G20 countries.
Keywords: Environmental Pollution; Economic Growth; Energy Consumption; Militarization; Pedroni Test; Kao; PARDL; Dumitrescu and Hurlin Causality Test.
Using Data Analytics for Business Decisions in the UK Energy Sector a Case Study Integrating Gas Demand with Weather Data
by Warren Yabsley, Shirley Coleman
Abstract: Data analytics has been highlighted in many sectors as providing a pivotal role in business operations and strategy. The energy and utility sectors in the UK are becoming increasingly aware of the value of their operational data and investigation into how statistical analysis can improve operational efficiency and performance, leading to savings and reduced consumer bills. Vast resources of open data are accessible and analysing integrated data sets enhances the opportunities for insight. This paper demonstrates data analytics via a case study. Gas demand is highly volatile with many influencing factors. Regional weather measurements used to predict demand are inadequate and unrepresentative of local areas; daily discrepancies of over
Keywords: data analytics; business decisions; energy sector; gas demand; weather; open data; infrastructure; sustainability; gas transportation; regression; ARIMA; time series; data science; RIIO; UK; United Kingdom.
A Heterogeneous Model for Simulating Fluid Flow in Naturally Fractured-vuggy Carbonate Reservoirs
by Haixiang Zhang, Weihong Peng, Pengfei Hao, Menglin Du
Abstract: In this paper, a heterogeneous model named MFV (Matrix-Fracture-Vug), which considers the interactions of flow regimes in matrix, discrete natural fractures, large-scale fractures and vugs, is developed for simulating fluid flow in a fractured-vuggy reservoir. In the MFV model, coupling Darcy-Stokes equations are used to describe flow regime in matrix and vugs. Fluid flow follows the cubic law in each discrete natural fracture and different natural fractures are described by a discrete fracture model. An equivalent method is put forward to describe the flow regime in large-scale fractures. Three typical models are presented to demonstrate that the MFV model is a robust and viable alternative to fluid flow simulation schemes. The MFV model is then applied to an application, and the flow mechanisms in fractured-vuggy reservoirs are analyzed. The pressure distribution in a fractured-vuggy reservoir is strongly heterogeneous. Pressure distribution in diagonal is no longer a standard exponential form, and the pressure curve shows an S shape. In addition, the oil well productivity is demonstrated by investigating the influences of the matrix, fractures and vugs on the production rate and the cumulative production. The matrix is the main storage space and pathway in oil reservoirs. The matrix permeability controls the production rate in the whole production process. Fracture network constitutes the main channels of fluid flow, and the conductivity is the main influence factor in oil production process. Vugs have little or no effect on the productivity in the earlier period, while, the cumulative production will increase due to the storage capacity of vugs in later period. This model can provide insights into the history matching and the production prediction for a fractured-vuggy reservoir.
Keywords: heterogeneous model; fractured-vuggy reservoir; Darcy-Stokes; flow mechanisms; oil well productivity.
Laboratory and commercial investigation of ebullated bed residue hydrocracking performance during processing of Urals crude vacuum resid and its blends with vacuum gas oil and atmospheric residue
by Dicho Stratiev, Radoslava Nikolova, Magdalena Mitkova, Rosen Dinkov, Ivelina Shishkova, Ekaterina Nikolaychuk, Dobromir Yordanov, Ivaylo Tankov, Wessel Ijlstra, David McNamara, Hong Duc Nguyen, Stéphane Chapot
Abstract: This study focuses on investigating the conversion behavior of vacuum residue and blends with heavy VGO (480-540
Keywords: ebullated bed hydrocracking; vacuum resid; atmospheric resid; heavy vacuum gas oil; feedstock reactivity.
Environment of Paleomire of lignite seams of Bikaner-Nagaur Basin, Rajasthan (W. India): Petrological implications
by Pramod K. Rajak, Mahendra P. Singh, Prakash K. Singh, Vijay K. Singh, Alok K. Singh
Abstract: Petrological and chemical investigations of lignites from the Bikaner-Nagaur Basin, Rajasthan (Western India) have been undertaken to understand the petrographic characteristics and their depositional environment to properly address the characteristic of paleomire. These lignites have a huminite reflectance (VRr) between 0.21 and 0.26 percent, and are thus low rank C coals. Megascopically these lignites have mostly stratified bands, except a few non-stratified bands, of brown to black color. Huminite is the most abundant maceral group which is dominated by detrohuminite (densinite and attrinite). Telohuminite occurs next in abundance to detrohuminite and is mainly represented by ulminite-A and ulminite-B. Liptinite and inertinite group macerals occur in relatively low concentration. High GI and low TPI values in these lignites are indicative of a continuous wet condition in the basin with a slow rate of subsidence during the decay of organic matter. However, Gurha lignites, suffered few spell of relatively drier period as revealed by the increased inertinite content in some bands. The study indicates a limno-telmatic swamp with low subsidence rate and a slow fall in ground water table which happened because of the area having treeless open marsh and limnic plant communities. Further, the wet condition of the paleomire controlled the gelification and not the pH. This study is substantiated in the ternary model which indicates that the lignites of the Bikaner-Nagaur Basin evolved under wet moor with moderate flooding with increasing bacterial activity. Such environment prevailed under coastal marshy setting during the transgressive phase.rn
Keywords: Key words: Paleomire; lignite; Rajasthan; petrology.
Comparison of a novel coupled hydro-mechanical model with typical analytical models in subsidence of coal seam gas extraction
by Guojun Wu, Shanpo Jia
Abstract: Although the influence of conventional oil and gas extraction on surface subsidence has been widely recognized and studied, few studies are carried out on the surface subsidence in coal seam gas fields and its impact on surface infrastructure and the environment. In predicting land subsidence caused by coal seam gas extraction, the hydro-mechanical behaviour of geological strata are different and their hydraulic connections to the coal seams are not well-understood, which makes the analytical models are difficult to be applied in the prediction of land subsidence. This paper develops a coupled fluid flow-geomechanical model which can consider the interrelation of fluid flow and geomechanics of the ground. By comparison of dewatering and degassing with typical analytical models including the disc-shaped reservoir model and the uniaxial compaction model, the typical analytical models cannot estimate the potential pressure distribution and predict the real subsidence induced by coal seam gas extraction; however, the coupled fluid flow-geomechanical model is capable of describing the transport properties of coal seam, including water flow, gas flow and desorption and rock deformation. Therefore, the proposed coupled model can be better used in analysis of subsidence of coal seam gas extraction.
Keywords: land subsidence; depressurization; gas extraction; analytical model; coal seam.
Total Organic Carbon from well logging statistical approach, Polish shale gas formation case study
by Jadwiga Jarzyna, Marcin Zych, Paulina Krakowska, Edyta Puskarczyk, Kamila Wawrzyniak-Guz
Abstract: Advanced statistical methods - Artificial Neural Networks (ANN) and Support Vector Machines (SVM) were used to calculate total organic carbon (TOC) on the basis of well logging. Data from three wells from the Silurian and Ordovician formations in the Baltic Basin in north Poland were used. In learning procedures TOC data as RockEval results were applied. Research was realised in four steps aiming to determine the best ANN in aspect of number and type of input variables. Regarding increase of cases number used in learning process data from two wells were combined and next, determined ANN and SVR were used to predict TOC. There were also made tests of number of input variables (results of standard and sophisticated well logs and laboratory data). Results obtained using standard logs when number of available cases for learning was big enough did not gave way to results based on very many input variables.
Keywords: total organic carbon (TOC); Polish shale gas formations; Baltic Basin; artificial neural networks (ANN); support vector machines (SVM).
Transient pressure behavior of multi-stage fractured horizontal well in stress-sensitive coal seam
by Zongxiao Ren
Abstract: As an alternative energy of conventional resources, coalbed methane (CBM) has been studied globally. Due to well-developed natural fractures, coal seam always described as stress sensitive dual media reservoir. So far, the pressure distribution model for multi-stage fractured horizontal well (MFW) in stress sensitive coal seam is almost solved by numerical method. In this paper, with consideration of multiple mechanisms including diffusion, adsorption/desorption and stress sensitivity, a transient pressure behavior model of MFW was established. Using perturbation transformation, Laplace transform, image theory and superposition principle the mathematical model was solved. Finally, by applying stehfest numerical inversion and perturbation inverse transform, we obtain the transient pressure for MFW in the time domain. According to the result of calculation, the flow process of MFW can be identified as six regimes: Ⅰ linear flow, Ⅱ the first radial flow, Ⅲ double radial flow, Ⅳ radial flow in the natural fracture system, Ⅴ cross flow, Ⅵ radial flow in the entire reservoir. Stress-sensibility primarily influences the latter five stages. The well bore dimensionless pressure drop is several times larger comparing with the situation that does not take the stress sensitive into account, and the dimensionless pressure drop derivative curve will tilt up in the later flow process, showing the characteristic of closed boundary. Accordingly, the influences of some of the critical parameters on the transient pressure behavior were studied, including the fracture number, permeability modulus, storage ratio, and so on.
Keywords: Coalbed methane; Stress sensitive; Fractured horizontal well; Source function; Flow regimes.
Moisture Content Estimation during Fixed Bed Drying Process with Design of Experiment and ANFIS Methods
by Mustafa Tahir Akkoyunlu, Engin Pekel, Mehmet Cabir Akkoyunlu, Saban Pusat, Coskun Ozkan, Selin Soner Kara
Abstract: In this study, a two stage methodology was applied to predict the exit coal moisture content during the drying process. The first stage included a design of experiment (DoE) study which made easy to determine the significance levels of drying parameters. At the end of the DoE stage, it was determined that the most significant parameter was bed height, and the least significant parameter was exit air relative humidity. The second stage included an adaptive-network-based fuzzy inference system (ANFIS) method which was applied to estimate the exit coal moisture content at any time during the fixed bed drying process. The experimental studies were conducted with different levels of the parameters (drying air temperatures (70, 100, 130 and 160
Keywords: ANFIS; Design of experiment; Drying; Moisture estimation; Low rank coal; Lignite.
Enhanced Nitrogen Foams Injection for Improved Oil Recovery: from Laboratory to Field Implementation in Viscous Oil Reservoirs offshore Bohai Bay China
by Yanmin Liu, Shaoran Ren, Liang Zhang, S.T. Wang, G.R. Xu
Abstract: Foam injection has been a proven technique for improved oil recovery in light oil reservoirs, while for heavy oil reservoirs, foams with high stability or enhanced foams are needed under harsh reservoir conditions. In this study, the feasibility of nitrogen foam injection for IOR from viscous oil reservoirs was evaluated via comprehensive laboratory experiments (including foam testing and sand-pack flooding) and a field pilot testing. A polymer enhanced foam system was investigated and selected with enhanced foam stability, high blocking capability and displacement efficiency. The targeted oilfield is located offshore Bohai Bay (China), featured with high oil viscosity and severe heterogeneity. Water flooding has been applied, but low recovery factor (＜20%) and high water cut (over 85%) has been observed. The pilot testing of the foam injection indicates that wellhead injection pressure can be effectively increased after the foam injection, and nearly all producers around the injector exhibited good response with incremental oil recovery and the average water cut dropped by 6.3%. The experimental and field pilot data are presented in this paper to demonstrate the effectiveness of the enhanced nitrogen foam injection technique, which can be an effective IOR method for the targeted oilfield and other similar viscous oil reservoirs.
Keywords: IOR; foam stability; polymer enhanced foams; heterogeneous viscous oil reservoirs; pilot testing.
Characteristics of Graphite-like Crystallites in Coal with Increasing Coalification
by Xianbo Su, Qian Wang, Fengde Zhou, Qing Si, Jinxing Song, Haixiao Lin
Abstract: This paper presents a study on the characteristics of graphite-like crystallites (GCs) in coals with different maximum vitrinite reflectance (Ro,max) which can be used to describe the rank of coal. Laser Raman spectroscopy (LRS), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used in testing 17 coal samples with different ranks. Results show that the GCs in coal undertook through three consecutive processes including aromatization, condensation and polymerization. Five coalification upgrading yield to six stages that are corresponding to six different ranges of Ro,max. In Stage-I (Ro,max less than 0.6%), coal contains a large amount of amorphous carbon and basically inherits the molecular structures of plant and peat. In Stage-II (Ro,max ranges from 0.6% to 1.3%), the aromatization is intensive and the layering distance between GCs decreases and GCs have already taken preliminary shape. In Stage-III (Ro,max ranges from 1.3% to 2.5%), the aromatization keep increasing, the condensation starts to show, and the GCs grow larger but contains plenty of defects. In Stage-IV (Ro,max ranges from 2.5% to 3.5%), the condensation is dominant, and the GCs appear with higher orderliness and continuity and the vertical stacking height reaches a maximum value. Stage-V (Ro,max ranges from 3.5% to 4.5%) is a transition from condensation to polymerization; in this stage, the lateral growth of GCs is significant, a lot of flat GCs are formed, and the defects contained in GCs decrease significantly. In Stage-VI (Ro,max is greater than 4.5%), the polymerization is dominant, and the GCs grow slowly in general and the internal defects are being eliminated continuously. With the increasing coal rank, the GCs grow larger with improving quality and eventually evolve into graphite crystals. HRTEM observation also reveals that GCs in coal have undergone a graphitization process with increases in percentage, size, and order.
Keywords: Graphite-like crystallite; Coal rank; Coalification upgrading; Coal deformation; Evolution.
Classification of adsorption isotherm curves for shale based on pore structure
by Qing Chen, Yuanyuan Tian, Changhui Yan, Peng Li, Hucheng Deng
Abstract: In the study of shale gas reservoir, the characteristic of pore structure can be determined according to the shape of adsorption isotherm curve. When applying conventional classifications known as BDDT, de Boer and IUPAC classification to categorize adsorption isotherm curves for shale, these classifications cant accurately demonstrate pore structure in different shale reservoirs. Based on characteristic of pore structure in shale, we choose pore shape, pore size and pore throat sorting as parameters to study changes in adsorption isotherm curve due to different grades of these three parameters and then generate 27 types of adsorption isotherm curves to match corresponding characteristic of pore structure in shale respectively. This new classification method is applied to categorize 101 adsorption isotherm curves measured by shale samples, and analyze the characteristic of pore structure. In comparison of analysis results from other methods, the new classification method is justified to be more practical.
Keywords: Shale; Classification of adsorption isotherm curve; pore size; pore shape; pore and throat sorting.
Determination and predication on three zones of coal spontaneous combustion at fully-mechanized working face with nitrogen injection
by Xiaowei Zhai, Tingyan Wang, Haitao Li, Kai Wang, Václav Zubíček
Abstract: Coal mine fire is one of the major disasters for coal enterprises. Among which spontaneous combustion of float coal in the goaf is particularly serious, what's worse, the float coal in goaf of fully mechanized working face in a large number of coal mines are more vulnerable to spontaneous combustion. Therefore, it is of great significance to determine and predict the dangerous zone of coal spontaneous combustion of in goaf of fully mechanized working face. This paper we took the 21305 working face of the CuiMu coal mine as an example, experimental research, field observation and numerical simulation were adopted to determine the dangerous zone of goaf. Results showed that the field measured data before and after nitrogen injection were in good agreement with the numerical simulation results. Nitrogen injection can effectively prolong the period of spontaneous combustion and reduce the probability of spontaneous combustion of coal. The research results and method of this paper provide theoretical guidance and reference significance for the prevention and control of coal fires.
Keywords: three zones;coal spontaneous combustion;fully-mechanized workingface;nitrogen injection.
Experimental study of gas pressure and effective stress influencing on gas seepage characteristics of bituminous coal in both axial and radial directions
by Lei Zhang, Dingyi Hao, Zhiwei Ye, Cun Zhang, Shuai Chen
Abstract: The effects of factors including effective stress, gas pressure, and Klinkenberg effect on the axial and radial gas seepage characteristics of bituminous coal, and the strain of the coal in the radial seepage process, are investigated with self-built GFDTA System. The concept of effective stress sensitivity coefficient is proposed, and the sensitivity of the permeability to the effective stress is negligible when the effective stress sensitivity coefficient is 0.01. It is concluded that the effective stress sensitivity coefficient decreases with increasing effective stress, and increases with increasing gas pressure. With the confining pressure and gas pressure increasing, the effect of unloading on the decrease degree of coal axial permeability decreases. In the axial seepage process, the sensitivity of permeability to confining stress is higher than that of axial pressure. In the radial seepage process, the influence of gas pressure on permeability is larger than that of axial pressure.
Keywords: bituminous coal; gas pressure; effective stress; axial seepage; radial seepage.
Upgrading of Light Cycle Oil for Ultra Low Sulfur Diesel Production by a Solvent Extraction Procedure
by Georgina C. Laredo, Pedro Vega-Merino, Patricia Perez-Romo, Ricardo Agueda-Rangel
Abstract: The upgrading of light cycle oil (LCO) present in straight run gas oil/light cycle oil mixtures (SRGO/LCO) was studied by an extraction procedure, using acetone/water (AW) combinations. The effect of the experimental conditions (LCO content in the SRGO/LCO mixtures and water content in the acetone/water solution) was studied firstly in batch experiments. The effectiveness of the procedure was carried out by measuring nitrogen removal as the distribution coefficient (DN) and raffinate yield as the percentage of weight change (WCh, wt.%), setting high DN and near zero WCh values as goals, which were reached with a water in acetone mixture of 5/95 (AW5). Considering these results, a countercurrent system was implemented with the AW5 mixture as solvent with a solvent/feed ratio of 2. SRGO/LCO mixtures up to 60/40 represented feedstocks with nitrogen, sulfur and aromatic hydrocarbon contents that may provide a specification complying diesel after the upcoming hydrotreatment (HDT) process.
Keywords: Light cycle oil; Ultra low sulfur diesel; Upgrading; Extraction; Hydrodesulfurization; Hydrodenitrogenation; Hydrodaromatization.
Improving the Capability of Detecting Joint and Fractures in Rock Mass from Roofbolt drilling Data by Using Wavelet Analysis
by Wenpeng Liu, Samer Saab Jr, Jamal Rostami, Asok Ray
Abstract: Roof bolting has been a dominant technique for ground support and is widely accepted and applied in underground mining, tunneling, and underground construction, and installing bolts in entries is a legal/regulatory mandate in coal mines. To improve and optimize the ground-support using rock bolts and mitigate incidents of ground instability, a proper understanding of the ground conditions is critical and in turn it requires a characterizing the rock mass. The concept of monitoring drilling parameters recorded from a bolter, for ground characterization, has been studied in the past few decades. This concept refers to identifying geological features, including distribution of joints, locating voids, and measuring strengths of rock layers, which are the typical input for coal mine roof rating (CMRR) that is used for ground support design. Several detection systems and intelligent drilling units, have been developed for joint detection, however, the available units have limited capabilities in accurately identifying the joints. For instance, they fail to discriminate joints with the aperture of less than 3.175 mm along a hole. Besides, the existing systems tend to generate false alarms, meaning indicating joints and/or voids that do not actually exist in the ground. The main objective of this research was to develop more efficient and sensitive detection programs, based on pattern recognition algorithms, while reducing the number of false alarms. To achieve this objective, a series of laboratory tests, involving various simulated joint conditions, have been conducted, and new detection programs have been proposed. In order to further improve the reliability and precision of the proposed detection programs, wavelet analysis has been applied to pre-process collected drilling data. This paper briefly reviews testing procedures, data analysis, logic/algorithms used in the programs, and discusses improvements to detection results by using wavelet analysis of data collected in full-scale drilling tests.
Keywords: Wavelet analysis; CUSUM algorithm; roof bolter; drilling parameters; joint detection; ground support optimization.
Pressure transient analysis of multiple vertical fractures in a composite reservoir model
by Guoqiang Xing, Mingxian Wang, Shuhong Wu, Hua Li, Min Tong
Abstract: This work developed a composite reservoir model with the inner region containing multiple hydraulic fractures and the outer region showing conventional natural fractures. Using the model, transient pressure, flow regimes and parameter sensitivities of this composite system are investigated. A vertical fractured well in this reservoir may exhibit five flow regimes: fracture linear flow, transition flow, radial flow, inter-porosity flow and pseudo-steady flow. Two characteristic V-shaped segments are observed on pressure derivative curves, one corresponding to transition flow, which may be absent at a high fracture diffusivity ratio or a low fracture conductivity ratio, and the other corresponding to inter-porosity flow. In the pseudo-steady period, the pressure and pressure derivative curves for different fracture diffusivity ratio, fracture conductivity ratio and interporosity coefficient normalize while the curves for different storativity ratio parallel to each other. In addition, regressed solution of fracture linear flow and approximate solution of pseudo-steady flow are derived in detail.
Keywords: pressure-transient analysis; composite reservoir model; multiple vertical fractures; naturally fractured reservoirs; analytical solution; parameter influence.
Development of Dust Ignition Protected Electrically Powered Forklift Truck for Combustible Dust Environment
by R.K. VISHWAKARMA
Abstract: Industries dealing with explosive gases and combustible dusts in processing or production are always at higher risk of gas or dust explosion. PTA (Purified Terephthalic Acid) plant of Indian Oil Corporation Ltd. (IOCL), Panipat, India has similar risk of dust explosion hazard, since PTA is a combustible substance in the form of dust or layer. To load, unload and transport the PTA bags in the plant, special forklift trucks are required. A prototype forklift truck for combustible dust atmosphere was developed in collaboration with M/s Action Construction Equipment Ltd. (ACE), Palwal, India. The electrical components with dust ignition protected design have been manufactured by ACE in consultation with CSIR-CIMFR, Dhanbad, India. All other possible sources of ignition are identified and suitable components/ parts of forklift are used for hazardous atmosphere. This paper presents the design requirements of a dust ignition protected and battery operated forklift truck for safe use in Zone 22 combustible dust atmosphere of the plant.
Keywords: combustible dust; dust ignition protection; electric forklift truck; purified terephthalic acid; zone 22.
Modelling Mine Gas Explosive Pattern in Underground Mine Gob and Overlying Strata
by Jianwei Cheng, Chang Qi
Abstract: Coal gas explosions in an underground mine gob often cause serious injuries and fatal accidents in and around underground mine working faces. It is well-known that the coal gas volumetric concentration must be maintained below 1% in an active mine ventilation system in order to avoid any gas explosion hazards. However, due to the ventilation effect, gas emitted from the residual coal pieces, coal wall and adjacent coal seams gather sin gob spaces and caved zones, which would change the atmospheric compositions. Hence, the gas concentration could be built up to reach the explosive limit and thus to form gas explosion zones. Once a spark appears to ignite such gas-mixture, an explosion event would be inevitable. Therefore, it is advisable for mining engineers to know where the explosion zones are and how they could deal with the influence factor sin order to minimize the explosion risk. In this paper, based on the physical simulation analysis, a 3D physical experimental model is well designed to simulate a U-type underground mine working face. The ventilation system is simulated by the plastic tubes with holes punched and the formation of gob and development of overlying strata caving are simulated with physical materials with the help of designed hydraulic system to model the ground. In the experiment, based on two important influence factors, the air quantity delivered into the ventilation system and the gas release rate (GRR) in gob, a series of experiments are designed to examine the range pattern of gas explosive zone changing in the mine gob with following various combinations of air velocities and GRRs. By sampling works, the gas concentration could be obtained at different horizontal levels and vertical lines in the experiment model. The experimental results show various shapes and areas of explosive zone sin gob and in overlying caved spaces as the GRR and air velocities change. This research work is of great reference for mining engineer sin following two points: to apply the ventilation design practices to minimize the explosion hazard risk and to guide the gas drainage work to effectively reduce the amount of gas in a mine gob area.
Keywords: Mine gas; Explosive zone; Physical simulation; Underground ventilation.
A practical method to construct capillary pressure curves of reservoir using NMR logging date
by Wenfeng Sun, Chunyang Liu, Ying Wang, Lili Bai
Abstract: The mercury injection capillary pressure (MICP) curve is an important evidence for the determination of pore structure of reservoir. However, for some complex formations, core data is difficult or unable to obtain. Thus, the mercury injection experiments to obtain the capillary pressure curves cannot be carried out, which brings trouble to reservoir evaluation. To solve this problem, a new method to construct the pseudo-capillary pressure curve using nuclear magnetic resonance (NMR) logging data is established. In this method, for a certain reservoir, the displacement pressure can be predicted using the maximum relaxation time of T2 spectrum of nuclear magnetic resonance (NMR) logging. Next, the effective porosity and density of rock, calculated from logging data, are used to predict the maximum mercury saturation. Then the mercury saturation at displacement pressure point and threshold pressure point can be estimated according to empirical data. Thus, the four important points on the capillary pressure curve can be obtained, namely zero point, displacement pressure, threshold pressure and end point. Then, referring to the 4 pressure points above, the pseudo-capillary pressure curve is constructed in two sections with the dividing point of threshold pressure.
This new method is used to predict the pseudo-capillary pressure curve of a rhyolite reservoir. The accuracy of its MICP prediction result is proved good compared with the measured capillary pressure curve. The method has a wide range of application and it is convenient especially for the evaluation of deep and complex formations where the coring is difficult.
Keywords: nuclear magnetic resonance logging; T2 spectrum; displacement pressure; capillary pressure curve; pore structure; maximum mercury saturation.
Fracture-initiation pressure analysis of horizontal well in anisotropic formations
by Tianshou Ma, Yang Liu, Ping Chen, Bisheng Wu
Abstract: Lost circulation is a classic wellbore instability problem encountered during drilling. To minimize or avoid lost circulation, preventing the initiation of fracture is the best measure. However, because rocks are naturally anisotropic, the classic fracture pressure model is not applicable for anisotropic formations. Some researchers therefore investigated the influence of transverse isotropic material parameters, but they ignored the influence of anisotropic tensile strength. The present work proposes a novel fracture-initiation pressure model of a horizontal well to investigate the influence of anisotropy on fracture-initiation pressure. Laboratory hydraulic fracturing testing verified the present method. The results indicated that anisotropic modulus and tensile strength have distinct influences on fracture-initiation pressure. Fracture-initiation pressure declines obviously under the influence of anisotropic modulus and anisotropic tensile strength; thus, the anisotropy of modulus and tensile strength cannot be ignored. The present model provides more accurate predictions of fracture-initiation pressure for horizontal wells in anisotropic formations.
Keywords: lost circulation; fracture-initiation pressure; fracture pressure; horizontal well; anisotropic formation; anisotropic tensile strength.
Interfacial interaction and emulsification of crude oil to enhance oil recovery
by Rahul Saha, Aditi Sharma, Ramgopal V.S. Uppaluri, Pankaj Tiwari
Abstract: This work addresses the characterisation of crude oil to examine opportunities for chemical enhanced oil recovery. Interfacial tension (IFT) studies were conducted for alkalis (NaOH and Na2CO3), surfactants (cetyltrimethylammonium bromide and sodium dodecyl sulphate), and their combinations. IFT studies revealed that the optimum concentrations of individual alkalis, NaOH and Na2CO3 are 0.1 wt%, 0.25 wt% for which IFT values of 5.15 x 102 and 0.40 mN/m have been obtained respectively. For synergy of alkali-surfactant, the complex IFT behaviour indicated values in the range of 102 mN/m. Emulsification and sandpack flooding studies affirmed that alkali and alkali-surfactant flooding can provide 24.25% and 38.79% residual oil recovery, respectively. [Received: August 20, 2017; Accepted: December 24, 2017]
Keywords: interfacial tension; IFT; alkalis; surfactants; sandpack flooding; enhanced oil recovery; EOR; emulsification.
Decommissioning of deep and ultra-deep water oil and gas pipelines: issues and challenges
by Sheik Koroma, Isaac Animah, Mahmood Shafiee, Kong-Fah Tee
Abstract: When production facilities reach the end of their economic life in the offshore oil and gas industry, field owners must decide whether to replace, extend the life of, or decommission assets. The decommissioning of deep and ultra-deep water oil and gas pipelines has become a serious issue in recent years because it is a complex process and presents challenges to stakeholders. In this paper, we review the current practices of pipeline decommissioning in different regions of the world and then highlight issues and challenges related to such activities in deep and ultra-deep waters. These issues and challenges can be broadly categorised into technical (e.g., selection of appropriate decommissioning procedures for handling hazardous pipelines), financial or economic, health and safety legislation, environmental, and human or organisational issues (such as lack of requisite skills, knowledge and expertise). In order to address the challenges identified in the study, some directions for future research are suggested. [Received: 7 December 2016; Accepted: 17 October 2017]
Keywords: end-of-life; EOL; decommissioning; subsea pipeline; life extension; oil and gas; deep-water installation.
Gas emission through coal particles using instantaneous gas diffusion coefficients: Experimental and modelling study
by Guangshan SHI
Abstract: Similarity theory and the second law of diffusion were used to develop a diffusion model to accurately characterize the behaviour of gas emissions from coal particles. A method for calculating instantaneous diffusion coefficients, D(t), was established. These were incorporated into the diffusion equation and its analytical solution obtained via separation of variables. The results indicated that changes of D(t) as a function of time were described by a power function. The model accurately characterizes the entire process of gas emission from coal particles and reflects the complexities of pore size. It provides a new calculation method and theoretical reference for determination and prediction of parameters for gas emission from coal seams.
Keywords: Coal particles; Methane; Diffusion coefficient; Similarity theory; Fick’s law; Instantaneous diffusion; Diffusion model; Unipore model; Pore structure;
Mean free path.
True rheological behaviors of spacer fluid with consideration of wall slip effect
by Cheng Cao, Xiaolin Pu, Gui Wang, Zhengguo Zhao
Abstract: Based on the modified coaxial cylindrical measuring systems, experiments on the rheological behaviors of spacer fluid have been done. Tikhonov regularization is used to acquire the rheological parameters for its advantage. Then the characteristics of rheology and the wall slip effect of spacer fluid have been analyzed in detail. The results show that wall slip effect tends to occur in the flow of spacer fluid and should be removed in the measurement of rheological behaviors. The apparent rheological behaviors can be characterized by Herschel-Bulkley model. However, it is far away from the true rheological behaviors of the spacer fluid, which can be characterized by Bingham model. The slip velocity of spacer fluid increases with the increases of wall shear stress. Besides, the critical wall shear stress of spacer fluid varies from 3.26 Pa to 16.64 Pa, and the wall slip effect of spacer fluid will occur even if in a low shear stress region.
Keywords: spacer fluid; rheological behaviors; wall slip effect; slip velocity; Tikhonov regularization.
Multi-Media Reservoirs Depleted by Horizontal Wells: Analysis of Pressure Behaviors, and Rate Transient Accompanied by Developing Analytical Models for Flow regimes
by Salam Al-Rbeawi
Abstract: This paper focuses on analyzing pressure behaviors and rate transient of multi-porous media formations such as Carbonate reservoirs depleted by horizontal wells. Several analytical models (Pressure transient and rate transient) have been developed using the well-known dual-porosity models for naturally fractured formations and modified for triple-media formations considering the existence of hydraulic fractures. The solutions of these models demonstrate different flow regimes corresponding to different production times. The study has pointed out that the impact of multi-media on pressure behaviors can be observed at intermediate production time shortly after the production pulse has reached the lower and upper boundaries. While The flow regimes created by multi-media are characterized by two parallel lines on pressure derivative curves. These two lines can be used to identify the type of natural fracture system. It has been found that type-1 NFR is characterized by perfectly parallel lines wherein the vertical distance between these two lines equals the horizontal distance. The study emphasized that rate transient behavior may not exhibit same flow regimes that could be developed by pressure transient.
Keywords: Multi-porous media reservoirs; Pressure transient analysis; Rate transient analysis; Reservoir characterization; Horizontal wells.
Solidgas coupling law during methane seepage from a coal mass in the advanced pressure relief area of a mining seam
by Wei Qin, Jialin Xu, Guozhong Hu
Abstract: The variations of stress and methane flow in the coal mass in front of the working face were obtained by a field test at the 15201 working face in the Xindadi Coal Mine. Experimental schemes were designed for the entire evolution of the stress in the coal mass in front of the working face, and an experimental study on methane seepage from the coal mass in the advanced pressure relief area was conducted. Fitting functions for the permeability of the coal sample and its vertical stress were obtained by fitting the experimental data. A numerical calculation model was established with these fitting functions at different stages. The effect of mining height and mining depth on the law of methane seepage in the advanced pressure relief area was numerically simulated. With the increase in mining height and depth, the range of influence of the advanced abutment pressure increased, and the peak position of the advanced abutment pressure moved away from the coal wall. However, the peak value of the advanced abutment pressure decreased constantly with the increase in mining height but increased with the increase in mining depth. The higher the mining height and the greater the mining depth, the larger the area of pressure relief and greater the permeability increase.
Keywords: Methane extraction; Solid–gas coupling law; Numerical simulation; Green mining.
Conductivity performance evaluation of fractures filled with proppant of different sizes in shale with LBM-DEM
by Hong Zuo, Shouchun Deng, Zhenghong Huang, Chengxu Xiao, Yongqing Zeng, Jinlin Jiang
Abstract: The conductivity of proppant-filled fractures in rocks is one of the major concerns for evaluating the performance of hydraulic fracturing in reservoirs, especially in extremely low permeability reservoirs, e.g. sandstone/shale reservoirs. In this paper, numerical simulation methods: Discrete Element Method (DEM) and Lattice Boltzmann Method (LBM), were adopted to compute the conductivity of fractures filled with proppant of different sizes in shale as a function of the closure pressure. The particle discrete element, developed in our previous study, was applied to model proppant-shale interaction process, the deformation of proppant-filled fractures and the redistribution of proppant under variable closure stress. A three-dimensional digitized model was reconstructed from the deformed proppant-filled fractures at each of the stress changes, and the pore-scale simulation was carried out by LBM to model gas movement in the reconstructed digitized model (the deformed proppant-filled fractures) under extremely low pressure gradient and to evaluate the deformed fractures conductivity. In addition, the laboratory bench-scale experiments were conducted in support of the numerical modeling examining the proppant embedment into the shale as a function of closure stress and measuring the conductivity of proppant-filled fractures as the proppant embedment experiments were conducted under different axial load conditions. On the basis of the LBM-DEM numerical results and the laboratory bench-scale experiments, a number of conclusions can be drawn. First, as the proppant filled in fractures became more compact under gradually increasing axial load, more axial load was required to compress the proppant, and the larger the proppant size, the faster the conductivity of proppant-filled fractures decreased as the applied stress increased. Second, large proppant tended to preserve the main favorable pathways of gas flow in hydraulic fracture unchanged before the proppant were crushed, and demonstrate greater fracture conductivity under the same axial load conditions. The numerical results calculated by LBM-DEM were validated by a calibration test and the laboratory bench-scale experiments. In general, The LBM-DEM results were consistent with the experimental results. Moreover, the combined LBM and DEM method can effectively serve as a replacement of experiments to predict the conductivity of proppant-filled fractures in shale matrix. Furthermore, it offers the advantage to exactly capture the detailed information and reveal the microscopic mechanism.
Keywords: Shale; LBM; DEM; Permeability; Proppants; Hydraulic fracturing; Laboratory bench-scale experiments.
Experimental Verification of the Water-methane Displacement Effect in Gassy Coal
by Weiyong Lu, Bingxiang Huang, Shuliang Chen, Xinglong Zhao
Abstract: To verify that water-methane displacement effect in gassy coal exists objectively, a pseudo-triaxial experimental system of water-methane displacement was independently developed and tested. First, methane was injected into the standard cylindrical coal sample until the methane adsorption equilibrium state was reached. Then, the methane in the coal sample spontaneously desorbed. Finally, water was injected into the coal sample. It is shown that: (1) Water-methane displacement effect exists objectively. (2) Water-methane displacement effect includes the process of free methane generated by competitive adsorption and displacement desorption effect, the consumption caused by methane pressure increase, and water driving methane. (3) Competitive adsorption and displacement desorption between methane and water can generate free methane. Due to water injection, increase of methane pressure leads to consumption of free methane. The net free methane of the combined action provides methane source for the water-methane displacement effect.
Keywords: gassy coal; water-methane displacement effect; competitive adsorption; displacement desorption.
A new approach for predicting critical gas rate in condensate gas wells
by Ruiqing Ming, Huiqun He
Abstract: Previous models for predicting critical gas flow rates in condensate gas wells were established without considering the influence of parameter variation (critical Weber number and drag coefficient) on liquid carrying. Experimental results show that the two parameters vary over a wide range; therefore, previous models cannot accurately predict critical gas flow rates in condensate gas wells. To solve the problem, a new model for predicting the critical liquid-carrying flow rate of a condensate gas well was established. The variations of the two parameters (critical Weber number and drag coefficient) were added as improvements to previous models, and the calculation methods of the above parameters were also added. Calculations were analyzed in 30 condensate gas wells of the Xinjiang field. The correct prediction rate of the new model is 90%, with the status of 27 wells correctly predicted (loading/unloading), and the calculation accuracy of the new model is 6%～70% higher than that of previous models (Wan, Zhao, and Li). The research in this paper is of vital significance in guiding well stimulation (e.g., coiled tubing velocity string) to avoid liquid loading and increase gas recovery rate.
Keywords: Condensate gas well; Critical liquid-carrying flow rate; New model; Liquid drainage and gas production; Gas recovery rate.
Multidisciplinary Study of the Problems of Big Data Technologies in the Oil and Gas Industry
by Ramiz Aliguliyev, Fargana Abdullayeva
Abstract: This paper is devoted to the analysis of the multidisciplinary problems of the Big Data technology in the oil and gas industry. Application capabilities of Big Data technologies in issues such as reducing the exploitation risks, crude oil price forecasting, optimal management of the oil wells, health and safety ensuring in an organization, overcoming environmental problems and so on are investigated.
Keywords: Oil and Gas; Crude Oil; Big Data; Exploration and Production; Health; Safety; Environment.
3D Numerical and Experimental Study on Upscaling Two Phase Relative Permeability Curve of Naturally Fractured Reservoirs
by Reda Abdel Azim
Abstract: Relative permeability plays a critical role in evaluating the production potential and recovery factor for conventional and unconventional reservoirs and yet it is considered to be one of the most uncertain parameters in the governing equations of multiphase fluid flow. The multiphase fluid flow is traditionally simulated by using grid based relative permeability which is up-scaled from laboratory derived core scale relative permeability. Presence of fractures makes the reservoir highly heterogeneous and upscaling of core scale permeability to grid based permeability is complicated because the fracture dip and azimuth as well as fracture density varies grid block to grid block (Carlson 2003, Yang et al. 2013 and Fahad and Rahman 2016).In addition, fine grid scale simulation yields non-uniform sweep which is more representative to actual condition, however, this demands generation of relative permeability for varying deep azimuth and fracture density and field scale characteristic properties of fractures (Fahad and Rahman 2017).
In this paper, an integrated approach of upscaling of laboratory derived relative permeability to reservoir grid block scale under poroelastic frame work is presented. In this approach, capillary and viscous forces are assumed to be dominating which allows us to obtain a reasonable up-scaled relative permeability curves. In order to improve the computation efficiency first, the reservoir is divided into a number of grid blocks (20m
Keywords: Fractured reservoirs;upscaling;Relative permeability curve.
Underground coal gasification techniques for different geo-mining conditions
by Ranjeet Mandal, Raj Kumar, Md. Shahnawaz Ansari, Dinesh Kumar, Swades Kumar Chaulya, Girendra Mohan Prasad, Ajay Kumar Singh, Tanmoy Maity
Abstract: Underground coal gasification (UCG) technique provides facilities for converting underground coal into synthetic gas by remote ignition and injecting steam as well as air into the coal seam. This product, which is also known as syngas, is a mixture of combustible gases like carbon monoxide, hydrogen and methane; and non-combustible gases like carbon dioxide, nitrogen and water vapour. This syngas is utilised for generation of emission-free power, ultra-clean diesel and manufacture of ammonia, fertiliser and other various valuable chemical products. The UCG technique is not only cost-effective but also environment friendly. This technique can also be employed for recovering coal from areas where conventional mining is either difficult or uneconomical. Due to this remarkable feature, UCG technique is going to play a greater role in coming years with the depletion of easy exploitable coal day by day. [Received: February 2, 2017; Accepted: February 2, 2018]
Keywords: underground coal gasification; UCG; shaft; shaftless; linked vertical well; LVW; controlled retractable injection point; CRIP; single well integrated flow tubing; SWIFT.
Kinetics Features of Natural Gas Hydrates Crystallization and Dissociation in Water/Crude Oil and Water/Asphaltene-Resin-Paraffin Deposit (ARPD) Emulsions
by Vladilina Koryakina, Izabella Ivanova, Matvey Semenov
Abstract: The processes of crystallization and dissociation of natural gas hydrates synthesized in paraffin oil emulsions of the Irelyakh deposit (Eastern Siberia) and in emulsions of asphaltene-resin-paraffin deposits (ARPD) originated from this oil have been studied with application of high-pressure differential scanning calorimetry (HP DSC). The Avrami equation application to calculation of kinetic parameters of hydrate phase transition in the investigated emulsions has been shown as possible. The half-life periods and the rate constants of hydrates crystallization/ dissociation were calculated. Crystallization of hydrate-containing phase in the water-in-ARPD (W/ARPD) emulsions with formation of natural gas hydrates enriched with methane and ethane has been defined to proceed much slower than the rate of formation and composition of hydrates formed in water-in-oil (W/O) emulsions. An analysis showed that the hydrates grow better in emulsified water droplets than in bulk water, while the hydrate content decreases with increase of water cut in emulsion, and a slower rate of hydrate formation in the W/ARPD emulsion, as compared with W/O emulsion, leads to a greater conversion of water droplets into hydrate phase. It has been shown that the rates of hydrates decomposition in W/O and W/ARPD systems are of the same order, while more stable hydrates are formed in W/ARPD. Decomposition mechanism of natural gas hydrates in emulsions is more complicated as compared with the crystallization process.
Keywords: natural gas hydrate; asphaltene-resin-paraffin deposits (ARPD); crude oil; emulsion; kinetics; HP DSC.
Well Completion Operations in Gas Hydrate Reservoirs
by Sukru Merey
Abstract: With the consumption of conventional oil and gas resources, gas hydrate reservoirs have become very popular recently. Due to the sensitive nature of gas hydrate reservoirs, special cares and equipment designs are necessary during drilling and well completion of gas hydrate wells. Therefore, in this study, it was aimed to describe special well completions operations such as cementing, perforations, sand screen or gravel packing, and well completion strings during completing gas hydrate wells.
Keywords: gas hydrates; well completion; cementing; perforation; tubing string.
Extraction of Phenols from Coal Tar Oil using Binary Solvents and Ionic Liquid Mixture
by Subhash Kalidindi, Abhishek Vinayak S., Shoumitra Biswas, Duraisamy Kumaresan, R. Krishna Prasad
Abstract: The extraction of Phenols from coal tar oils using acetonitrile solutions of ionic liquids (ILs) through a new extraction method is studied. The IL containing acetonitrile solution formed a clear immiscible layer with hexane containing coal tar oil, which facilitated superior extractions of phenol and p-cresol with high distribution coefficient values. The IL with lower carbon chain length (3 carbons) showed extraction efficiency greater than 96% for phenol and p-cresol extractions from coal tar oil. The process models for extraction of phenol and p-cresol from coal tar oil were studied to comprehend the interactions of various factors.
Keywords: Coal tar; Ionic liquids; Phenols extraction; Acetonitrile-hexane mixture.
SELECTION OF OPTIMUM BIO-DIESEL FUEL BLEND USING FUZZY TOPSIS AND FUZZY VIKOR APPROACHES
by Sivaraja C.M, Gnanasekaran Sakthivel, Jegadeeshwaran R
Abstract: The demand for the energy has increased drastically as a result of the rapid growth in industrialisation, urbanisation and higher standard of living. One such potential substitute to fossil fuels is biodiesel that ensures sustainable energy source. The selection of appropriate source of biodiesel and proper blending of biodiesel plays a major role in alternate energy production. In the present work, a novel hybrid Multi Criteria Decision Making (MCDM) technique was proposed to evaluate and select the optimum fuel biodiesel blend for the IC engine with conflicting criteria. Exploratory analysis were carried out on a single cylinder four stroke, air cooled, constant speed, direct injection diesel engine with a rated output of 4.4 kW at 1500 rpm at different loads. BTE, MRPR, NOx, CO2, CO, HC, SMOKE, ID, CD and Exhaust gas temperature were considered as the evaluation criteria and similarly Diesel, B20, B40, B60, B80 and B100 were considered as the alternatives.Two hybrid MCDM models were proposed, namely Fuzzy TOPSIS Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) and Fuzzy VIKOR VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR). The obtained preference order of the blends for Fuzzy TOPSIS and Fuzzy VIKOR are B40>B20>B60 >B80>Diesel>B100 and B40>B20>Diesel>B60>B80>B100 respectively. The ranking performance of both the methods is also compared with each other and selected B40 is the best blend to operate the engine. This paper highlights a new insight into MCDM techniques to evaluate the best fuel blend for the decision makers such as engine manufactures and R& D engineers to meet the fuel economy and emission norms to empower the green revolution.
Keywords: Energy; MCDM; FUZZY; TOPSIS; VIKOR.
Modelling of design parameters of intrinsically safe instruments for the safety of oil, gas and coal industries
by Jitendra Kumar Singh, Gautam Banerjee
Abstract: Intrinsic safety is the safest technique to prevent explosions that might occur in underground coal mines and process industries in the presence of explosive gases, ignition sources and oxygen. Energy produced by the intrinsically safe equipment is far below the minimum ignition energy of the explosive gas for which it is designed. In this work, intrinsic safety and some of its parameters such as open circuit voltage, short circuit current, permitted capacitance and inductance have been studied. Three empirical relations, based on standard IS/IEC 60079-11, have been proposed for the first time in this work. These relations can be used in the calculation of short circuit current (I), permitted capacitance (C) and inductance (L) of intrinsically safe circuits designed for application in hazardous areas of gas groups IIA, IIB, IIC and I. The calculated values of I, C and L are compared with the available experimental and reported values. A fairly good agreement has been obtained between them. The average percentage deviations of calculated values have also been estimated, which lie between 9.52% to 14.58% for I and 17.98% to 36.34% for C. No deviation is observed for inductance L. The designers of intrinsically safe circuits can use these relations as a very handy and useful tool especially for the explosive gas atmosphere of underground coal mines and process industries. This research will contribute to the reduction of fatal accidents due to explosive gases.
Keywords: Capacitance; Explosive gas group; Inductance; Intrinsic safety; Short circuit current.
Aromatization and desulphurisation of liquefied petroleum gas over Zn-containing zeolite catalysts modified by transition metals
by Balga Tuktin, Larissa Shapovalova, Nurzhan Nurgaliyev, Aliya Tenizbayeva, Bates Bagasharova
Abstract: In this paper, treatment of liquefied petroleum gas (LPG) over Zn-containing zeolite catalysts modified by Mn, Cu and Fe was studied. The authors investigated catalytic activity in the aromatization and desulphurization reactions of propane-propylene and propane-butane fractions (PPF and PBF respectively). It was found that the feedstock composition did not actually affect conversion at elevated temperatures (550-600
Keywords: catalysts; zeolite; aromatization; desulphurization; liquefied petroleum gas.
Thermal Degradation and Kinetic Studies of Ionic Liquid and Mixed Solvent pretreated Indian Coals
by Sanjukta Bhoi, Kaustubha Mohanty, Tamal Banerjee
Abstract: This work focuses on the interaction of coal with three different ionic liquids (ILs) and mixed solvent for analysing the oxidizing effect on Indian Coal. The ILs; 1-butyl-1-methylpyrrolidinium methyl carbonate [BMPYR][CH3CO3], 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], and 1-butyl-4-methylpyridinium tetrafluoroborate [BMPY][BF4] were subsequently used for dissolution studies. The Thermogravimetric Analysis result shows that the mass loss was less for both [BMPYR][CH3CO3] and mixed solvent ([BMPYR][CH3CO3] + pyridine) pre-treated coal as compared to other. Hence the IL has the largest ability to fractionate the more active oxygen containing functional groups present in the coal. The thermal degradation study shows that the thermal stability of mixed solvent and IL-pretreated coal provides a temperature of above ~630
Keywords: Activation energy; coal; combustion; devolatilisation; dissolution; fragmentation; ionic liquids; pyrolysis.
Simplification of Complex Fracture Morphology and Its Impact on Production
by Palash Panja
Abstract: Significant amounts of oil and natural gas in the USA are produced from fractured reservoirs. Fracture morphology and effectiveness of fracturing job depend on various factors such as geological properties (permeability, porosity, and heterogeneity), mechanical properties (Youngs modulus, Poissons ratio, stress anisotropy, maximum horizontal stress) and fracturing operational parameters (fluid injection rate, fluid viscosity). Reservoir engineers job is to import the fracture geometry into reservoir flow simulator in order to forecast the production of hydrocarbons to evaluate a plays potential. In this research, various issues related to simplification of rigorously-generated fractures are investigated. A systematic approach including practical flow consideration in hydraulic fracture with heterogeneous permeability and width along the length is developed. The complex fractures morphology is simplified in two proposed models with mathematical formulations. Simplified models show promising alternatives in rapid forecasting of production of hydrocarbon without losing the characteristic of fracture properties like complex morphology and bottleneck. Oil recovery, cumulative gas oil ratio (GOR), oil rate and average reservoir pressure are compared with results from complex fracture morphology. One field case is used to demonstrate the validity of the method.
Keywords: Fracture morphology; simplified fracture models; Bottleneck of flow; oil recovery; GOR;.
A Modified Exponential Decline Method for Shale Gas Reservoirs
by Shaolei Wei
Abstract: Compared with conventional reservoirs, the production rate in shale gas reservoirs declines rather quickly during the early production period and gradually becomes shallow. The sharp decline is a specific characteristic of the transient flow period which may last for a number of years due to the extra low permeability in shale gas reservoirs. Conventional decline analysis with production data in the transient period often obtains a constant decline exponent larger than 1, which leads to unlimited cumulative production and overestimation of gas reserves. A predetermined terminal decline rate is manually given to solve this problem. However, different values of terminal decline rate lead to variant reserve estimation and no common sense about how to determine this value has been achieved.
In this article, we build a four parameter empirical decline model considering the varying decline exponent and terminal decline rate and propose a simple but efficient calculation method. By analyzing the sharp-to-shallow decline trend, a more sophisticated decline rate form was assumed, which can take the initial decline rate, terminal decline rate as well as the curvature of the decline rate curve into consideration. An empirical decline formula with four production parameters can be derived by integrating the decline rate equation with respect to time. Direct regression of the four parameters is rather complicated because the production rate equation is strongly nonlinear. By integrating the log-production rate, the nonlinear problem is reduced to a linear problem, which can be easily solved with matrix operation. The above solution process is applicable for shale gas production prediction with a long production history. For shale gas reservoirs with short production time and little production data, the early production data may not reflect the real terminal decline rate. A modification for such cases is also proposed. Model-based analyses and diagnosis curves are employed to determine the decline exponent, which is then employed to determine a reasonable terminal decline rate.
Field examples from a synthetic shale gas reservoir, Barnett shale gas, Haynesville shale gas and Fuling shale gas were used to test our newly proposed model. Estimated ultimate recovery (EUR) was employed as a key comparison index. The synthetic shale gas reservoir was constructed by Imad Brohi et al., which was introduced to test the effectiveness of our newly proposed model. Barnett shale gas was a representative for cases with a long production history, while Haynesville and Fuling are representatives for cases with medium-short production history. The results indicate that the new method is able to provide a reasonable EUR estimation and is much easier to handle than other alternative methods. Besides, the integration processing rather than difference processing are more tolerant of poor quality production data.
Keywords: shale gas; reserve estimation; varying decline exponent; terminal decline.
A Transient Flow Model for Multilateral Horizontal Wells in Bottom Water Drive Reservoirs
by Ping Yue, Chunqiu Guo, Xiaofan Cheng, Liandong Tang
Abstract: The aim of this paper is to describe the pressure dynamic behavior around a multilateral horizontal well in bottom water reservoir by establishing an analytical transient flow model. An exact solution of the model is derived by means of Orthogonal Transformation, method of Mirror Images and the theory of Potential Superimposition. For bottom water reservoirs, there is a supplementary boundary from the water aquifer. Given enough time, the transient flow will change to steady flow gradually. Correspondingly, the productivity index for wells in bottom water drive reservoirs can be calculated. We conclude that the analytical solution to the model can provide a valuable tool to compute the productivity and pressure dynamic behavior of the multilateral horizontal wells in the bottom water reservoirs. Moreover, the case study shows that the calculated results agree with the practical situation.
Keywords: multilateral horizontal; transient flow; volumetric source; orthogonal transformation; bottom water reservoirs; productivity index.
Analysis of distillate product in the direct coal liquefaction of a Chinese bituminous coal
by Ruili Tong, Haiyong Zhang, Yonggang Wang, Xiangkun Meng
Abstract: To understand the reaction mechanism of coal liquefaction process and further improve the direct coal liquefaction (DCL) technology, a certain kind of DCL oil, which was prepared from a Chinese bituminous Yulin coal, was first separated into different fractions using improved silica-gel column chromatography (SGCC) coupled with the UV-absorbance detector, and then identified by gas chromatography-mass spectrometer (GC-MS), the comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometer (GC
Keywords: bituminous coal; direct coal liquefaction; distillate product; oil; SGCC; GC×GC-TOFMS.
Preparation of ZnO-MWCNTS Nanocomposite: Structural Features and Applications for Enhanced Oil Recovery
by Noorhana Yahya, Muhammad Kashif, Nadeem Nasir, Zia Ur Rehman
Abstract: Since last few decades, the importance of tertiary oil recovery is increasing day by day. Quest for novel hydrophobic materials compatible to oil for enhanced recovery using electromagnetic is the major focus in this field. In the present study, we present ZnO-MWCNT nanocomposite prepared using sol-gel technique for the application of enhanced oil recovery. The effects of annealing temperature on the structural and optical properties of ZnO-MWCNT nanocomposite were investigated. Phase analysis revealed that material formed possess single phase, hexagonal wurtzite structure with major peak of  and average particle size in the range of 30-39 nm. Furthermore, the crystallinity of ZnO increased with the annealing temperature. Morphology analysis showed that ZnO are coated on the surface of the MWCNT. Vibrational analysis indicated that ZnO-MWCNT nanocomposite exhibited E2 (high) mode of ZnO and G (sp2 carbon) bands of MWCNTs and intense sharp peak of Zn-O stretching bond. A 11.11 % of oil recovery was observed using ZnO-MWCNT composite nanofluid. This recovery further enhanced to 16.10 % under the effect of electromagnetic field. Hence this novel material can be used to enhance oil recovery with application of EM waves, as well as can find applications in other chemical reactions using electromagnetics.
Keywords: ZnO-MWCNTS; nanocomposite; EOR; electromagnetics.
Production calculation of multi-cluster fractured horizontal well accounting for stress shadow effect
by Qingdong Zeng, Jun Yao
Abstract: The objective of this study is to investigate the effect of stress shadow in the process of multi-cluster fracturing on the production of horizontal well. First, the model of simultaneous propagation of multiple fractures is established with coupling rock deformation, fluid flow in fracture and wellbore. This model is solved by using iterative procedure. Based on the solution of hydraulic fracturing, a modified method is presented to calculate transient production of horizontal well by using source function and superposition principle. Two scenarios in regards to fracture conductivity have been considered. In the situation that fracture conductivity is varying, the variation of fracture width is captured by joint element method. Thus, the relation between model of hydraulic fracturing and of production calculation is well established. Both models have been verified, and the effect of stress shadow on well production has been analyzed. Results show that accounting for stress shadow helps to increase well production. As fluid is extracted out from wellbore, the fracture conductivity would decrease rapidly, and then it leads to decrease well production. Moreover, the model is extended to calculate production of simultaneously fractured wells.
Keywords: horizontal well; hydraulic fracturing; stress shadow; displacement discontinuity method; joint element method; source function.
Experimental Study on Methane Hydrate Formation and Evaluation in Porous Medium
by Zhiqiang Wang, Shuxia Li, Fubo Wu, Jian Hou
Abstract: Methane Hydrate (MH) is considered as a potential energy resource, and its laboratory research is very significant. Although many patterns about MH formation have been proposed by many researchers, the formation rate and formation efficiency of MH have rarely been reported. In this work, two patterns of gas injection (intermittent gas injection and continuous gas injection) have been conducted to simulate the hydrate reservoir formation process. It is shown that the continuous gas injection pattern can result in higher hydrate saturation in a relatively short time, while in the intermittent pattern, the early formation of MH near the gas inlet valve will prevent the later injected CH4. The continuous gas injection pattern can keep higher pressure in the reactor, which is beneficial to the MH formation. Moreover, two evaluation indicators, hydrate formation efficiency (Es) and formation rate (Ve), have been proposed to compare the performance of the two patterns. The continuous gas injection pattern has higher Es of 0.837 and Ve of 9.03E-04 min-1, while in intermittent gas injection, Es is 0.754 and average Ve is 7.41E-05 min-1. It is recommended that continuous gas injection pattern is used in the laboratory.
Keywords: methane hydrate; porous medium; injection pattern; formation efficiency; formation rate.
Micro-fracture Development Impact Factors Analysis and its Effects on Well Production of Hua-qing Area Ordos Basin in China
by Feng-juan Dong, Yuan Cao, Da-zhong Ren, Wei Sun
Abstract: Micro-fractures, which are characterised by complex-non-structural
geneses, are critical in tight sand reservoir production. Taking the Chang 6
reservoir of the Huaqing area, the Ordos basin, as an example, the influential
factors of the micro-fracture development are analysed from a novel
perspective. Studies show that the influences of above factors on micro-fracture
are listed as follows: brittle mineral content > median grain size > stratum
thickness > overburden pressure. In same lithology, enrichment position of
rigid compositions is a key factor to the micro-fracture generation. However,
sandstones are rigid and prone to forming micro-fracture. The effect of
diagenesis on micro-fracture development is quite complex. Micro-fractures
generate at the contact position between soft and hard materials. And then, the
effects of micro-fractures on the well production have been analysed, which
hence offers scientific guidance for further high-efficiency development of the
Chang 6 tight sandstone oil reservoir in this area.
Keywords: HuaQing area; Chang 6 reservoir; micro-fracture; influencing
factors; well production; China.
Study on the methane adsorption characteristics of coal with heterogeneous potential wells
by Dong Zhou, Zengchao Feng, Yangsheng Zhao
Abstract: Due to the various components and the complex inner structures, the coal has the heterogeneous adsorption potential wells. The methane adsorption laws of the coal with heterogeneous potential wells are theoretically analyzed and experimentally studied. It is concluded that the coverage of the potential wells with different depth obeys the law of the Logistic (S) curve with the parameters of the adsorption pressure and the temperature. During the methane adsorption in coal, the Langmuir parameter a of coal has a fluctuate growth with the adsorption pressure increase, which is indicated that the number of the potential wells in coal with different depth tends to increase with the depth decrease. The Langmuir parameter b shows decrease trend with the adsorption pressure increase as the methane molecules in coal tend to be adsorbed in the deep potential wells. The heterogeneous potential wells method (HPWM) for the methane isothermal adsorption amount calculation is put up. From the experiment, the high positive errors are shown in low adsorption pressures based on the Langmuir's equation while the high negative errors are shown in high adsorption pressures. The methane adsorption amount calculation based on the HPWM is much accurate than that based on the Langmuir equation.
Keywords: adsorption potential well; heterogeneity; adsorption pressure; methane adsorption amount; calculation accuracy.
A high temperature furnace for in-situ SAXS measurement of coal carbonization
by Fei Xie, Dongfeng Li, Zhenzhong Li, Zhihong Li
Abstract: High temperature carbonization is one of the main ways of coal utilization. Small angle X-ray scattering (SAXS) with synchrotron radiation can be used for in-situ measurement of the carbon network structure change during heating coal. Recently, we developed a high temperature (1200
Keywords: Coal; High temperature carbonization; Furnace; Small angle X-ray scattering; Fractal.
Coal tar refining by aromatic-aliphatic solvent extraction for preparing QI-free pitch
by Yonggang Wang, Jianhong Hu, Dan Liu, Zhe Liu, Haiyong Zhang, Shu Zhang
Abstract: This study is to refine coal tar using solvent extraction method to obtain suitable raw material for making needle coke. The aromatic solvent (coal tar fraction) and aliphatic solvent (petroleum fraction) were used as mixed solvents for extracting desirable compositions from coal tar and simultaneously removing the heavy components, particularly quinoline insoluble (QI). The results show that the very low QI content (0.06 Wt%) in refined coal tar was acquired when the aromatic portion in the mixed solvent was around 30 Wt%, while the yield of refined tar increased with increasing aromatic solvent in the mixture. Under the given ratio of aromatic to aliphatic (2:3 by mass), the QI contents and refined tar yields both reduced as the ratio of mixed solvent to coal tar increased. The fractions (HS, HI-TS, TI-QS) in the refined tar were largely affected by the ratios of aromatic to aliphatic solvents and the mixed solvent to tar. The distribution of molecular sizes in refined tars (revealed by GC-MS analysis) were determined by the solubility of tarry compositions in the mixed solvent and the precipitating process due to the agglomeration of QI-like materials in the solvent.
Keywords: coal tar; QI; aromatic solvent; aliphatic solvent; solvent extraction.
Atmospheric Monitoring Systems (AMS) in Underground Coal Mines Revisited: A Study on Sensor Accuracy and Location
by Kemal BARIS, Yusuf AYDIN
Abstract: This study covers the long-term measurements and applications done between 15.01.2015 and 21.10.2016 in the Kozlu Colliery, one of the five collieries of Turkish Hardcoal Enterprise (TTK), Zonguldak, Turkey. It intends to address the practical problems encountered with the gas and air velocity sensors used in underground coal mines, and attempts to justify the accuracy of sensors. It also aims at determining the correct locations of the gas and air velocity sensors within cross-section of mine entries. Moreover, air densities were calculated to interpret the positions of individual gases within the mine air. The results showed that the infrared CH4 sensors used in the mine do not accurately measure CH4 concentrations at their current locations. Moreover, they are affected by relative humidity and thus necessitates more frequent calibration at places having high relative humidity. The air velocity sensors used in the mine are completely ineffective in their current state. Changing their locations led to better yet ineffective results. It was found that a correction factor of 1.25 is needed to correct air velocity sensor readings. It was concluded that air velocity, CH4 and CO sensors must be installed to points where air flow is higher, considering the Amagats law.
Keywords: AMS; gas sensors; methane; air velocity; underground mining.
Prediction of Methane Content of Deep Coal Seams in the Sunan Mining Area in Anhui Province, China
by Zhigen Zhao, Fengtang Sui, Jiaping Yan
Abstract: The prediction of the methane content in deep coal seams in the Sunan mining area is an important goal and an exploratory investigation. In this study, the pressure-adsorption curve method is used to predict the theoretical adsorption quantity of methane and the free quantity of methane at different burial depths using the No. 82 coal seam in the Qidong coal mine in the Sunan mining area as an example. The methane contents at different burial depths of the coal seam are predicted based on the gas saturation and the theoretical methane content. The proposed prediction method not only solves the problem of predicting the methane content of deep coal seams in the Sunan mining area but also provides a valuable reference for the methane content prediction of deep coal seams in other mining areas.
Keywords: Sunan mining area; deep coal seam; methane content; prediction; burial depth; reservoir pressure; reservoir temperature; coal quality; theoretical adsorption quantity; pore volume coefficient; methane pressure; free quantity of methane; gas saturation.
Lattice Boltzmann method for simulation of shale gas flow in kerogen nano-pores considering temperature dependent adsorption
by Yudou Wang, Jiankang Xue, Diansheng Wang, Qingzhong Xue
Abstract: Adsorption is an important factor of shale gas transport in a kerogen pore. The combined action of adsorption, surface diffusion and gas slippage could result in complicated non-Darcy effects in shale gas production, and so classical simulation approaches based on Darcys law may not be appropriate for simulating shale gas flow in shale. In this work, a novel lattice Boltzmann (LB) model is proposed to study shale gas flow in a kerogen pore by introducing temperature dependent thickness of adsorption layer. The thickness of adsorption layer is related to temperature based on Langmuir isotherm equation. The surface diffusion, which is caused by gradient of adsorption density, is considered as the slippage velocity on the surface of adsorption layer. The proposed LB model was adopted to simulate shale gas flow in a nano-pore. The results show that adsorption can significantly decrease the permeability of nano-pores. Gas in organic pores, where more gas is adsorbed, is more difficult to produce than that in pores where no adsorption occurs. Surface diffusion improves the gas movement in nano-pores at lower pressure. With the decrease of the pore size, the adsorbed layer had more impacts on gas permeability. Increasing temperature improves gas flow ability in nano-pores. When pore size is larger than 10nm, the effect of temperature on permeability can be ignored.
Keywords: Lattice Boltzmann method; temperature dependent adsorption; surface diffusion; slippage; shale gas; flow in nano-pore.
Process Monitoring and Troubleshooting of a local Refinerys Hydrogen plant using Multivariate Methods
by Mohamed Bin Shams, Abdalrahman Abdulla, Osama Khalaf, Saed Al-Tamimi
Abstract: Modern refineries are equipped with distributed control systems (DCS) for monitoring and regulation. Process measurements are acquired and stored in data historian. These measurements are inherently correlated, and therefore, multivariate based techniques becomes an appropriate tool for monitoring and troubleshooting. This paper demonstrates the use of principle component analysis (PCA) as an analytics tool for process monitoring and troubleshooting. A real case study from a local refinery in Bahrain was used to prove the proficiency of PCA. To demonstrate the ease and flexibility of the proposed scheme, all model buildings and testing were done using a specialized commercial software. The aim is to assist operators and engineers in refineries and petrochemical plants to realize the advantages of multivariate methods for troubleshooting plant and equipment upsets. The latter is necessary to assure safe, reliable and profitable operation.
Keywords: Multivariate Analysis; PCA; Contribution plot; Hydrogen plant; Troubleshooting; Fault detection and diagnosis.
Impact of variables on the naphthalene hydrogenation for the tetralin formation towards BTX production.
by Pedro M. Vega-Merino, Roberto Quintana-Solórzano, Georgina C. Laredo, Elva Arzate-Barbosa, Eli Hazel Olmos-Cerda
Abstract: To achieve high naphthalene conversion and selectivity to tetralin as a first step for BTX production, experiments were carried out in a bench-scale setup processing four model mixtures with a commercial CoMo/Al2O3 catalyst at 250-375
Keywords: Light cycle oil; BTX; hydrogenation; tetralin.
Hydraulic fracturing and its effect on gas extraction and coal and gas outburst prevention in a protective layer: A case study in China
by Liang Cheng, Zhaolong Ge, Jiufu Chen, Lishuang Zou, Yugang Cheng, Songqiang Xiao
Abstract: Mining a protective layer is an effective means for preventing coal and gas outbursts in underground coal mines; it has been used widely. However, if the protective layer is a seam with coal and gas outburst risk, gas extraction to eliminate that risk is important to ensure safe and efficient coal production. In this paper, Tonghua coal mine, China, is taken as an example to demonstrate the effects of gas disasters prevention using hydraulic fracturing (HF). The effects of HF-aided gas extraction on rock crosscuts coal uncovering, on the coal roadway excavation, and on a protective coal seam are investigated. The results show that: (1) HF can effectively improve the efficiency of gas extraction. Comparing layers from which gas has been extracted both with and without HF shows that with HF, the gas production and gas extraction rate increased by 62.12% and 55.18%, respectively, and the time and the borehole number of gas pre-drainage decreased by 37.6% and 45.66%, respectively. (2) Efficient gas extraction reduces the occurrence of mine gas safety violations significantly. The gas exceeding the limit accidents decreased by 89.3% in mine areas in which HF was used. (3) The production efficiency of the protective layer increased significantly. Working face preparation time decreased by 38.52%, average monthly working face advance increased by 49.5%. (4) The average methane content in the gas extracted reached 39.49% and thus coalbed methane was used for power generation instead of being vented to the atmosphere. This study could be used as a valuable example for other coal deposits being mined under similar geological conditions.
Keywords: mining safety; gas disaster; hydraulic fracturing; coal and gas outburst; coalbed methane.
Selecting Best Painting Colour for Crude Oil Storage Tanks Exterior Surface
by Mahmood Farzaneh Gord
Abstract: The crude oil temperature, which highly influenced by solar heat and ambient temperature, has strong effects on the sludge formation and evaporative loss. Here, a numerical method has been presented for predicting the transient average crude oil temperature in storage tanks and the evaporative losses. In addition, the method has been presented to estimate sludge build up at the bottom of an in-use crude oil storage tank. The API AP-42 standard and the measured data have been used to validate the predicted crude oil temperature. For sludge formation validation, a comprehensive effort has been made to measure the sludge height in the bottom of a crude oil storage tank over evenly distributed intervals for more than a year. The good agreement is obtained between the numerical and measured value of the sludge height. Results show that the annual evaporative losses rise up to 125% if the tank exterior surface absorptivity is increased as 90% of the solar irradiation is absorbed. Passive voice to- In contrast to the evaporative losses, the sludge build up is decreased as the tank exterior surface absorptivity is decreased and consequently the crude oil temperature is increased. It was found that, the sludge height is reduced about 50 mm per months, when the absorptivity of the tank exterior surface is increased from
Keywords: crude oil storage tank; crude oil; sludge build up; exterior surface paint color; evaporation loss.
The Design of Two-stage Gas and Liquid Cylindrical Cyclone and Numerical Simulation of Internal Flow Field Characteristics
by Zhaoming Yang, Jianlei Chen, Yunrui Han, Limin He, Xiaoming Luo
Abstract: High gas-liquid ratio condition exists in offshore gas field frequently and for this condition, a novel two-stage gas and liquid cylindrical cyclone is designed. The size parameters of the separator is designed by using effective volume transformation methods, and a new method for diameter determination is also proposed based on the characteristics of liquid drop breaking in swirl field. Different turbulence models, different meshing schemes and different discrete formats are compared in order to choose one best numerical simulation plan and this plan also have been validated by existing experimental data. The characteristics of asymmetry and vortex-core boundary are analyzed by CFD about the internal flow field of the simplified model and the influences of structural parameters and operational parameters are obtained.
Keywords: high gas-liquid ratio; cyclone separation; numerical simulation; asymmetry; vortex-core boundary.
Difference in Perforation Rates of Jetting Tool Nozzles and Influencing Factors
by Jiarui Cheng, Yihua Dou, Zhen Li, Lu Cui
Abstract: Variations in the rates of hydraulic perforation among different jetting nozzles are common in gas well development, especially the multi-stage perforation of horizontal wells. A laboratory experiment was conducted to analyse the effects of flow rate, liquid viscosity and particle size on the perforation rate of a multi-nozzle structure under liquidsolid flow. The spatial distributions of particles and sample erosion rates were documented for multi-stage multi-angle nozzles with a variable difference in liquid properties and flow parameters using three particle sizes. Results showed that the difference in perforation rates among the nozzles was affected by the particle distribution inside the jetting tool and the energy of the particles ejected by each nozzle. Furthermore, the difference in perforation rates of nozzles with different jet angles was markedly affected by particle size, then by the flow rate and finally the liquid viscosity.
Keywords: hydraulic perforation rate; multistage and multi-angle nozzles; jet erosion test; perforation non-uniformity; particle following property.
Preventing gas migration after hydraulic fracturing using mud cake solidification method in HTHP tight gas well
by Jun Gu, Hangxian Gao, Pin Gan, Penghui Zeng, Jiahe Chen, Haiyang Hao
Abstract: The mud cake solidification (MCS) at cement-formation interface (CFI) is a key to improve the liner cementing quality and zonal isolation ability for preventing gas migration after hydraulic fracturing in high temperature high pressure (HTHP) tight gas wells. This paper introduces a new method of MCS, consisting of mud cake solidification agents (MCSAs) (GJE-I and GJE-II) as spacers in front of cement slurry. The results of experimental evaluation show that when the curing time is 3, 7 and 15 days at 132 C and 21 MPa, compared with the conventional method, the bond strength at CFI was improved by 907.16%, 829.57% and 988.45%, respectively. Moreover, the compatibility among the cement slurry, flushing spacer, drilling fluid, and MCSAs meets the requirements for liner cementing operation of HTHP tight gas wells. The image evidences of MCS were obtained. The mechanism of MCSAs for the improvement of the bond strength at CFI was discussed.rnThe field application shows that the qualified ratio of cementing quality is 100%，the ratio of high quality is up to 92.31% and the gas migration rate after well cementing and hydraulic fracturing decrease rapidly to zero. Compared with the conventional method, the qualified ratio of cementing quality was improved by 15.56 percentage points and the gas migration rate after well cementing and hydraulic fracturing decreased from 23.33% to 0. It proved that the MCS method has the best capability for improving zonal isolation ability and preventing gas migration in HTHP tight gas wells. A case of new method in a HTHP tight gas well was also presented.
Keywords: HTHP tight gas well; hydraulic fracturing; gas migration; liner cementing; zonal isolation; mud cake solidification agents; MCS method; cement-formation interface.
Development of a Gas Injection Rate Model for Gas-drilling Horizontal Wells Based on the Onset of Cutting-particle Motion
by Xiaohua Zhu, Biao Liu
Abstract: Gas-drilling horizontal wells (GDHWs) can increase the rate of penetration in hard formations, help protect hydrocarbon reservoirs and enhance recovery efficiency. Given currently there are few effective models modified by reproductive experiments to predict the minimum gas injection rate in GDHWs. In this study, a new model is developed to predict the minimum gas injection rate in GDHWs based on the onset of cutting-particle motion, meanwhile a simulation equipment is designed to mimic a GDHW to understand the onset of cutting-particle motion and modify the model innovatively. The results provided by the modified model show that the minimum gas flow rate required to start cutting-particle motion rises with increases in the size and degree of flatness of the cuttings and the subsidence constraints of the borehole. Analysis using field data in the published article demonstrates that the modified model can accurately predict the minimum gas injection rate in GDHWs.
Keywords: Gas injection rate; Onset of cutting; Gas-drilling horizontal well; Experimental verification; Predictive model.
Semi-analytical evaluation for water-alternating-CO2 injectivity in tight oil reservoirs
by Fankun Meng, Yuliang Su, Wendong Wang, Qun Lei, Dongbo He
Abstract: The loss of injectivity during water-alternating-CO2 flooding in tight oil reservoirs has become one of key factors seriously influencing enhanced oil recovery (EOR), particular for water injection process. It is significant to evaluate the injectivity accurately and efficiently during watet-alternating-CO2 flooding. This paper presents a new semi-analytical model to estimate the bottom-hole pressure drop for a water-alternating-CO2 injection well in a horizontal, linear, homogenous tight oil reservoir with constant-pressure boundary. In this model, the dissolution of CO2 in crude oil and injected water, and the vaporization of light components from oil are considered by modifying the conventional Buckley-Leverett (B-L) equations. Both water and CO2 are injected into the formation at a constant rate. Laplace transformations and Stehfest inversion algorithm are employed to calculate the bottom-hole pressure drop to reflect the variation of water injectivity. There is a good agreement of pressure profile at different times between the proposed and numerical models, then the validity of the proposed model is verified. In addition, the accuracy of this model is validated by comparing the pressure drop with experiments and numerical simulation data collected from published paper. A synthetic case is used to study the effects of the interfacial tension between CO2 and oil, the CO2 slug size, and the reservoir permeability on injectivity. The sensitivity analysis indicates that with the reduction of interfacial tension and the increase of the CO2 slug size, the water injectivity will be improved. The water injectivity strongly depends on the reservoir permeability. The larger the reservoir permeability, the higher the water injectivity. When the formation permeability is lower than 0.075mD, the injectivity will decline drastically, and more attentions should be paid to the evaluation of water injectivity.
Keywords: Water-alternating-CO2 flooding; injectivity; modified B-L equations; tight oil reservoirs; sensitivity analysis.
Investigations on Geological Aspects of Capillary Transition Zones of Carbonate Reservoirs by Applied Imaging Techniques
by ACHINTA BERA, Hadi Belhaj, Jiayi Wand
Abstract: This study focuses on the petrographic analysis of thin sections of the rock composites such as grain and cement, pore types and geometry, diagenetic events like dissolution and compaction, their modifications on the pore systems, factors that decide wettability and rock-fluid interaction, which has an impact on relative permeability. An imaging technique such as computerized tomography (CT) scan has been used to find out more information on the geometry, texture, and distribution of the pore systems of the transition zone samples which control petrophysical properties of seventeen rock samples. Thin section and petrophysical study were conducted to examine the diagenesis of the samples. It has been found that five major diagenetic processes have affected this transition zone including micritization, dissolution, cementation, dolomitization, and compaction. Medical CT scan confirmed the presence of three types of heterogeneities varying from low to medium to high in the rock samples of the transition zones.
Keywords: Transition Zones; Carbonate reservoirs; Petrographic analysis; Diagenesis; CT scan.
A novel model of initial fracture pressure in fractured formation
by Yi Ding, Pingya Luo, Xiangjun Liu
Abstract: Initial fracture pressure is the basic parameter in design and optimization of hydraulic working, having significant impact on reservoir stimulation. In fractured formation, abundant natural fractures make formation have strong anisotropy, increasing the complication and uncertainty of predicting initial fracture pressure. Without accurate initial fracture pressure, reservoir stimulation efficiency will be hugely impaired. Therefore, in this paper, according to linear elastic and space geometry theory, stress distribution around perforated borehole has been obtained. Meanwhile, in combination with tensile and shear failure mechanism, we apply superposition theory to develop shear and tensile strength criterion with multiple natural fracture planes. By using these criteria and stress distribution, fracture initiation model for reservoir with rich natural fractures has been established. Based on this model, influences of natural fracture occurrence, fracture number and engineering parameters on fracture initiation have been analysed. These results indicate that in fractured formation, initiation type could be tensile failure or shear failure along natural fracture plane, which both will decrease the initial fracture pressure. The distribution of initial fracture pressure is related to natural fracture occurrence. The decline of initial fracture pressure is becoming large due to increasing fracture number. In particular, with multiple natural fractures condition, initiation is totally controlled by natural fractures. Under the constant geological condition, drilling and perforation parameters are able to change the initiation pressure distribution and the affecting degree of natural fracture. In the application, this model is used to MH well of oilfield in Western China. Its results are good consistent with hydraulic fracturing data, proving its practicability. Thus, this model can be used for prediction of fracture initiation and offer guidance for hydraulic fracturing in oilfield.
Keywords: fractured formation; natural fracture; hydraulic fracture; initial fracture pressure.
Rock Failure by thermal stress in Gas Drilling
by Jun Li, Shunji Yang
Abstract: The factors that contributing high penetration rate of gas drilling are complex. Isentropic flow was generated when gas pass through bit nozzle during gas drilling. This phenomenon would lead to cryogenic effects. The thermal stress on the bottom hole rock was formed by the effect, which can reduces the strength of the rock and promotes the mechanical rock breaking. First, the temperature distribution model of bottom hole rock under the condition of asymmetric cooling was built in the paper. The three-dimensional dynamic thermal shock stress distribution model was established based on the temperature model. Then, the change of the rock cohesion was analysed by using the Moore Coulomb criterion. The results demonstrate that with the temperature decreases, the strength of rock is greatly reduced, can improve ROP. Last，the liquid nitrogen cooling test and real time measurement of acoustic wave were conducted to verify the above analyse. The First wave amplitude has a dramatic delay, which illustrate the cooling have an important impact on rock internal structure. The paper clearly depicts the mechanism of rock failure under the condition of dynamic low temperature in gas drilling.
Keywords: Gas drilling; Low temperature; Thermal stress; Moore Coulomb criterion; Acoustic test.
A new combination model for delay outburst of coal and gas
by Lehua Xu, Haina Jiang
Abstract: Sudden ejection of coal and gas in a delay outburst accident usually causes even heavier losses than an instantaneous outburst accident. A new combination model composed of outburst-prone soft coal and barrier layer was proposed to better categorize instantaneous outburst and delay outburst. The model offered an explanation for the delay outburst phenomenon, which demonstrates that it is the barrier layer between the work space and the soft coal that defers the occurrence of an outburst accident. Based on this model, delay outburst accidents in China from 2006 to 2016 were investigated. There were 42 delay outburst accidents resulting in 251 deaths, and the frequency of delay outburst accidents during operation of drilling accounted for 38.1%. Furthermore, the delay outburst process was numerically simulated. The simulations show that creep strain increases with the increase of stress, and gas pressure drops with increasing permeability of the barrier layer.
Keywords: coal and gas outburst; delay time; soft coal; gas pressure; operation mode.
A new analysis model for heterogeneous shale gas reservoirs
by Wei-Hong Peng, Feng Gao, Haixiang Zhang, Guohua Cao
Abstract: In this paper, a new analysis model (MNH), which considers the interactions of flow regimes in matrix, discrete natural fractures and discrete hydraulic fractures, is developed for a heterogeneous shale gas reservoir. In this MNH model, the gas flow in shale matrix is described by non-Darcy law and gas desorption is also considered. Gas flow in discrete natural fractures follows the cubic law in each fracture and these natural fractures are described by a discrete fracture model. An equivalent method is put forward to describe the flow regime in hydraulic fractures. This MNH model is then used to analyze the flow regimes of shale gas flow within a multi-stage fractured horizontal well. The numerical results suggest that the pressure distribution within shale gas reservoir is strongly heterogeneous. The pressure decline propagates first in hydraulic fractures, then in natural fractures and finally in shale matrix. This makes the gas flow from shale matrix to natural fractures, then to hydraulic fractures and finally to the horizontal wellbore. It also investigates the influences of gas desorption, natural fracture aperture (dn), hydraulic fracture aperture (dh), hydraulic fracture spacing (Lf) and natural fracture number (fn) on the gas production rate. Eight cases with various combinations of dn, dh, Lf and fn are numerically studied to explore the total influence of these parameters on shale gas production. Further, the impacts of attenuation coefficient (τ) and stability coefficient (n) are analyzed in details. It is found that the cumulative production at the 1000 days can be increased almost 5 times with the desorbed gas than without the desorbed gas. Hydraulic fracture apertures have a greater impact on gas production rate in earlier time, however, natural fracture apertures affect the gas production rate in the whole production process. Hydraulic fracture spacing has a significant influence on gas production rate in the whole production period, and its effect become weaker and weaker with production time. Increasing hydraulic fracture aperture and reducing hydraulic fracture spacing are the most effective measure to enhance the shale gas production. The results show that this MNH model can provide insights into flow mechanisms and production prediction for a multi-stage fractured horizontal well in shale gas reservoirs.
Keywords: MNH; Heterogeneous shale gas reservoir; non-Darcy; Gas desorption; Gas production rate.
Analysis of Transient Production Rate Performance of Horizontal Well in Fractured Low Permeability Reservoirs Based on Finite Element Method
by Fulei Zhang, Ruizhong Jiang, Haijun Fan, Ming Yang, Yongzheng Cui, Zeyang Shen
Abstract: The proportion of oil produced from low permeability reservoir has increased in China in recent years and the nonlinear seepage exists in low permeability reservoirs widely according to laboratory tests and field experiences. Most previous scholars research only focus on threshold pressure gradient, which cause large errors when interpreting transient production rate performance due to nonlinear seepage and stress sensitivity in low permeability reservoirs. A mathematical model of horizontal wells in fractured low permeability reservoirs considering nonlinear coefficient is established in this paper, which is solved by finite element method(FEM). Sensitive analysis is conducted on relevant parameters including permeability modulus, nonlinear coefficient and so on. With the effect of nonlinear cross flow, the concaves of derivative curves of pressure and production rate become shallower and move to the right. The paper significantly improves the reliability of interpretation results of fractured low permeability reservoir production rate data.
Keywords: transient production rate performance; low permeability reservoir; stress sensitivity; dual-porosity; horizontal well; FEM.
Investigation of the factors causing the coalbed methane production differences in Shizhuangnan Block, Southern Qinshui Basin, North China
by Guoqiao Yang, Shuheng Tang, Songhang Zhang, Zhongcheng Li
Abstract: The geology and engineering characteristics are investigated in the Zaoyuan area of the Shizhuangnan Block, Southern Qinshui Basin to determine variations in the water/gas production not only amongst regions, but wells within the same region. Using geophysical logging, hydraulic fracturing and production data, it appears that a roof/floor with low shale content may be the cause of excessive water production when a coal reservoir predominantly develops horizontal fractures due to hydraulic fracturing. Maintaining a slowly bottom hole pressure decline rate before gas production and stable after producing gas is favorable for the extension of the pressure drop funnel. This is also more likely to help wells have high gas production over their lifetime. Whether or not a coal reservoir depressurizes fully is crucial for gas production in both north and south regions.
Keywords: coalbed methane (CBM); Qinshui Basin; coal seam roof/floor; hydraulic fracture; drainage system.
Modeling air injection in shale oil reservoirs: Physical process and recovery mechanism
by Hu Jia
Abstract: In this paper, reservoir simulation approach is conducted for qualitative analysis on EOR mechanisms of air injection in shale oil reservoirs. Effects of oxygen molecular diffusion, reaction enthalpy, activation energy, reaction scheme, and flowing well-bore pressure on the well performance of air injection are examined in detail. Results show that oxygen molecular diffusion has great effect on spontaneous ignition temperature, heat transfer and oil recovery, which should be considered in simulating air injection in shale oil reservoir for better understanding the real mechanisms. Reaction enthalpy and activation energy can significantly affect ignition temperature, but not on the production performance. High oil recovery can be favorably achieved when the crack reaction dominates, while the combustion reaction exhibits a negative effect on production performance. The development scheme with lower flowing well-bore pressure is more favorable for the air injection process. In-situ combustion and heat transfer cannot sustain due to the air low injectivity. More hydraulic fractures as well as an improved understanding of fracture and its distribution is helpful for enhancing air injectivity to better perform synergic recovery mechanisms of air injection in shale reservoirs.
Keywords: air injection; shale oil; mechanism study; reservoir simulation; enhanced oil recovery; reaction model.
Experimental Study on Gas-Solid Flow Performance of a Jet J-valve
by Yuwei Zhang, Xiaocheng Liu, Xiang Xu, Xiaoyong Xue, Xiquan Li
Abstract: To solve the problem of a high pressure drop in an ordinary J-valve, this paper describes the design of a new type of J-valve, namely, the Jet J-valve. We contrast the ordinary J-valve with the Jet J-valve and analyse the material transport capacity and stability of pressure drops. The experimental results show that the pressure drop fluctuations of the riser, standpipe and J-valve are slightly greater in the states of dilute-phase and dense-phase transport for the Jet J-valve than for the ordinary J-valve. However, under the same operating conditions, the solids circulation rate is 41-84 kgm-2s-1 higher when the Jet J-valve is used. In addition, the pressure drop of the Jet J-valve is approximately 18% lower than that of the ordinary J-valve. When the steady state transitions to a slugging state, the solids circulation rate decreases by 76.5% and the pressure drop of the J-valve decreases by 23.3%, which is relatively small compared with that of the riser and the standpipe.
Keywords: Jet J-valve; solids circulation rate; dense-phase transport; fluidization number; pressure fluctuation; coefficient of variation.
Numerical investigation of single and multiple fractures propagation in naturally fractured reservoirs
by Han Li, Yushi Zou, Shuai Liu, Peter Valko
Abstract: The properties of Natural fractures (NFs), including fracture size, aperture width, and mechanical properties, etc., cannot be neglected when developing a model of hydraulic fracturing. Without considering the geological characterization of NF properties, hydraulic fracture simulations will give much less accurate prediction of complex fracture propagation pattern.
In this research, a novel two-dimensional Finite-Discrete Element Method model has been developed to describe complex fracture propagation in unconventional formations. We developed a natural fracture network builder by considering natural fractures geological observations.
Simulations have been conducted to investigate single fracture and complex fracture network propagation in naturally fractured reservoirs. In hydraulic fracturing treatments, opening of natural fractures is determined by geological properties of NFs. For multiple fractures propagation in naturally fractured reservoirs, stress shadowing effect plays a key role in fracture network evolution.
This work provides a framework for more realistic prediction of complex fracture geometry in naturally fractured formations.
Keywords: Natural fractures; Finite-discrete element method; Hydraulic fracturing; Discrete fracture network.
Mechanical Properties and Energy Features of High-water Material under Cyclic Loading and Unloading
by Xiaolong Li, Changwu Liu
Abstract: The mechanical properties and energy features of high-water material under cyclic loading and unloading were studied. Results show that: cyclic loading and unloading has a weakening effect on the peak strength and has a strengthening effect on the residual strength of high-water material. During cyclic loading and unloading process, the stress-strain hysteresis effect is obvious. In the cyclic loading and unloading test with gradual increase of stress level, elastic modulus increases first and then decreases, total work, elastic energy, dissipation energy and energy dissipation rate of specimens increase as cycle number increases. In the cyclic loading and unloading test with constant stress level, elastic modulus decreases gradually, total work, elastic energy and dissipated energy of specimens remain stable overall as cycle number increases. Comparing with cyclic loading and unloading test with constant stress level, mass loss rate and energy dissipation rate of the same water to cement ratios specimen are greater in the cyclic loading and unloading test with gradual increase of stress level, it is easier to promote the accumulation and development of internal damage of high-water material.
Keywords: high-water material; cyclic loading and unloading; mechanical properties; hysteresis effect; energy features.
Numerical simulation study on hydraulic fracture propagation in heavy oil reservoir with THM coupling
by Yongquan Hu, Qiang Wang, Jinzhou Zhao, Ziyi Guo, Yong Zhang, Chun Mao
Abstract: The aim of the study involves examining the effect of heavy oil viscosity on fracture geometry in detail by establishing a heavy oil fracturing model and conventional fracturing model based on thermal-hydraulic-mechanical (THM) coupled theory, Walther viscosity model, and K-D-R temperature model. We consider viscosity and density within the heavy oil fracturing model as functions of pressure and temperature while that as constants within the conventional fracturing model. A heavy oil production well is set as an example to analyze the differences between the two models to account for the thermo-poro-elastic effect. The results show that temperature exhibits the most significant influence on the heavy oil viscosity while the influence of pressure is the least. In addition, a cooling area with a width of 01 m and varied length is generated near the fracture. The heavy oil viscosity increases sharply in this area, thereby indicating an area of viscosity increment. The heavy oil viscosity increases faster and is closer to wellbore, and a high viscosity increment reduces the mobility of the heavy oil and prevents the fracturing fluid from entering into the reservoir. The special viscosity distribution results in significant differences in pore pressure, oil saturation, and changing trends between these two models. In the heavy oil reservoir fracturing model, the thermal effect completely exceeds the influence of pore elasticity, and the values of the fracture length, width, and static pressure exceed those calculated in the conventional fracturing model. Thus, a comparison of the measured values indicates that the results obtained by considering viscosity as a function of temperature and pressure are more accurate. Therefore, the results of this study are expected to provide good guidelines for the design of heavy oil fracturing.
Keywords: Heavy oil fracturing; Thermo-Hydro-Mechanical coupling; Heavy oil viscosity; Fracture morphology; Conventional fracturing;.
Integrated Field Development Plan Optimization of water flood Multiple Complex Carbonate Reservoirs
by Ajay Mandal, Mohammad Yunus Khan
Abstract: This paper describes a step by step work flow to optimize field development plan of three vertically adjacent complex carbonate reservoirs by using multiple strings in a given well to access them. It also provides an innovative view on how to develop multiple vertically separated, adjacent complex reservoirs from artificial (man-made) island with maximum reservoir contact (MRC) wells to get economically viable production. The focus was to revise the development plan of the major reservoir and use the future development wells of this reservoir to access other vertically adjacent minor reservoirs that are within the drilling reach from different artificial islands. The study addresses optimized well spacing, completion layers of well placement, well drill sequence, well type; and number of economic infill well placement and sectorization strategies for optimal production. This study also includes assessment of the value of infill wells, dual-lateral, dedicated lateral and single-lateral wells to target more than one reservoir. An optimized integrated field development plan of major and minor reservoirs is formulated with new long horizontal MRC wells which include both single and dual-lateral wells accessing one, two or three reservoirs depending upon location and accessibility.
Keywords: Field development plan; water flood; dual completion wells; optimization; numerical simulation; artificial (man-made) island.
Performance Prediction of Different Recovery Mechanisms during Steam Injection in Non-Fractured and Naturally Fractured Light Oil Reservoirs
by Hamid Rahnema
Abstract: Steam injection, which is a thermally based enhanced oil recovery process, is used to improve the fluid mobility within the reservoir. It is well known that steam injection exhibits positive result in heavy oil reservoirs. In theory, the same application has the potential to be applied in light oil reservoirs to boost the production. In this paper, the potential of steam injection for light oil extraction in naturally fractured and non-fractured reservoirs is evaluated.
The performance prediction model for a 9-spot steamflood pattern reservoir was developed using the SPE fourth comparative solution model to analyze the impact of different recovery mechanisms during steam injection for the light fluid sample in non-fractured and naturally fractured reservoirs. This model accounts for the variation in permeability and thickness for each layer generated. The heterogeneous model was represented by 1/8 of a 9-spot pattern unit. The simulation model examines the comparison between non-fractured and naturally fractured reservoirs.
Simulation results indicate that recovery mechanisms vary for non-fractured and naturally fractured light oil reservoirs. Vaporization is the dominant recovery mechanism in a naturally fractured reservoir, whereas fluid displacement and wettability are the dominant recovery mechanisms for a non-fractured light oil reservoir.
Keywords: Light oil reservoir; Steam injection; non-fractured reservoir; fractured reservoir; recovery mechanisms.
Effects of ambient pressure on diffusion kinetics in coal during methane desorption
by Bing Zhang, Hanpeng Wang, Liang Yuan, Zhongzhong Liu, Yuqiang Zhang, Shucai Li, Junhua Xue, Shugang Wang
Abstract: To elucidate the influence of ambient pressure on diffusion kinetics during gas desorption, which is of great significance to the efficient development of coalbed methane, a methane desorption experiment was carried out on coal particles under different ambient pressures, and diffusion coefficients for each test time were solved by the unipore diffusion model. The experiment was carried out using our independently developed coal particle methane desorption meter to overcome the difficulty that the existing equipment could not achieve a constant ambient pressure higher than atmospheric pressure. The results show that during methane desorption in coal particles, the diffusion coefficient was not constant but gradually decreased with time, showing a power function relationship. In addition, the diffusion coefficient decreased linearly with increasing ambient pressure, and the degree of influence was related to time. This research will play an important role in improving the unipore diffusion model and elucidating the gas production mechanisms.
Keywords: coal particle; methane desorption; ambient pressure; desorption time; diffusion kinetics; diffusion coefficient; coalbed methane; unipore diffusion model.
Numerical investigations of airflow patterns on a longwall face
by Zhongwei Wang, Ting Ren, Jian Zhang
Abstract: Longwall ventilation has always been a concern for mine operators. To thoroughly understand the ventilation flow characteristics on a longwall face, three dimensional (3D) Computational Fluid Dynamics (CFD) modelling studies were conducted. Six CFD models representing six consecutive longwall operating scenarios were developed. Key features of the longwall equipment and an immediate goaf which significantly affect the flow patterns were embedded into the models for the purpose of obtaining more realistic ventilation flow field. Mesh independent study and validation of modelling results were carried out to verify the reliability of this modelling approach. The occurrence of flow separation at both intersections of maingate/tailgate and face together with its range of influence were identified. Control measures are therefore suggested to minimise the potential accumulation of hazardous gas and dust within the flow separation zones. Significant air leakage to the goaf was also revealed by the model results when maingate curtain was not used, and air exchange between face and goaf was mainly observed at the two ends of face. The impact of shearer position and its cutting direction on face ventilation was regional, indicating the stability of face ventilation system which complies with the real situation. These new insights into the complex longwall ventilation flow patterns which will eventually be beneficial to the hazardous gas and dust management at longwall faces of underground coal mines.
Keywords: CFD modelling; longwall airflow patterns; flow separation; shearer position; cutting sequence.
Analyzing and Characterizing Horizontal Well Performance in Rectangular Closed Gas Reservoirs Considering Non-Darcy Flow Conditions
by Salam Al-Rbeawi
Abstract: This paper investigates the impact of non-Darcy flow, represented by non-Darcy flow coefficient (D) and/or rate-dependent skin factor (DQ_sc ), on pressure profiles, flow regimes, and productivity indices of horizontal wells extending in conventional and unconventional gas reservoirs. It introduces as well as new simplified technique for characterizing reservoir performance under different non-Darcy flow impacts at any production time. For this purpose, several analytical models have been generated for horizontal wells and modified for the existence of non-Darcy flow. A comparison for reservoir performance with and without non-Darcy flow was conducted for different reservoir configurations, i.e. reservoir drainage area (〖2x〗_e & 〖2y〗_e ), and wellbore length. A set of plots was developed for productivity index, pseudo-pressure normalized rate, and pseudo-pressure normalized cumulative rate.
Keywords: Horizontal wells; non-Darcy flow; Reservoir modeling and simulation; reservoir characterization.
Real-Time Hydrocarbons Sweet Spot Identification in Shale Formations While Drilling Horizontally using Geo-mechanical and Geophysical Parameters
by Alberto Lopez Manriquez, Kamy Sepehrnoori
Abstract: This work presents an innovative comprehensive approach to properly identify intervals with the most favorable potential and properties to produce hydrocarbons known as hydrocarbons sweet spots. The approach is applied to horizontal wells in shale formations but not limited to this scenario. One of the singularities of this work rests on the proposal that rock properties are obtained from logging while drilling (LWD) techniques. This self-supported methodology is applied to characterize the reservoir from the stand points of geo-mechanics, geophysics, and geopressure. Rock and fluid properties measured along the horizontal section of the well while drilling served to generate a synthetic acoustic log. Changes in trends of geo-mechanical and geophysical properties such as brittleness and acoustic impedance are used as indicators of hydrocarbons presence. Ultimately, the methodology is proposed to properly select the intervals to complete and to optimize the length of the horizontal section of the well.
Keywords: Hydrocarbons sweet spots identification while drilling; geo-mechanics; brittleness; acoustic impedance; logging while drilling (LWD); unconventional shales; reservoir pressure prediction.
Well Test Analysis for a Well with Stress-Sensitive Natural Fracture Permeability and Stress-Dependent Hydraulic Fracture Conductivities
by Mengmeng Li, Jiaen Lin, Jing Zhang
Abstract: The commonly used methods in dual-porosity systems assume constant reservoir permeability over an entire range of formation pressure and constant hydraulic fracture conductivity inside the fractures. In this paper, the hydraulic fracture conductivity and natural fracture permeability were considered as a function of stress/pressure. Based on the model of finite-conductivity vertical fracture bilinear flow in stress sensitive dual-porosity reservoirs, the pressure sensitive analytical solutions were solved by perturbation method. The features of type curves were studied and calculated pressures from models with and without stress-sensitivity were compared. The influences of inter-porosity transfer coefficient, storativity ratio, wellbore storage coefficient, permeability modulus and pressure sensitive hydraulic fracture conductivity on the typical curves were analyzed by studying the new model with different seepage regimes. The results show that both the pressure and pressure derivative curves move upward in pressure-sensitive formations, especially for the end of the curves, the upward trend behaves more obviously due to the existence of stress-sensitive media. Field examples were applied in order to verify the validity of the proposed model. The novel well test model improves the accuracy of well test interpretation results, which is essential to the design and evaluation of stimulation treatments in these reservoirs.
Keywords: well test analysis; stress-dependent hydraulic fracture conductivity; pressure sensitive natural fracture permeability; dual-porosity reservoirs; hydraulic fractured well.
Reactivity and spontaneous combustion characteristics of high-sulfur coal during low-temperature oxidation
by Li Ma, Li Zou, Lifeng Ren, Jianli Wang, Weifeng Wang
Abstract: This study investigated the spontaneous combustion characteristics and the microscopic reaction mechanism of high-sulfur coal during low-temperature oxidation. Five coal samples with different levels of sulfur content (including 3.13, 4.18, 5.06, 6.28 and 7.00%) were selected, and experiments were conducted with a temperature-programmed system and Fourier transform infrared spectroscopy (FTIR). It was shown that the O2 consumption rate, CO and CO2 production rates all rose with increased sulfur content, while they gradually fell after the sulfur content exceeded 5.06%. Conversely, when the sulfur content went up, the apparent activation energy dropped and showed a minimum at a sulfur content of 5.06% and was higher thereafter. The key functional groups participating in the oxidation reaction before the critical temperature was reached were methyl and carbonyl. Furthermore, the key functional groups were alkyl ether and carbonyl before and after the crack temperature, respectively.
Keywords: coal spontaneous combustion; low-temperature oxidation; sulfur in coal; apparent activation energy; characteristic temperature; key functional groups.
Multi-well Placement Optimisation Using Sequential Artificial Neural Networks and Multi-level Grid System
by Ilsik Jang, Seeun Oh, Hyunjeong Kang, Juwhan Na, Baehyun Min
Abstract: This study suggests a sequential artificial neural network (ANN) method coupled with a multi-level grid system to optimise multi-well placement in petroleum reservoirs. As the number of scenarios for placing wells increases exponentially with the number of wells, the difficulty in finding the global optimum increases accordingly due to the intrinsic uncertainty of ANNs. The multi-level grid system is capable of reducing the size of the search space by allocating only one well grid block per several grid blocks in the basic grid system. A higher level of the grid system consists of finer grid blocks to gradually improve the resolution of the grid system. A repetitive implementation of the sequential ANN at each level of the grid system narrows down the search space, and the global optimum is determined. The proposed algorithm is validated with applications to two- and three-infill-well problems in a coal-bed methane (CBM) reservoir.
Keywords: Sequential artificial neural network; multi-level grid system; multi-well placement; optimisation.
Key factors influencing the low-field NMR characterization of gas- and oil-bearing shales: A case study of the shales from the southern Sichuan Basin and Dongying sag, China
by Chen Chen, Shuangfang Lu, Pengfei Zhang, Junqian Li, Wenbiao Li, Siyuan Wang
Abstract: The pore microstructure characteristics of shale reservoirs, such as the porosity and pore size distribution (PSD), are critical parameters for the evaluation of the resource potential and effective exploitation of shale oil and gas. Low-field nuclear magnetic resonance (NMR) has been used to quantitatively characterize the microstructure due to the advantages of a wide detection range, high precision, good repeatability and no damage to the sample. In this paper, the response characteristics of the transverse relaxation time (T2) of various parameters, including key experimental parameters (waiting time (TW), number of scans (NS) and echo number (NECH)), sample size and probe fluid, are analyzed systematically based on NMR experiments of oil- and gas-bearing shales from the Shahejie Formation in the Dongying sag in southeastern Bohai Bay Basin and the Wufeng and Longmaxi Formations in the southern Sichuan Basin. The results indicate that for the oil- and gas-bearing shales, (1) the optimized NMR experimental parameters for TW, NS and NECH are 1500 ms, 64 and 6000, respectively, which will ensure higher accuracy and signal-noise ratio (SNR) but also greatly improve experimental efficiency. (2) The total signal amplitude of the T2 spectrum increases with decreasing grain size. The T2 spectra of the shale samples with a grain size of 10 mesh are similar to the plug samples, which can characterize the pore structure of shales without fractures. (3) Compared with porosity that was tested using an n-dodecane-saturated sample, water porosity clearly decreases with increasing brittle minerals but increases when the clay content rises to a certain threshold. Furthermore, the range of the T2 spectra tested when saturated with water is smaller and generates a new main peak near 1 ms, which indicates that the hydration of clay and brittle minerals together controls the reconstruction of the pore structure and PSD.
Keywords: Shale; low-field nuclear magnetic resonance (NMR); waiting time (TW); number of scans (NS); grain size; probe liquid.
Geological controls on coalbed methane accumulation and optimization strategy for gas productivity: A case study in eastern Ordos Basin, China
by Kui Zhu, Xinyi Song, Fan Lu, Bo Jiang, Changshen Wang, Guoyong Yang, Zhengjie Chen
Abstract: Coalbed methane (CBM) production is accomplished by reducing the gas partial pressure in the coal seam. This can be achieved by pumping the formation water or gas injection. The output of a CBM well is affected by the drainage conditions, such as the ground water level and by water production. Incorrect drainage conditions can lead to diminished methane production. In this study, the Baode region is selected to study the drainage conditions and production characteristics on the early stage of CBM production. Water production, wellhead pressure and gas production were collected from four CBM wells. The temporal trends of those factors have been analyzed, and the effects of drainage conditions are studied by using statistical analysis. These analyses show that the favorable burial depth for CBM accumulation between 500 and 700 m. Sandy mudstone and mudstone are beneficial to CBM preservation. The wellhead pressure should be maintained between 0.4 MPa and 1.0 MPa, and the optimal range of wellhead pressure lies between 0.5 and 0.8 MPa for stable production. The gas production increases with increased water production when the wellhead pressure has become progressively stable in the middle phase of early stage, and a significant positive correlation can be detected between them.
Keywords: coalbed methane production; water production; wellhead pressure; gas production.
Inhibition of Asphaltene Precipitation by Hydrophobic CaO and SiO2 Nanoparticles during Natural Depletion and CO2 Tests
by Yaser Ahmadi, Babak Aminshahidy
Abstract: This paper addressed the effects of hydrophobic synthesized CaO and commercial SiO2 nanoparticles on the inhibition of asphaltene precipitation after asphaltene adsorption on the nanoparticles surface. First, asphaltene characterization performed with FTIR and its stability was analyzed with screening methods. Second, experimental and isotherm models including Langmuir and Freundlich were used to observe the effects of CaO and SiO2 nanoparticles on asphaltene adsorption. Third, CO2-oil IFT behaviors were used as a second method for surveying asphaltene adsorption in the presence of nanoparticles. Finally, natural depletion and CO2 tests were done as a source of precipitation methods. The studied crude oil was located in unstable regions from the aspect of asphaltene precipitation with CII of 1.392. The results of asphaltene precipitations during natural depletions and CO2 tests were in good agreement with CO2-oil IFT behavior, and CaO not only adsorbed more asphaltene but also had the best application for precipitation inhibition.
Keywords: CaO nanoparticle; SiO2 nanoparticle; Asphaltene precipitation; Asphaltene adsorption.
Experimental study on the viscosity-temperature characteristics and rheological properties of offshore heavy oil
by Meng Cao, Linsong Cheng, Shijun Huang, Yongchao Xue, Mengge Du
Abstract: The viscosity-temperature characteristics and rheological properties of heavy oil were investigated experimentally. Experimental results indicate that viscosity is sensitive to temperature, and it is a binary function of temperature and shear rate meeting preferably Arrhenius equation. In addition, the semi-log curve of viscosity-temperature can be divided into three regions and there is no obvious turning point, which exhibits that the internal microstructure of heavy oil during the heating process changes gradually. Besides, activation energy of low temperature range is higher than that of high temperature range. Moreover, the heavy oil always behaves as Newtonian fluid when temperature is higher than crystallization temperature. Furthermore, on condition that temperature is less than crystallization temperature, the heavy oil behaves as Pseudo-plastic fluid characterizing shear thinning phenomenon when shear rate is less than critical shear rate, and it presents as Bingham fluid with yield stress when shear rate falls between 10 and 50 s-1.
Keywords: Offshore heavy oil; Viscosity-temperature characteristics; Rheological property; Activation energy; Crystallization temperature; Critical shear rate.
The effect of alkaline on combination system properties during long distance migration: comparison of SP and ASP flooding in Daqing Oilfield
by Yunfei Ma, Jirui Hou, Fenglan Zhao
Abstract: Surfactant-polymer (SP) flooding and alkaline-surfactant-polymer (ASP) flooding, serving as two types of combination flooding, are being widely applied in Daqing Oilfield to increase both sweep volume and oil displacement efficiency. Researches showed that alkaline, especially strong base (e.g., sodium hydroxide), can reduce the oil-water interfacial tension (IFT) and decrease the adsorption of surfactant and polymer. However, the presence of alkaline could result in problems like cost improvement, etc. There remains controversy as to whether to use alkaline or not during combination flooding. To study the effect of alkaline on combination flooding, contrast experiments were conducted to simulate SP flooding and ASP flooding using typical formula in Daqing Oilfield. A 30-meters long sand-packed model was built in laboratory for the investigation of property changes during long distance migration. The fluid samples were obtained from sampling points along the model, and the properties such as viscosity, IFT and components concentration were analyzed. The results showed that ASP flooding improved oil recovery by 3.89% higher than SP flooding, which was mostly derived from the near inlet area. In comparison to SP flooding, alkaline in ASP flooding decreased near inlet surfactant retention from 68.43% to 59.35% and polymer retention from 48.10% to 39.57%. Moreover, alkaline could also facilitate the viscosity maintaining with an effective distance of 1/3 of the well spacing. In the presence of alkaline, lower IFT was observed in ASP flooding than in SP flooding in the near inlet area. As a consequence, the effects of alkaline on ASP system was remarkable in the near inlet area, and gradually weakened with the increasing of migration distance. Better performance can be achieved with the existence of alkaline during combination flooding, and the advantage can be more obvious under short well spacing conditions.
Keywords: ASP flooding; SP flooding; alkaline; long distance migration; retention.
SYNERGY OF FLUID SAMPLING AND SUBSEA PROCESSING, KEY TO MAXIMISING OFFSHORE ASSET RECOVERY
by Nimi Abili, Athanasios Kolios
Abstract: The acquisition of accurate fluid samples for deepwater development is crucial for the correct evaluation of oil reserves, and for design optimisation of subsea production and processing facilities, to maximize asset value. Samples collected from topside facilities do not represent the fluid being measured on the seabed. The injections of chemicals such as methanol, corrosion, asphaltene, ethylene glycol (Meg) inhibitors and emulsion breaker, etc., downstream of the meter, and possible liquid separation or hold-up, are typical issues. This is a challenge due to multiphase flow commingling on the seabed. Employing subsea multiphase flowmeter measurements in the underwater environment presents some significant challenges. Due to the fact that subsea multiphase flowmeter is not ‘fit-and-forget’ subsea instrumentation hardware (that requires fluid properties data as input), changes in the inputs from the flow stream’s actual properties can lead to errors in flowmeter data capture. Therefore, collecting direct and representative fluid samples from the subsea production system will provide benefits to the subsea multiphase flowmeter and thus reservoir production management to maximise recovery. A mechanistic (transient multiphase flow) model is employed, using the fluid properties that are equivalent to the flow stream being measured, to predict reliable reservoir fluid characteristics on the production flow stream. The benefit of the mechanistic model is that it adds value in the decision to employ subsea processing in managing water breakthrough as the field matures. The failure to obtain representative samples could have considerable impact on the operational expenditure and consequently the asset value, to sustain or enhance production volume for increased margin over the life of the field. The present paper explores the synergy in successful application of subsea fluid sampling and subsea processing to maximize offshore asset recovery.
Keywords: Synergy, Multiphase Flowmeter, Mechanistic model, Fluid Sampling, Subsea Processing, OPEX, Deepwater Asset Recovery