International Journal of Oil, Gas and Coal Technology (97 papers in press)
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.
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.
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.
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.
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.
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.
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 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 behaviour around a multilateral horizontal well in bottom water reservoir and get the productivity 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 for 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 behaviour of the multilateral horizontal wells in the bottom water reservoirs. Moreover, the case study shows that the calculated results agree with the practical situation. [Received: August 12, 2017; Accepted: March 16,
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. XRD analysis shows that average particle size in the range of 3039 nm. 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. Therefore, this novel material can be used to enhance oil recovery with application of EM waves. [Received: September 7, 2017; Accepted: March 28, 2018]
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.
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.
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: In underwater gas fields, the ratio of gas phase and liquid phase has become higher and higher. Focusing on the special condition above, the design of a new kind of two-stage gas and liquid cylindrical cyclone (GLCC) has been proposed which is different from the traditional one with rectangle inlet. The equivalent volume transforming method has been used in the design of size. Based on the research of the liquid drops breaking in swirl field, a new test method of GLCC diameter has been proposed, according to Navier-Stokes equations. For the structure of this cyclone separator, the optimised numerical simulation has been used to study the internal flow field, which adopts better turbulence models, meshing schemes and discrete formats after comparison. The effects of parameters such as H and Dc on the asymmetric characteristics and vortex-core boundary have also been obtained and analysed. [Received: February 12, 2018; Accepted: May 21, 2018]
Keywords: cyclone separator; numerical simulation; asymmetry characteristics; vortex-core boundary; gas-liquid cylindrical cyclone; GLCC; flow field characteristics; undersea separator; gas-liquid separation; oil-gas technology; 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 basic parameter in design of hydraulic working. In fractured formation, abundant natural fractures increase complication of predicting initial fracture pressure. Without accurate initial fracture pressure, reservoir stimulation efficiency will be impaired. Therefore, in this paper, in combination with shear and tensile strength criterion in multiple natural fracture planes condition, a new fracture initiation model has been established. Based on this model, influence factors of fracture initiation have been analysed. Results indicate that initiation type could be tensile or shear failure along fracture plane, decreasing the initial fracture pressure. Initial fracture pressure is related to fracture occurrence and its decline becomes large due to increasing fracture number. With multiple natural fractures, initiation is totally controlled by natural fracture. In the application, results of this model are good consistent with oilfield data. Thus, this model can offer guidance for hydraulic fracturing.
Keywords: fractured formation; natural fracture; hydraulic fracture; initial fracture pressure.
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, natural fractures and hydraulic fractures,is developed for heterogeneous shale gas reservoirs. In this 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 model is used to analyse the flow regimes of shale gas flow within a multi-stage fractured horizontal well. It also investigates the influences of gas desorption, fracture aperture, spacing and number on the gas production rate. The results show that the MNH model can provide insights into flow mechanisms and production prediction for a multi-stage fractured horizontal well in shale gas reservoirs. [Received: November 2, 2017; Accepted: June 19,2018]
Keywords: MNH; heterogeneous shale gas reservoir; non-Darcy; gas desorption; gas production.
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.
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 streams 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.
Nexus between energy consumption, health expenditure and economic growth in Australia
by Ronald Ravinesh Kumar, Peter Stauvermann, Syed Jawad Hussain Shahzad
Abstract: Focussing on Australia, we examine the effects of energy consumption and health expenditure on output within the extended neo-classical Solow growth model. We use the ARDL bounds and non-Granger causality procedures for a sample period 1971-2014, to analyse the short-run and long-run effects of energy consumption and health expenditure on economic growth. Additionally, we examine the threshold values of energy and health expenditure. It is noted that in the long-run, energy consumption vis-
Keywords: energy consumption; health expenditure; economic growth; non-linear; Australia.
Research on Gas Percolation and Catastrophe Behaviour of Gas-bearing Coal under Low Index
by Tie Li, Xianwei Hu, Zongzhi Wu
Abstract: Abnormal gas emission, coal and gas outburst may occur on the coal seam whose gas pressure and content are below catastrophe threshold, when the mine is deeply exploited. In order to study this catastrophe mechanism, solid-fluid coupling experimental system with single degree of freedom and bidirectional loading is proposed. Gas percolation and catastrophe behavior are studied through low pressure loading in this experiment, obtaining the following conclusions. (1) Gas flow curve of gas-bearing coal shows asymmetric U shape. (2) Coal sample suffers catastrophe gas emission after its rupture and instability under low pressure of 0.4 MPa and 0.15 MPa. Catastrophe mixture of gas and solid is also generated under pressure of 0.4 MPa. (3) Stress threshold of catastrophe gas-bearing coal sample is negatively related with coal gas pressure. The stress threshold lowers if coal gas pressure rises. (4) Primary fracture of gas-bearing coal sample is consolidated when elastic deformation reaches 50% ~ 60% of elastic process, blocking gas percolation. However, gas percolation channel will be reopened after one yield or several yields. On condition that the reopening takes longer time due to mining stress, desorption amount of coal gas becomes larger, leading to abnormal emission of aggregated gas and outburst of coal and gas once the yielding coal is instable.
Keywords: Gas-bearing Coal Sample; Solid-fluid Coupling; Gas Percolation; low index; Coal and Gas Outburst.
An Improved Ultrasonic Disaggregation Method for Analysis of Minerals in Shales
by Wenda Zhou
Abstract: Traditional disaggregation methods for mineral separation of sedimentary rocks are not appropriate for shales with complex mineralogy and grain sizes. In this study, we improved the ultrasonic disaggregation and stepwise separation method for minerals in shales, and applied it to analyse shale samples from the Silurian Longmaxi Formation of the Sichuan Basin, China. The Longmaxi Formation shales are mainly composed of clay minerals, quartz, calcite, dolomite, albite, and K-feldspar, and are cemented by SiO2. This method processes shale samples as ultrasonic disaggregation followed by
stepwise separation of minerals using gravitational deposition and centrifugation. Field emission scanning electron microscope (FE-SEM) images were obtained for different components of this ultrasonic disaggregation and stepwise separation method. Information obtained by this method can also be used to quantify the hydrodynamic forces acting on the Longmaxi Formation sediments during the syngenetic stage. [Received: 25 October 2018; Accepted: 21 November 2018]
Keywords: disaggregation; shale minerals; ultrasonication; mineral grain size; critical incipient velocity.
Evaluating the Effect of Using Micronized Barite on the Properties of Water-Based Drilling Fluids
by Abdelmjeed Mohamed, Salaheldin Elkatatny, Mohamed Mahmoud, Reyad Shawabkeh, Abdulaziz Al-Majed
Abstract: Solids sag and formation damage are serious problems encountered while drilling with barite-weighted drilling fluids. The objective of this study is to investigate the effect of reducing barite particle size on rheological properties, fluid stability, and filter cake removal. Barite samples with different particle sizes were prepared using sieve analysis and ball milling technique. Micronized barite (8 m) showed a moderate stability with zeta potential measurements for a pH range greater than 8. Solubility tests showed good enhancement in barite removal as the particle size was reduced, with a difference of around 11 g/L between the largest size (75106 m) and the micronized size of barite. HPHT filtration test results confirmed the solubility
results with 5 wt.% enhancement in filter cake removal efficiency as barite particle size was reduced to micronized size. [Received: December 4, 2017; Accepted: December 17, 2018]
Keywords: micronised barite; weighting material; water-based; drilling fluid; rheological properties; stability; filter cake removal.
Potential Application of the CO2-Assisted Gravity Drainage Process in A Mature Oil Field: Insights from Reservoir-Scale EOR Evaluation
by Watheq Al-Mudhafar, Dandina Rao
Abstract: The Gas-Assisted Gravity Drainage (GAGD) process was implemented through continuous and cyclic immiscible injection to enhance the recovery of bypassed oil in the upper sandstone reservoir in the South Rumaila oil field, located in Southern Iraq. A compositional simulation model was constructed for the CO2 flooding evaluation through the GAGD process implementations. After achieving history matching, 20 vertical injectors and 11 horizontal producers were placed for CO2 injection and oil production, respectively. The immiscible CO2-GAGD performance was evaluated for 10 years of future prediction. The continuous and cyclic immiscible GAGD cases resulted in reaching recovery factor of 14.5% and 21.3% given the remaining oil, respectively. However, the recovery factor given the remaining oil was 7.6% through primary production by the end of prediction period. Additionally, the obtained amount of oil in 10 years primary production can be obtained in only one year by the continuous case and in 8 months by the cyclic case. Consequently, the continuous and cyclic simulation of CO2 flooding proven the effectiveness of GAGD process to efficiently enhance the recovery of oil.
Keywords: Gas-Assisted Gravity Drainage; Immiscible CO2 Flooding; Enhanced Oil Recovery; South Rumaila Field; Insights Learned.
Insights into the Co-Combustion of Coal and Biomass mixtures using a Copper based oxygen carrier in Chemical Looping Combustion
by Tamal Banerjee, Mayur Kevat
Abstract: Chemical looping combustion (CLC) is one of the energy efficient technologies with inherent CO2 capture without expending the use of additional energy. Chemical looping with oxygen uncoupling (CLOU) is working on strategies to transport gaseous oxygen for fuel combustion. The present work reports the process simulation and energy analysis of CLOU of a coal-biomass mixture with copper-based oxygen carrier. Variations in different parameters such as the gas concentration in reactors, oxygen carrier conversion, and carbon capture efficiency are compared by replacing pure coal with an equal fraction of coal-biomass mixture. The presence of alkaline earth metals in biomass is seen to increase the coal char conversion in the fuel reactor results in higher carbon capture efficiency. The predicted carbon capture efficiency is found to increase with the fuel reactor temperature range of 900 to 965C irrespective of pure coal and coal-biomass mixture. The carbon capture efficiency was also varied with the solids flow rate varying from 3.48 to 13.64 kg/h at a constant fuel reactor temperature of 940C for the coal-biomass mixture. The thermal power output for the coal-biomass mixture is further compared with published literature for pure coal in context of its CLOU mode of operation. The trend of thermal energy output is found to be same for pure coal (660-709 W) and coal-biomass mixture (571-612 W) as CLOU fuel with the considered fuel reactor temperature range.
Keywords: CLC; CLOU; Coal; Biomass; ASPEN.
Measurement of Coalbed Gas Content of Indian Coalfields: A Statistical Approach
by Mohammad Asif, Mallikarjun Pillalamarry, Durga Charan Panigrahi, Paul Naveen, KEKA OJHA
Abstract: Sixty coal samples from different Indian coal fields were collected and characterised to analyse the gas content, petrography and composition. The gas content of coal samples was directly determined using a canister desorption test and statistically correlated with various parameters using regression analyses. The newly developed correlations are based on Langmuir, Ryan, and Kim correlations and modified to fit the data best. The gas content was observed to be a strong function of the proximate parameters i.e. fixed carbon, volatile matter, moisture content, and ash content as resulted from regression analyses. Vitrinite reflectance was also found to affect the gas content of the coal seams. To check the significance of calculated results, a paired-samples t-tests have been performed for 42 coal samples. Results confirmed the validity of the New Langmuir and New Ryan correlations with good confidence, i.e., t = 2.1, p < .05. [Received: April 26, 2018; Accepted: December 24, 2018]
Keywords: coalbed methane; gas content; proximate analysis; adsorption isotherm.
Thermal and kinetic characteristics of the catalytic effect of different catalysts on the combustion of coal-char blends
by Yingjie Hu, Zhiqiang Wang, Xingxing Cheng, Chunyuan Ma
Abstract: Thermal and kinetic characteristics of the catalytic effect of CaO/MnO2/Fe2O3 on the combustion of coal-char blends were investigated with thermogravimetric analysis. Different characteristic parameters obtained from TG-DTG curves were used to determine the combustion characteristic of samples. A sectioning method was adopted to study the kinetics at the stage I and II of samples combustion. The kinetic parameters of samples were also determined according to the Coats-Redfern method. The experimental results indicated that, in stage I, the catalysts promoted volatile matter release and combustion, decreased the ignition temperature; in stage II, the catalysts accelerated the combustion of fixed carbon in char. The ignition properties and the combustion properties all increased with catalysts addition. Fe2O3 and CaO exhibited effective catalytic effect on reducing the activation energy in the stage I and II of coal-char blends combustion. The catalytic effect of MnO2 in the stage II was not obvious. Therefore, Fe2O3 and CaO were considered having more catalytically active than MnO2 in coal-char blends combustion.
Keywords: Coal-char blends; Catalysts; Kinetics; Combustion; Thermal analysis; Ignition properties; Combustion properties;.
An investigation of the performance of an ignition compression engine using ethanol-butanol-diesel mixtures
by Roberto Pereira, Ithamar Rangel
Abstract: The low solubility of ethanol in the diesel oil has motivated the study of ternary mixtures using butanol like co-solvent. Within this approach several mixtures were tested in the MBB OM355/6A engine, obtaining, in some cases, a performance equal to or greater than that of diesel oil. The volume proportions of butanol, ethanol and diesel for each fuel tested were, respectively: 3%, 7% and 90%; 3.5%, 8% and 88.5%; 5%, 7.5% and 87.5%; 4.5%, 8% and 87.5%; 5%, 10% and 85%. The results obtained in the dynamometric bench tests, the rheological parameters and the physicochemical properties of the mixtures are presented. The mixture with 3% of butanol, 7% of ethanol and 90% of diesel (MD10(3+7)BE) showed the best performance in the engine tests, with brake specific fuel consumption lower than diesel fuel, for all engine speed at full load, and with brake thermal efficiency higher than diesel fuel, for all engine speed at full load.
Keywords: energy; diesel engine; ethanol; butanol.
Engine performance and emission profile of Simarouba glauca biodiesel and its blends
by Kandasamy Sabariswaran, Sundararaj Selvakumar
Abstract: Engine performance and emission characteristics of biodiesel produced from Simarouba oil were investigated in the present study. The biodiesel of Simarouba oil and its blends were run in single cylinder Kirloskar make four stroke, water cooled engine at different load conditions. The maximum brake thermal efficiency (BTE) was observed in the blend of B20 and the average percentage of efficiency obtained was 47.5% whereas the efficiency of standard diesel was 49.01%. The maximum brake specific fuel (BSFC) consumption was found in the blend of B20. The average percentage of BSFC obtained was 0.367 kg/kWh whereas 0.359 kg/kWh obtained for diesel. In terms of emission profile, emissions of carbon monoxide (CO), hydrocarbon (HC), carbon dioxide (CO2) and smoke emission were reduced with a marginal increase in NOx emission. [Received: December 12, 2017; Accepted: January 12, 2019]
Keywords: Simarouba biodiesel; brake thermal efficiency; CO2 emission; NOx emission; Smoke emission; blends; Smoke density.
Risk Assessment of Large Crude Oil Depot Based on Interpretative Structural Model
and System Dynamics
by Liqiong Chen, Yuxiang Feng
Abstract: In this paper, the interpretative structural model is used to determine the causality among the risk factors and a system dynamics model is established. The method is applied to the risk analysis of a large crude oil depot. The results show that the safety atmosphere and supervision play critical roles on the risk of the oil depot. At the mature stage of risk development, improvements in the equipment risk and management risk has the greatest impact on the overall risk. The degree of education, equipment usage time, safety atmosphere and supervision are the key risk factors for the human, equipment, environmental and management risk subsystems, respectively. This result provides a scientific basis to understand the trend of risk dynamic, risk evolution mechanism and fundamental risk factors and fundamentally prevent the occurrence of large crude oil depots.
Keywords: risk assessment; interpretative structural model; system dynamics; large crude oil depot.
Efficient prediction for porosity only using logging data: A case study of lacustrine carbonate reservoirs of IARA oilfield
by Yufeng Gu, Zhidong Bao, Zhenhua Rui
Abstract: Physical models, such as Archie's formula and Wyllie time-averaged equation, to name only a few, are universally considered as the most effective tools to evaluate reservoirs, because the inner characteristics and changing situations of the reservoirs can be reasonably interpreted by those models. However, before using those models, geophysicists should determine the values of some model parameters, such as conductivity of formation water or compensation coefficient of mudstone. Thus, under the lack of information of those parameters, the application of the physical models, to some degree, will be severely limited. Statistical methods are capable of revealing variation trends of study cases by only processing source data. N-way analysis of variance and multivariate linear fitting are a few excellent examples. Then in order to cast off the reliance on using physical model parameters, a statistical method combined N-way analysis of variance and multivariate linear fitting is proposed so as to create an efficient way to solve the problems regarding reservoir evaluation. This article discloses the function of proposed method in terms of porosity prediction when only logging data is available. The data used for verification derives from the lacustrine carbonate reservoirs of IARA oilfield. Five experiments are well-designed to analyze capability of the method on porosity prediction. Experiment results prove that the proposed method can utilize logs, without taking advantages of other kinds of data, to predict porosity, and the predicted outcomes are accurate because the mean absolute errors of the results are small enough to omit. The proposed method can be viewed as a new tool to obtain porosity data when only logs are handled.
Keywords: logging interpretation; porosity prediction; N-way analysis of variance; multivariate linear fitting; fitting correction.
Optimisation of the LNG supply chain: a literature overview
by Ignacio De La Peña-Zarzuelo, Maria Jesus Freire-Seoane, Carlos Pais-Montes
Abstract: Liquefied Natural Gas (LNG) is playing a prominent role in current global maritime transport and port operations, with strong growth rates and a wide multiplicity of agents involved. Nevertheless, the applied research on LNG Operations Research (OR) is still at an initial stage. rn The goal of this research is to perform an in-depth overview on the ORs LNG logistic chain literature. As a result, the existing studies fall into two groups: those considering pricing as the main factor; and those focused on the Inventory & Routing Problem (IRP) and the Routing & Scheduling Problem (RSP).rn Once reviewed the literature seven important topics of new research emerge linked to the use of new programming paradigms, the introduction of climate factors, and the consideration of new trade flow patterns (for instance the widening of the Panama Canal or the opening of the Artic Bridge).rn
Keywords: Operations Research; Simulation; LNG; Routing & Scheduling Problem; Inventory & Routing Problemrn.
Trends and dynamic relations between crude oil prices and energy employment: A panel analysis approach
by Shuming Bai, Kai Koong, Fan Wu
Abstract: This research employs panel data to analyze the trends of 21 energy occupations in 10 energy sectors in the USA and the relationships among oil prices, oil production, and energy jobs by sector and nationwide from 2002 to 2016. We highlight several major findings. (i) The largest and smallest energy hires are consistent and robust. (ii) The most and best jobs are mostly created in the upstream and related services sectors. (iii) Majority of the energy occupations grow faster than those for the nation. (iv) Energy sectors do matter for the same job titles. (v) Energy jobs are strongly associated with oil prices and production. (vi) Energy jobs, oil prices, and U.S. oil production play significant roles in the national employment. To our knowledge, this panel analysis of energy jobs is the first of its kind. The findings could be useful to various energy stakeholders and policy-makers for adopting effective employment strategies and policies.
Keywords: U.S. oil field production; WTI oil prices; NAICS Energy sectors; energy occupational employment; Panel data.
Mechanistic Study and Performance Evaluation of Steam Assisted Gravity Drainage (SAGD) Using Direct Visualization of Pore-Level Experiments
by Omidreza Mohammadzadeh, Nima Rezaei, Ioannis Chatzis
Abstract: It is essential to understand pore-level physics of the steam assisted gravity drainage (SAGD) process to develop reliable mathematical models for simulating the field-scale performance. In this paper, insights into the pore-scale physics of the SAGD process are presented using qualitative and quantitative analysis of the experimental results. A systematic series of SAGD visualization experiments were conducted with the aid of optical imaging technique and glass-etched micromodels of capillary networks to capture the pore-level physics of this process.
The mechanistic investigation of the SAGD process at the pore-level revealed that in this recovery process, gravity drainage proceeds through a layer of pores near a well-established oil-steam interface. The mobile oil drainage occurs due to the interplay between gravity and capillary forces. The steam chamber propagation was found to be influenced by the randomly-distributed fingering of the invading steam front near the mobile oil-steam chamber interface. This phenomenon occurs within a region of a few pores near the oil-filled pores that attain mobility due to heat transfer. The steam fingering was observed to be extensive during the vertical growth of the steam chamber where the steam buoyant front was protruding through the pores containing a continuum of oil. The steam fingering phenomenon was also observed during the outward propagation of the steam chamber at the proximity of its side wings, but to a limited extent. Simultaneous co-current and counter-current flow of different phases was observed near the lateral sides of the steam chamber, which was responsible for the horizontal expansion of the invaded region.
The quantitative analysis of the experimental results showed that the rate of pore-scale horizontal interface advancement in the SAGD experiments was constant at each elevation along the height of the micromodels. The average pore-level SAGD sweep rates were correlated using an analytical model. The net Cumulative Steam to Oil Ratio (net CSOR) data were scaled using the theory of gravity drainage applicable to the SAGD process, and a good correlation was found for the experimental results.
Keywords: Steam Assisted Gravity Drainage (SAGD) – Pore-scale – Visualization – Heavy oil – Bitumen – Heat Losses.
Optimization of Biodiesel Production and Engine Performance from Simarouba Oil in Compression Ignition Engine
by ASHISH DEWANGAN, Ashis Mallick
Abstract: In present work, Simarouba seed oil has been evaluated as a feasible feedstock for biodiesel production. An optimum yield of 98.1% was achieved at a temperature of 45
Keywords: Simarouba Oil; Optimization; Taguchi method; Biodiesel: Transesterification; CI engine Performance & Emissions.
Volumetric flow and pressure gradient based leak detection system for oil and gas pipelines
by Mukarram Riaz, Ishtiaq Ahmad, Muhammad Nasir Khan, Muhammad Asim Mond, Amna Mir
Abstract: The leakage in oil and gas pipelines results economic losses to petroleum companies and causes damages to the environment. It may occur due to corrosion in the pipe or intentional or unintentional damage by third party intervention. A prompt and accurate leak detection and localization system is very essential. In this paper, we have developed a nonlinear adaptive model for detection and localization of leak based on correlation of pressure and volumetric flow at the pipe inlet and outlet. The characteristic changes in the flow mechanics and thermodynamics along a given length of pipeline such as pressure, flow and temperature are adopted in the model. A compensated volume balancing method is proposed for leak detection based on conservation laws of mass, momentum and energy. Leak localization is based on presence of pressure gradient in the vicinity of the leak. The simulation results show the superior performance of our proposed model.
Keywords: Leak detection; volumetric flow; pressure gradient; volume balancing.
Numerical Simulation and Three-Phase Pressure Transient Analysis Considering Capillary Number Effect Case Study of a Gas Condensate Reservoir
by Kambiz Davani, Shahin Kord, Omidreza Mohammadzadeh, Jamshid Moghadasi
Abstract: The production behavior of gas condensate reservoirs is relatively different and more complex than a conventional oil reservoir. When the wellbore pressure drops below the dew point pressure of gas in a gas condensate reservoir, there is the possibility of condensate bank buildup and wellbore blockage. This phenomenon triggers some operational and testing difficulties including reduction of gas relative permeability in the near wellbore region which leads to loss of well deliverability, and development of different mobility zones around the wellbore. The latter issue complicates the pressure transient test analysis due to the presence of multi-phase flow and changes in gas mixture composition that occurs near the wellbore region. There are other complexities with well test analysis in gas condensate reservoirs such as difficulty in interpreting and distinguishing reservoir effects from that of reservoir boundaries, fluid behavior, and phase redistribution and segregation effects in the wellbore. In such complex system, numerical simulation is a helpful tool to identify the key features recognized in data processing as well as to estimate and evaluate effective reservoir parameters through well test data analysis.
The focus of this study is on the analytical and numerical analysis of pressure testing data obtained from a well in a target gas condensate reservoir. First, the well test data were analytically interpreted through which several well and reservoir parameters were identified such as radius of the condensate bank, gas effective permeability, mechanical skin and skin due to non-Darcy flow around the wellbore. A three-phase compositional reservoir model was then built using the analytical solution, for numerical analysis of the pressure transient data as well as validation of the analytical results. This numerical model was then used to estimate well deliverability and predict future reservoir performance.
Keywords: Gas condensate reservoir; well testing analysis; Condensate dropout; numerical simulation.
Investigation on gas hydrate formation properties in a spiral flow using a flow loop
by Yong Chao Rao, Yi Sun, Shu Li Wang, Hao Ge, Bo Yang Ding
Abstract: The formation and accumulation of hydrates have been a major hazard to the operating safety of deep- sea oil/gas transportation pipeline. Although many studies have been conducted to investigate the hydrates formation and slurry flow during the transportation, studies of the hydrates formation in a spiral flow using a flow loop are still almost blank. a series of experiments were performed in a high pressure hydrate experimental loop using spiral flow which has been constructed. by the Jiangsu Key Laboratory of Oil-gas Storage and Transportation Technology.. The impacts of varying flow rate, pressure, temperature, and twist rate on hydrate formation have been studied in this paper. The experimental results showed that the flow patterns occurring in the experiments were classified into the spiral wavy stratified flow, the spiral bubble flow, the spiral annular flow, and the spiral dispersed flow. The spiral dispersed flow occurred at high gas superficial velocity. The induction and formation time in a spiral flow loop decreased with increasing pressure, and increased with the increasing temperature. The twist rate of twist-tape had an influence on hydrate formation. The hydrate formation time decreased with decreasing twist rate. The initial gas liquid rate and twist rate had significant effects on the gas consumption during hydrate formation. When the initial gas liquid ratio was 8:1, the formation rate and gas consumption increased more rapidly. The kinetic model of hydrate formation in a spiral flow loop was established. The proposed model was verified both qualitatively and quantitatively. This work helped research the effects of spiral flow on the gas hydrates formation and gas hydrate transportation.
Keywords: Gas hydrates; Spiral flow; Flow pattern; Formation kinetic model.
Numerical simulation of hydrate slurry flow characteristics in vertical pipes based on population balance theory
by Shupeng Yao, Yuxing Li, Wuchang Wang, Guangchun Song, Kai Jiang, Zhengzhuo Shi
Abstract: In the study of non-diagenetic hydrate mining methods, Academician Zhou Shouwei proposed the method of solid fluidized mining. Solid fluidized mining uses mechanical means to break down hydrates in the seabed. Then the hydrates will be mixed with seawater and transported to secondary crushing and other pretreatments. Finally, the hydrates will enter the vertical lift pipe and be sent to the platform or mining ship. Therefore, the study of the flow characteristics of hydrate slurry in vertical pipes is of great significance for hydrate mining. To study the effect of different working conditions on the flow characteristics of hydrate slurry in vertical pipes, the flow characteristics of hydrate slurry in vertical pipes were simulated using the population balance theory based on hydrate particle aggregation dynamics. This paper focuses on the simulation of the flow characteristics of hydrate slurry with different initial particle sizes, concentrations and velocities, and according to the simulation results, the flow characteristics of hydrate slurry such as pressure drop, concentration distribution, and hydrate particle size distribution are analyzed. The results of this study can provide referenced for the flow characteristics of hydrate slurry in hydrate mining.
Keywords: hydrate slurry; vertical pipe; numerical simulation; flow characteristics; population balance theory.
Micro-nano pore throat structure and occurrence characteristics of tight sandstone gas: A case study in the Ordos Basin, China
by Fengjiao Wang, Chaoyang Hu, Yikun Liu
Abstract: To characterize the pore structure, pore throat size and movable fluid occurrence state, a case study is performed on the Sulige tight sandstone gas field in Ordos Basin of China by conducting a series of experiments including mercury intrusion capillary pressure, nuclear magnetic resonance (NMR), centrifugal test, and routine core analysis. Quantitative NMR parameters and petro physical properties were integrated to build up the relationship between microscopic pore structure and macroscopic performance. The pore throat network of the tight sandstone gas reservoir is mainly made up of micropores, mesopores, and macropores. The micropores of the Sulige tight sandstone gas field is the dominant factor affecting the microscopic pore throat structure characteristics. In addition, the transport ability of the fluid in pore throat is mainly affected by the size of throat and the pore-throat ratio. As the mainstream throat radius of tight sandstone gas reservoir is very small, the rock wall exhibits strong binding ability to the fluid. Therefore, the movable water mainly exists in macropores and some mesopores. Due to the frequent alternation of larger pores and smaller pores, the fluid seepage resistance increases greatly, which is attributed to poorer percolation capacity of tight sandstone gas reservoir. The results are also of great significance for the quantitative characterization of pore structure characteristics and for industry petroleum exploration of tight sandstone gas reservoirs.
Keywords: tight sandstone gas reservoir; pore throat structure; fluid occurrence state; constant speed mercury intrusion; nuclear magnetic resonance; Sulige gas field; Ordos Basin.
Investigating reservoir stresses and strain effects during production from Coal Bed Methane gas reservoir on reservoir properties and gas production- A numerical study.
by Subhashini Nainar, Suresh Kumar Govindarajan
Abstract: The effects of stresses and strains, occurring in a reservoir, on the cumulative gas production and the petrophysical properties are studied. Existing strain and stress model equations have been used to analyze the coupled effect of matrix shrinkage and cleat compressibility change on reservoir properties. A Coal Bed Methane (CBM) gas reservoir, low permeable and undersaturated, is semi-analytically modeled. A nearly suitable model from among them is eventually proposed to predict the cleat permeability and gas production existing in the field using a Dynamic Drainage Area (DDA) approach. These results vary with the production time. The strain model predicts gas production values and the stress models predict a range of cleat permeability variation values close to field values. Cleat permeability and cleat porosity both affect gas productivity but in the opposite manner.
Keywords: Stress models; Strain model; Cleat compressibility; Sorption strain; Dynamic Drainage Area.
Analysis of fluid property variations across the Barnett and Eagle Ford Shale using fuzzy logic
by Ting Sun, Hamid Rahnema, Ali Takbiri-Borujeni, Shan-E-Zehra Lashari, Ali Reza Edrisi
Abstract: The objective for this study is to perform an investigation of the areal and vertical geospatial fluid property variations across the Barnett and Eagle Ford based on publicly-available PVT data (97 Barnett wells and 153 Eagle Ford wells). A modified multi-contact recombination procedure has been implemented to the PVT data of the reported well stream compositions for Barnett to improve estimates of in-situ reservoir composition. The Eagle Ford data were utilized without modifications as this shale play is known to be highly under-saturated. The results of modified multi-contact recombination procedure for Barnett are plotted on a ternary diagram and show that the majority of the wells were dry gas to retrograde gas. For Eagle Ford, ternary diagrams indicated the fluid type, vertical variations of OGR, C7+ and API gravity. Maps were created to review areal variations of these properties (API gravity, C7+, and initial OGR). The study was further speculated by applying fuzzy pattern recognition algorithms. The application of fuzzy logic provided additional insight to the reservoir fluids PVT behavior in understudy shale formations.
Keywords: Barnet Shale; Eagle Ford Shale; PVT; Fuzzy Logic.
Experimental Study and CFD Investigation of Environment Friendly Drilling Fluid
by Soheil Akbari, Seyed Hassan Hashemabadi
Abstract: Environment-friendly drilling fluids have been developed recently, which protect environment and satisfy needs of drilling engineering. In this study, to investigate the advantage of using environment-friendly drilling fluid, four oil-based fluids were prepared and its rheological properties were compared. Results showed that all fluids follow non-Newtonian Herschel-Bulkley model with high accuracy. Also, elevation of temperature contributes to a decrease in the fluids apparent viscosity. In order to study the cutting carrying capacity of the prepared drilling fluids in wellbore, a 3D form of steady-state Computational Fluid Dynamics (CFD) model is used to simulate the flow in different conditions. The CFD results indicated that the vegetable oil muds represent better cutting transportation especially in lower flow rates. For fluid velocity of 0.75 m/s by increasing temperature from 320 to 363 K in constant pressure, the cutting transportation has been decreased 4.21 % and 3.07 % for diesel and vegetable muds respectively.
Keywords: Oil-based drilling fluid; Vegetable oil; Diesel oil; Computational Fluid Dynamics (CFD); Cutting transport; Temperature.
Biodiesel Production from Waste Cooking Oil using Copper Doped Zinc Oxide Nanocatalyst - Process Optimization and Economic Analysis
by Sandhya R., Velavan R, Ravichandran J
Abstract: Indias energy consumption consists of 44% coal, biomass and waste 24%, petroleum and other liquids 23% and other renewable sources such as wind, solar, nuclear and biofuels. Due to the shortage of diesel and increasing prices, biodiesel gained its importance as an alternate to the petroleum based fuels. Even though there are many methods for biodiesel production, transesterification process is widely used. This paper deals with the transesterification of waste cooking oil to biodiesel with copper doped zinc oxide nanocatalyst. Results show that the maximum yield of about 97.7% was obtained at optimum reaction conditions such as 8% (w/w) nanocatalyst concentration, 1:3 Oil to methanol molar ratio at 60
Keywords: Biodiesel; Waste Cooking Oil; Transesterification.
Development of Oil-based Drilling Fluid using Iron Oxide Magnetic (Fe3O4) with Superior Properties Leading to Real Time Rheological Control
by Masoud Ghasemi Dehkordi, Pacelli L.J. Zitha, Yasaman Hosseinzadeh Dehaghani, Morteza Belbasi
Abstract: Magnetorheological fluids have the ability to exhibit a wide range of rheological properties when exposed to an external magnetic field. In this paper, an applicable oil-based magnetorheological drilling fluid is prepared using iron oxide magnetic particles (Fe3O4). In order to prove the ability and performance of the prepared fluid, Vibrating Sample Magnetometer (VSM) and Magnetorheology tests have been performed. VSM measurements showed that permeability and saturation magnetization are 0.1615 and 135.3017 emu /gr, respectively. This test generates the hysteresis curve of the sample which shows that the behaviour of this fluid is soft magnetism i.e. it is very sensitive and is easily magnetized by the application of very small magnetic fields. Furthermore, magnetorheology measurements were conducted for magnetic
fields ranging from 0 to 0.1T and the measured values are compared with rheology tests of conventional drilling fluids. The results indicate a noticeable increase in apparent viscosity and shear rate. [Received: January 29, 2019; Accepted: June 17, 2019]
Keywords: smart fluids; magnetorheological drilling fluid; magnetorheology; vibrating sample magnetometer; oil-based mud; rheological control.
Assessing the Influence of Key Parameters on an Iterative Ensemble-based Method
by Ricardo Vasconcellos Soares, Celio Maschio, Denis José Schiozer
Abstract: Ensemble Smoother with Multiple Data Assimilation (ES-MDA) is an iterative ensemble-based method derived from Kalman Filter (KF). It is an important tool for history-matching (HM) process, since it can deal with a large amount of data with low computational effort. Ensemble-based methods used in conjunction with covariance localization are proved to generate interesting results regarding data match and final responses of petrophysical parameters. However, there are several parameters that can have a large impact on the final response of the process. Therefore, this work presents a comprehensive study of the following parameters of an ensemble-based method, the ES-MDA: different petrophysical images in the initial ensemble, inflation factor (α), measurement error (CD) and truncated singular value during the matrix inversion process (TSV); aiming to understand how each parameter affects data match, uncertainty reduction and production forecast. To verify the impact of these parameters, we changed their values separately. Results showed that different initial ensembles have a major impact when using a small number of models, such as 100, and minor effects for a large number of models, such as 500. Inflation factor and CD have a high impact on the whole process (data match, uncertainty reduction and production forecast), and TSV has a minor impact on the process. Finally, careful analysis of these parameters and further research is required to obtain better results.
Keywords: History Matching; Ensemble Smoother with Multiple Data Assimilation; Localization; Covariance inflation: Truncated Singular Value (TSV); Measurement error; initial ensemble.
An improved cubic law for shale fracture considering the effect of loading path
by Yiyu Lu, Xiayu Chen, Honglian Li, Jiren Tang, Lei Zhou, Shuaibin Han
Abstract: Massive multi-stage hydraulic fracturing to form one large-scale stimulated reservoir volume (SRV) with a complex fracture network is a key technique in shale gas development. A natural fracture system may contribute significantly to gas production. Fracture aperture are the key parameter for determining flow characteristics of jointed rock media and changes due to loading and unloading behavior. In this study, according to the consolidation model for soil, a hydraulic aperture model was proposed to describe aperture variation in a complex loading path with a parabolic function. The numerical results and experimental data showed good agreement. A numerical study of the hydro-mechanical model was conducted to determine the influences of loading path and nonlinear effects on fluid flow at field scale. In this specific simulation, the total flow volume considering the influence of loading path only decreased by 14%, and considering the influence of loading path decreased by 28%, meanwhile influence of two factors resulted in a 39% reduction of the total flow volume.
Keywords: shale fracture;loading-path;hydraulic aperture model;improved cubic law.
Experimental study on the feasibility of using water emulsified diesel as CI engine fuel
by Pijush Kanti Mondal, Bijan Kumar Mandal
Abstract: In this article, authors have investigated the combustion, performance and emission characteristics of a four-stroke water cooled CI engine using water emulsified diesel (WED) as fuel containing 5% to 20% water by volume. The emulsions have been prepared using ultrasonicator. The stability behaviours of these prepared WEDs are analysed based on the measured values of polydispersity index (PDI) and water particle size in the emulsion. Improved combustion characteristics are found for WEDs than those with pure diesel. Higher brake thermal efficiency and mechanical efficiency are found for emulsified diesel compared to pure diesel. The neat SFC is found to be lower than that with pure diesel. Significant reductions in emissions of pollutants like NOx and smoke are observed. At full load, no significant difference is observed in CO emission. The emissions of CO2 and O2 have also been measured and analyzed.
Keywords: Water emulsified diesel; ultrasonicator; combustion; brake thermal efficiency; emission.
Narrow Distillation Cuts for an Improved Characterization of Crude Oil: An Insight on Heteroatoms in Heavy Fraction Molecules
by Hendrik Muller, Qasim Saleem, Emad A. Alawi, Donya A. Alsewdan, Imran A.S. Naqvi, Asem H. Al-Saleh, Tawfiq A. Al-Rowaished
Abstract: A light Arabian crude oil was separated by distillation into 27 fractions, including 25 very narrow distillation cuts, the light ends, and a vacuum residue (VR) , which were extensively characterized using standard methods. Overall, the properties matched well with those predicted by H/CAMS software, indicating a successful distillation. Then, quantitative 13C NMR spectroscopy, SIMDIS, and molecular weight (MW) distribution by mass spectrometry were used to derive an improved correlation between the MW and boiling point for the entire crude oil, in particular for the VR fraction. This allowed determining the mass fractions of sulfur and nitrogen containing compounds across the crude oil boiling range, reaching up to approximately 100 % in the VR fraction. The corresponding low abundance of pure hydrocarbon molecules in the VR fraction is important for modeling purposes and processing technologies.
Keywords: Petroleum crude oil; distillation; ASTM; APPI time-of-flight mass spectrometry; sulfur content; 13C NMR.
Comparison of polymer-based slag-mud slurries used for drilling jobs of steam stimulated wells in the Lagunillas oilfield (Venezuela)
by Juan Jesús Martín-del-Río, Gonzalo Márquez, Vicente Flores-Alés, Emilio Romero, Olga Rey, Marco Guzmán
Abstract: The mud-to-cement conversion or slag-mix technology displays several advantages when compared to conventional well cementing operations. This alternative method means to combine drilling fluids, accelerators, and finely granulated slag as the hydraulic material. Steam injection is commonly used to improve crude oil production in the Lagunillas field (state of Zulia, NW Venezuela). This work compares the use of two slag-mix systems containing two polymer-based drilling muds during cementing of injection wells: an aqueous drilling fluid and an oil-in-water emulsion mud. The aqueous formulations under study and a typical slag-mud slurry containing lignosulfonate show relatively similar values for most physic-mechanical properties. In contrast, the slag-mix emulsion system under consideration shows distinctive rheological and filtration behaviors compared to the other study polymer-based slag-mud slurry, but similar mechanical properties.
Keywords: slag-mud slurry; polymer-based drilling mud; mechanical behavior; steam injection; Lagunillas field.
Estimation of carbon dioxide injection into reservoirs potential to enhance oil production and reduce CO2 emissions to the atmosphere
by Edyta Kuk, Jerzy Stopa, Pawe? Wojnarowski, Micha? Kuk
Abstract: The carbon dioxide injection into mature oil reservoirs makes it possible to increase the oil recovery and reduce CO2 emissions to the atmosphere. The analysis of the CO2-EOR method applicability on a given reservoir requires forecasting of the production most often conducted with the use of compositional simulators with a high degree of complexity. Due to the increasing popularity of the CO2-EOR method a new methodology for preliminary evaluation of its impact on the oil recovery based on the material balance equation was proposed in this paper. On the basis of the proposed methodology the novel computer application was developed. The obtained results indicate that the developed solution makes it possible to quickly and effectively estimate the potential of the carbon dioxide injection into oil reservoirs to achieve a synergistic environmental effect.
Keywords: CO2-EOR; material balance; production forecasting; CO2 sequestration; enhanced oil recovery.
Effect of moisture content on methane diffusion in kaolinite by Molecular dynamics simulations
by Bin Zhang, Tianhe Kang
Abstract: The diffusion behaviors of methane in kaolinite with water contents ranging from 0-5wt% have been analyzed by molecular dynamics (MD) simulations. The results indicate that methane molecules can jump between adjacent holes in the kaolinite matrix. Methane diffusion coefficient is very low (3.28
Keywords: molecular dynamics; kaolinite; moisture content; diffusion.
A Numerical Scheme and Real Options Modeling for Evaluation of a Hypothetical Oil Field under Uncertainties
by Behnam Aminrostamkolaee, Ali Safdari-Vaighani, Mahdiye Rostamkhani, Matin Sadat Borghei, Mohammad Hossain Poorkazemi, Abbas Shakeri, Teymour Mohammadi
Abstract: This paper uses real options for evaluation of a hypothetical oil field under uncertainties. We have supposed that this oil field is located in Saudi Arabia. Our evaluation includes uncertainties of oil price and exchange rate. The analysis is done both for the fixed exchange rate regime and for the floating exchange rate regime. The proposed approach enables us to take the advantage of real option valuation to overcome the shortcoming of the discounted cash flow (DCF) method which neglects uncertainties. This paper uses an explicit finite difference method (FDM) to approximate the solution of the resulting equation. The numerical experiments show that the impact of the exchange rate, oil price volatility and the correlation coefficient between returns of oil price and exchange rate on the value of an oil extracting project is significant. In addition, the behavior of the project value is studied as a function of exchange regime.
Keywords: Fixed and Floating Exchange Rate Regimes; Oil Field Value; Real Option; Uncertainties; Hypothetical Oil Field; Finite Difference Method.
Ensembling methods for countrywide short term forecasting of gas demand
by Andrea Marziali, Emanuele Fabbiani, Giuseppe De Nicolao
Abstract: Gas demand is made of three components: Residential, Industrial, and Thermoelectric Gas Demand. Herein, the one-day-ahead prediction of each component is studied, using Italian data as a case study. Statistical properties and relationships with temperature are discussed, as a preliminary step for an effective feature selection. Nine "base forecasters" are implemented and compared: Ridge Regression, Gaussian Processes, Nearest Neighbours, Artificial Neural Networks, Torus Model, LASSO, Elastic Net, Random Forest, and Support Vector Regression (SVR). Based on them, four ensemble predictors are crafted: simple average, weighted average, subset average, and SVR aggregation. We found that ensemble predictors perform consistently better than base ones. Moreover, our models outperformed Transmission System Operator (TSO) predictions in a two-year out-of-sample validation. Such results suggest that combining predictors may lead to significant performance improvements in gas demand forecasting.
Keywords: Natural gas; time series forecasting; neural networks; statistical learning; ensemble methods.
Research on Molecular Engineering and Molecular Management for petroleum energy and its Applications
by Qing Wu, Baocheng Qiu, Baoqing Deng, Yi Liu, Yi Zhang
Abstract: How to utilize petroleum resource, re-recognize and re-match resources, catalysts, and processes, have been a critical topic. Based on above mentioned points, molecular engineering & management for petroleum has attracted more and more attention from industrial and academic community. The molecular engineering and management should be framework of many key techniques, which include the following aspects: 1) The molecular level characterization of petroleum and its fractions; 2) Informational description of oil molecule information; 3) The correlation between oil molecule information and reactivity and the establishment of molecular dynamics model; 4) Simulation and optimization to maximize the value of oil resources and assets. Meanwhile, the molecular engineering and management should focus on the simulation and computing techniques, such as Molecular Type Homologous Series matrix (MTHS), Monte Carlo, Lumping and Refactoring of Entropy Maximum (REM), et.al. Many examples of the application in research, production and operations management were also introduced in this paper.
Keywords: Molecular engineering; Molecular management; Characterization; Molecular database; Reaction rule database; Dynamic models; Simulation and optimization.
Experimental Research and Numerical Simulation: Strength and Rupture patterns of Coal under Brazilian Tensile Test
by Jun Zhang, Xiaoxuan Li, Yuwei Li, Feiyu Tao, Maosen Yan
Abstract: Coal seam contains well-developed weak planes known as cleats. The strength and rupture patterns of coal with different cleat directions are significantly different in Brazilian tensile test (BTT). In this paper, a series of Brazilian tensile tests of coal specimens under different inclination angles of face cleat were carried out. Based on the experimental data, the influence of cleat direction on the failure strength (FS) and rupture patterns of coal specimens was analyzed. Then the analytical model to calculate the anisotropic failure strength of coal under Brazilian test conditions was derived. The model cannot only predict the rupture patterns of coal specimens with different cleat directions and calculate the corresponding failure strength, but also can reflect the effect of cleat density on the strength. In the simulation, the rupture patterns of numerical model also fall into four types, which are consistent with the experimental results. The cleat density has no influence on the rupture patterns, but will decrease the failure strength. The connectivity of butt cleats is the key to determine whether the coal shear along the face cleats or butt cleats.
Keywords: Coal; Brazilian tensile test; rupture patterns; failure strength; cleat density; cleat connectivity.