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International Journal of Petroleum Engineering (2 papers in press)
Analytical Multiphase Fluid Flow Model for Reservoirs Producing under Bottom Water Drive Mechanism by Jalal Al-Sudani, Ali Al-Mashat Abstract: Many oil reservoirs with underlying aquifers undergo a capillary transition zone across the free level of the contacted fluids, and thus multiphase fluid flow of oil and water predominate in the reservoirs causes alteration in pressure response of the wells producing from such reservoirs and distort the accuracy of the models which analyze the reservoir drop behavior for predicting some reservoir characteristics.
In this paper, analytical multiphase flow model for oil reservoirs producing under aquifer drive mechanism has been developed to predict the accurate reservoir pressure drop during the transient flow period, as well as the capillary-saturation relationship under reservoir conditions. The model retains the natural coupling of oil reservoirs with the aquifer zone and treat them as explicit single-phase zones taken its own fluid and rock properties; and thus, the exact solution of diffusivity equation can be used explicitly for each region. The contacted fluid zones are linked across free water level which reflects the interaction between the contacted fluids and rock properties; this interaction degree depends on both of reservoir-aquifer rocks and their own fluid properties, and found to be well represented by a dimensionless capillary pressure term.
The principle of superposition theorem has been applied to perform this link throughout reflecting the created pressure drop behavior in the oil zone across the free-water level to estimate the exact reservoir pressure drop behavior, as well as the pressure drop at the free water level.
The results show that the conventional flow models which assume single phase fluid flow in porous media mislead the accuracy in predicting reservoir pressure. The error of these models increases with increasing the interaction degree between the reservoir and the aquifer, which depends on both of reservoir-aquifer rocks and their own fluid properties.
The new presented model involves the interaction degree between the reservoir and aquifer zones, which has the capability to estimate water saturation distribution along the capillary transition zone thickness across the free water level. Moreover, it gives the exact estimation of the pressure drop in the reservoir zone and at the free water level; since, it enables to extract more accurate reservoir properties using the transient response, in addition to more accurate calculation of water influx.
Keywords: Multiphase flow; porous media; Transient reservoir pressure drop; dynamic capillary pressure; water drive reservoir; Aquifer strength,Transition zone.
Cased Hole Formation Resistivity Contribution in Water Management and Production Enhancement of Mature Reservoirs by Ghareb Hamada, Osama Elmahdy, Murugravel Chandran Abstract: Due to continuous demand of oil market, it is increasingly important to improve production and increase proven reserves in the most efficient way possible. Hydrocarbon detection and saturation evaluation have long been a problem in cased holes. Determining hydrocarbon and water saturation behind casing plays a major role in reservoir management. Saturation measurements over time are useful for tracking reservoir depletion, enhancing recovery strategies and diagnosing production problems such as water production that is one of the main challenges facing oil and gas producers. It is necessary to manage water production to enhance oil production. In order to identify watered out zones, traditionally thermal decay time logging (TDT) and carbon/oxygen (C/O) logging are used, these tools have shallow depths of investigation and their effective application is limited in low porosity and salinity. With the introduction of cased hole formation resistivity technology (CHFR) a new dimension has been added to cased hole evaluation. A deep reading formation resistivity can now be obtained through steel casing, that means no effect of borehole fluid invasion on measurements as it has been the case with pulsed neutron tools.
In cased hole evaluation, cased hole resistivity finds it utility in two circumstances; as a first resistivity measurement in old and new wells to assess the formation in present conditions, or as a time-lapse technique to describe temporal behavior of reservoir dynamic and reservoir fluids movements to mainly detect bypassed oil zones and water invaded zones. Five case studies of mature reservoirs suffer from water production problems attributed to different geological and reservoir conditions. In all cases, the remedial workover operations based on the cased hole resistivity results have allowed a significant enhancement of the oil production and the implementation of an optimum field management strategy. Keywords: Water Management; bypassed oil; CHFR; TDT; Workover.