Abstract
We investigate the productivity and product selectivity of diverse thermal in situ upgrading processes in oil shale reservoirs. In situ upgrading processes applying the ideas of Shell In situ Conversion Process, ExxonMobil Electrofrac, and Texas A&M Steamfrac are simulated by using sector models with the assumption of symmetric patterns. In-house fully functional simulator is used, which has been developed for the kerogen pyrolysis and hydrocarbon production. In the simulation cases, sensitivity analyses to the factors having major influence on the productivity and product selectivity are conducted. The effects of the temperature of vertical heaters, the spacing of hydraulic fractures, and the position of horizontal production wells are analyzed in the applied In situ Conversion Process, Electrofrac, and Steamfrac, respectively. In the applied In situ Conversion Process cases, hydrocarbon production increases with the increasing heater temperature. In the applied Electrofrac cases, hydrocarbon production increases with the increasing spacing of hydraulic fractures, even though longer time period for the process is needed. In the applied Steamfrac cases, the case of production well located at the same depth to the injection well shows the least hydrocarbon production. Among the processes, the applied In situ Conversion Process cases show the highest weight percentage of total hydrocarbon components in the produced fluid, and the applied Electrofrac cases follow it. The applied Steamfrac cases show far lower weight percentage of hydrocarbon production than the other methods. In terms of the mass ratio of produced hydrocarbon to decomposed kerogen, the applied Steamfrac cases show the largest value among the processes by aqueous phase sweeping liquid organic phase, but they also show the huge water oil mass ratio by the continuous injection of hot water. All the applied In situ Conversion Process cases and the Electrofrac case with the short spacing of hydraulic fractures show good heating efficiency by decomposing whole kerogen in the system.
Highlights
Oil shale is a sedimentary rock that contains solid hydrocarbon called kerogen
There still exist considerations for the application of in situ upgrading processes; excess heat should be avoided for better shale oil quality and higher recovery efficiency; natural or induced fracture systems are needed for the effective distribution of heat, because shale is not a good conductor; longer heating time is needed than the mining and subsequent surface pyrolysis; effective means for sweeping the generated hydrocarbon are needed (Crawford and Killen, 2010)
We investigate the in situ upgrading methods applying the ideas of Shell In situ Conversion Process (ICP; Vinegar, 2006), ExxonMobil Electrofrac (Symington, 2006), and Texas A&M Steamfrac (Thoram and Ehlig-Economides, 2011)
Summary
Oil shale is a sedimentary rock that contains solid hydrocarbon called kerogen. Kerogen generates a number of solid and fluid components including hydrocarbons when it is heated to a high temperature above 563 K. We examine the effects of factors on the productivity, product selectivity, and process efficiency of the diverse in situ upgrading technologies in the oil shale reservoir system by conducting numerical simulations. Because the heat is mainly transferred into the oil shale formation by conduction as the ICP method, the dimensions and geometry of hydraulic fractures are expected to significantly affect the process efficiency and productivity. Steamfrac method involves steam or hot water injection into the horizontal well system containing multiple vertical hydraulic fractures as shown in Figure 3 (Lee, 2014; Thoram and Ehlig-Economides, 2011). We conduct the numerical simulations by applying the ideas of ICP, Electrofrac, and Steamfrac to examine the production behavior and process efficiency, which are sensitive to the implementation details of thermal processes. The factors are significant to the production of phases and components by controlling chemical reactions, heat conduction, and transport properties of fluids and porous media
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