Oil shale is a highly abundant energy resource, though commercial production has yet to be realized. Thermal in-situ upgrading processes for producing hydrocarbons from oil shale have recently gained attention, however, in part because of promising results reported by Shell using their In-situ Conversion Process. This and similar processes entail heating the oil shale to about 325°C, when the kerogens in the shale decompose through a series of chemical reactions into liquid and gas products. In this paper we present a detailed numerical formulation of the in-situ upgrading process. Our model, which can be characterized as a thermal-compositional, chemical reaction and flow formulation, is implemented into Stanford's General Purpose Research Simulator (GPRS). The formulation includes strongly temperature-dependent kinetic reactions, fully-compositional flow and transport, and a model for the introduction of heat into the formation through downhole heaters. We present detailed simulation results for representative systems. The model and heating patterns are based somewhat on information in Shell patents; chemical reaction and thermodynamic data are from previously reported pyrolysis experiments. After a relatively modest degree of parameter adjustment (with parameters restricted to physically realistic ranges), our results for oil and gas production are in semi-quantitative agreement with available field data. We also investigate various sensitivities and show how the produced hydrocarbon components are impacted by heater temperature and location. The ability to model these effects will be essential for the eventual design and optimization of in-situ upgrading operations.

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