Thermal-reactive-compositional flow simulation in porous media is essential to model unconventional thermal oil recovery processes for extra-heavy hydrocarbon resources, e.g., the In-situ Conversion Process (ICP) for oil-shale production. Computational costs can be very high for such a complex system, which may make simulation studies prohibitively time consuming for large field-scale applications on fine grids. On the other hand, significant errors are introduced with the use of coarse-scale models. In this paper, we developed an innovative multipoint multiscale modeling method to effectively capture the fine-scale reaction rates in coarse-scale ICP-simulation models. In our multiscale method, coupled thermal-reactive-compositional flow equations are solved only on the coarse-scale, with the kinetic parameters (frequency factors) calculated based on fine-scale reaction rates. We perform the temperature downscaling by solving the heat diffusion equation in local regions subject to temperature-gradient boundary conditions obtained from a multipoint evaluation on the coarse grid. A multiscale treatment is also developed for the heater well model. Coarse-scale heater well indices are calculated from fine-scale well models using downscaled temperatures. The newly developed multiscale method is applied to realistic cross-sectional ICP-pattern models with a vertical production well and multiple horizontal heater wells operated subject to a time-varying power. It is shown that the multiscale model delivers results that are in close agreement with the fine-scale reference results for all quantities of interest. Despite the fact that the multiscale method is implemented at the simulation-deck level, using the flexible scripting and monitor functionalities of our proprietary simulation package, significant computational improvements are achieved for all cases considered.

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