A coupled thermo-hydro-mechanical-chemical model for production performance of oil shale reservoirs during in-situ conversion process

The in-situ conversion process (ICP) is an effective approach to exploiting oil shale, which involves chemical reaction, fluid flow, heat transfer, and mechanical response (i.e., thermo-hydro-mechanical-chemical coupling, THMC). Based on the coupled thermo-hydro-chemical (THC) model reported in recent studies, a fully coupled THMC model is established to consider the key effect of mechanical response during ICP, where the continuity equation is improved by introducing rock deformation and integrating the mass source terms from kerogen pyrolysis, and the stress- and temperature-dependent model is developed to characterize the evolution of porosity and permeability. To address the challenge of the complex THMC problem with dramatic stress change, a segregated scheme with an automatic time-stepping algorithm is adopted to accelerate the solution, and the reliability of the THMC model and solution strategy is verified with the field data. The results show that the maximum Mises stress in shale formation exceeds 150 MPa, and the mean principal stress decreases by more than 70 MPa, resulting in a significant change of porosity and permeability during the heating process, which subsequently alters the heat transfer and fluid flow processes. On this basis, comprehensive analyses of various engineering parameters are carried out to optimize the in-situ conversion technology.