Simulation of in-situ steam-driven oil seepage in single-fracture oil shale CT digital cores after pyrolysis at different temperatures

Based on digital cores of oil shale obtained from high-temperature steam in-situ pyrolysis and micro-CT scanning experiments, the real structures of oil shale after pyrolysis at different temperatures were seamlessly integrated into COMSOL through precise grid partitioning. This enabled the simulation of in-situ steam-assisted oil recovery two-phase flow fields. The study examines the dynamic evolution of phase interfaces, pressure fields, velocity fields, and oil displacement efficiency during the in-situ two-phase flow process in pore structures with varying degrees of development. The research indicates that: Firstly, the development and connectivity of pore structures significantly influence the advancement speed of the phase interface — the better the pore structure development, the faster the phase interface advances. Secondly, as seepage progresses, the stability of phase interface advancement improves, with the difference between the peak δ a value before stabilization and the stabilized δ a value decreasing over time. Thirdly, at the moment of steam injection, a surge in P a within the seepage zone occurs. The complexity of the pore structure effectively mitigates the surge in P a caused by the instantaneous gas drive effect. Finally, the total seepage volumetric flow rate Q total increases with time. The oil production ratio α at the outlet decreases slightly with time, but remains above 97.6 %, demonstrating the effectiveness of steam-assisted oil recovery.