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

Abstract

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 δa value before stabilization and the stabilized δa value decreasing over time. Thirdly, at the moment of steam injection, a surge in Pa within the seepage zone occurs. The complexity of the pore structure effectively mitigates the surge in Pa caused by the instantaneous gas drive effect. Finally, the total seepage volumetric flow rate Qtotal 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.

Keywords

• Single-fracture oil shale
• Pyrolysis
• Digital rock core
• In-situ
• Steam-driven oil seepage
• Numerical simulation