A mathematical model of the non-stationary filtration process for oil-supercritical CO2 system in a homogeneous porous medium under various modes of oil displacement

Abstract The phase diagram of the system “transformer oil-supercritical CO2” is built. The modes of miscible and microbubble displacement of oil are determined. Oil was displaced by carbon dioxide in a supercritical state on isotherms 313 and 333 K in the pressure range up to 12 MPa at the experimental bench created by the authors. New data have been obtained on the coefficient of oil displacement by supercritical CO2 from a model of a homogeneous oil reservoir in a miscible and micro-bubble mode of supercritical CO2 filtration. It was revealed that the miscible regime of oil displacement by supercritical CO2 has the greatest technological efficiency. For the region of a mixed filtration regime, a mathematical model was created and solved for the process of filtering the unsteady flow of “supercritical CO2-oil” in a homogeneous terrigenous porous medium in the pressure range up to 12 MPa, temperatures up to 333 K, the calculated curve agrees with the experimental data on the oil displacement coefficient. The convergence and stability of the difference scheme of the computational process is ensured. It was found that in the transition region of supercritical CO2 filtration on the boundary curve in the phase diagram and in the region of microbubble filtration of supercritical CO2, the process of oil displacement is more intense, which is associated with the appearance of a supercritical sublayer on the pore surface, which leads to slipping of the fluid inside the pore. For the transition-filtering region on the boundary curve in the phase diagram and in the region of the microbubble displacement of oil by supercritical carbon dioxide, a method for increasing technological efficiency is proposed based on the injection of supercritical CO2 and water rims to prevent the transition of microbubble carbon dioxide to the free phase.