Pore-Level Study of the Effect of Miscibility and Wettability on Oil Recovery during Gas Assisted Gravity Drainage

摘要

The effect of the gas-oil interfacial tension and wettability on the performance of gas assisted gravity drainage (GAGD) process was investigated at the pore-level to explore conditions leading to high oil recoveries. This work extends the previous investigation of GAGD parameters, i.e., the contribution of film flow and wettability, that we presented in 2015 and 2016. GAGD experiments were conducted in a new micromodel with an improved capillary continuity to reflect mechanisms of oil recovery effectively. The result of the experiment showed that the heterogeneities of the porous medium causes the gasfront to bypass oil in small pores surrounded by large pores. The subsequent drainage of bypassed pores was possible where the gas-oil capillary pressure was sufficiently increased due to a reduction in the hydrostatic pressure of oil. The strong hydraulic continuity of oil in an oil-wet porous medium compared to a water-wet porous medium contributed to a low residual oil saturation under immiscible conditions. In water-wet micromodels, a nearcomplete oil recovery was obtained under miscible conditions as no interface between oil and gas was formed, and no oil was bypassed when the miscible displacement is developed.