Effect of Reservoir Heterogeneity on CO2 Flooding in Tight Oil Reservoirs

Carbon dioxide (CO2)-enhanced oil recovery (EOR) has great potential and opportunity for further development, and it is one of the vital carbon capture, utilization, and storage (CCUS) technologies. However, strong heterogeneity is one of the several challenges in developing reservoirs, especially for China's continental tight oil reserves. This study investigates the effects of heterogeneous porosity and permeability on CO2 flooding evolution in low-permeable tight formation. We simulated CO2-EOR using a numerical model developed on the platform of TOUGH2MP-TMVOC to evaluate the effect of different levels of heterogeneity on oil production, gas storage, and flow behaviors in a tight reservoir, controlled by standard deviation and correlation length. A comparison of nine cases reveals that porosity heterogeneity commonly intensifies flow channeling, and there is an oil production decline with higher standard deviation and longer correlation length of porosity field. In addition, the porosity correlation length has a negligible effect on reservoir performance when the standard deviation is relatively low. Furthermore, strong heterogeneity also has a negative impact on the storage capacity of CO2 and oil production. Notably, as the standard deviation was raised to 0.1, a small sweep region arose with the early CO2 breakthrough, which led to a worse flooding effect. Finally, this study exemplifies that a higher injection/production rate and CO2 alternating N-2 injection strategies can improve oil recovery in highly heterogeneous reservoirs.

Automated summary

Carbon dioxide-enhanced oil recovery (CO2-EOR) is a promising carbon capture, utilization, and storage (CCUS) technology. This study investigates the effects of heterogeneity on CO2 flooding in low-permeable tight formations and finds that porosity heterogeneity intensifies flow channeling and reduces oil production. It also demonstrates that higher injection/production rates and CO2 alternating N-2 injection strategies can improve oil recovery in highly heterogeneous reservoirs.