Reservoir heterogeneity controls of CO₂-EOR and storage potentials in residual oil zones: Insights from numerical simulations

Residual oil zones (ROZs) have large potential for CO₂ enhanced oil recovery (EOR) and geologic storage. During CO₂ injection, the migration of CO₂ in ROZs controls the performance of both EOR and storage. However, it has not been clearly visualized and understood that how geological heterogeneity factors control the transport of CO₂ in ROZs. In this study, the oil recovery performance and geologic storage potential during continuous CO₂ injection in a representative ROZ are studied based on geostatistical modelling and high-fidelity three-phase flow simulation. We examined the influence of autocorrelation length of permeability, global heterogeneity (Dykstra–Parsons coefficient), and permeability anisotropy on cumulative oil recovery and CO₂ retention fraction. Simulation results indicate that, as the permeability autocorrelation length increases, the cumulative oil recovery and CO₂ storage efficiency decrease. This results from the accelerated migration of CO₂ along high permeability zones (i.e., gas channeling). The increase in global heterogeneity and permeability anisotropies can lead to low oil recovery and poor CO₂ sequestration performance, depending on the degree of CO₂ channeling. The net utilization ratio of CO₂ (CO₂ retained/oil produced) unfavorably increases with both autocorrelation length and Dykstra–Parsons coefficient, but decreases with the increase ink_v/k_h. Such a decrease is attributed to enlarged swept volume induced by gravity override. The study provides important implications for field-scale CO₂ EOR and storage applications in ROZs.