Numerical Simulation Study of CO2 EOR and Sequestration in Heterogeneous Tight Reservoir
Abstract
CO2 injection is a critical method for the efficient development of tight oil reservoirs. However, tight oil reservoirs are characterized by complex nanoscale pores and severe heterogeneity. Fluid flow within such formations is governed by dual influences, resulting in significant variations in field development performance. Consequently, achieving geological sequestration while effectively utilizing CO2 to enhance oil recovery remains a substantial challenge. In this paper, a heterogeneous tight reservoir model incorporating the nano-confinement effect was established using numerical simulation methods. Through mechanism simulation and parameter sensitivity analysis, the impacts of the nano-confinement effect, reservoir heterogeneity, and injection parameters on CO2 enhanced oil recovery and geological sequestration were systematically analyzed. The results show that the nano-confinement effect significantly enhances oil recovery in heterogeneous tight oil reservoirs. Specifically, during the CO2 flooding stage, the final recovery under the 10 nm pore scale is improved by approximately 6.05% compared to bulk conditions. CO2 tends to channel along main fractures, limiting sweep efficiency in the tight matrix. However, controlling injection pressure at 1-1.15 times the MMP yields optimal results. With this strategy, the utilization CO2 displacement ratio remains above 0.7 t/t, and sequestration efficiency exceeds 71%. Furthermore, while injection timing has a negligible impact on the ultimate CO2 sequestration efficiency, switching to CO2 injection after 3–6 months of primary depletion allows for the full utilization of formation energy, significantly improving both the utilization CO2 displacement ratio and oil recovery. Overall, these results validate the feasibility of simultaneous CO2-EOR and sequestration via short horizontal wells in heterogeneous tight reservoirs, offering important insights for efficient development strategies.