Mechanism of enhanced oil recovery by supercritical CO2 in nanopores, a molecular dynamics simulation

Using CO2 for enhanced oil recovery (EOR) in reservoirs is a Carbon Capture, Utilization, and Storage (CCUS) technique that achieves both economic and social benefits. Supercritical CO2 demonstrates unique advantages in unconventional oil and gas extraction, but its mechanisms require further exploration and study. Current research has primarily focused on studying the miscibility and adsorption mechanisms of supercritical CO2 with simple alkane mixtures. This paper uses molecular simulation methods to investigate the microscopic mechanisms of dynamic extraction of crude oil in rock pores by supercritical CO2 during the oil EOR process. The study compares the distribution of crude oil in pores during the supercritical CO2 flooding process under varying conditions of temperature, pressure, injection pressure, and alkane composition. CO2 receives such cycle of stripping, driving, adsorbing, and transporting alkanes adsorbed on the surfaces. Additional research indicates that changing the composition ratio of crude oil in the pores affects the extraction efficiency of CO2. With increased injection pressure, the extraction efficiency improves for higher-density crude oil, while for lower-density crude oil, the extraction efficiency decreases. Therefore, in practical development, considering that crude oil density gradually increases as extraction progresses, it is recommended to begin with a lower injection pressure and gradually increase it over time to maximize recovery efficiency. This study provides support and recommendations for the investigation of the mechanisms of EOR using supercritical CO2.