Research on the Extraction Efficiency of Tight Oil in Porous Media Under Varying CO2 Injection Pressures

Developing complex fault-block low-permeability reservoirs faces great challenges in constructing efficient injection-production flow pathways, which often leads to unsatisfactory waterflooding development performance. To improve the recovery efficiency of this type of reservoir, this study first carried out laboratory extraction experiments and then conducted CO2 extraction numerical simulations on low-permeability porous media via ANSYS to validate the experimental results. Based on investigations targeting the target reservoir, the key findings are summarized as follows: Supercritical CO2 preferentially extracts light hydrocarbon components lighter than C10, which accounts for more than 60% of the total extracted components; when the pressure exceeds 20 MPa, a small amount of heavy components C15+ can also be extracted. Under the experimental conditions adopted in this study, the optimal CO2 reinjection pressure range is determined as 12–20 MPa. Within this range, the extraction efficiency increases by 2.0–2.5% per 1 MPa increment of pressure, and this pressure condition can effectively dissolve medium hydrocarbon components and promote the formation of uniform plug flow. However, when the reinjection pressure continues to rise beyond 20 MPa, the CO2 extraction efficiency will gradually decrease. The numerically simulated CO2 extraction efficiency of crude oil shows high consistency with the experimental measurements. This study confirms that CO2 huff-n-puff can be effectively applied for crude oil extraction in the peripheral areas of tight reservoirs and fault-block reservoir units. Nevertheless, in field application, it is imperative to optimize the reinjection pressure design: accurately customizing injection pressure parameters according to different reservoir types and their specific development requirements is a core measure to improve CO2 extraction efficiency.