A Study on the Miscibility Mechanisms and Patterns of High CO2 Content Associated Gas Reinjection
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To investigate the enhanced oil recovery mechanisms during the reinjection of CO₂-rich associated gas, analyze the miscibility behavior between associated gas and crude oil, and provide guidance for further improving oil recovery in field development, this study conducted gas injection expansion experiments, solubility measurements of various gases in crude oil, and slim tube experiments. The experimental results demonstrated that CH 4 and N 2 reduce the solubility of associated gas in crude oil, the solubility of associated gas without CH 4 and N 2 in crude oil is 1.05 to 3.22 times that of CO 2 while their removal enables the solubility of associated gas in crude oil to surpass that of CO 2 . Both CO 2 and associated gas can cause crude oil to swell and reduce its viscosity, and the absence of CH 4 and N 2 amplifies these effects. The minimum miscibility pressure (MMP) for CO 2 flooding is 24.29 MPa, while the reservoir pressure of 21 MPa is insufficient to achieve miscible flooding. Removing CH 4 and N 2 from the associated gas can reduce the MMP by up to 48%, resulting in a 25.59% improvement in oil recovery efficiency.
