Abstract
To investigate the enhanced oil recovery mechanisms during the reinjection of CO(2)-rich associated gas, analyse the miscibility behaviour between associated gas and crude oil, and provide guidance for increasing oil recovery in field development, in this study, gas injection expansion experiments, solubility measurements of various gases in crude oil, and slim tube experiments were conducted. The experimental results demonstrated that CH(4) and N(2) could reduce the solubility of associated gas in crude oil. The solubility of associated gas without CH(4) and N(2) in crude oil was 1.05 to 3.22 times greater than that of CO(2), whereas their removal enabled the solubility of associated gas in crude oil to surpass that of CO(2). Both CO(2) and associated gas could cause crude oil to swell and reduce its viscosity, and the absence of CH(4) and N(2) amplified these effects. The minimum miscibility pressure (MMP) for CO(2) flooding is 24.29 MPa, while a 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% increase in the oil recovery efficiency.