Study of phase and physical property changes during gas lift injection of high CO ₂ ‐content associated gas in the offshore M oil field

Abstract The gas lift in the offshore M field will be performed with high CO 2 ‐content associated gas, but the change of wellbore temperature and pressure during the injection process will lead to the change of phase and physical parameters of associated gas, which has a great impact on the design of gas lift. To ensure the smooth implementation of gas lift in the offshore M field, this paper conducts a study on the physical parameters of associated gas considering the change of CO 2 phase state. We obtained the density, viscosity, compression factor, constant pressure specific heat capacity, thermal conductivity, and Joule Thomson coefficient at each temperature and pressure by Hysys calculation, and regression analysis to obtain the regression model of the physical parameters; finally, the regression model was compared with the flash experiment and Hysys calculation results. The results show that the CO 2 phase change has a large influence on the physical parameters; R 2 > 0.8, which indicates that the regression model has sufficient reliability; the results of the comparison show that the empirical formulas of all physical properties have sufficient accuracy and superiority except Joule–Thomson coefficients. In addition, the empirical formula of the Joule–Thomson coefficient also has good accuracy and superiority at the pressure not exceeding 22 MPa. The study of phase changes and physical parameters of associated gas with high CO 2 content provides a basis for subsequent gas lift design in the offshore M field and multiphase flow calculations in the wellbore during the gas lift. Although this study is only applicable to this sample, it also provides a feasible research method for other samples.