Research on Temperature and Pressure Prediction in the Wellbore of Offshore High CO ₂ Content-Associated Gas Injection Wells and Analysis of Influencing Factors

Offshore platforms can utilize associated gas with a high CO₂ content as an injection gas source, enhancing reservoir displacement efficiency while reducing gas sourcing costs. To ensure that the high CO₂ content associated gas is injected into the reservoir at the expected temperature and pressure and to achieve miscibility, it is essential to investigate the wellbore's temperature and pressure distribution during the injection process. For this purpose, a nonsteady-state coupled calculation model was developed to simulate the temperature, pressure, and physical property parameters of the wellbore during offshore high CO₂ content associated gas injection. The model was applied to an actual offshore injection well and validated against field production data, demonstrating maximum relative errors of -2.51% for temperature calculations and -3.54% for pressure calculations. Based on the parameters from the production site, the model was employed to analyze the effects of different injection parameters on the wellbore temperature and pressure distribution. The results indicate that while injection temperature and pressure exert minimal influence on bottomhole temperature, they significantly affect bottomhole pressure. Increasing the injection flow rate reduces the wellbore temperature while elevating bottomhole pressure. Variations in gas composition directly induce substantial changes in the physical properties of the high CO₂ content associated gas, consequently exerting a pronounced impact on the overall wellbore temperature and pressure profiles. The findings could provide a theoretical foundation and practical reference for optimizing the design and ensuring the safe implementation of offshore high CO₂ content associated with gas injection operations.