Study on the phase state and temperature-pressure distribution of CO2 injection wellbore and its effect on tubing stress conditions

This study investigates the phenomena observed during CO2 injection processing in wellbores, particularly the annular pressure buildup typically attributed to inadequate packer sealing. We propose that temperature, pressure, and phase changes during CO2 injection induce equivalent stresses, leading to packer unsealing. A detailed CO2 injection model was developed, incorporating temperature-pressure coupling and phase transitions using the state equation. The model evaluates the effects of injection temperature, pressure, and volume on CO2 density, temperature, pressure, phase state, and velocity, and calculates the stress on the tubing at various depths. Validation against actual measurements showed errors of 1.43% for pressure and 0.66% for temperature, confirming the model's accuracy. Key findings reveal that injection temperature significantly affects CO2 phase changes, while injection temperature and volume respectively impact stress at the wellhead and bottom. The model provides a robust tool for optimizing CO2-EOR processes, confirming that changes in injection parameters can indeed cause packer unsealing, and its reliance on precise input data highlights the need for accurate field measurements.