Establishment of temperature-pressure coupling model of CO2 looding injection string and analysis of its sensitivity factors.

In order to accurately analyze the stress of CO₂ flooding injection string, it is necessary to consider the phase distribution of CO₂ fluid in the injection string, and reasonably predict the temperature field and pressure field distribution of CO₂ flooding injection string. Firstly, the coupling differential equations of temperature, pressure and physical parameters of CO₂ flooding injection string were established by three conservation laws. Then, according to the calculation steps of fourth-order Runge Kutta algorithm, MATLAB program was compiled to analyze the temperature field and pressure field of four CO₂ flooding injection strings in an oilfield. Finally, the sensitivity factors of temperature field and pressure field distribution of CO₂ flooding injection string were analyzed. The results indicate that in the process of CO₂ flooding injection, the temperature and pressure of CO₂ flooding injection string increase approximately linearly with the increase of formation depth. The fluid temperature exceeds the critical temperature by 31.1 °C after 1-100 m of the string, and the phase state of CO₂ fluid changes to supercritical state. The temperature field distribution of injection string is most significantly affected by the injection rate of CO₂ fluid, and its sensitivity coefficient reaches 3.10. The pressure field distribution of injection string is most significantly affected by the injection pressure of CO₂ fluid, and its sensitivity coefficient reaches 6.00. [ABSTRACT FROM AUTHOR]