Coupled temperature–pressure model of fracture for phase state prediction in supercritical carbon dioxide fracturing

Abstract

ABSTRACT Supercritical carbon dioxide (SC-CO2) fracturing can reduce reservoir damage and increase fracture complexity, making it more promising to develop unconventional reservoirs. Accurate prediction of the CO2 phase state in the fracture can improve the SC-CO2 fracturing effect. This study aimed to establish a coupled temperature–pressure model of fracture for phase state prediction in SC-CO2 fracturing, considering heat conduction, convective heat transfer, kinetic energy change, and Joule–Thomson (J-T) effect. The temperature, pressure, physical parameters, and phase state of CO2 in the fracture were simulated and analyzed based on the model. The research results showed that the temperature was higher after considering the local influence of the J-T effect; the maximum increment was 1.74°C at a fracture length of 42 m. However, the fracture pressure was slightly lower, and the maximum reduction was only 0.015 MPa at the fracture root. As the injection displacement increased, the relative error of the length of liquid CO2 without the local influence of the J-T effect was larger; it could be as high as 9.7% when the displacement was 6 m3/min. In SC-CO2 fracturing, the local influence of the J-T effect could not be ignored for accurately predicting the phase of CO2 in the fracture.