Simulation of coupled thermal-hydro-mechanical processes in fracture propagation of carbon dioxide fracturing in oil shale reservoirs

Supercritical carbon dioxide fracturing can effectively relieve the environmental pressure caused by in-situ production of oil shale. In order to study the process of fracture propagation during supercritical carbon dioxide fracturing, a fracture propagation model of supercritical carbon dioxide fracturing is established in this paper, and an unsteady temperature field model is introduced. Based on the discrete fracture model, the fluid temperature field in one-dimensional fracture is coupled with the temperature field of two-dimensional reservoir rock. The new model also takes into account the real-time variation of carbon dioxide physical parameters, which are calculated by Span-Wagner and Vesovic equations. Based on this model, the influencing factors of fracture propagation in supercritical carbon dioxide fracturing are analyzed. The results show that the leak-off coefficient has an obvious effect on fracture propagation, so an additive needs to be developed to reduce the leak-off. Since carbon dioxide is a compressible fluid, the reservoir temperature and the original in-situ stress also have a significant impact on the fracture propagation. The temperature of carbon dioxide at the bottom of the well has no significant effect on fracture propagation, because carbon dioxide will quickly reach reservoir temperature when it enters the formation. Comprehensive considering the fracture length, width, filtration, and potential effect on proppant transport during supercritical carbon dioxide fracturing, the injection rate should be as high as possible.