Supercritical CO2 Injection-Induced Fracturing in Longmaxi Shales: A Laboratory Study

Although supercritical CO2 (SC-CO2) fracturing has shown promise in oil and gas development with demonstrated potential, its application in shale gas extraction remains in its infancy globally. In this study, fracturing experiments were conducted with water, liquid CO2 (L-CO2), and SC-CO2, as well as SC-CO2 at varying pump rates. The results reveal that SC-CO2 fracturing produces a highly complex fracture network characterized by fractures of varying numbers, deflection angles, and tortuosity. Analysis of CO2 temperature and pressure data showed a sharp drop in injection pressure and temperature at breakdown, followed by fluctuations until injection stopped. Acoustic emission (AE) monitoring demonstrated that energy released during main fracture initiation significantly exceeded that from CO2 phase transition-driven fracture extension, underscoring the dominant role of main fractures in energy dissipation. Compared to hydraulic fracturing, SC-CO2 fracturing created a seepage area 2.2 times larger while reducing the breakdown pressure by 37.2%, indicating superior stimulation performance. These findings emphasize the potential of SC-CO2 to form intricate fracture networks, offering a promising approach for efficient shale gas extraction.