Abstract：
In unconventional reservoir stimulation, Supercritical (SC) CO2 fracturing can not only increase oil/gas production, minimize formation damage and conserve water resources, but also promote CO2 geological storage, which draws broad attention in both industry and academia. This work reviewed the current studies with respect to experimental techniques, characteristics and mechanisms of fracture initiation and propagation, and related existing problems and suggestions in SC-CO2 fracturing. The mechanisms of coupled thermo-hydro-mechanical-chemical (THMC) processes between SC-CO2 and rockare induced stress and weakened fracture toughness. The induced stress includes the thermal stress and pore pressure field induced by the low viscosity and high diffusionof SC-CO2, which can lower the effective stress and even create shear failure (TH-M effects). Thedynamic load and thermal stress created by the SC-CO2 phase change can enhance micro-fracture initiation and propagation (TH-M effects). The weakened fracture toughness includes SC-CO2 of zero surface tension, tending to penetrate into the micro-cracks to lower fracture net pressure for crack growth (H-M effects). CO2 adsorption can lower the surface energy of rock and this in turn reduces the critical stress for crack growth (C-M effects). Therefore, SC-CO2 fracturing tends to create multiple fractures characterized by I-II type failure, which can be applied for stimulation of fracturedtight reservoirs. So, in the future, it will be necessary to conduct SC-CO2 fracturing experiments, to be used to reconstruct and evaluate the induced 3D fractures. The research scale is upgraded with the theoretical and numerical models to accelerate the process of SC-CO2 fracturing in the field.
Key words：SC-CO2 fracturing; fracture mechanism; experimental study; THMC coupling; unconventional reservoirs
Corresponding Authors： zhangguangqing@cup.edu.cn
Cite this article：ZHOU Dawei, ZHANG Guangqing. A review of mechanisms of induced fractures in SC-CO2 fracturing. Petroleum Science Bulletin, 2020, 02: 239-253.
