Analysis of Fracturing Expansion Law of Shale Reservoir by Supercritical CO 2 Fracturing and Mechanism Revealing

The rapid expansion of reservoir fractures and the enlargement of the area affected by working fluids can be accomplished solely through fracturing operations of oilfield working fluids in geological reservoirs. Supercritical CO 2 is regarded as an ideal medium for shale reservoir fracturing owing to the inherent advantages of environmental friendliness, excellent capacity, and high stability. However, CO 2 gas channeling and complex propagation of fractures in shale reservoirs hindered the commercialization of Supercritical CO 2 fracturing technology. Herein, a simulation method for Supercritical CO 2 fracturing based on cohesive force units is proposed to investigate the crack propagation behavior of CO 2 fracturing technology under different construction parameters. Furthermore, the shale fracture propagation mechanism of Supercritical CO 2 fracturing fluid is elucidated. The results indicated that the propagation ability of reservoir fractures and Mises stress are influenced by the fracturing fluid viscosity, fracturing azimuth angle, and reservoir conditions (temperature and pressure). An azimuth angle of 30° can achieve a maximum Mises stress of 3.213 × 10 7 Pa and a crack width of 1.669 × 10 −2 m. However, an apparent viscosity of 14 × 10 −6 Pa·s results in a crack width of only 2.227 × 10 −2 m and a maximum Mises stress of 4.459 × 10 7 Pa. Additionally, a weaker fracture propagation ability and reduced Mises stress are exhibited at the fracturing fluid injection rate. As a straightforward model to synergistically investigate the fracture propagation behavior of shale reservoirs, this work provides new insights and strategies for the efficient extraction of shale reservoirs.