Effects of In-Situ Temperature in Deep Reservoirs on Shale Fracture Properties

The development of deep shale reservoirs is a major strategic demand to meet national energy requirements. However, the high-temperature characteristics of in-situ reservoirs make it difficult to understand the fracture properties of deep shale clearly, which restricts the development of reservoir stimulation technologies. Aimed at the issue of rock fracture parameter testing in high-temperature environments, based on the digital image correlation method and fracture mechanics theory, this study builds an in-situ high-temperature environment rock fracture visualization test system that can dynamically capture crack-tip initiation and propagation. Further, the influence law of temperature on shale fracture behaviour has been analysed. The results have shown that, under the condition of no confining pressure, with increases in the temperature, the macroscopic material stiffness and fracture toughness of shale increase; this shows that high temperatures inhibit crack initiation and propagation. Further, with increases in the temperature, the local plasticity of the crack tip region increases, the crack initiation strength of cohesive cracks in the fracture process zone increases, and the critical crack opening displacement increases; however, the length of the fracture process zone decreases. When considering high-temperature conditions alone, the fracture tip still experiences a small-scale yield state; the research conclusions can provide a reference for studies on deep reservoir fractures.