关键词: 深层页岩, 走滑应力, 层理, 水力压裂, 物理模拟

Abstract: Currently, deep shale has become the main position for shale gas exploration and development. As the main battlefield for shale gas development in China, the southeastern region of Chongqing is characterized by unique geological features such as high temperature, bedding development, and strike-slip stress, which limit the high-propagation of hydraulic fractures and severely hinder the stimulation and transformation of shale gas production. Based on this, a large-scale triaxial physical simulation fracturing test on real shale was conducted under the influence of temperature-structure-stress to systematically investigate the influence mechanisms of key parameters, such as temperature, viscosity of fracturing fluid, injection displacement, and in-situ stress difference on the fracturing modification effect. The modification effect of hydraulic fracturing in reservoirs was quantitatively evaluated using the fractal dimensionality calculation method. The results show that under the effect of three control mechanisms, the fracture network morphology after fracturing is characterized by flattening. The thermal shock activated laminae induces fracture steering, which significantly inhibits the expansion of fracture height. The increased stress difference, the use of high-viscosity fracturing fluids, and the construction of high fluid injection displacement can promote fracture expansion across layers. Although the high temperature environment weakens the rupture strength of the rock, it enhances the plasticity characteristics of the rock, resulting in higher extension pressure. The viscosity of the fracturing fluid has a nonlinear regulation on the extension pressure, and the medium viscosity balances the filtering loss effect and viscous resistance to optimize the extension pressure. The analysis of the overall transformation effect of the reservoir shows that high temperature and large-displacement pumping significantly enhance the fractal dimension of the fracture network. The temporary plugging fracturing technique is effective in promoting the volume transformation and improving the complexity of the fracture network. Thermal shock triggers weak tensile extension and generates a large number of microcracks in the bare eye section, and the use of temporary plugging fracturing process can reconstruct the fluid energy distribution and effectively communicate with the unutilized fracture system.

Key words: deep shale, strike-slip stress, lamination, hydraulic fracturing, physical modeling