基于离散元的层理页岩水力裂缝扩展行为研究

Study on Hydraulic Fracture Propagation Behavior of Bedding Shale Based on Discrete Element Method

摘要: 水力压裂是开发页岩气等非常规油气资源的核心技术，而层理作为页岩等沉积岩的典型结构特征，对水力裂缝的扩展路径、形态及压裂效果具有显著影响。文章建立了流固耦合的水力压裂数值模型，系统研究了不同注水压力、层理角度及层理厚度条件下水力裂缝的扩展行为。研究结果表明：注水压力对起裂压力影响较小，存在最优压力窗口(25~35 MPa)，过低则裂缝扩展受限，过高则裂缝网络复杂度降低；层理角度控制裂缝偏转与分支行为，当倾角为45˚时最易形成复杂缝网，而0˚或60˚时裂缝形态趋于简单；层理厚度增加显著增强裂缝穿层阻力，裂缝由穿层主导逐渐转向沿层偏转主导，纵向延伸距离受限。研究结果对层理页岩水力压裂的裂缝形态控制与压裂参数优化具有重要意义。

Abstract: Hydraulic fracturing is the core technology for the development of unconventional oil and gas resources such as shale gas. As a typical structural feature of sedimentary rocks such as shale, bedding has a significant impact on the propagation path, morphology, and fracturing effect of hydraulic fractures. In this paper, a numerical model of fluid-solid coupling hydraulic fracturing is established, and the propagation behavior of hydraulic fractures under different water injection pressures, bedding angles, and bedding thicknesses is systematically studied. The results show that the water injection pressure has little effect on the initiation pressure, and there is an optimal pressure window (25~35 MPa). If the water injection pressure is too low, the fracture propagation is limited, and if the water injection pressure is too high, the fracture network complexity is reduced. The bedding angle controls the fracture deflection and branching behavior. When the dip angle is 45˚, it is most likely to form a complex fracture network, while the fracture morphology tends to be simple when the dip angle is 0˚ or 60˚. The increase in the bedding thickness significantly enhances the resistance of the crack through the layer. The crack is gradually dominated by the layer through the layer and gradually turns to the deflection along the layer, and the longitudinal extension distance is limited. The research results are of great significance to the fracture morphology control and fracturing parameter optimization of hydraulic fracturing of bedding shale.