页岩地层水力裂缝起裂影响因素模拟分析

Simulation Analysis of Factors Affecting Hydraulic Fracture Initiation in Shale Formations

在水力压裂施工过程中,研究水力裂缝的起裂过程对施工具有重要意义。页岩中存在的大量天然裂缝使储层非均质性以及应力计算过程中非线性程度增加,同时使应力分布更加复杂。为研究天然裂缝对水力裂缝起裂的影响,基于有限元方法,建立了一个考虑天然裂缝对水裂缝起裂影响的流-固耦合模型。研究表明:水力裂缝尖端张、剪破坏受裂缝流压影响表现出一定规律;当桥接角为30°时,张性应力集中于裂缝尖端,水力裂缝趋于张性破坏;当桥接角为0°、60°、90°时,剪切应力集中于裂缝尖端,水力裂缝趋于剪切破坏。

In the process of hydraulic fracturing operation,it is of great significance for operation to study the hydraulic fracture initiation process.A massive number of natural fractures in shale increase reservoir heterogeneity and non-linearity in stress calculation,and at the same time make stress distribution more complex.Based on finite element method,a fluid-structure coupling model was established to study the effect of natural fractures on hydraulic fracture initiation.The results show that the tensile and shear failure at the tip of a hydraulic fracture is affected by the flow pressure of the fracture;when the bridging angle is 30°,the tensile stress is concentrated at the tip and the hydraulic fracture tends to tensile failure;when the bridging angle is 0°,60°and 90°,the shear stress is concentrated at the tip and the hydraulic fracture tends to shear failure.