摩尔-库伦强度准则在水压致裂数值模拟中的应用

Application of Mohr-Coulomb Strength Criterion in Hydraulic Fracturing Numerical Simulation

水压致裂的基本计算原理是以最大张应力准则为基础的。一般认为水压致裂过程中,孔壁在水压力的作用下只会发生拉张破坏。最近的实践表明,孔壁的破坏不仅会产生张性破坏还会产生剪切破坏。本文基于摩尔-库伦准则,通过理论推导得出水压致裂过程中孔壁不仅产生张性破坏,也产生剪切破坏,同时验证了摩尔-库伦准则在水压致裂孔壁破坏机理研究中的适用性;利用数值模拟的手段以莫尔-库伦准则来说明水压致裂应力测量中裂缝并不总是拉张破坏引起的,也有可能是剪切破坏,且起裂位置与应用最大拉应力准则时重合;由于围压对莫尔-库伦剪切破坏准则破裂应力有较大影响,因此即使同一种岩石在不同的应力状态下的破裂对应正应力也将不同,该研究为摩尔-库伦准则在水压致裂中的应用有重要的参考价值。

The basic calculation principle of hydraulic fracturing is based on the maximum tensile stress criterion.It is generally believed that during the process of hydraulic fracturing,the rock will break by tensile damage under water pressure.Recent practice has shown that the destruction of the borehole wall not only produces tensile damage,but also produces shear failure.Based on the Mohr-Coulomb criterion,it is concluded that the borehole wall in the process of hydraulic fracturing not only produces tensile damage but also shear failure.Therefore,it proves the applicability of the Mohr-Coulomb criterion in the study of the hydraulic fracturing mechanism.Through numerical simulation,the Mohr-Coulomb criterion is used to illustrate that both tensile and shear failure occur simultaneously in hydraulic fracturing,and the initiation position is same as the one of maximum tensile stress criterion.Moreover,the Mohr-Coulomb failure criterion is greatly influenced by the confining pressure,the rock failure pressure in different stress states increases as the confining pressure ratio decreases.This study has important reference value for the application of Mohr-Coulomb criterion in hydraulic fracturing.