含有硬包裹体分布的非均质岩石水力压裂特性研究

基于完全流-固耦合的弹塑性理论给出了水力压裂数值计算的弥散裂缝模型，其中材料的弹性部分采用线弹性本构关系，塑性部分采用摩尔-库仑破坏准则及强化准则。依据当前的有效应力状态修正渗透系数来模拟压裂液在裂缝中的流动。渗透系数的修改使用双曲正切函数，并采用平均有效应力作为水力裂缝的起裂判据。在ABAQUS软件中通过用户自定义程序添加了该模型。根据岩石的切面照片建立了含有硬包裹体分布的非均质岩石的有限元计算模型，模拟了中心点注水条件下的水力压裂传播过程，讨论了在常应力状态下非均质岩石中开裂区域、典型位置的应力路径变化和裂缝传播范围随时间变化的特点。进行了多种条件下含有硬包裹体分布的岩石材料的数值试验，得出了基岩材料的弹性模量、凝聚力和渗透系数以及注水速率对峰值注水压力、平均注水压力和裂缝开度的影响规律。

Hydraulic fracturing characteristics of heterogeneous rock with hard inclusion distributed

A smeared crack model of hydraulic fracturing numerical calculation is proposed based on the complete liquid-solid coupled elastoplastic theory. In this model, the elastic part of the material uses the linear elastic constitutive relations; the plastic part adopts the Mohr-Coulomb failure criterion and hardening criterion. To simulate the fluid flow in the crack, the permeability is modified according to the current state of effective stress. The relation between the permeability and the effective mean stress is assumed to be a hyperbolic tangent function. The onset of crack is determined by the mean effective stress. Using the user defined subroutines provided by ABAQUS software, the smeared crack model is added. According to section photo of the in-situ rock sample, a finite element model of heterogeneous material with hard inclusions distributed is generated. The progress of hydraulic fracturing under the loading condition of centered injection is well simulated and the results show the characteristics of fracture zone, stress path located at typical location and range of fracture propagation. Numerical tests on the rock with hard inclusions distributed are carried out under different conditions. The paper concludes the influences of elastic modules, cohesion, permeability, and injection rate on the maximum injection pore pressure, average injection pore pressure and fracture aperture.