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.