Hydraulic stimulation is a technique in which a mixture of viscous fluids is pumped through an injector well in order to initiate and/or propagate fractures in the rock formation to enhance well-reservoir connectivity. Analytical and numerical methods have been proposed in the literature for predicting the evolution of the induced hydraulic fractures. Most of those studies are limited to some assumptions, such as fracture propagation through intact materials that follow a linear elastic behavior. However, those assumptions do not apply in naturally fractured porous media. The presence of geological discontinuities such as faults, joints, and natural fractures increases the complexity of the hydraulic fracturing treatment, affecting the final configuration of the hydraulic fracture network. This work investigates the effect of natural fractures on hydraulic fracture propagation in two limiting propagation regimes: toughness-fracture storage and viscosity-fracture storage dominated.
The model fully couples permeable rock deformation and fluid flow inside and across the fractures. The hydromechanical triple-nodded zero thickness interface element has been combined with a cohesive zone model to simulate hydraulic fracture propagation. Mohr-Coulomb criterion and a contact model represent frictional and closure behavior of natural fractures, respectively. The longitudinal flow within the fracture is governed by Reynold's lubrication theory through smooth narrow parallel plates (i.e., Poiseuille flow). An innovated intrinsic mesh fragmentation technique is used to simulate complex crack patterns during hydraulic crack propagation.
The results of the new approach are compared with analytical solutions. Moreover, the influence of parameters such as rock permeability, fluid viscosity, initial stress state, and natural fracture orientation on the hydraulic fracture propagation is analyzed.