Numerical study of hydraulic fracture propagation accounting for rock anisotropy

Abstract

The objective of this study is to investigate the effect of rock anisotropy on hydraulic fracture propagation. The coupled model of rock deformation and fluid flow is established to study hydraulic fracturing of orthotropic formation. Stress field is solved by using the extended finite element method with special tip enrichment functions for orthotropic formation. The coupling between stress field and pressure field is treated by Picard iterative procedure. The modified circumferential tensile stress criterion is used to determine fracture propagation, in which stress intensity factors are determined by an interaction integral method. Numerical results show that when fracture doesn't initiate from the direction of material axis with larger modulus, the fracture propagation direction would change and divert to the direction of material axis with larger modulus. And as Young's modulus ratio between two material axes increases, the phenomenon becomes more obvious. Moreover, shear modulus also enhances the diversion phenomenon of fracture propagation direction. However, the in-situ stress difference could weaken the effect of rock anisotropy. The results indicate that the propagation process of hydraulic fracture is influenced by comprehensive factors including material axis angle, Young’ modulus ratio, shear modulus and in-situ stress difference.