The influence of deviatoric and horizontal differential stress and pore pressure on hydraulic fracture opening by fully coupled 3D cohesive elements method

Abstract

Estimation of hydraulic fracture opening is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells since proppant transport as well as any possible premature screen out are considerably affected by hydraulic fracture opening (or width). In this study, the influences of deviatoric and horizontal differential stress as well as pore pressure regimes on hydraulic fracture opening in vertical and horizontal oil wells with normal fault regime are investigated. Novel three-dimensional cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracture initiation and propagation in a fluid-solid coupling finite element model. The stress intensity factor is verified for both XFEM-based cohesive law and analytical solution to show the validation of cohesive law in fracture modeling, where the compared results are in a very good agreement with less than 1% error. Moreover, the propagation of the hydraulic fracture by cohesive elements approach was also validated by KGD M-vertex solutions with negligible error about 1.6%. The results showed that, generally, by increasing deviatoric and horizontal differential stress, the fracture opening has been strongly affected for both vertical and horizontal oil wells. Additionally, increasing pore pressure from under-pressure regime to over-pressure state of formation pressure has made a considerable rise on fracture opening.