oa Stress Concentration in Fractured Medium Due to Formation Pressure Changes

It is well known that the hydraulic fracturing is a tool commonly used for stimulating hydrocarbon reservoirs and that the orientation and the propagation length of fractures created by hydraulic pressure influenced in by in-situ stress field. It is, however, difficult to predict the behavior of fracture propagation from boreholes in a medium under regional stress due to a lack of numerical schemes to simulate rock failures. In order to solve this problem of hydraulic fracturing, we have developed a program to simulate fracture propagation from a borehole due to increasing fluid pressure using an extended finite difference method (X-FEM), which deals with any fractures independent from grid or mesh for the numerical simulation. Numerical simulations are conducted for a 2D elastic medium having a borehole and a fracture. We first confirmed that our program could simulate the stress distribution whose local stress field near the borehole showed some deviated orientation from the regional stress field. We then confirmed that the tendency of fracture propagations to be a function of fluid pressure to induce the extension of fracture. The orientation of the fracture propagation converges to that of the principal stress. However, the higher the fluid pressure is, the smaller the curvature of fracture trace becomes. We would like to conclude that the orientation of maximum in-situ principal stress and the fluid pressure for fracturing is a major parameters to control the propagation of fractures due to increasing fluid pressure.