Numerical simulations of a hydraulic fracturing test including pre-existing fractures

摘要

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