Numerical simulation of the formation of distributed microcrack zone induced by hydraulic fracturing

A number of rock types exhibit a nonlinear deformation induced by distributed microcracking, followed by a post-peak softening behavior due to grain bridging action, when subjected to a uniform tension. Numerical analyses of hydraulically induced geothermal reservoirs at great depths conducted to date neglect the effect of the distributed microcracking. In this paper, the formation of the distributed microcracking is studied using a numerical technique in order to characterize the growth of artificial subsurface cracks by hydraulic fracturing. A numerical fracture model based on a finite element method is developed. The progressive nonlinear deformation is analyzed on the basis of the Rankine criterion. A cohesive crack model is adopted to analyze the crack growth. In the numerical simulation, the crack is represented using an embedded crack element. The results obtained by numerical analyses show that the distributed microcrack zone induced by hydraulic fracturing at great depth conditions is significantly suppressed by tectonic stress. An energy consumption of the distributed microcrack zone is much smaller than that of the bridging zone.