An implicit criterion of fracture growth direction for 3D simulation of hydraulic fracture propagation

Validation of the previously proposed implicit criterion of fracture propagation was carried out. The implicit criterion at each step of the propagation considers the rock stress state both before and after the propagation. It is based on the assumption that the fracture tends to propagate in the direction where II and III modes of stress intensity factor (SIF) are zero. Since in most cases both conditions cannot be satisfied simultaneously, the values of the SIF modes II and III are combined in one function and are integrated along the whole front. A few possible propagation directions are considered at each step of the propagation and the one is chosen to provide the minimum of the integral. The criterion parameters was chosen using the comparison with experiment results and semi analytical formulas obtained from three point bend test with twisted fracture.