A criterion for a hydraulic fracture crossing a frictional interface considering T-stress

Abstract

Hydraulic fracturing has been widely used to stimulate oil and gas production from low permeability reservoirs. However, the geologic discontinuities, such as natural fractures, joints, and bedding planes, can significantly affect the propagation direction of the hydraulic fracture. Considering the effect of the non-singular stress term of Williams’ series expression for stress field near the fracture tip (i.e., T-stress), an analytical criterion for a hydraulic fracture crossing a frictional interface (such as the natural fracture and bedding plane under compression-shearing) was proposed. The present criterion was validated by comparing it to the published experiments, and the effect of T-stress on the propagation of the hydraulic fracture crossing a frictional interface was analyzed by comparing the present criterion to the published criteria. The results show that the accuracy of the present criterion depends on the difference in geomechanical properties of the rock on either side of the interface. The effect of T-stress on the hydraulic fracture propagation can be divided into the facilitation and the inhibition, which depend on the intersection angle between the hydraulic fracture and the frictional interface. No matter what the intersection angle between the hydraulic fracture and the frictional interface is, the effect of T-stress can inhibit the change of propagation direction when the hydraulic fracture crosses the interface.