Numerical Study on the Formation of Shear Fracture Network

Shear fracture network is important to the hydraulic fracturing treatment of a shale gas reservoir. In this paper, the formation of shear fracture network is investigated by a Displacement Discontinuity Method (DDM) based model. The results show that the sliding of fracture surface is irreversible but may change significantly after fluid pressure dissipates. The final sliding distance is different for natural and hydraulic fractures. Most of the shear fractures are natural fractures while the newly formed hydraulic fractures tend to be totally closed after pressure dissipates. The effects of in situ stress are investigated. The affected area reaches its maximum value when the maximum principle stress direction is perpendicular to the principal fracture direction. The effects of the injection rate are also investigated. The increasing of the injection rate is helpful in increasing the fracture aperture, but has no effect on the final sliding distance. Moreover, the effects of the injection rate on the affected area depend on the connectivity of natural fractures. The affected area increases with the injection rate when the connectivity is poor but decreases slightly with injection rate when the connectivity is good.