Effect of mechanical heterogeneity on hydraulic fracture propagation in unconventional gas reservoirs

The mechanical heterogeneity of unconventional gas reservoirs is a significant factor affecting the nucleation and propagation of hydraulic fractures. The ignorance of mechanical heterogeneity in the numerical calculation has been demonstrated to result in huge deviations from actual fracture propagation. In the present study, the eXtended Finite Element Method (XFEM) is used to simulate the propagation of a hydraulic fracture in a heterogeneous reservoir. The evolution of a hydraulic fracture encountering hard blocks at different positions near the initial fracture tip is investigated. The mechanical heterogeneity of reservoir rock leads to the redistribution of strength and stress, which eventually affects the evolution of hydraulic fracture. The effects of soft-hard rock interbedding and randomly distributed irregular blocks are also investigated. Generally, the hard blocks distributed in a reservoir promote the growth of hydraulic fracture in length, but limit the fracture growth in width.