Competition growth of biwing hydraulic fractures in naturally fractured reservoirs

Hydraulic fracturing, combined with horizontal wells, is one of the key technologies that enables production from shale gas reservoirs. However, data from several fields in the United States verified that the total production is only contributed by a small portion of designed fractures (Miller et al., 2011). In this paper, we aim to provide an explanation about this phenomenon and propose corresponding suggestions to improve stimulation efficiency. Here, a multi-fracture propagation model in reservoirs containing cemented natural fractures (NFs) is presented based on phase field method. The fracture growth resistance of each wing for varying properties of NFs is quantitatively investigated. We found that NFs toughness, roughness and intersection angle play a vital role on the fracture growth resistance. It was demonstrated that the discrepancy of fracture growth resistance of each wing can suppress fracture propagation in heterogeneous reservoirs. Fracture propagation in mixed-regime was found to favor creation of biwing fractures, which can be used to improve stimulation performance. The simulations of simultaneous fracturing in naturally fractured formations demonstrated that the existence of NFs alters the extending paths of hydraulic fractures (HFs), which may result in fracture coalescence. In this case, the presented model can be utilized to improve stimulation efficiency through optimizing design parameters.