Numerical investigation on the critical factors in successfully creating fracture network in heterogeneous shale reservoirs

The heterogeneous characteristics of shale formations play a significant role in creating a fracture network during stimulation treatments. The hydraulic fracturing in naturally fractured shale formations is investigated using an explicitly integrated discrete-finite element approach. Parametric studies are presented for the distribution of natural fractures, rock toughness, in-situ stress, the layers properties and the injection rate. Numerical results show that the distribution patterns of natural fractures determine the creation of a fracture network. The propagation of hydraulic fracture mainly along parallel distributed natural fractures results in several branch fractures. The weak interfaces between different layers will alter the propagation direction of hydraulic fractures to the horizontal plane, which facilitates to intersect with the far field of natural fractures. The initiation and opening of natural fractures are confined in large in-situ stresses and stress contrast formations, which is unfavorable to generate a large field of fracture network. The fracture complexity will be significantly improved in the reservoirs of axis-orientated natural fractures as simultaneous fracturing stimulation is implemented. The results presented in this paper provide some new insights into generating a fracture network to optimize hydraulic fracturing designs of shale gas reservoirs.