The Propagation of Hydraulic Fractures in a Natural Fracture Network: A Numerical Study and Its Implications

Natural fractures play a significant role in creating a fracture network simulation treatment. In this work, global cohesive elements were incorporated into the cohesive zone method to realize the unprompted propagation of a hydraulic fracture. The step-by-step propagation patterns of hydraulic fractures in a random natural fracture network were discussed. An effective area was defined to quantitively assess the influenced area of induced fractures. The results showed that the hydraulic fracture tips were attracted by local natural fractures when the horizontal stress difference was low. Bifurcations and secondary fractures occurred at the natural fracture intersections, which contributed to the complexity of the induced fracture network on a local scale. The length of the main hydraulic fracture reached the maximum when the in situ stress ratio was 1.12. The influence of natural fractures on the overall trend of fracture propagation was limited when the in situ stress difference increased. It also suggested that a lower rock tensile strength and natural fractures cementation strength improved the main fracture length. A higher tensile strength of rock increased the initiation pressure of the induced fracture, while the cementing strength of the natural fractures showed no impact on it. The results presented in this paper could improve the basic understanding of the fracture development in a natural network and help to predict a complex fracture network in a real situation.