Influence of slip and permeability of bedding interface on hydraulic fracturing: A numerical study using combined finite-discrete element method

Shale is a common layered sedimentary rock containing bedding interfaces in oil and gas reservoirs. In hydraulic fracturing of shales, the fracturing fluid could flow into bedding interfaces and cause slipping, thus affecting the propagation of hydraulic fractures. Currently, the interaction mechanism between hydraulic fractures and bedding interfaces is still unclear because of the difficulty in monitoring fractures in laboratory experiments and the lack of appropriate numerical tools to model the dynamic hydraulic fracturing process. In this paper, the emerging combined finite-discrete element method (FDEM) is used to numerically study the main controlling factors of the interaction between hydraulic fractures and bedding interfaces, as it is known for its advantage of simulating material transition from intact solid to crack initiation and propagation. Our results show that the slip property of bedding interfaces determines whether hydraulic fractures can cross over bedding interfaces. Interestingly, the high permeability of bedding interfaces does not hinder the crossing but only delays the time needed for such crossing. We also find that both the slip type and permeability of bedding interfaces can give rise to a change in the width of hydraulic fractures when propagating across bedding interfaces, and result in a discontinuous distribution of local stress and fluid pressure near bedding interfaces accompanied by a strong stress shadow area. Therefore, in the process of hydraulic fracturing in reservoirs with bedding interfaces, the problem of multi-fracture interference could be more deteriorative. This paper aims to provide a new understanding of the hydraulic fracture crossing mechanism and hydraulic fracture morphology in reservoirs with bedding interfaces.