Influence of High-Density Bedding Plane Characteristics on Hydraulic Fracture Propagation in Shale Oil Reservoir

The existence of high-density bedding planes is a typical characteristic of shale oil reservoirs. Understanding the behavior of hydraulic fracturing in high-density laminated rocks is significant for promoting shale oil production. In this study, a hydraulic fracturing model considering tensile failure and frictional slip of the bedding planes is established within the framework of the unified pipe-interface element method (UP-IEM). The model developed for simulating the interaction between the hydraulic fracture and the bedding plane is validated by comparison with experimental results. The hydraulic fracturing patterns in sealed and unsealed bedding planes are compared. Additionally, the effects of differential stress, bedding plane permeability, spacing, and the friction coefficient of the bedding plane are investigated. The results showed that a single main fracture crossing the bedding planes is more likely to form in sealed bedding planes under high differential stress. The decrease in bedding plane permeability and the increase in the friction coefficient also promote the fracture propagating perpendicular to the bedding planes. Shale with high-density bedding planes has a poorer fracturing effect than that with low-density bedding planes, as the hydraulic fracture is prone to initiate and propagate along the bedding planes. Moreover, higher injection pressure is needed to maintain fracture propagation along the bedding. An increase in bedding density will lead to a smaller fracturing area. Fracturing fluid seepage into the bedding planes slows shale fracturing. It is recommended that increasing the injection flow rate, selecting alternative fracturing fluids, and employing multi-well/multi-cluster fracturing may be efficient methods to improve energy production in shale oil reservoirs.