Numerical investigation of the interactions between hydraulic fracture and bedding planes with non-orthogonal approach angle

Weak bedding planes (interfaces), a critical factor in determining the fracture height growth and the propagation pathway of the fractures, is pervasively distributed in the unconventional reservoirs. In the real world, multi-layered bedding planes, regarded as frictional discontinuities, are not horizontally distributed in the formation. In this paper, a three-dimensional fracture model, based on the three-dimensional displacement discontinuity method, was developed to simulate the interactions between vertical/slanted hydraulic fractures and frictional discontinuities (such as natural fractures or horizontal/oblique bedding plane segments) with non-orthogonal approach angle. Comparison of width profiles between the developed fracture model and Abaqus simulator showed a good agreement. In the case studies, width profiles and shear displacement discontinuity along the interface were analyzed under the influence of approach angle, ratio of distance between the injection source and interface to the fracture height, fluid pressure, Young's modulus and Poisson's ratio. A positive relation exists between shear sliding along the interface and approach angle, which conforms to the numerical experiments from the three-dimensional Discrete Element Method model. Interface location from the injection source has unconspicuous impact on the interface opening and shear sliding along the interface with non-orthogonal approach angle. The increment of fluid pressure makes alteration of vertical fracture more apparently in the non-orthogonal case. Smaller Young's modulus makes the interface easier to be opened in the orthogonal case. This model enables to calculate fracture width distribution at the intersection area, which provides a guideline for proppant transport and avoid potential bridging and screen-out of the proppant.