Hydraulic-Fracture Modeling With Bedding Plane Interfacial Slip

Abstract Interfacial slip is one of the mechanisms that can alter the growth of a hydraulic fracture when it encounters weak planes or natural fractures. In shallow or over-pressured formations, interfacial slip between formation bedding planes is possible when the effective normal stress on the bedding interfaces is low. Fracture height growth could be hindered or stopped by interfacial slip when a vertical hydraulic fracture propagates in such formations. An interfacial slip model has been developed and implemented in a pseudo-three-dimensional (P3D) hydraulic fracture simulator. In the model, the width deformation of a fracture with interfacial slip is calculated using a displacement discontinuity (DD) method. An interface crossing criterion (Renshaw and Pollard, 1995) is used to determine if the hydraulic fracture crosses a particular bedding plane during height growth. Two interface properties of a coefficient of friction and a shear stiffness, required by the model, are defined, and the application of the Renshaw and Pollard criterion and the DD method is explained. The direct effect of bedding plane interfacial slip is on fracture height growth and width deformation, but because of the coupling effects in hydraulic fracturing, the entire fracture geometry and fracture pressure will be affected. The simulation results based on the interfacial slip model are compared with the fracture height and pressure measured from a fracturing treatment with tracer logs, as well as with the fracture length inferred from post-fracturing production analysis. In this field case, a T-shaped fracture was considered likely to be generated based on the observed field measurements, and there is a good match in fracture height, length, and pressure between the simulation results using the interfacial slip model and the measured data. A hydraulic fracturing simulator that includes an interfacial slip model can be used to better simulate fracturing in coalbed methane and other formations where slip between bedding planes is possible, and to improve fracture design and evaluation for such treatments.