Physical Significance of Interfaces on Fracture Growth

Abstract

Details of the interfaces between two geologic materials are normally neglected in predicting the growth of hydraulic fractures. In addition, perfect bonding is assumed across the interface. However, due to a combination of reasons, the perfect bonding assumption is violated to various degrees. Assessment for potential slippage is important to fracture-growth modeling. As a fracture approaches an interface, both mode I (for a fracture crossing the interface) and mode II (for a fracture extending in the interface) stress-intensity factors need to be evaluated. Should the interface properties be such that the mode I stress-intensity factor reach the critical value, the fracture will cross the interface. Should the converse happen and the mode II stress-intensity factor become critical, slippage along the interface will occur. If both the critical stress intensity factors are reached simultaneously, both fractures across the interface and slippage will occur. Good description of the interface material is needed to model the fracturing process. Methodology to model the physical significance of interfaces for calculating two-dimensional fracture growth includes descriptions of applications to oil/gas recovery and the injection of contaminants in isolated formations.