Study on the Propagation of Interface Cracks in Layered Reservoirs for Hydraulic Fracturing

The behavior of interface cracks at different rock characters greatly affects fracturing efficiency. In this paper, stress intensity factor (SIF) derived through interface model is analyzed theoretically for predicting interface crack behavior. Then hydraulic fracturing experiments on samples of shale and salt combination were carried to verify the criterion. Based on these, the effects of stress state, lithological difference, displacement, fracturing fluid viscosity and pump pressure on interface cracks are discussed and quantified. The results indicate that the SIF is the function of geostress difference Δσ and lithology difference factor ξ. Wherein Δσ depends on the distribution of geostress, and ξ is determined by rock mechanical properties (Young's modulus E and Poisson's ratio µ ) ; Higher pumping pressure facilitates the opening of the interface. However, with the increase of displacement and fluid viscosity, the crack is reluctant to propagate along the interface.