Properties of a shale bedding plane and its influence on the geometric parameters of fracture propagation in volume fracturing

Abstract

The most significant feature of shale reservoirs, which differ from other oil and gas reservoirs, is the weak bedding plane. This plane determines the complexity of the fracture network and affects the final shale volume fracturing effect. To research the effect of bedding planes on the geometric parameters of fractures in shale reservoirs, the outcropping shale in the Weiyuan area was taken as the research object. Combined with digital image correlation (DIC) technology, the mechanical characteristic parameters of cores were tested by indoor three-point bending (TPB). A mathematical model of shale gas volume fracturing bedding fracture propagation was established by a pseudo-three-dimensional (P3D) method and solved by the Fourier transform method. The corresponding calculation model was developed into software to analyze the influence of the stiffness, density and strength of bedding planes on hydraulic fracture propagation. The results showed that (1) a smaller stiffness of the bedding plane corresponded to a greater amount of bedding shear slip; (2) the main fracture communicated with more bedding planes when the bedding density increased, although communication with too many planes seriously restricts the propagation of hydraulic fractures in the length and height directions; and (3) improved strength of the bedding plane corresponds to increased difficulty of opening the bedding plane and an increased likelihood of propagating hydraulic fractures through these planes. This study has certain guiding significance for fully understanding the mechanical properties of shale and its influence on hydraulic fracture propagation.