Fiber optic strain monitoring of interlayer deformation induced by hydraulic fracturing

ABSTRACT: Unconventional reservoirs, represented by shale oil and gas, exhibit significant development of laminated interfaces, which may induce interlayer slip during hydraulic fracturing. As a high-precision deformation monitoring method, fiber Bragg grating (FBG) sensors offer potential advantages for monitoring interlayer deformation. In this study, the FBG strain sensors were put in artificial layered rock specimens to monitor the interlayer deformation during fracturing. The results indicate that hydraulic fractures exhibit intermittent propagation during fracturing, and the fracture propagation can induce interlayer slip. The slip is relatively small in the stage of fracture stagnation, increases as the fracture propagates, and reaches the maximum when the fracture propagates across layers. The amplitude and range of slip differ on either side of the hydraulic fracture, exhibiting asymmetry, and the slip displacement decreases with the distance from the fracture. After the fracture propagates across layers, the interlayer slip is influenced by injection pressure and remains relatively constant as the fracture propagates to the far field. This study can provide insights into the mechanisms of interlayer deformation induced by fracture propagation in laminated reservoirs.