Bedding Plane Slippage and Fault Reactivation Captured by Crosswell Low-Frequency Distributed Acoustic Sensing Monitoring during Hydraulic Fracturing

Summary With this study, we provide the first direct observations of horizontal bedding plane slippage detected using crosswell low-frequency distributed acoustic sensing (LFDAS) during hydraulic fracturing stimulation in the Sichuan Basin, China. Traditional completion designs assume vertical tensile fracture propagation; however, under certain stress and geological conditions, fractures may grow horizontally, reducing stimulation efficiency and posing risks such as induced seismicity and wellbore deformation issues. Distributed strain signals captured in a horizontal observation well displayed elliptical contours spanning multiple stages (300–700 m), characteristic of horizontal fracture growth. Additionally, fault reactivation triggered by the horizontal fracture propagation is identified through a paired dipole-stripe signature in the strain signal. To validate these interpretations, a displacement discontinuity method (DDM)–based geomechanical model was applied, history-matching the LFDAS strain signals observed during selected treatment stages. The model confirmed that a shear deformation component is required for horizontal fractures to match field signals, implying bedding plane slippage. It also verified hydraulic connectivity between several natural faults and the horizontal fracture plane during injection, leading to fault reactivation. These findings demonstrate the value of crosswell strain monitoring combined with advanced modeling techniques in understanding fracture behavior in complex geological settings. Recognizing the role of geological factors, such as weak bedding planes and natural faults, is essential for accurately predicting fracture growth, optimizing stimulation strategies, and minimizing risks in unconventional reservoir development.