Fracture Initiation and Propagation of Multiple Hydraulic Fractures Across Bedding Planes in Shale Oil Horizontal Well

Abstract

The Jimsar shale reservoir is characterized by low porosity and low permeability. Multistage fracturing of horizontal wells is an effective development method. However, interference between multiple fractures and the presence of well-developed bedding planes limit the effective extension of fractures. To elucidate the initiation and propagation mechanisms of inter-bed fractures in horizontal multi-stage fracturing within shale reservoirs, this study focuses on the Jimusar Shale outcrop and employs large-scale true triaxial hydraulic fracturing physical simulation experiments to construct an experimental model of horizontal multi-stage fracturing. By analyzing fracture morphology, propagation paths, and bedding plane activation characteristics, the study elucidates the fracture propagation patterns under various conditions. Results indicate the following: (1) Increasing the fluid injection rate enhances the net pressure at the fracture tip, effectively overcoming the resistance of bedding planes and promoting the continued propagation of hydraulic fractures across bedding interfaces. (2) Stage spacing affects the coordinated propagation of hydraulic fractures by modifying the stress shadow effect between adjacent fractures. A smaller stage spacing intensifies stress interference, leading to the suppression of local fracture propagation and an increased likelihood of fracture communication. (3) The horizontal stress difference is the primary controlling factor governing fracture propagation direction and bedding penetration capability. A larger horizontal stress difference promotes stable fracture propagation along the direction of the maximum horizontal principal stress and facilitates penetration through bedding planes, whereas a lower horizontal stress difference favors bedding plane activation and fracture deflection, resulting in the formation of a more complex fracture network. The study has established an understanding of the fracture expansion laws under different parameter conditions, which can provide theoretical basis and technical support for the optimization design of multi-stage fracturing parameters in horizontal shale oil wells and the efficient modification of reservoirs.