Hydraulic fracturing behavior of shale-sandstone interbedded structure under true triaxial stress conditions: A comprehensive experimental analysis

Reservoirs characterized by shale-sandstone interbedded structures are extensively dispersed throughout China, and understanding the propagation mode of hydraulic fractures is a prerequisite for shale gas exploitation engineering. In this study, hydraulic fracturing tests were conducted using horizontal wells subjected to true triaxial compression conditions to elucidate the mechanism by which the initiated layer lithology and stress state influence the fracture morphology. Furthermore, the propagation mode of the fractures and the consequential effects on fracture network formation were investigated. The findings demonstrate four distinct interaction modes between the shale-sandstone interfaces and hydraulic fractures. The lithology of the initiated layer influences the fracture propagation trajectory, thereby affecting the propagation modes at the shale-sandstone interface and resulting in varying effects on layer penetration. The stress difference exerts a significant controlling influence on the fracturing behavior, enhancing the possibility of interconnecting multiple rock layers characterized by substantial stress differences. Hydraulic fracturing tests of shale-sandstone interbedded structure were conducted.Four interaction modes between fracture and lithology interface are noted.Fracture propagation modes are explored using acoustic emission parameters.Formation effect of the fracture network was evaluated using fractal dimension method.