Study on the Mechanism and Regulation Method of Longitudinal Penetration of Hydraulic Fractures in Multilayered Shale

Shale reservoirs have longitudinally developed multilayered weak surfaces. The strong geological discontinuity and the stress heterogeneity caused by it lead to the complicated morphology of hydraulic fracture propagation, and the longitudinal propagation mechanism of the hydraulic fracture is still unclear. The extended finite element 3D numerical model of the single-cluster fracture and multicluster fracture extension has been established. The effects of vertical stress difference, bonding strength of bedding plane, fracturing fluid displacement, fracturing fluid viscosity, and cluster spacing on fracture propagation morphology are analyzed by numerical examples. The results show that as the vertical stress difference and the bonding strength of the bedding plane increase, the bedding plane becomes more difficult to activate, and the fractures are more likely to realize the longitudinal penetration. As the cluster spacing decreases, the interfracture interference becomes stronger, and the hydraulic fractures are more likely to activate the bedding plane and form the orthogonal network fracture. At a high injection rate, the fracture passes easily through the layer and activates the bedding plane. Low-viscosity fracturing fluid is conducive to the activation of the bedding plane, and high-viscosity fracturing fluid can better achieve fracture penetration. Based on the research results, the fracturing parameters of Well X-1 are optimized, and the fracture monitoring results are in good agreement with the design objectives. This study reveals the longitudinal penetration mechanism of multilayered shale hydraulic fractures and provides a reference for the optimization of hydraulic fracturing parameters of multilayered shale.