A study of Hydraulic fracture propagation in laminated shale using extended finite element method

Layered stacking structures, also known as laminations, are characteristic features of shale formations. These laminations with varying properties significantly influence the propagation path of hydraulic fractures. In this study, different laminations exhibit varying mechanical properties (mechanical contrasting). The interfaces between laminations are continuously stacked weak planes (lamination weak interfaces, or LWIs) with fracture toughness significantly lower than the rock matrix. The propagation mechanism of hydraulic fractures within laminated shale is not yet fully understood, particularly the complex propagation behavior crossing LWIs. This paper effectively predicts hydraulic fracture propagation patterns and paths based on He-Hutchinson's theory. Several typical mechanical behaviors during the interaction between the hydraulic fractures (HFs) and LWIs can be characterized. A fully coupled numerical solver to simulate the propagation of hydraulic fractures in laminated shales is developed based on the discrete fracture model and the extended finite element method (XFEM), which can accurately capture the local features of the physical field by using different enrichment functions. The study investigates the effects of varying elastic modulus and stress differences on the interaction between hydraulic fractures and LWIs. And two multi-lamination problems containing inclined laminations are studied, demonstrating the potential widespread application prospects of the method in this paper.