Abstract
Joints are a common structure of heterogeneous shale rock masses, and in situ stress is the environment in which heterogeneous rock masses can be found. The existence of joint plane and confining pressure difference influences the physical properties of shale and propagation of fractures. In this study, jointed shale specimens were simulated under different confining pressures to explore the failure patterns and fracture propagation behavior of hydraulic fracturing. Different from the common research of hydraulic fracturing on signal parallel joint rock mass, the simulations in this study considered three points (parallel joint, multi-dip angle joint, and no-joint points). The effects of the single-dip angle joint, multi-dip angle joint, and confining pressure difference on the hydraulic fracture evolution and stress evolution of the jointed shale were studied comprehensively. The confining pressure difference coefficient proposed in this study was used to accurately describe the confining pressure difference. Results indicate that the larger is the confining pressure difference, the stronger is the control of the maximum principal stress on fracture evolution; by contrast, the smaller is the confining pressure difference, the stronger is the control of the joint plane on fracture evolution. Under the same confining pressure difference, the hydraulic fracture propagates more easily along the small dip angle joint plane. As the value of the confining pressure difference coefficient moves closer to zero, the hydraulic fracture propagates randomly, the tensile stress region around the fracture tip widens, and the joint planes fractured by tensile increase. This study can offer valuable guidance to the design of unconventional reservoir reconstruction.
Highlights
Shale is a kind of unconventional reservoir with strong heterogeneity and low permeability [1, 2]
Hydraulic fracturing is an important consideration in ensuring production efficiency, a measure that is commonly used in petroleum engineering [2, 3]
When the joint dip angle was increased to 45°, the hydraulic fracture propagated partly along and partly across the joint plane, and the fracture propagated in the maximum principal stress direction macroscopically. erefore, the maximum principal stress and the weak joint plane both controlled the fracture evolution
Summary
Shale is a kind of unconventional reservoir with strong heterogeneity and low permeability [1, 2]. Discontinuities dominate the geometry, deformation modulus, strength, failure behavior, and permeability of rocks, and the existence of joints promotes the formation of complex fracture networks [9]. Erefore, the study regarding the growth process of hydraulic fractures of jointed shale under different confining pressures is essential, as this topic is one of the important aspects of shale. Many scholars have recently investigated the hydraulic fracture evolution of jointed rocks and established that they can positively contribute to unconventional reservoir reconstruction. A simulation investigation of the influence of single-dip angle joint, multi-dip angle joint, and confining pressure difference coefficient on the hydraulic fracture evolution and stress evolution of jointed shale was conducted using the rock failure process analysis (RFPA) system developed by Professor C.A. Tang in 1995. As a numerical simulation code, the RFPA code can simulate the progressive failure process of materials, and it has been widely used and recognized by scholars worldwide [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]. e simulation results of jointed shale on hydraulic fracturing can provide relevant reference about the formation of complex fracture networks in jointed shale
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
