Formation conditions and evolution of fractures in multiple tight rocks: Implications for unconventional reservoir exploitation

Abstract

Physical simulation experiments of rock fracturing can effectively simulate the extension of artificial fractures within different lithology and interbedded rocks. Previous studies have focused on the conditions of artificial fracture initiation and propagation, while few studies have been conducted on the evolution and influencing factors of fractures in reservoir rocks. In this study, fracture evolution simulation was performed using a self-developed physical fracturing simulation device and a real-time acoustic emission fracture monitoring system. Results show the presence of four main fracture patterns within the selected lithologies and their combinations, including simple shear, simple, network, and X-shear fracture patterns. The variation trend of the principal stress difference and fracture pressure, as well as the values of the network, X-shear, simple, and simple shear fracture patterns all increased successively. The values of the network and X-shear fracture patterns were smallest, while the fracture pressure and principal stress difference were less than 65 and 40 MPa, respectively. Furthermore, the trends of the brittle mineral content and brittleness index were opposite.The interlaminar modulus difference mainly controls the cracks extending at the interface of the interlayer, and is conducive to the extension of cracks at values less than 3 GPa. Furthermore, the tendency of network, X-shear, simple, and simple shear fracture patterns to gradually simplify implies that the fracturing treatment effect and fracturing performance may have sequentially deteriorated. This study may provide a reference for the determination of reservoir fracturing ability and fracturing reconstruction design in unconventional reservoir development.