Research on Shale Fracture Characteristics and Developmental Controlling Factors

Abstract

This study focuses on the shale fracture characteristics and their developmental master factors in the southeastern Sichuan Basin, aiming to gain a deeper understanding of the fracture network in shale gas reservoirs and its impact on hydrocarbon exploration. Through geological investigation and core sample analysis of Longmaxi Formation shales within the Dingshan-Dongxi and Songkan formations, the characteristics and main controlling factors of shale fractures were deeply studied by using fracture measurements, chi-square projection method and electron microscopy. The results show that: the inclination of cracks is mainly dominated by high-angle cracks and upright cracks, with the upright cracks of the Silurian system accounting for 57.35%, and the high-angle cracks of the Triassic system accounting for 43.85%. The fracture filler is mainly calcite and pyrite, in which the calcite and the analysis of fracture density shows that the density of Silurian fracture lines is mainly 3-8 lines/m, accounting for 70.5% of the total number; the development of microfractures also plays an important role in shale gas storage and transportation, and there are various types of microfractures, including open and filled seams, which provide an important storage space for shale gas exploration; the degree of development of shale fractures is related to the mineral components, organic carbon content and thickness of the rock formation. The degree of shale fracture development is closely related to the mineral fraction, organic carbon content and formation thickness. Shales with high brittle mineral content and organic carbon content have a higher degree of fracture development, while the greater the thickness of the formation, the lower the fracture density. These findings indicate that the development degree and types of shale fractures vary significantly among different geological periods and tectonic blocks, and that their complexity and diversity have important implications for shale gas storage and transportation.