Brittleness Characteristics of Organic-rich Shale and Its Relationship with Fracture Development of Changning Area

doi:10.11885/j.issn.1674-5086.2020.07.20.01

Abstract

Abstract: The brittleness of shale controls the formation and evolution of fractures, which is crucial to the volume transformation of shale gas reservoir and the production increase of shale gas well. Taking Longmaxi Formation in Changning area of South Sichuan as an example, the mineral composition, organic geochemistry, pore fracture structure and mechanical properties of the lower Long 1 sub section were tested by rock and mineral, geochemical and mechanical experiments. Combined with experimental method of scanning electron microscopy, the relationships between the fracture development and different shale characteristics of brittle minerals, organic matter and buried depth were analyzed. The results show that the organic-rich siliceous shale facie has the highest brittleness in lower Long 1sub section. The total content of brittle minerals such as quartz, feldspar, and pyrite is greater than 50%. They can regulate the shear slip of rock blocks, and the energy accumulated in the rock is greater than the energy required to complete the overall rock failure. The organic matter and the organic pores and microfractures produced in the process of maturity can promote the development, connection and connection of fractures. The higher the organic carbon content, the more developed the fracture system. With increasing burial depth, the brittleness of the shale decreases, and the rock failure mode changes from a complex cleavage type to a single shear type. The 1st and 2nd sublayers of lower Long 1 sub section have the highest content of brittle minerals and organic carbon, with brittleness indices of 61.31% and 60.70%, respectively. They can be selected as sweet spot section with good fracturing performance, and complex fractures can be formed after fracturing.

Key words: organic-rich shale, brittleness, fracture, control mechanism, compressibility, sweet spot

CLC Number:

TE122

ZHAO Shengxian, LIU Yong, FENG Jiangrong, FAN Cunhui, JI Chunhai. Brittleness Characteristics of Organic-rich Shale and Its Relationship with Fracture Development of Changning Area[J]. Journal of Southwest Petroleum University(Science & Technology Edition), 2022, 44(4): 1-13.

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