Experimental Study on the Effect of Bedding on the Fracture Process Zone of Shale

Tiewu Tang, Xiaoshan Shi (), Xiaojing Zhu and Liyun Li
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Tiewu Tang: Chinese Institute of Coal Science, Beijing 100013, China
Xiaoshan Shi: Chinese Institute of Coal Science, Beijing 100013, China
Xiaojing Zhu: Chinese Institute of Coal Science, Beijing 100013, China
Liyun Li: School of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China

Energies, 2022, vol. 15, issue 17, 1-25

Abstract: The conventional fracture in shale hydraulic fracturing belongs to the type-I fracture, and the size of the fracture process zone (FPZ) is an important index to measure the fracability of rock mass. This index is also one of the feasible entry points to study the complexity of the fracture network. In order to visually observe the type-I FPZ at the tip of shale fractures, and to study the relationship between the mechanical properties, the shape and size of the FPZ, and the bedding structure, Notched Semi-Circular Bend (NSCB) tests were conducted with three typical fracture direction-bedding orientations (splitter, arrester, divider). The digital image correlation (DIC) method was used to realize the intuitive observation of the real fracture process and the FPZ near the fracture tip. The test found that the FPZ of shale is narrow and long as a whole and is “flame-like”. The height-to-length ratio of the FPZ at the fracture tip determines whether bending and deflection happen between the new fracture and the prefabricated cracks when the fracture occurs. Most of the specimens often appear in the FPZ with a beaded high shear strain zone before the fracture, which is caused by the oblique communication of micro-cracks in the FPZ before the fracture. The appearance of a beaded zone of high shear strain indicates that macroscopic fracture is imminent. The research results can be used for the design of disaster early warning and prevention programs.

Keywords: NSCB; DIC; fracture process zone; high shear strain; shale (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
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