The evaluation criteria for rock brittleness based on double-body analysis under uniaxial compression
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The evaluation criteria for rock brittleness based on doublebody analysis under uniaxial compression Tingting Wang . Huaitao Zhang . Ranjith Pathegama Gamage . Wanchun Zhao . Jing Ge . Yuwei Li
Received: 23 March 2020 / Accepted: 2 June 2020 Ó Springer Nature Switzerland AG 2020
Abstract The brittleness of rocks plays an important role in the fracture network fracturing process of unconventional oil and gas reservoirs, the drilling efficiency of rock breaking and wall stability, and mining engineering. Rock brittleness has become one of the key parameters in the study of many rock mechanics and related engineering problems. However, there is still no widely accepted definition of brittleness. Although many criteria have been proposed to characterize rock brittleness, their
applicability and reliability have yet to be verified. Therefore, brittleness evaluations require further study. In this paper, we divided the rocks under an external load into the unruptured area (body I system) and ruptured area (body II system). We considered that the body I system provided energy for the fracture of the II body. The brittleness of rock is understood as the ability of energy release when a post-peak fracture occurs in the II system. Therefore, the quasi-static energy-balanced equation of a double-body system
T. Wang H. Zhang School of Electrical Engineering and Information, Northeast Petroleum University, Daqing 163318, Heilongjiang, China
W. Zhao Key Laboratory of Continental Shale Accumulation and Development (Northeast Petroleum University), Ministry of Education, Daqing, China
T. Wang Heilongjiang Provincial Key Laboratory of Networking and Intelligent Control, Daqing 163318, Heilongjiang, China
J. Ge Y. Li (&) School of Petroleum Engineering, Northeast Petroleum University, Daqing 163318, Heilongjiang, China
R. P. Gamage Deep Earth Energy Laboratory, Department of Civil Engineering, Monash University, Building 60, Melbourne, VIC 3800, Australia W. Zhao (&) Institute of Unconventional Oil & Gas, Northeast Petroleum University, Daqing 163318, Heilongjiang, China e-mail: [email protected]
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was established and a new brittleness index was defined as the elastic energy release between an unsteady quasi-static state to the stable state of body II. The new index for brittleness evaluation proposed in this paper can not only quantify the brittleness of rock through the relation between the extremum of a softening modulus at the inflection point in the postpeak deformation curve of body II and the elastic modulus of body I but also ensure the position of the failure strain in the post-peak stage as well as reviewing the instant characteristics of the rock’s brittle crack. It is a new method to evaluate rock brittleness. Taking sandstone with different contents of brittle minerals as an example, the variation of the brittle index with the content of brittle minerals was studied. Keywords Brittleness index Fold catastrophe theory
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