Journal
MATERIALS
Volume 15, Issue 20, Pages -Publisher
MDPI
DOI: 10.3390/ma15207143
Keywords
shale; nanoindentation; brittleness index; friability
Categories
Funding
- National Natural Science Foundation of China [41941018]
- major Science and Technology Project in Yunnan Province [202002AF080003]
- Fundamental Research Funds for the Central Universities - Institute for Deep Underground Science and Engineering [XD2021022]
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In this study, nanoindentation tests were conducted on the surface of shale to propose a novel micro-brittleness index. By exploring the distribution characteristics of the brittleness index on the shale surface and the variation laws between mineral and brittleness index, the research revealed the brittleness features of shale and the heterogeneity on its surface. The results showed that the dimensionless brittleness index involved parameters such as indentation irreversible deformation, elastic modulus, hardness, and fracture toughness.
Shale is a special kind of rock mass and it is particularly important to evaluate its brittleness for the extraction of gas and oil from nanoporous shale. The current brittleness studies are mostly macro-evaluation methods, and there is a lack of a micro-brittleness index that is based on nanoindentation tests. In this paper, nanoindentation tests are carried out on the surface of shale to obtain mechanical property, and then a novel micro-brittleness index is proposed. Drawing a heat map by meshing indentation, the distribution characteristics of the brittleness index for the surface of shale and the variation laws between the mineral and brittleness index are explored. The results showed that the dimensionless brittleness index involved parameters including indentation irreversible deformation, elastic modulus, hardness and fracture toughness. The micro-brittleness index of the shale ranged from 7.46 to 65.69, and the average brittleness index was 25.837. The brittleness index exhibited an obvious bimodal distribution and there was great heterogeneity on the surface of shale. The crack propagation channels were formed by connecting many indentation points on the shale surface with high brittleness. The total brittleness index of quartz minerals was high, but the cementation effect with different minerals was various. Although the general brittleness of clay was low, the high brittleness index phenomenon was also exhibited. Studying the micro-brittleness of shale provides a more detailed evaluation for the shale friability, which is used to determine the optimal shale oil and gas recovery regime.
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