Evaluation of shale fracture toughness based on micrometer indentation test

Abstract

It is an important mechanical parameter for fracture toughness that affects hydraulic fracturing. Some methods such as indoor test core and logging data interpretation are commonly used to obtain fracture toughness. These methods, however, have their own limitations. Liu's method has focused the mechanical properties of shale including fracture toughness based on micro-/nano-indentation experiments. Zeng's method has pointed that the former method of calculating fracture toughness ignores the maximum holding stage in the indentation-displacement curves, they point out and correct the fracture stress intensity factor model, but the final calculation of the fracture toughness of the numerical difference is of two orders of magnitude. In this paper, micro-indentation experiments were carried out to further analyze and correct the model by collecting and analyzing Longmaxi shale cuttings. After Zeng and Liu's methods are combined, the irreversible elastic energy by energy area actually was measured. To some extent, the difference between the two kinds of fracture toughness is reduced.

Keywords

Fracture toughness / Micro-indentation experiment / Rock mechanical properties

Acknowledgments

This work is Supported by the National Natural Science foundation of China (Grant No. 51604230), the Young Elite Scientists Sponsorship Program by CAST (2017QNRC001), and the Scientific Research foundation of International Cooperation and Exchanges of Sichuan Province (Grant Nos. 2017HH0061 & 2016HH0001).

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