基于能量平衡的新脆性指标与页岩失效机制分析

doi:10.13722/j.cnki.jrme.2021.0732

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Abstract Aiming to establish the brittleness index for characterizing deep shale gas reservoirs，a new brittleness evaluation method，characterizing the brittleness of rock from three aspects such as rock failure rate()，post-peak instability() and pre-peak plastic yield()，was proposed based on energy balance theory in consideration of the energy conversion rate of the rock system to the outside and the effect of radial expansion on brittleness characteristics，and a series of triaxial compression tests designed according to shale-formation information were conducted to verify the applicability of the index. The test results show that the brittleness characteristics of shale decrease with increasing “formation level”(i.e.，the confining pressure and the temperature)，and compared with the existing brittleness indices，the new brittleness index is superior in describing the brittleness characteristics of shale under different test conditions，especially in the condition of high confining pressure(at 100 MPa) and high temperature(at 190 ℃). Besides，the brittle failure mechanism of shale was analyzed in terms of strength factors，and it is revealed that the strength envelope curve of shale presents bilinear characteristic. Meanwhile，a critical condition for macroscopic fracture patterns of shale was quantified by establishing the correlation of the macroscopic fracture pattern，the brittleness characteristics and the critical principal stress ratio. It is also found that the damage degree of shale can reduce the brittleness characteristics of shale by increasing the pre-peak plastic yield and the contribution rate of the elastic energy.

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rock mechanics shale brittleness evaluation energy balance formation brittle failure mechanism macroscopic failure characteristics

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	LIU Junxin1
	2
	LI Junrun1
	2
	YIN Binrui1
	2
	TANG Wei1
	2
	3
	YUAN Yusong4
	ZHU Baolong1
	2

Cite this article:

LIU Junxin1,2,LI Junrun1, et al. New brittleness index based on energy balance and analysis of failure mechanism of shale[J]. , 2022, 41(4): 734-747.

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http://rockmech.whrsm.ac.cn/EN/10.13722/j.cnki.jrme.2021.0732 OR http://rockmech.whrsm.ac.cn/EN/Y2022/V41/I4/734

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