液氮注入煤体致裂全过程真三轴试验系统研发与应用

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Abstract Most of the coal seams in China have low permeability. Liquid nitrogen(LN2) fracturing，an anhydrous fracturing technology，induces coal seam rupture and forms a fracture network，significantly enhancing permeability. The actual coal seam is in a three-dimensional stress environment，making the damage and fracture characteristics of the coal more complex. To investigate the fracture initiation and expansion law of LN2 fracturing coal under true triaxial stress，a true triaxial experimental system for LN2 injection fracturing coal has been independently developed by considering the real stress environment of the coal seam and the low-temperature LN2 characteristics. The system mainly includes the true triaxial stress loading，LN2 pressurized injection，pressure holding，and data acquisition modules. The specimen size of the system is 150 mm×150 mm×150 mm，the maximum loading stress of true triaxial is 1 500 kN and the maximum pressure of the injection is 20 MPa，and the pressure-bearing capacity of the hydraulic fracturing system is more than 25 MPa. The test system was utilized to carry out tests on fracturing coal by LN2 injection at different horizontal stress ratios. The results show that the pressure-time curve of the LN2 fracturing coal process can be divided into three stages：stable pressure，rising pressure and sharp pressure drop. An increase in the horizontal stress ratio results in an earlier coal rupture time，a reduction in the rupture pressure and a gradual decrease in the cumulative ringing count. When the horizontal stress ratio increased from 1 to 3，the rupture pressure decreased from 11.37 to 5.21 MPa，with a decrease of 54.18%. The fractures in the coal samples primarily expanded along the direction of the maximum horizontal principal stress，with the main fracture producing branching fractures. The fracture morphology evolved from a three-wing fracture pattern to a single fracture structure. The experimental system provides a certain experimental basis for further exploring the crack expansion law of LN2 fracturing coal and revealing the penetration enhancement mechanism of LN2 fracturing coal.

Key words： mining engineering coal seam permeability enhancement test system development true triaxial stress liquid nitrogen fracturing fracture propagation

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	Articles by authors
	LIN Haifei1
	2
	LI Botao3
	LI Shugang1
	2
	WEI Zongyong1
	2
	YAN Min1
	2
	QIN Lei1
	2
	WANG Pei1
	LUO Rongwei1
	LIU Zeran1

Cite this article:

LIN Haifei1,2,LI Botao3, et al. Development and application of true triaxial experimental system for the whole process of coal fracturing induced by liquid nitrogen injection[J]. , 2025, 44(2): 276-291.

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https://rockmech.whrsm.ac.cn/EN/Y2025/V44/I2/276

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