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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摘要我国大部分煤层渗透率较低，液氮致裂作为一种无水压裂技术，促使煤层破裂产生裂隙网络，有效改善煤层渗透特性。实际煤层处于三维应力环境，使得煤体损伤破裂特性更为复杂，为进一步研究真三轴应力下液氮致裂煤体裂缝起裂扩展规律，综合考虑煤层真实应力环境和液氮低温特性，自主研发液氮注入致裂煤体真三轴试验系统，主要包括真三轴应力加载、液氮增压注入、回压保压和数据采集等模块。试件尺寸150 mm×150 mm×150 mm，真三轴最大加载应力1 500 kN，最大注入压力20 MPa，压裂系统承压能力大于25 MPa。利用试验系统开展不同水平应力比下液氮注入致裂煤体试验，结果表明：液氮致裂煤体过程压力–时间曲线可分为压力平稳、压力上升和压力急剧下降3个阶段。水平应力比越高，煤体破裂时间越早，破裂压力越低，累积振铃计数逐渐减小。水平应力比由1增加到3时，破裂压力由11.37 MPa降低到5.21 MPa，降幅54.18%。煤样主裂缝沿着最大水平主应力方向扩展，主裂缝产生分支裂缝，裂缝形态从三翼断裂裂缝转化为单一裂缝。试验系统为进一步探讨真三轴应力下液氮致裂煤体裂缝扩展规律，揭示液氮致裂煤体增透机制提供一定试验基础。

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	林海飞1
	2
	李博涛3
	李树刚1
	2
	魏宗勇1
	2
	严敏1
	2
	秦雷1
	2
	王裴1
	罗荣卫1
	刘泽然1

关键词 ：采矿工程, 煤层增透, 试验系统研发, 真三轴应力, 液氮致裂, 裂缝扩展

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

引用本文:

林海飞1，2，李博涛3，李树刚1，2，魏宗勇1，2，严敏1，2，秦雷1，2，王裴1，罗荣卫1，刘泽然1. 液氮注入煤体致裂全过程真三轴试验系统研发与应用[J]. 岩石力学与工程学报, 2025, 44(2): 276-291.
LIN Haifei1，2，LI Botao3，LI Shugang1，2，WEI Zongyong1，2，YAN Min1，2，QIN Lei1，2，WANG Pei1，LUO Rongwei1，LIU Zeran1. Development and application of true triaxial experimental system for the whole process of coal fracturing induced by liquid nitrogen injection. , 2025, 44(2): 276-291.

链接本文:

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

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