坚硬顶板定向水力压裂裂纹起裂机制及影响因素分析

doi:10.13722/j.cnki.jrme.2021.0838

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Abstract To study the steering mechanisms of directional water pressure fracturing in the hard roofs of coal mines，the equations for evaluating the stress intensity factor，the fracturing initiation angle and the critical water pressure of the mechanical model of directional hydraulic fracturing involving wellbores and pre-slits were deduced under water pressure and geo-stresses based on the theory of linear elastic fracture mechanics. On this basis，the parameters affecting the stress intensity factor the fracturing initiation angle and the critical water pressure were analyzed and the fracture characteristics of directional water pressure fractures were discussed. The results show that during the critical initiation state of directional hydraulic fracturing，tension fractures or tension-shear composite fractures occur at varied pre-slit angles. The fracturing initiation angle decreases with increasing the stress intensity factor ratio / . At smaller / ，the hydraulic fracture initiation deviates from the pre-slit direction under the action of shear dislocation. To control the directionality of hydraulic fractures，the influence factors of and should be considered comprehensively. Specifically， is much larger than when the pre-slit angle is low and the water pressure is high. is also larger in wellbores with a large radius and a low pre-slit angle. With a low angle and a high pre-slit length， arrives at a larger value，while with a 45° pre-slit angle and a high pre-slit length， can reach a larger value. Both and are sensitive to the coupling effect of the lateral pressure coefficient and the pre-slit angle. When the lateral pressure coefficient is small， is larger than . When the lateral pressure coefficient is large， is greater than at a low pre-slit angle，while is greater than at a high pre-slit angle.

Key words： mining engineering directional hydraulic fracturing composite crack stress intensity factor critical water pressure crack angle

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	LI Yingjie
	NI Ting
	ZUO Jianping
	LIU Dejun
	SONG Yihao

Cite this article:

LI Yingjie,NI Ting,ZUO Jianping, et al. Analysis of crack initiation mechanism and influencing factors of hard roofs due to directional hydraulic fracturing[J]. , 2022, 41(10): 2015-2029.

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http://rockmech.whrsm.ac.cn/EN/10.13722/j.cnki.jrme.2021.0838 OR http://rockmech.whrsm.ac.cn/EN/Y2022/V41/I10/2015

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