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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摘要为研究煤层坚硬顶板定向水压裂纹转向机制，基于线弹性断裂力学理论，推演水压和地应力作用下含井筒和预割缝的定向水力压裂力学模型的应力强度因子计算公式，及裂纹起裂角和临界水压计算方程，以此为基础分析应力强度因子和起裂角以及临界水压的影响因素，探讨定向水压裂纹断裂特征。研究结果表明定向水压裂纹临界起裂状态下，不同预割缝倾角下水力裂缝将发生张拉或者拉–剪复合断裂，裂纹起裂角随应力强度因子比 / 的增大而减小，当 / 较小时，水力裂缝在剪切错动作用下将偏离预割缝方向发生起裂。为了实现水力裂缝的定向控制，应综合考虑和的影响因素：低预割缝倾角、高水压时远大于；低倾角、高井筒半径下值较大；在低倾角、高预割缝长度时取得较大值，而45°预割缝角度下、高预割缝长度时取得较大值；和对侧压力系数和预割缝角度的耦合作用较为敏感，侧压力系数较小时，＞。当侧压力系数较大时，低预割缝角度下＞，高预割缝角度时＞。

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	李英杰
	倪婷
	左建平
	刘德军
	宋宜豪

关键词 ：采矿工程, 定向水压致裂, 复合型裂纹, 应力强度因子, 临界水压, 起裂角

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

引用本文:

李英杰，倪婷，左建平，刘德军，宋宜豪. 坚硬顶板定向水力压裂裂纹起裂机制及影响因素分析[J]. 岩石力学与工程学报, 2022, 41(10): 2015-2029.
LI Yingjie，NI Ting，ZUO Jianping，LIU Dejun，SONG Yihao. Analysis of crack initiation mechanism and influencing factors of hard roofs due to directional hydraulic fracturing. , 2022, 41(10): 2015-2029.

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

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