Analysis of crack initiation mechanism and influencing factors of hard roofs due to directional hydraulic fracturing

被引：0
|
作者：
Li Y. [1 ]
Ni T. [1 ]
Zuo J. [1 ]
Liu D. [1 ]
Song Y. [1 ]
机构：
[1] School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing
来源：
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | 2022年 / 41卷 / 10期
基金：
中国国家自然科学基金;
关键词：
composite crack; crack angle; critical water pressure; directional hydraulic fracturing; mining engineering; stress intensity factor;
D O I：
10.13722/j.cnki.jrme.2021.0838
中图分类号：
学科分类号：
摘要：
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 KI / KII. At smaller KI / KII, 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 KI and KII should be considered comprehensively. Specifically, KI is much larger than KII when the pre-slit angle is low and the water pressure is high. KI 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, KI arrives at a larger value, while with a 45° pre-slit angle and a high pre-slit length, KII can reach a larger value. Both KI and KII are sensitive to the coupling effect of the lateral pressure coefficient and the pre-slit angle. When the lateral pressure coefficient is small, KI is larger than KII. When the lateral pressure coefficient is large, KI is greater than KII at a low pre-slit angle, while KII is greater than KI at a high pre-slit angle. © 2022 Academia Sinica. All rights reserved.
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页码：2015 / 2029
页数：14
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