摘要
坚硬顶板破断释放巨大冲击动能是诱发煤矿动力灾害的重要因素之一,在特定位置断顶实现岩层的定向断裂、减小坚硬顶板悬顶长度是防治煤岩动力灾害的关键。多孔套筒压裂技术具有操作简单、适用条件广泛等优点,在坚硬顶板弱化领域有着广泛的研究前景。为深入了解多孔套筒压裂机理,采用理论分析与数值模拟方法开展了多孔套筒压裂力学机制研究,揭示了不同影响因素下孔间应力变化规律,获得了压裂过程裂缝扩展规律及力链分布特征。通过钻孔切槽可提升套筒压裂预裂效果,为确定合理的布孔参数,基于线弹性断裂力学建立了含预制缝多孔套筒压裂力学模型,给出了缝端应力强度因子、临界膨胀力及裂缝临界起裂角计算方程,获得了不同影响因素下缝端应力强度因子、临界膨胀力及临界起裂角的变化规律。研究结果表明:①侧压系数k对钻孔最小起裂应力影响显著,当侧压系数k>1时,最小起裂应力随布孔角度的增大而减小;当侧压系数k<1时,最小起裂应力随布孔角度的增大而增大。②数值模拟结果表明:套筒间存在应力叠加效应,接触力链呈“放射状”分布。套筒压裂过程以张拉破坏为主,孔心连线处变形破坏最剧烈,均沿布孔方向形成了“条带状”断裂面。③缝槽改变了缝端附近的应力分布,相较无缝槽模型环向拉应力更大。当缝槽长度为0.5倍孔半径时,临界膨胀力最小,裂缝最易发生扩展。④临界起裂角由KⅠ与KⅡ共同决定,且小于70.53°。在泵压与地应力条件无法改变的情况下,可通过调节布孔角度与预制缝槽长度实现岩石的定向压裂。
The huge impact of kinetic energy released by the breaking of hard roof is one of the important factors that in-duces dynamic disasters in coal mines.The key to preventing and controlling coal and rock dynamic disasters is the direc-tional fracture of strata at a specific position and reducing the length of hard roof suspension.The multi-hole sleeve frac-turing technology has the advantages of simple operation and wide application conditions and has a wide research pro-spect in the field of hard roof weakening.In order to understand the mechanism of multi-hole sleeve fracturing,the mech-anical mechanism of multi-hole sleeve fracturing was studied using theoretical analysis and numerical simulation.The variation law of inter-hole stress under different influencing factors was revealed,and the crack propagation law and force chain distribution characteristics in the fracturing process were obtained.The pre-cracking effect of sleeve fracturing can be improved by changing the drilling structure through grooving.In order to determine the reasonable hole arrangement parameters,a mechanical model of the multi-hole sleeve fracturing with prefabricated cracks was established based on lin-ear elastic fracture mechanics.The calculation equations of stress intensity factor,critical expansion pressure,and critical crack initiation angle of cracks were given,and the variation rules of stress intensity factor,critical expansion pressure,and critical crack initiation angle of cracks under different influencing factors were obtained.The results show that:①The lateral pressure coefficient k has a significant effect on the minimum crack initiation stress of the borehole.With the later-al pressure coefficient k>1,the minimum crack initiation stress decreases with the increase of the hole angle.With the lat-eral pressure coefficient k<1,the minimum crack initiation stress decreases with the increase of the hole angle.②The numerical simulation results show that there is a stress superposition effect between the sleeves,and the contact force chain is a'radial'distribution.The fracturing process of the sleeve is mainly a tensile failure,and the deformation and fail-ure at the connection of the hole center is the most severe,forming a'banded'fracture surface along the direction of the hole.③The stress distribution near the slot end is changed by the slot,and the circumferential tensile stress is larger than that of the seamless slot model.When the slot length is 0.5 times the radius of the hole,the critical expansion pressure is the smallest,and the crack is most likely to expand.④The critical initiation angle is determined by KI and KII,which is less than 70.53°.Under the condition that the pump pressure and in-situ stress conditions cannot be changed,the direction-al fracturing of the rock can be realized by adjusting the hole angle and the length of the prefabricated slot.
作者
胡善超
韩金明
程亚飞
亓佳利
黄俊鸿
高志豪
郭世豪
杨磊
HU Shanchao;HAN Jinming;CHENG Yafei;QI Jiali;HUANG Junhong;GAO Zhihao;GUO Shihao;YANG Lei(College of Energy and Mining Engineering,Shandong University of Science and Technology,Qingdao266590,China;Luxi Mining Co.,Ltd.,Shandong Energy Group,Heze 274700,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2024年第8期3366-3380,共15页
Journal of China Coal Society
基金
国家自然科学基金资助项目(52274087,51904166)
山东省自然科学基金资助项目(ZR2023ME189)。
关键词
套筒定向压裂
孔间应力分布
应力强度因子
临界膨胀力
起裂角度
sleeve directional fracturing
stress distribution between holes
stress intensity factor
critical expansion pressure
initiation angle
