胡善超,韩金明,程亚飞,等. 多孔套筒定向压裂力学机制及影响因素分析[J]. 煤炭学报,xxxx,xx(x): x−xx. doi: 10.13225/j.cnki.jccs.2023.0990
引用本文: 胡善超,韩金明,程亚飞,等. 多孔套筒定向压裂力学机制及影响因素分析[J]. 煤炭学报,xxxx,xx(x): x−xx. doi: 10.13225/j.cnki.jccs.2023.0990
HU Shanchao,HAN Jinming,CHENG Yafei,et al. Analysis of mechanical mechanism and influencing factors of directional fracturing of multi-hole sleeve[J]. Journal of China Coal Society,xxxx,xx(x): x−xx. doi: 10.13225/j.cnki.jccs.2023.0990
Citation: HU Shanchao,HAN Jinming,CHENG Yafei,et al. Analysis of mechanical mechanism and influencing factors of directional fracturing of multi-hole sleeve[J]. Journal of China Coal Society,xxxx,xx(x): x−xx. doi: 10.13225/j.cnki.jccs.2023.0990

多孔套筒定向压裂力学机制及影响因素分析

Analysis of mechanical mechanism and influencing factors of directional fracturing of multi-hole sleeve

  • 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KK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。

     

    Abstract: The huge impact of kinetic energy released by the breaking of hard roof is one of the important factors that induces dynamic disasters in coal mines. The key to preventing and controlling coal and rock dynamic disasters is the directional fracture of strata at a specific position and reducing the length of hard roof suspension. The multi-hole sleeve fracturing technology has the advantages of simple operation and wide application conditions and has a wide research prospect in the field of hard roof weakening. In order to understand the mechanism of multi-hole sleeve fracturing, the mechanical 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 linear 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: ① The lateral pressure coefficient k has a significant effect on the minimum crack initiation stress of the borehole. With the lateral pressure coefficient k > 1, the minimum crack initiation stress decreases with the increase of the hole angle. With the lateral pressure coefficient k < 1, the minimum crack initiation stress decreases with the increase of the hole angle. ② The 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 failure at the connection of the hole center is the most severe, forming a 'banded' fracture surface along the direction of the hole. ③ The 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. ④ The 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 directional fracturing of the rock can be realized by adjusting the hole angle and the length of the prefabricated slot.

     

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