Jinneng Holding Coal Industry Group Co., Ltd.
College of Safety & Emergency Management Engineering, Taiyuan University of Technology

水力割缝技术通过高压水射流在煤层中构建人工裂隙,可实现低渗煤层的区域性卸荷增透和瓦斯高效抽采。然而,经典的COMSOL软件难以对钻割煤体的三维卸压瓦斯流场进行解算,严重制约了水力割缝技术的工程应用。鉴于此,采用FLAC3D-COMSOL序贯耦合的数值解算方法,以中厚煤层钻割卸荷增透为例,对不同割缝半径、割缝厚度、埋深和割缝方式下钻割煤体的三维卸压瓦斯流场进行了数值分析。结果表明:水力割缝过程中,钻割煤体发生了卸荷损伤,形成了较大范围的圆台形塑性损伤区,煤体渗透率可大幅提高2~3个数量级;随着割缝半径和割缝厚度的增加,煤体的增透范围和瓦斯抽采半径逐渐增大,但在相同出煤量情况下增加割缝半径更有利于中厚煤层的卸荷增透和瓦斯抽采;深部高地应力环境导致煤层初始渗透率下降,但也可提高钻割煤体的增透范围和增透幅度,因此钻孔早期瓦斯抽采效果好,后期抽采效果差,在抽采过程中应尽量增加钻孔密度,缩短抽采周期;割缝方式对中厚煤层的整体卸压瓦斯抽采效果具有显著影响,单缝钻孔平行布置情况下煤层卸压瓦斯抽采效果最好,单缝交错布置情况下次之,而双缝间隔布置情况下最差。

Hydraulic slotting technology could achieve regional stress-unloading, permeability-increas- ing and efficient gas extraction in the low-permeability coal seam through creating artificial fractures u- sing the high-pressure water jet. Unfortunately, the three-dimensional pressure-relief gas migration field in the hydraulic slotting coal mass could not be solved by adopting the typical COMSOL software, which seriously restricts the field application of hydraulic slotting technology. Given this, the FLAC3D-COM- SOL combined numerical solution technology was adopted in the research to analyze the three-dimen- sional pressure-relief gas migration fields in medium thick coal seam under different slotting radii, slot- ting thicknesses, buried depths and slotting manners, respectively. The following conclusions could be obtained from the numerical simulation results. A stress-unloading and plastic damage occur in the coal mass during the hydraulic slotting process, the plastic damage zone presents a circular platform shape, and the coal permeability increases by 2 ~ 3 orders of magnitude. The coal’ s permeability-increasing range and amplitude both increase with the slotting radius and the slotting thickness, but increasing the slotting radius is much more conducive to the stress-unloading, permeability-increasing and gas extrac- tion in the medium thick coal seam. The high in-situ stress in the deep coal seam could not only de- crease the coal permeability, but also increase the permeability-increasing range and the amplitude in the hydraulic slotting coal mass, therefore the borehole’ s gas extraction effect is much better in the ear- ly stage and the gas extraction period should be decreased by improving the borehole density during the field application process. Slotting manner has a great influence on the overall pressure-relief gas extrac- tion effect in the coal seam: the pressure-relief gas extraction effect is the best under the condition of single slotting drilling parallel arrangement, and the next is the single slotting-staggered arrangement, followed by double slotting interval arrangement, the worst.

国家自然科学基金项目(52104210);山西省应用基础研究计划项目(20210302124350,202203021212291);中国博士后科学基金项目(2022M710595);山西省高等学校科技创新项目(2021L058)

张浩,郭军伟,王穗芳,等.基于FLAC3D-COMSOL序贯耦合的钻割煤体三维卸压瓦斯流场数值分析[J].西安科技大学学报,2024,44(3):478-489.

ZHANG Hao, GUO Junwei, WANG Suifang, et al. Numerical research on 3D pressure-relief gas migration field in the hydraulic slot-ting coal mass by adopting a FLAC3D-COMSOL coupled method[ J] . Journal of Xi’an University of Science and Technology, 2024, 44( 3) : 478-489.