承压破碎无烟煤气体渗透特性影响因素实验研究

An experimental study of factors influencing gas seepage in confined broken anthracite

垮落带破碎煤岩体空隙结构演变直接影响垮落带气体渗透特性,进而影响废弃矿井采空区煤层气运移富集规律。利用自主设计研发的第二代破碎煤岩体压实-渗流-CT扫描试验系统,开展5种粒径破碎无烟煤在不同气体压力、轴向应力及空隙率条件下162组渗透实验。结果表明:(1)气体在破碎无烟煤中运移时气体压力、流量随时间一直处于动态变化直至达到吸附平衡,流量、压力恒定。(2)低雷诺数下气体在破碎无烟煤中流动需要拟启动压力梯度,其值处于158.89~1408.64 Pa/m,并随着轴压增大、空隙率减小而增大。(3)破碎无烟煤渗透率处于10^(-12)~10^(-10)m^(2),且渗透率随气体压力、空隙率增加分别呈现对数、指数函数式增长趋势。(4)颗粒粒径越大则相同装料空间内破碎煤样初始空隙越大,更易于气体流动,因此相同空隙率时破碎无烟煤渗透率随粒径的增大而增大;不同粒径颗粒渗透率平均变化幅度均随空隙率减小而减小;然而颗粒粒径越大,减小相同空隙率时破碎无烟煤渗透率变化幅度减小越明显。废弃矿井采空区煤层气地面抽采时,地面钻井应优先布设在垮落带破碎煤岩体连同纵向“高位环形裂隙体”共同构成的“U”型高渗煤层气富集区内。

The void structure evolution of broken coals in a caving zone directly affects the gas seepage characteristics of the zone,further influencing the gas migration and enrichment patterns in abandoned coal mine goaves.With the second generation of compaction-seepage-CT scanning experimental system for broken coals independently designed and developed,this study performed 162 sets of permeability experiments on broken anthracite samples with five particle size ranges under varying gas pressures,axial stresses,and void fractions.Key findings are as follows:(1)When gas migrated in broken anthracite,its pressure and flow rate kept dynamically changing until the adsorption equilibrium was reached.(2)Under a low Reynolds number,a quasi-starting pressure gradient was required for gas flow in broken anthracite.This gradient ranged between 158.89 and 1408.64 Pa/m,increasing with an increase in axial pressure and a decrease in void fraction.(3)The broken anthracite exhibited permeability ranging from 10^(−12) to 10^(−10) m^(2),increasing logarithmically and exponentially with increasing gas pressure and void fraction,respectively.(4)A larger particle size corresponded to larger initial voids in broken anthracite samples within the same loading space,more conducive to gas flow.Therefore,under the same void fraction,the permeability of broken anthracite increases with particle size.(5)The average changing amplitude of the permeability of particles with varying sizes all decreased with a decrease in the void fraction.For particles with a larger size,the changing amplitude decreased more significantly under the same decrease in the void fraction.To achieve the surface extraction of coalbed methane(CBM)from an abandoned coal mine goaf,ground drilling should be preferably arranged in a U-shaped high-permeability CBM-rich zone composed of broken coals in a caving zone and circular overlying zones at the longwall panel in the vertical direction.