煤层注水具有防突降尘、预防煤层自燃和冲击地压等作用，为提高煤层低压注水综合消突作用，增大煤层透气性，以河南省耿村煤矿13230综放工作面为工程背景，选取局部区域注50 ℃过硫酸钠(SPS)溶液进行化学增透后测定煤层透气性和瓦斯抽采纯量。使用Kruss DSA25光学测量仪测量煤样表面接触角θ，以考察SPS溶液质量分数、活化温度对煤样润湿性的影响，优选50 ℃作为SPS溶液的最佳活化温度;采用等温吸附实验测定煤样吸附常数a，b值，使用压汞实验测试孔隙特性并用分形理论计算孔隙粗糙度，采用扫描电子显微镜观察煤样表面形貌变化，采用TOC分析仪对返排液进行总有机碳(TOC)测试。分析结果表明：升温可有效活化SPS产生具有强氧化性能的硫酸根自由基(SO-4·)、并氧化水生成羟基自由基(·OH)，质量分数为1%的50 ℃活化SPS溶液可将耿村煤样的接触角θ由106.80°降低至45.05°，接触角下降57.82%，显著改善煤样的润湿性，增强煤表面与注水溶液的作用;耿村矿13230工作面注活化过硫酸钠溶液后煤样对瓦斯的吸附能力显著降低，吸附常数a值下降17.27%，吸附常数b值下降37.39%，煤样总孔容增加57.74%，孔隙率增加70.35%，中大孔孔容及孔容占比增大，微小孔的孔容及孔容占比减小，煤样的渗透容积增加、吸附容积减小;活化SPS溶液能将煤中占据或封堵孔道的部分小分子相物质氧化溶出，使得孔裂隙得到延伸和疏通，同时使煤表面出现新的微裂纹，改善煤体内孔隙连通性。耿村矿13230工作面在注活化SPS溶液后其单孔瓦斯抽采纯量提高137.14%，达到8.3 L/min;瓦斯体积分数及煤层透气性系数分别提高220%,1 650%，达到32%，0.101 5 m2/(MPa2·d);钻孔瓦斯流量衰减系数降低83.48%，低至0.011 5 d-1，煤层瓦斯抽放难易程度由较难抽放水平提升为可以抽放水平，增透效果显著。

Coal seam water injection has the functions of preventing outburst,coal seam spontaneous combustion,rock burst and dust.To improve the comprehensive effect of eliminating outburst by low-pressure water injection in coal seam and increase the permeability of coal seam,the 13230 fully mechanized caving face of Gengcun coal mine was selected to perform the engineering tests.Coal seam permeability and gas extraction quantity were determined by injecting 50 ℃ sodium persulfate (SPS) solution into the local area for chemically improving coal seam permeability.Kruss DSA25 optical measuring instrument was used to measure the surface contact angle of coal samples (θ) for investigating the influence of SPS solution concentration and activation temperature on the wettability of coal samples.A temperature of 50°C was selected as the optimum activation temperature of SPS solution.The adsorption constants a and b of different coal samples were determined by isothermal adsorption experiment.The pore characteristics of coal samples were investigated using mercury injection experiment and the pore roughness could be calculated by fractal theory.The surface morphology of coal samples obtained from different water injection conditions was observed by scanning electron microscope.The total organic carbon (TOC) of the flowback solution was determined by using TOC analyzer.The results demonstrate that heating can effectively activate SPS to produce sulfate radical (SO-4·) with strong oxidative property,and oxidize H2O molecules to generate hydroxyl radical (·OH).The SPS solution with 1% concentration activated at 50°C can reduce the contact angle of Gengcun coal sample from 106.80° to 45.05°.The contact angle decreases by 57.82%,which significantly improves the wettability of coal samples and enhances the interaction between the coal surface and water injection solution.After injecting activated sodium persulfate solution into the 13230 working face of Gengcun mine,the adsorption capacity of coal samples to gas decreased significantly.The adsorption constant a value of coal sample decreased by 17.27% and the adsorption constant b value decreased by 37.39%.The total pore capacity and porosity of treated coal samples increased by 57.74% and 70.35%,respectively.The pore volume and the corresponding proportion of middle and large holes increased,while the pore volume and the corresponding ratio of micro and small holes decreased.The permeability volume of the treated coal sample increased and the adsorption volume decreased.Heat-activated SPS solution could oxidize and dissolve partial small-molecular phase substances that occupy or block the pores in coal,extending and unblocking the pores and cracks.At the same time,new micro-cracks could be observed upon the surface of the treated coal samples,which improved the pore connectivity in coal body.After injecting the activated SPS solution into the 13230 working face of Gengcun mine,the gas extraction quantity of single-pore increased by 137.14%,reaching 8.3 L/min.The gas volume fraction and permeability coefficient of coal seam increased by 220% and 1 650% respectively,reaching 32% and 0.1015 m2/(MPa2·d).The attenuation coefficient of borehole gas flow decreased by 83.48% to 0.0115 d-1.The difficulty degree of coal seam gas drainage was improved from difficult drainage level to feasible drainage level,indicating the significant effect of permeability improvement via injecting heat-activated SPS solution.In conclusion,the method of injecting activated sodium persulfate solution under low pressure provides a novel idea for the development of comprehensive outburst elimination technology by coal seam water injection.

1 实验方法

2 实验结果与分析

   2.1 影响过硫酸钠溶液润湿煤样的因素

   2.2 煤层注入活化SPS溶液对煤体吸附甲烷能力影响

   2.3 煤层注入活化SPS溶液对煤样孔隙结构的影响

   2.4 煤层注入活化SPS溶液对煤表面的氧化溶蚀

3 煤层注入活化SPS溶液增透效果工程试验

4 结论