二氧化氯对煤储层孔隙结构的影响

在煤储层低温条件下，二氧化氯（ClO₂）不仅实现了煤层气井水力压裂时高黏压裂液的快速破胶和返排，还降低了煤的亲甲烷能力，但其强氧化性对煤储层孔隙结构的影响问题却还没有搞清楚。为此，采集了3种不同煤阶煤样（样品分别来自河南省义马市千秋矿井、焦作市中马村矿井和山西省柳林县沙曲矿井），将其粉碎（筛选粒径为2 mm左右），采用浓度为4 000 μg/g的ClO₂溶液浸泡72 h，利用压汞法分析ClO₂溶液处理前后煤样的孔隙度、孔径分布、孔容、比表面积等孔隙结构的变化特征。实验结果表明：①处理后煤样的孔隙度、孔容得到不同程度的提高，大孔和中孔的孔容比增加；②进-退汞曲线的滞后现象消失及张开度变小，孔隙的连通性增强；③孔隙比表面积值降低，其中，小孔和微孔的比表面积比有所减小。结论认为：二氧化氯对煤储层具有氧化刻蚀增透作用，能够改善煤储层的孔隙结构，一定程度上增大了煤储层的渗透率，有利于煤层气的运移和产出，值得在煤层气行业进行推广应用。

Impact of chlorine dioxide on pore structure of coal reservoirs

With chlorine dioxide (ClO₂) adopted under low temperatures of coal reservoirs, not only can rapid gel breaking and flowback of high viscosity fracturing fluids be achieved, but a coal′s affinity can be lowered for methane. However, the impact of the strong oxidation of ClO₂ on pore structure is still not fully understood. Three coal samples with different ranks were collected from different coal mines. After being crushed into grains with a diameter of about 2 mm, the samples were soaked in ClO₂ solutions with a concentration of 4000 μg/g for 72 hours. Then the mercury injection method was used to analyze the coal samples to reveal the variations of porosity, pore size distribution, pore volume and specific surface area before and after being treated with the ClO₂ solution. The following results were obtained. a. The porosity and pore volume of coal samples both get enhanced to varying degrees, and the pore volume ratios of macropores and mesopores increase after treatment. b. The hysteresis on the mercury intrusion and extrusion curves disappears, the joint opening decreases and the pore connectivity is improved. c. The specific surface areas of pores decrease, so does the ratio of specific surface area between micro and nano pores. In conclusion, chlorine dioxide can improve pore structure and enhance permeability of coal reservoirs, thus is favorable for migration and recovery of CBM.