ABSTRACT

A systematic understanding of the effects of different fracturing fluids on the chemical and pore structure of coal is of great significance for the exploitation of coalbed methane (CBM). In this study, Fourier-transform infrared spectroscopy and mercury intrusion porosimetry were used to analyze the chemical and pore structure of coal samples treated by different fracturing fluids. The results show that fracturing fluid treatment has little effect on the coal aromatic structure. The oxygen-containing and hydroxyl structures of the coal samples treated by acidic and viscoelastic surfactant (VES) fracturing fluids increased by >17%, which is beneficial for gas desorption and thereby increases CBM yield, whereas those of the coal sample treated with deionized water decreased by 3.8%. The acidic and VES fracturing fluid treatments are also beneficial for coal pore connectivity, which promotes gas migration. The three types of fracturing fluids increased the macropore volume by >350%. The deionized water treatment reduced mesopores and micropores by 20% and 5%, respectively, while the transition pores increased by 2.3%, resulting in a 2.6% increase of the specific surface area, which is not conducive to gas desorption and migration. The acidic fracturing fluid treatment increased the mesopore volume by 53.3%, reduced the transition pore and micropore volumes by 5.3% and 32.5%, respectively, and reduced the surface area by 13.2%, which reduces the amount of adsorption sites and facilitates gas migration. However, the adsorption pores and mesopores after VES fracturing fluid treatment decreased by 17.6% and 26.7%, respectively, which indicates that this treatment does not transform most adsorption pores into migration pores.

摘要

系统了解不同压裂液对煤化学和孔隙结构的影响，对煤层气的开采具有重要意义。本研究采用傅里叶变换红外光谱和压汞孔隙率测定法对不同压裂液处理后的煤样进行化学分析和孔隙结构分析。结果表明，压裂液处理对煤芳烃结构影响不大。酸性粘弹性表面活性剂（VES）压裂液处理煤样含氧和羟基结构增加>17%，有利于气体解吸，从而提高煤层气产量，而去离子水处理煤样的含氧和羟基结构增加下降了 3.8%。酸性和 VES 压裂液处理也有利于煤孔隙连通性，促进气体运移。三种类型的压裂液使大孔隙体积增加>350%。去离子水处理使中孔和微孔分别减少了20%和5%，而过渡孔增加了2.3%，导致比表面积增加了2.6%，不利于气体的解吸和迁移。酸性压裂液处理使中孔体积增加53.3%，过渡孔和微孔体积分别减少5.3%和32.5%，表面积减少13.2%，减少了吸附位点数量，有利于气体运移。然而，VES压裂液处理后的吸附孔和介孔分别减少了17.6%和26.7%，