Wettability Characteristics of Low-Rank Coals Under the Coupling Effect of High Mineralization and Surfactants

This paper investigates the unclear influence mechanism of the surfactant effect on improving coal seam wettability and CO₂-enhanced coalbed methane technology to enhance the gas extraction efficiency in some coal mines under highly mineralized environments in China. Specifically, the microinfluence mechanism of the coupling effect of nonionic surfactant OP-10 and highly mineralized coal samples under special treatment on the wettability of coal seam is examined. By measuring the contact angle and surface tension of the samples, it is confirmed that high mineralization can limit the effect of surfactants on improving the wettability of coal seams to a certain point. Infrared spectroscopy and X-ray diffraction measurements were conducted on the samples under coupling conditions. It is found that high mineralization impedes the effectiveness of surfactants in enhancing the wettability of coal seams. The surfactants interact with coal samples at the functional group level, producing new hydrophilic functional groups and increasing the content of kaolin with strong hydrophilic properties, thereby increasing the wettability of coal seams. However, these hydrophilic functional groups disappear under coupling conditions and hydrophobic functional groups are produced. Additionally, high mineralization inhibits the effect of surfactants on the phase composition of coal samples. The findings of this research provide a theoretical basis for water injection of highly mineralized coal seams and methane replacement recovery by carbon dioxide technology, promoting the practical application of water injection and gas injection displacement of coal seams.