Influence of wettability alteration on water-blocking effect and gas desorption of coal

Abstract

To resolve the water-blocking effect that reduces gas extraction after implementing hydraulic measures, alkyl polyglycoside (APG) and polyacrylamide (PAM) were used to treat coal samples to make wettability enhancement and medium wettability conversion, respectively. The contact angle, surface tension, solid surface energy, infrared spectroscopy, and high-pressure water injection desorption were performed to investigate the effects of reagents on the wettability alteration mechanism and desorption characteristics of coal. The results demonstrated that the surface energy, hydrogen bonds and oxygen-containing functional groups of coal alter wettability and gas desorption. The APG-treated coal samples exhibited increased surface energy, hydrogen bonds and oxygen-containing functional groups, whereas the PAM-treated coal samples demonstrated the opposite trend. The surface energy of coal reflects the state of APG and PAM molecules adsorbed on the coal surface, and the polar force of surface energy in coal follows a quadratic relationship with the volume of gas displacement desorption. Increasing the number of hydrogen bonds and oxygen-containing functional groups can improve wettability and decrease the interaction force between coal and methane molecules. This contributes to the lower atmospheric desorption of the APG-treated coal samples at high pressure. The total desorption volume of the APG-treated coal samples was 10–34% of that of the original coal at 0.737, 1.027, and 2.004 MPa gas pressures. The total desorption volume of PAM-treated samples at 2.004 MPa was 2.3474 cm3/g, which exceeded that of the original coal. Therefore, APG and PAM promoted gas desorption, and wettability enhancement yielded better results. This study provides an experimental approach for selecting the best reagent and excellent guidance for field applications.