Microscopic seepage mechanism of CO2-alkaline-water in coalbed and its influence on coal wettability

Abstract

The new developed technique, CO2-alkaline-water two-phase displacing gas and wetting coal (CADW), can obviously improve coal seam water injection effects. In this work, the microscopic seepage mechanism of CO2-alkaline-water in coalbed and its influence on coal wettability were investigated in detail. The results indicated that, the CADW measure could clearly increase coal wettability. After the CADW, the specific surface area of LS and ZX coals increased by 33.44%, 14.61% and the total pore volume increased by 121.60%, 19.48% respectively. Besides, the contact angle of two coals decreased by 25.30% and 6.62% severally. Further investigation showed that, the polar force increased evidently after using the CADW. As a result, the surface free energy of LS and ZX coals calculated by the Owens-Wendt method increased by 13.82% and 6.03%, that acquired by the Van Oss model increased by 10.26% and 6.32%, respectively. In addition, the CADW could obviously increase contents of hydrophilic groups in coal. The content of -OH in two coals increased by 20.09% and 32.10%, the CO density increased by 27.27% and 70.77% respectively. The results can provide valuable reference for preventing gas outburst risk and reducing mine dust concentration.