Study on elimination of water blocking effect in coal seam and its influence on methane desorption characteristics

In order to study the effect of gas wettability reversal agent on alleviating the water blocking effect of coal seam and improving the gas desorption effect, the gas wettability reversal technology was used to change the wettability of coal body, and reduce the free energy of coal body surface, thereby improving the effect of gas drainage. The two kinds of gas wetting reversal agents were diluted with mass fractions of 0, 0.2%, 0.5%, 0.8%, 1% and 1.5% to prepare gas wetting reversal agent solutions with different concentrations and they were used for coal samples for processing. Firstly, the contact angle and surface tension of coal samples were measured by contact angle measuring instrument to verify the basic characteristics of two kinds of surfactants. Then, the desorption capacity and desorption rate of the dry/water-bearing coal samples were measured under different adsorption equilibrium pressure conditions, and the effect difference before and after treatment with the gas wetting reversal agent was compared. At the same time, the desorption formula was used to fit the desorption quantity, and the limit desorption quantity and fitting degree were obtained. The results show that with the increase of surfactant concentration, the surface contact angle of coal sample increases gradually and the surface tension of solution decreases gradually. When the concentration of gas wetting reversal agent reaches 0.5%, the wettability of coal surface changes from hydrophilicity to hydrophobicity, and the surface tension is low. The two kinds of surfactants have the characteristics of hydrophobicity and low surface tension, which are in line with the basic characteristics of the gas wetting reversal agent. In the dry and hydrous coal samples, the desorption capacity and desorption rate were improved within 1 hour after treatment with the gas wetting inversion agent, of which FC117 has a better and more significant effect. By fitting the desorption amount with the desorption formula, the obtained limit desorption amount is consistent with the variation law of desorption amount measured within 1 hour, and the fitting effect is better, and the fitting degree is basically above 0.98. Through the evaluation of desorption characteristics of coal samples before and after the treatment of gas wetting reversal agent, it provides a certain theoretical basis and science for the gas wetting inversion technology to eliminate the "water lock effect" of the coal seam, and improves the desorption characteristics of coal seam and increasing gas extraction effect.