Water blocking effect caused by the use of hydraulic methods for permeability enhancement in coal seams and methods for its removal

To research techniques for removing the water blocking effect caused by hydraulic applications in coal seams, the use of surfactants is proposed, based on the mechanics of the water blocking effect. Centrifugal experiments were used to validate the effects of using surfactants; the results show that after dealing with vacuum saturation with water, the volume of micropores decreases, which results in a larger average pore size, and the volume of transitional pores, mesopores, macropores and total pores increases. Based on the distribution of pore size, the operation mode of “water infusion after gas extraction, then continuing gas extraction” is recommended to improve the volume of coal mine gas drainage. When the reflectance of vitrinite in coal samples is less than 1, using the surfactants Fast T, 1631, APG, BS can mitigate the damage caused by the water blocking effect. But when the reflectance of vitrinite is larger than 1.4, the damage caused by the water blocking effect can be increased. When the surfactant CMC is used in hydraulic applications, the capillary forces of coal samples are almost negative, which means the capillary force is in the same direction as the gas extraction. The direction of capillary forces benefits the gas flow. So, using CMC can play an active role in removing the water blocking effect. Centrifugal experiments confirm that using CMC can effectively remove the water blocking effect, which has a beneficial effect on improving the gas drainage volume.