Study on gas-water two-phase flow coupling model and gas drainage simulation

In view of the problem that water in coal seam is mostly ignored in the simulation of gas drainage at present, a fluid-solid coupling model of gas drainage considering gas-water two-phase flow was established.On the basis of gas single-phase interaction, the stress field equation and seepage field equation were deduced by considering the influence of coal seam water seepage and pore water pressure, and the dynamic evolution model of permeability was established as the coupling equation, based on this, the law of gas-water migration was analyzed.The results show that considering the gas-water two-phase flow, the gas production rate has a peak point; the gas drainage amount will be overestimated if the influence of water is not considered; the farther away from the borehole, the more obvious the inhibition effect of water on gas migration, and the inhibition effect is greater than the promotion effect brought by the decrease of effective stress and the increase of permeability of coal; the initial permeability of coal seam plays a decisive role in gas drainage; the higher the temperature of coal seam, the more difficult it is to reduce the gas pressure, and the effect of gas desorption caused by temperature increase is greater than the adsorptive strain effect of coal seam itself.