Experimental study on effect of saturation on the permeability of gas hydrate bearing coal

Coal and gas outburst prevention technology based on the hydrate method can make gas hydration and reduce gas pressure. Previous study shows that the formation of gas hydrate can fill coal pores,improve coal strength and the mechanical properties of coal,which is supposed to reduce the risk of coal and gas outburst. The permeability of gas hydrate bearing coal is the key parameter to test the hydration and solidification effect of gas-hydrate-coal system. Using stress- seepage-hydration integrated triaxial testing machine, the authors carried out the coal permeability experiments under three meshes and three saturation conditions,and determined the permeability of gas bearing coal and gas hydrate bearing coal. Subsequently,the distribution modes of gas hydrate was discussed by referencing permeability models of hydrate porous media. The results show that under the influence of hydrate formation,the coal permeability decreases from 19.9% to 93%,in which the decreased permeability of 40-60 mesh coal samples with 60% saturation is the largest. With the increase of saturation,the gas permeability of 20-40 mesh and 40-60 mesh coal samples first decreases and then increases,while that of 60-80 mesh coal samples always shows an increasing trend. Comparing the test results with the permeability theoretical models,it is found that the distribution mode of gas hydrate is mainly cementing model,hydrate formation has obvious blocking effect on gas seepage channel in coal. This research work is expected to provide an experimental reference for gas hydration and solidification outburst prevention technology and its application.