Experimental study on gas-water relative permeability characteristics of broken coal and rock mass

In order to explore the relative permeability characteristics of gas-water in the crushed coal rock mass around the drilling hole of gas extraction, the gas-water coupling permeation test system of the crushed rock mass was used to carry out the gas-water coupling permeation test by using the steady-state osmosis method, and the variation characteristics of the coal sample permeability parameters with osmotic pressure and axial pressure were obtained, and the interaction relationship between the permeation parameters was analyzed. The results show that the porosity of the crushed coal mass under pressure shows a rapid decline, a slow decline and stabilization with the increase of axial pressure. With the increase of water saturation, the relative permeability of coal-like gases decreases rapidly, the relative permeability of water increases linearly, the relative permeability of gases and water shows a competitive relationship, and the sensitivity of gas permeability to water saturation is higher. The total permeability of gas and water decreases with the increase of the effective force, obeying the exponential function relationship, the effective force will affect the deformation process of the pore structure of the crushed coal rock mass, and with the decrease of porosity, the effective permeability of the gas decreases and the relative permeability increases. The influence of osmotic pressure on the relative permeability of water and gas can be divided into gas dominant stage, isotonic stage and water dominant stage, and the critical osmotic pressure extraction value ranges from 0.4 MPa to 0.6 MPa.