Experimental study on the outburst potential energy caused by added water under stepwise depressurization

The research on the mechanism of coal and gas outburst is still in the hypothesis stage, and exploration of the outburst mechanism fro m an energy perspective often focuses on the calculation of coal rock elastic energy and gas expansion energy. There are some studies on elastic energy and gas expansion energy of coal rock caused by added water during outburst, although hydr aulic measures not only improve the permeability of coal seam, but also increase the water content. For calculating the gas expansion energy, the atmospheric gas desorption characteristic is generally utilized, while the gas desorption is completed on the condition of dropping pressure in outburst, and the expansion energy research, based on that law, inevitably brings about errors, thus affecting the objectivity of the potential research. In this study, uniaxial cyclic loading experiments were carried out on briquette coal samples with water content of 0%, 1%, 2% and 4%, whose elastic energy density was analyzed, in addition to examining how the added water affected the mechanical properties and the elastic energy of coal. The pressure drop gradient of the experiment is set 2.5 –2 MPa, 1.5 –1 MPa, 0.5 MPa-0 Pa. By stepwise depressurization desorption of coal samples after water injection, the gas expansion energy in different moisture is measured in each pressure drop stage, and the influence of moisture on gas expansion energy is quantitatively explored. Research has shown that the higher the water content, the lower the elastic energy density, while the higher the stress, the greater the elastic energy of coal. The gas expansion energy grows linearly with the increase of adsorption equilibrium pressure and diminishes in negative exponential law with the increasing moisture. Under the experimental conditions, the expansion energy decreases by 7%–9% and the elastic energy by 9.7% on average for every 1% increase in added water, and the influence gradually weakens when the moisture exceeds the critical value. This study innovatively simulates the pressure swing desorption when a coal and gas outburst occurs in the laboratory, confirms the critical moisture that affects the outburst potential, and is a useful exploration in the coal and gas outburst mechanism. Significantly the research results can guide the engineering practice when using hydraulic measures to prevent and control outburst disasters. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.