Laws of changes in the energy of gas hydrate-bearing coals under different confining pressures and saturations

Gas hydration for the solidification of coal seams susceptible to outbursts is a novel technology used to prevent coal and gas outbursts by reducing gas pressure and enhancing coal strength. However, an unclear understanding of the failure characteristics and the energy dissipation law of gas hydrate-bearing coals under different confining pressures and saturations leads to the lack of a theoretical basis for the prevention of dynamic disasters such as field coal and gas outbursts in deep mines. Based on the deviatoric stress-strain curves obtained using triaxial compression tests, this study calculated and analyzed the laws of changes in energy of gas hydrate-bearing coals during triaxial compression under different confining pressures (12, 16, and 20 MPa) and saturations (20%, 50%, and 80%). The results are as follows: (1) The total energy, elastic energy, and dissipation energy of gas hydrate-bearing coals increased with an increase in the axial strain during triaxial compression. The external work was mainly converted into the elastic energy in the elastic stage and the early yield stage and was primarily converted into the dissipation energy in the late yield stage and the reinforcement stage. (2) In cases where the confining pressure increased from 12 MPa to 20 MPa and the saturation increased from 20% to 80%, the total energy at the critical failure point increased constantly, with increased amplitude of 120.30% and 81.60%, respectively. The energy storage limit and the dissipation energy at the critical failure point also increased with the confining pressure, with increased amplitude of 174.89% and 110.73%, respectively. Therefore, the gas hydrate-bearing coals were less likely to fail under a high confining pressure and saturation due to their enhanced abilities to absorb energy and resist deformations and failure, as well as elevated energy consumed by damage, compared to a low confining pressure. (3) The ratio of dissipated energy to elastic energy increased with the axial strain. Under saturations of 50% and 80%, the critical axial strain increased with the confining pressure, but its sensitivity to the confining pressure decreased with an increase in the saturation. (4) Under confining pressures of 16 MPa and 20 MPa, the energy storage limit increased with the energy storage coefficient. Both the energy storage coefficient and the energy storage limit exhibited comparable abilities to characterize gas hydrate-bearing coals’ storage capacity of elastic energy. (5) Hydrate formation in coals effectively reduced the gas pressure and enhanced the peak strength of coals, the total energy at the critical failure point, the energy storage limit, and the dissipation energy at the critical failure point, with the overall increased amplitude ranging between 21.11% and 42.11%. These are conducive to improving the coals’ ability to resist damage by external forces. The results of this study reveal the laws of changes in the energy of gas hydrate-bearing coals subjected to damage by external loads, serving as a theoretical guide for the prevention and control of dynamic disasters such as coal and gas outbursts in deep coal mines.