Abstract: In order to further understand the deformation mechanism of desorbed gas (coalbed methane) coal and to investigate the effects of pressure drawdown gradient and original reservoir pressure on the desorbed gas from coal (coalbed methane), desorbed gas (coalbed methane) coal deformation tests were performed using raw coal samples under different original reservoir pressures and pressure drawdown gradients. The results showed that the time required for desorption to reach equilibrium has a positive correlation with the original reservoir pressure and the pressure drawdown gradient. When the pressure is reduced to 0.3 MPa, the shrinkage strain decreases with an increase in the original reservoir pressure. When the pressure is reduced to atmospheric pressure, the variation in the shrinkage strain with the original reservoir pressure follows the trend that under 0.9 MPa it is higher than that under the 0.6 MPa, which is higher than that under 0.3 MPa. When the original reservoir pressure is the same, the shrinkage strain increases with an increase in the pressure drawdown gradient. When the original reservoir pressure is relatively small, the desorption capacity of the high pressure gradient reservoir is larger than that of the low pressure gradient reservoir.

Key words: reservoir pressure, pressure drawdown gradient, reservoir pressure, desorption, shrinkage deformation