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The change of coal permeability related to gas pressure is important to coal mining and CBM exploitation.The permeability evolution of various kinds of coal is different and changes with stress conditions. To investigate the permeability evolution of coal samples changed in gas pressure, the strain and permeability of coal samples collected from the No.9 coal seam in Zhaogezhuang mine,Kailuan,China were measured during gas pressure reduction under constant temperature, axial and confining stress by using Triaxial servo-controlled seepage rig.The experimental results showed that coal shrinkage strain increased with the decrease of gas pressure.And the permeability of coal cores may increase gradually or decrease firstly and then increase( The gas pressure cor-responding to permeability rebound is less than 1.0 MPa).When the gas pressure reduced to 0.3 MPa,the perme-ability was 1.9-2.9 times of the initial condition( gas pressure was 2.0 MPa).Considering that coal axial and radial strains are approximately equal,a theoretical model was established to describe the permeability evolution of the three-dimensional deformation coal.The model also reflected the effects of gas pressure and gas desorption on coal permeability.The analysis showed that in the process of reducing gas pressure, the permeability of coal will change from decreasing to increasing at a certain gas pressure( rebound gas pressure pr). The equation of rebound gas pressure pr was derived.It indicated that prwas determined by coal volume modulus ,K, and Langmuir coefficients related to the adsorption, εpand pL.The greater volume modulus K and the adsorption deformation coefficient εpare, the higher pris.And prwas independent of the external stress and the internal gas pressure. According to the derived permeability model, the permeability curves and the rebound gas pressure pr of coal samples under various stresses and gas pressures were calculated by referring to the experimental data of this paper and other published articles. The numerical results were close to the experimental data with a maximum relative error less than 8.9%.The trend of coal permeability changing with gas pressure in the experiment depends on the rebound gas pressure prand the experimental gas pressure.When pr≥pmax( the maximum gas pressure in the experiment), coal permeability decreases with gas pressure increasing.When pr≤pmin( the minimum gas pressure value in the experiment), coal permeability increases with gas pressure.When pmin

Unminable coal beds have been recommended as good CO2 sequestration. Coal strain due to sorption/desorption of CO2 is an important issue on carbon dioxide sequestration. To investigate CO2 sorption/desorption induced coal strain，coal axial and radial strains under gas hydrostatic pressure were measured for nearly 600 hours by means of test system for sorption-induced strain.The coal samples were from No.9 coal seam in Zhaogezhuang Mine.The experimental results indicate that coal swells when adsorbing CO2，shrinks when desorbing CO2.The sorption/desorption process is very slow and it takes 12 hours or even longer for the sorption-induced strain to stabilize.The coal strain due to sorption/desorption CO2 is anisotropy. Coal samples have different levels of residual deformation after a cycle of sorption and desorption. When gas pressure is less than 1.5 MPa，coal residual volumetric strain undergoing a cycle of sorption and desorption is less than 0.6 × 10-3. It is reasonable to consider that the process of coal deformation induced by adsorption and desorption is reversible. The fitting results of coal adsorption/desorption experimental data show that Langmuir equation is suitable to describe coal adsorption/desorption strain variation with CO2 gas pressure. [ABSTRACT FROM AUTHOR]