Laboratory measurement and modelling of coal permeability with different gases adsorption

Adsorption of gas on coal will induce coal matrix swelling. Under reservoir conditions these strain changes affect the coal permeability. A series of laboratory measurements of gas permeability of a coal sample from Qinshui basin has been conducted, using a new apparatus developed for measuring coal permeability with various gases adsorption, by use of the transient pulse decay technique. Results show that permeability measured using CH4, N-2 and CO2 all decrease with increasing gas pressure under the constant effective stress condition. The permeability decrease shows some variations with gas species. Permeability measured by CO2, CH4 and N-2 decrease almost 91%, 70% and 32% respectively, from gas pressure of 0.5 MPa to 4 MPa. The experimental results are then modelled using the Robertson and Christiansen permeability model. Results show the agreement between the modelled results and the experimental results in the pressure range of the experiments, especially for CH4 and N-2.