Laboratory studies of coal permeability under conditions corresponding to in situ, in terms of assessing the possibility of underground CO2 storage with CH4 recovery

Investigations of processes accompanying the exchange sorption of CO2/CH4 under confining pressure in the range of 1.5 MPa to 30 MPa have been carried out. The research was carried out on innovative apparatus for testing filtration, sorption and CO2/CH4 exchange sorption processes under isobaric conditions on sorbent subjected to confining pressure. This apparatus enables the analysis of occurring phenomena both in time and space of the tested sample. The effect of confining pressure on the kinetics of sorption processes and on the permeability of the coal material was investigated. The effect of swelling of the coal material during sorption processes was also investigated, with particular emphasis on the effects of this process on gas transport. The investigations were carried out under stationary confining pressure conditions, during which the He and CO2 flow rates were determined for various pressure gradients, and under dynamic conditions, where the confining pressure changed linearly in the range of 30-1.5 MPa with very rate (about 5 MPa per 24h), at constant gas pressure gradients. For the studied material, the permeabilities in relation to CO2 and He were in the range 5-200 mD. The decrease in permeability for a change in the confining pressure of 30-1.5 MPa was about tenfold.