Sorption-induced swelling/shrinkage and permeability of coal under stressed adsorption/desorption conditions

This paper presents experimental investigations on CO2/CH4 binary gas flow in bulk coal under controllable stress conditions, focusing on sorption-induced swelling/shrinkage and gas permeability associated with CO2-sequestration enhanced coalbed methane (CO2-ECBM) recovery. The gas flush tests with carbon dioxide were conducted on a specially designed true tri-axial stress coal permeameter (TTSCP) using a large coal sample pre-adsorbed methane. These tests simulate the in-situ conditions of CO2-ECBM recovery from coal and provided experimental information for better understanding of the gas transport in coals. The swelling/shrinkage coefficients of coal associated with CO2-ECBM process have been evaluated using the experimental data. The results show that adsorption and desorption of gases CH4 and CO2 can significantly affect the volumetric change of micro- and macropores in coal, leading to coal swelling/shrinkage and fluctuation of permeability, and hence controlling the transport and flow of gases through coal.