Impacts of volumetric strain on CO2 sequestration in coals and enhanced CH4 recovery

Abstract

Sequestration of CO2 into deep, unminable coal seams is an attractive option to reduce atmospheric emissions. However, coal seams commonly have low initial permeability, and CO2 adsorption causes the coal matrix to swell, which further reduces the permeability and may result in inefficient injection. We investigate numerically the impacts of coal swelling on coal permeability and, thus, CO2 injection efficiency with constraints determined by experimental adsorption-associated volumetric strain measurements on three western Canadian coals. Our results show that injecting pure CO2 markedly reduces permeability through time to the extent that it is not a feasible sequestration technology for almost all coals. However, injection of a gas mixture of N2 and CO2 (flue gas) markedly improved CO2 injection efficiency while mildly reducing CO2 sequestration capacity. The study also suggests that different geological settings and mechanical properties of specific coal seams strongly control coal seam permeability during gas injection and, thus, viability of CO2 sequestration.