Feasibility of carbon dioxide storage in post-burn underground coal gasification cavities

•A realistic post-burn underground coal gasification cavity model is constructed.•Various char walls and rubble floor with different CO2 adsorption capacity.•Coal swelling effect due to CO2 adsorption on the plume confinement is studied.•CO2 transport under various effects is examined. Supplementary to the prospect of carbon storage in the geological formations for carbon emission mitigation, the deep post-burn underground coal gasification (UCG) cavities are proposed to be good venues for carbon dioxide storage, albeit without substantial validation in any form. Using a modelling methodology, this paper intends to bridge that knowledge gap by exploring the feasibility of storing CO2 in the post-UCG venues. A 3D post-burn UCG cavity model was constructed taking into account of the various char walls and rubble floor. To better utilize the subsurface space, the migration of CO2 in a supercritical state was modelled for a span of 10,000 days. The modelling results show that it is possible to inject CO2 into UCG cavities for storage. Insight was achieved concerning the transport pattern of CO2 plume in the UCG cavity under various effects, e.g. CO2 buoyant flow, diffusion and adsorption are coupling behaviours, and coal adsorption and swelling have a complex effect on CO2 transport.