Environmental assessment of underground coal gasification in deep-buried seams

This study presents a preliminary assessment of the environmental impact of field-scale underground coal gasification (UCG) targeting deep-buried seams by studying the fate of the UCG products in the reactor vicinity. A series of simulation scenarios are conducted in three deep (900 m) areas of specific interest – namely, South Wales coalfield (UK), Upper Silesian coal basin (Poland) and Ruhr mining district (Germany) – to investigate the transport of gaseous and dissolved chemicals. The results indicate that the syngas propagation is limited to 2.0 m in the vicinity of the reactor after 30 days, except that it is limited to 4.4 m in shale (overburden) of the UK site. Transport of the dissolved chemicals, through diffusion, is limited to 2.0 m without considering adsorption and less than 0.5 m when adsorption is considered after 10 years. Moreover, the effects of hydrology condition, stratum adsorption properties and the thermally induced change in rock porosity and permeability on the propagation of UCG products are studied. The results suggest that unacceptable risks to the environment are unlikely to arise if standard operating conditions are applied, offering a great prospect of deep coal seams to be considered for UCG. This study also provides insights into the environmental evaluation for other potential UCG projects.