Gases and microbes in oil shale

摘要

Methane, carbon dioxide and hydrogen sulfide occur dissolved in groundwater in the Colorado oil shale sequence, with important water quality and operational implications. The methane derives from oil shale kerogen, carbon dioxide arises from the dissolution of sodium bicarbonate, and sulfide is generated by sulfate reduction where the sulfate reaches the subsurface via faults. Methane release from the oil shale has been well quantified by the former US Bureau of Mines, and is less than is released from western coals. Carbon dioxide is present at high concentrations in groundwater in contact with salt beds, and can complicate drilling. Hydrogen sulfide is not widespread, but has been a drilling safety issue. The sulfate reduction has unusual geochemical impacts such as precipitation of carbonates, which has not been previously explained. The phenomenon of methane oxidation coupled with sulfate reduction is now well known in various anoxic seafloor environments, but is here shown to be also widespread in terrestrial groundwater instances where it has not been widely recognized, including salt domes and coal strata.