Distinction of bacterial and thermogenic hydrocarbon gases

Carbon and hydrogen isotope ratios of methane, carbon dioxide and water allow to identify bacterial methane gases. These data and related fractionation ratios differentiate the generation reactions like CO2 reduction and acetate fermentation. Bacterial methane consumption can be identified, preventing mis-interpretation of isotope data. Thermal gases are also characterized by their carbon isotope ratios (CH4 through C3H8). Bacterial and thermal gases are often present as mixed gases. Examples are given, in which the data of mixing partners as well as the mixing proportions are calculated. (author) 25 refs., 9 figs., 2 tabs