Thermogenic gases

Thermogenic gas is produced when organic matter is deeply buried and - as a consequence - temperature rises. Thereby, increasing temperatures modify the organic matter due to various chemical reactions, such as cracking and hydrogen diproportionation in the kerogen. bonds are preferentially broken... 

Figure 7.5 Plot of Ci/(C2 + C3) against isotopic composition of C to distinguish biogenic and thermogenic gas. (Reproduced from Claypool, G.E., Kvenvolden, K.A., Ann Rev Earth Planet. Sci., 11, 299 (1983). With permission.)...

October 19,1988), in addition to biogenic dominance in ocean hydrates (Dillon and Max, 2000), with sporadic mixtures of biogenic and thermogenic gas in Alaska, Russia, offshore Canada, and the Gulf of Mexico. It is possible to have both means (in place generation and fast fluxes) of supplying biogenic gas, indicated by Kvenvolden et al. (1984) and Kvenvolden and Claypool (1985) at DSDP Site 570 in the Middle America Trench. 

Even with the high concentrations of the near-surface hydrates, the deeper (>20 m) hydrate deposits contain most of the gas in the hydrated reservoir. This deeper hydrated gas is mostly biogenic, with anecdotal incidents of 10% thermogenic gas. 

Sassen, R., MacDonald, I.R., Thermogenic Gas Hydrates, Gulf of Mexico Continental Slope, in Pmc. 213th ACS National Meeting, San Francisco, CA, April 13-17, 42(2), 472 (1997b). 

Sassen R, Joye S, Sweet ST, DeFreitas DA, Milkov AV, MacDonald IR (1999) Thermogenic gas hydrates and hydrocarbon gases in complex chemosyn-thetic communities, Gulf of Mexico continental slope. Org Geochem 30 485-497... 

Thermogenic gas—Natural gas that is formed by the combined forces of high pressure and femperafure (bofh from deep burial within the Earth s crust), resulting in the natural cracking of fhe organic matter in the source rock matrix. 

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