%0 Journal Article
%T Low-temperature gas from marine shales
%A Frank D Mango
%A Daniel M Jarvie
%J Geochemical Transactions
%D 2009
%I BioMed Central
%R 10.1186/1467-4866-10-3
%X The position that natural gas forms only at high temperatures over geologic time is based largely on pyrolysis experiments under oxic conditions and temperatures where low-temperature gas generation could be suppressed. Our results indicate two paths to gas, a high-temperature thermal path, and a low-temperature catalytic path proceeding 300ˇă below the thermal path. It redefines the time-temperature dimensions of gas habitats and opens the possibility of gas generation at subsurface temperatures previously thought impossible.The hydrocarbons in natural gases are believed to come from two sources, one biological ('biogenic gas'), and the other from thermal cracking, 'primary thermal gas' from kerogen cracking, and 'secondary thermal gas' from oil cracking [1,2]. Thermal cracking is a high-energy endothermic reaction that generates gas between 100 and 200ˇăC in the subsurface [2] and generally above 300ˇăC in the laboratory [3-13]. There are examples of gas deposits possibly generated at lower temperatures [14-19], and reports of gas generation over long periods of time at 100ˇăC [20], but we are aware of no reports of gas generation at temperatures substantially below 100ˇăC.We addressed the possible existence of a low-temperature path to gas catalyzed by low-valent transition metals (LVTM) [21-24]. Such a path could have escaped detection in the past because it was suppressed at high temperatures and the oxic conditions of pyrolysis [3-13]. Oxygen is a powerful poison of LVTM [25] and organometallic catalysts, like ordinary hydrocarbons, decompose at temperatures above 300ˇăC.Here we report anoxic experimental procedures in which some marine shales generate gas at extraordinarily low temperatures (50ˇăC). The gas differs in almost all respects from that generated at higher temperatures (> 300ˇăC) through thermal cracking and strongly suggests the existence of a second, low-energy catalytic path to natural gas.Under anoxic helium flow, most shales released between 1 and 1,0
%U http://www.geochemicaltransactions.com/content/10/1/3