GOLDSCHMID'/'CONFERENCE TOULOUSE 1998 Microbial production and modification of gases in sedimentary basins: constraints from isotopic compositions

Unconventional natural gas reservoirs, such as organic-rich shales and coalbeds, are gaining in economic significance worldwide. Many of these fields contain some portion of microbial methane, either enhancing or replacing thermogenic gas. Importantly, these microbes produce isotopic and compositional effects on the various gas components that often obfuscate their origin. An expanding data set for gases produced from Devonian black shales in the Michigan and Illinois basins, USA, has allowed for a detailed examination of the related chemical and isotopic compositional changes in gas-water systems that trace these processes. The Antrim Shale, within the northern margin of the Michigan Basin, has recently been shown t