Now researchers at the University of Michigan and Amherst College are reading chemical signatures of water in those areas to pinpoint places where gas is most likely to be found. Their most recent work is described in a paper published in the May/June issue of the Geological Society of America Bulletin.
Natural gas forms when organic materials trapped in sediments decompose. This can happen when the materials are exposed to high temperatures, producing thermogenic gas, or when bacteria break down the organic matter and, through the process of methanogenesis, produce microbial gas.
Finding and exploiting microbial gas deposits, which account for as much as 20 percent of the world's natural gas resources, is "becoming more and more important," said U-M doctoral student Jennifer McIntosh, lead author of the paper. "And if you're exploring for microbial gas, you need to know what areas have been affected by methanogenesis, because that's how the microbial gas is produced."
McIntosh and coauthors Lynn Walter, U-M professor of geological sciences, and Anna Martini, assistant professor of geology at Amherst College, studied Antrim Shale deposits in the Michigan Basin, a deep depression filled with sediments that date back to the Paleozoic Era. While thermogenic gas forms far below the surface in the centers of such depressions, microbial gas is produced along the shallow edges. In previous work, the researchers showed that freshwater seeping into basin edges from melting ice sheets made it possible for methanogenesis to occur. "The fluids in the Michigan basin are some of the most saline fluids in the world," McIntosh said. "When freshwater penetrated into these basin margins, it suppressed the salinity and created an environment that was conducive to methanogenesis
Contact: Nancy Ross Flanigan
University of Michigan