Andrew R. Scott1
(1) Altuda Geological Consulting, Austin, TX
ABSTRACT: A New Energy Resource: Microbially Enhanced Gas Generation
Naturally-occurring secondary biogenic gases represent a significant fraction of coalbed methane and gas shale resources worldwide. Coal gases in the Powder River Basin are entirely secondary biogenic, whereas shale gases from the Antrim Shale in the Michigan Basin and coal gases in the San Juan Basin a contain a significant secondary biogenic component. An estimated 2 Tcf of secondary biogenic gases has already been produced from the San Juan Basin alone. If only one-hundredth of one percent (1/10,000) of U.S. coal resources were converted into methane through microbial processes, coal gas reserves would increase by 23 Tcf, or approximately 10 percent of current reserves.
Microbially stimulated gas generation imitates and enhances the natural process of secondary biogenic gas generation in coal beds and organic-rich shales that occur in basins worldwide. The process involves the introduction of nutrients, including carbon dioxide, and/or anaerobic bacterial consortia, consisting of hydrolyzers, acetogens and methanogens, into coal beds and organic-rich shales to stimulate gas generation and increase production. Benefits of the process include the generation of additional methane, removal of pore-plugging waxes in coal beds, and permeability enhancement. Limitations to the process may include access to the reservoir, removal of waste products, and gas generation rates. However, under appropriate conditions, bacteria are capable of generating significant quantities of methane over relatively short time periods in the subsurface. Biogenic gas generation from municipal waste sites and biogenic gas generation from coal cutting canisters are examples of real-time gas generation.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado