Renewable Natural Gas? The Discovery of Active Methane Biogenesis in Coalbeds
16 November 2004
Researchers at Luca Technologies, a biotech firm focused on energy solutions, have announced the discovery of evidence pointing to ongoing, realtime natural gas generation by anaerobic (living without oxygen) bacteria resident deep in coal fields in Wyoming.
Methane (natural gas), while frequently developed with petroleum, also occurs in association with coal. Coalbed methane accounts for about 7.5% of current US natural gas production. Until recently, methane was thought to be thermogenic: derived from long-buried carbonaceous materials subjected to intense heat and pressures over geologic time. Additional work then determined that some percentage of the methane was biogenic in origin: created by ancient microbes that metabolized other hydrocarbon sources to generate methane. Most of this was thought to have occurred millions of years ago, when the hydrocarbon deposits were less mature and closer to the surface of the earth.
Luca researchers picked up on more recent research suggesting that living methanogenic organisms may be present and actively forming methane within some major coalfields. Luca has since confirmed the presence of such microbes within anaerobic core samples from its target coalfield (Powder River Basin). In addition to demonstrating that methane production by these microbes can be stimulated by the introduction of additional nutrient compounds, or suppressed by heat sterilization or the introduction of oxygen, Luca has shown that radio-labeled CO2 (carbon dioxide) introduced to the core samples is converted to radio-labeled methane, thus demonstrating that the methane formation is the result of a biological process occurring today.
According to Luca, the biogenic creation of methane from a higher molecular weight hydrocarbon source is a multi-step process, most likely accomplished by a consortium of anaerobic microbes acting together in a symbiotic fashion. Through a series of steps, various organisms in the consortium breakdown the large hydrocarbon molecules in coal or oil into intermediate, water-soluble compounds, which are then reduced to even smaller hydrocarbon molecules, and finally metabolized into methane by a group of organisms known as methanogens.
Luca has termed these areas where biogenic methane formation occurs Geobioreactors.
There’s an interesting twist to this. In order for a Geobioreactor to function, according to Luca, the appropriate environmental conditions must be present, including an abundant hydrocarbon substrate (such as a coal bed), a water-saturated environment, a complete absence of free oxygen (the microbes are anaerobes), and the presence of the correct consortia of organisms.
However, conventional techniques for extracting existing coalbed methane involve pumping groundwater out of the coal beds to enable recovery of the gas sequestered within them. An unforeseen consequence of this pumping is the influx of air, which contains abundant free oxygen that is toxic to the methane-producing microorganisms. The practice also removes water, damaging the microorganisms. In other words—assuming Luca’s scenario is correct—the extraction of coalbed methane destroys the mechanism for producing more methane.
There is much to do to confirm and to leverage this discovery. Luca is working to engineer methods for optimizing the natural gas-producing activity of natural Geobioreactors it identifies, as well as methods of turning other energy resources—such as oil wells that are no longer actively producing—into efficiently functioning Geobioreactors.
Background Paper: Active Biogenesis of Methane in Wyoming’s Powder River Basin
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