CHARACTERIZATION OF HYDROGEOCHEMISTRY AND COAL-ASSOCIATED BACTERIAL POPULATIONS FROM A METHANOGENIC COAL BED: IDENTIFICATION OF POTENTIAL BIOSURFACTANT PRODUCTION

Coalbed methane (CBM), a source of natural gas trapped within coal beds, has emerged as an important energy resource in many countries. Anaerobic coal degradation has been identified as the rate-limiting step of biogenic CBM formation, however specific bacterial populations and enzymes involved in degradation are relatively unknown. The U.S. Geological Survey has established a field site, (MT-2), in an undeveloped area of the Powder River Basin (PRB), with four wells completed in the Flowers-Goodale coal bed, one in the overlying sandstone formation and four in over- and underlying coal beds (Knoblach, Nance, and Terret). The wells were positioned to characterize the hydraulic conductivity of the Flowers-Goodale coal bed and were selectively cored to investigate the hydrogeochemistry and microbiology associated with CBM production at MT-2.

Aquifer-test results indicated the Flowers-Goodale coal bed, from 112-120m, has a very low hydraulic conductivity (0.6 cm/d) compared to other PRB coal beds. Consistent with microbial methanogenesis, groundwater in the coal bed and overlying sandstone contain dissolved methane (46 mg/L average) with low d¹³C values (-67‰ average), high alkalinity values (22 meq/kg average) with relatively positive d¹³C-DIC values (4‰ average), and no detectable higher chain hydrocarbons, NO₃ or SO₄. Bioassay methane production was greatest at the upper interface of the Flowers-Goodale coal bed near the overlying sandstone. Pyrotag analysis identified Aeribacillus as a dominant in situ bacterial community member near the sandstone and statistical analysis indicated Actinobacteria were more abundant in coal core samples than in claystone or sandstone cores. These bacteria, which have previously been correlated with hydrocarbon-containing environments such as oil reservoirs, have demonstrated the ability to produce biosurfactants to break down hydrocarbons. Our research provides evidence implicating the importance of biosurfactants in coal degradation and CBM production, suggesting the addition of nutrients that enhance in situ biosurfactant production could increase bacterial coal degradation, the rate-limiting step of microbial CBM production.