Skip to main content
U.S. flag

An official website of the United States government

Relationships between water and gas chemistry in mature coalbed methane reservoirs of the Black Warrior Basin

June 1, 2014

Water and gas chemistry in coalbed methane reservoirs of the Black Warrior Basin reflects a complex interplay among burial processes, basin hydrodynamics, thermogenesis, and late-stage microbial methanogenesis. These factors are all important considerations for developing production and water management strategies. Produced water ranges from nearly potable sodium-bicarbonate water to hypersaline sodium-chloride brine. The hydrodynamic framework of the basin is dominated by structurally controlled fresh-water plumes that formed by meteoric recharge along the southeastern margin of the basin. The produced water contains significant quantities of hydrocarbons and nitrogen compounds, and the produced gas appears to be of mixed thermogenic-biogenic origin.

Late-stage microbial methanogenesis began following unroofing of the basin, and stable isotopes in the produced gas and in mineral cements indicate that late-stage methanogenesis occurred along a CO2-reduction metabolic pathway. Hydrocarbons, as well as small amounts of nitrate in the formation water, probably helped nourish the microbial consortia, which were apparently active in fresh to hypersaline water. The produced water contains NH4+ and NH3, which correlate strongly with brine concentration and are interpreted to be derived from silicate minerals. Denitrification reactions may have generated some N2, which is the only major impurity in the coalbed gas. Carbon dioxide is a minor component of the produced gas, but significant quantities are dissolved in the formation water. Degradation of organic compounds, augmented by deionization of NH4+, may have been the principal sources of hydrogen facilitating late-stage CO2 reduction.

Publication Year 2014
Title Relationships between water and gas chemistry in mature coalbed methane reservoirs of the Black Warrior Basin
DOI 10.1016/j.coal.2013.10.002
Authors Jack C. Pashin, Marcella R. McIntyre-Redden, Steven D. Mann, David C. Kopaska-Merkel, Matthew S. Varonka, William H. Orem
Publication Type Article
Publication Subtype Journal Article
Series Title International Journal of Coal Geology
Index ID 70186889
Record Source USGS Publications Warehouse
USGS Organization Eastern Energy Resources Science Center