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

International Journal of Coal Geology
By: , and 

Links

Abstract

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.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Relationships between water and gas chemistry in mature coalbed methane reservoirs of the Black Warrior Basin
Series title International Journal of Coal Geology
DOI 10.1016/j.coal.2013.10.002
Volume 126
Year Published 2014
Language English
Publisher Elsevier
Contributing office(s) Eastern Energy Resources Science Center
Description 14 p.
First page 92
Last page 105
Country United States
State Alabama
Other Geospatial Black Warrior Basin