NITROGEN IN WATER AND NATURAL GAS PRODUCED FROM COALBED METHANE RESERVOIRS IN THE BLACK WARRIOR BASIN, ALABAMA
Ammonium and ammonia concentrations correlate strongly and positively with chloride content (r = 0.92), indicating a significant association with basinal brine. Ammonium and ammonia probably originated were concentrated in brine early in the hydrodynamic history of the basin by ion exchange among silicate minerals, organic matter, and formation water. Nitrate is an important nutrient that apparently helped sustain microbial communities in coal. Nitrate is present in variable concentrations in brine and is effectively depleted within fresh-water plumes, which along with other geochemical variables, is interpreted to reflect intense microbial activity in fresh formation water.
Stable isotopes in mineral cements and produced natural gas indicate that thermogenic gas in the coal has been augmented by late-stage microbial gas. Nitrogen is the only significant impurity affecting the calorific value of the produced gas. Much of the nitrogen, particularly within fresh-water plumes, was probably derived from meteoric sources. In the interior of the basin, however, a significant quantity of the nitrogen appears to have been derived from thermal and microbial denitrification of the compounds in formation water.