EXAMINATION OF ORGANIC COMPOUNDS IN PRODUCED WATERS FROM COALBED METHANE WELLS IN THE POWDER RIVER BASIN, WY

Coalbed methane (CBM) is a significant energy resource, accounting for about 7.5\% of natural gas production in the USA. One aspect of concern in the exploitation of CBM resources is the large volumes of produced water recovered from wells along with the natural gas. CBM produced waters may contain inorganic and organic substances of environmental concern, representing a potential disposal problem for CBM producers. While a considerable body of information exists on inorganic constituents in produced water from CBM production, little information exists on organics. As part of a larger study of the health and environmental effects of organic compounds derived from coal, we analyzed produced water from 25 CBM wells covering a broad area of the Powder River Basin, WY for dissolved organic substances, and beginning in 2001. A number of wells sampled early in the study were resampled in later years. Produced water was collected directly from each well and filtered on site. Organic compounds were isolated from produced water samples by liquid/liquid extraction with methylene chloride and identified and quantified by gas chromatography/mass spectrometry (GC/MS).

Organic compounds identified by GC/MS in extracts of the produced water samples, included: phenols, biphenyls, N-, O-, and S-containing heterocyclic compounds, polycyclic aromatic hydrocarbons, phthalates, aliphatic hydrocarbons, and fatty acids. However, most compounds had structures unidentified by GC/MS databases. Many of the identified organic compounds (phenols, heterocyclic compounds, polycyclic aromatic hydrocarbons) are likely coal-derived. Concentrations of individual compounds ranged from about 10 to 0.01 µg/l. Some CBM wells with high concentrations of dissolved organic compounds present in 2001 had much lower concentrations in later sampling, indicating temporal variability. Some of the organic compounds identified in the produced water samples are toxic (mutagenic and cancer promoters), but are unlikely to have acute health effects at the low levels present. Chronic health and environmental effects from long periods of low-level exposure, however, are possible. Continuing studies will expand the existing dataset on dissolved organic compounds in produced water, and evaluate the toxic effects of these compounds.