Knowledge Bank

Increased unconventional hydrocarbon production in the United States and Canada piqued interest in natural gas development, while simultaneously raising concerns regarding changing groundwater quality following hydrocarbon extraction. Adequate characterization of baseline groundwater geochemistry preceded hydrocarbon production in many areas. This study, based in the relatively undeveloped St. Edouard region of Quebec, Canada, and the moderately developed McCully gas field of New Brunswick, Canada, attempts to characterize naturally occurring hydrocarbon geochemistry prior to unconventional energy development. Specifically, I focus on characterizing the composition and origins of hydrocarbons and salts in regional groundwater in these areas. Eighteen samples were collected (eleven from St. Edouard and seven from McCully) and analyzed for hydrocarbon concentrations and hydrocarbon stable isotopic composition, major gas concentrations, noble gas elemental abundance and isotopic concentrations, tritium concentrations and dissolved ion concentrations. The data suggests that hydrocarbons represent a mixture of thermogenic natural gas and biogenic methane likely formed by primary and secondary biogenesis; noble gas geochemistry supports these conclusions. The ionic composition of water is consistent with a diluted brine associated with the thermogenic hydrocarbon gases that also showed signs of post genetic alteration via hydrocarbon oxidation.