Hydrocarbon gases associated with permafrost in the Mackenzie Delta, Northwest Territories, Canada

Molecular and isotopic analyses of core gas samples from 3 permafrost research core holes (92GSCTAGLU, 92GSCKUMAK, 92GSCUNIPKAT; sample core depths ranging from 0.36 to 413.82 m) in the Mackenzie Delta of the Northwest Territories of Canada reveal the presence of hydrocarbon gases from both microbial and thermogenic sources. Analyses of most headspace and blended gas samples from the ice-bonded permafrost portion of the core holes yielded C-1/(C-2 + C-3) hydrocarbon gas ratios and CH4-C isotopic compositions (delta(13)C CH4) indicative of microbially sourced CH4 gas. However, near the base of ice-bonded permafrost and into the underlying non-frozen stratigraphic section, an increase in ethane (C-2) concentrations, decreases in C-1/(C-2 + C-3) hydrocarbon gas ratios, and CH4-C isotopic (delta(13)C CH4) data indicate the presence of hydrocarbon gases derived from a thermogenic source. The thermogenic gas below permafrost in the Mackenzie Delta likely migrated from deeper hydrocarbon accumulations and/or directly from thermally mature hydrocarbon source rocks. (C) 1999 Elsevier Science Ltd. All rights reserved.