Implications for Investigations of Stray Gas Migration: Geochemistry of Natural Gases in Quaternary through Devonian Age Strata in the Northern Appalachian Basin

Presented on Tuesday, November 29, 2011

More than 2,000 gas samples were analyzed and evaluated for molecular and isotope geochemistry to determine gas origin, mixing, and thermal maturity. Samples were collected throughout the stratigraphic section from Quaternary to Middle Devonian deposits in northeastern Pennsylvania from mud gas samples during drilling of Marcellus formation gas wells, and during background groundwater water quality testing programs. Evaluation of our geochemical database reveals microbial, mixed microbial/thermogenic and thermogenic gases occur in some shallow aquifer systems that pre-date drilling activity in the Marcellus Formation. The data reveal a complex thermal history with distinct thermogenic gases, gas mixtures, and isotope reversals (ä13C1>ä13C2>ä13C3) throughout the stratigraphic section. Defining a specific source of stray natural gas migration requires the investigation and synthesis of different data types at a site specific level. Molecular and isotope geochemistry provides evidence of gas origin, and focus for investigations where pre-existing and multiple potential stray gas sources occur.

Fred Baldassare, P.G.
Echelon Applied Geoscience Consulting, Murrysville, PA
Fred Baldassare is Principal Geoscientist and owner of Echelon Applied Geosciences Consulting. He has more than 20 years of experience investigating incidents of stray gas migration. He previously served as the statewide consultant for the Pennsylvania Department of Environmental Protection for investigating and characterizing sources of stray carbon dioxide and methane. Baldassare helped pioneer the application and advancement of isotope geochemistry to identify the origin of stray and natural gases in the Appalachian Basin. He has authored and co-authored numerous professional papers for peer-reviewed publications on the application of isotope geochemistry.

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