This presentation provides an updated analyses of the gas geochemistry for a five county study area in the Appalachian Basin in northeastern Pennsylvania. We evaluate >2,500 gas and water samples for molecular composition and stable isotope compositions of methane and ethane. The samples are from Quaternary- to Middle Devonian-age strata collected from >200 gas wells during Mudgas Logging programs and >75 private water supply wells during baseline groundwater-quality testing programs.

Evaluation of this database reveals that microbial, mixed microbial/thermogenic, and thermogenic gases occur in some shallow aquifer systems, and that the gas occurrences pre-date Marcellus Formation drilling activity. Isotope data reveal that thermogenic gases in the regional Quaternary/Upper Devonian shallow subsurface typically are distinct from gases in Middle Devonian strata. Gas Geochemistry at the site-specific level reveals a complex thermal and migration history.

Primary Author / Conference Presenter:
Fred Baldassare
Owner/Principal Geoscientist
ECHELON Applied Geochemicstry
Aspinwall, PA, USA

Mark McCaffrey, Geoscience Manager-Interpretive Services, Weatehrford Laboratories, Dallas, TX
John Harper, Retired Manager, Oil & Gas Division, PA Geological Survey