Natural hydrocarbon gas seeps are surface expressions of petroleum seepage systems, where gas ascends through faults and conduits from pressurized reservoirs that are typically associated with sandstones or limestones. These rare natural gas seeps provide opportunities for direct sampling of gas from subsurface hydrocarbon accumulations without the need for drilling or other costly means of petroleum exploration. We have documented a site in the northern Appalachian Basin, at Chestnut Ridge County Park, New York, where gas seepage has supported a spectacular �eternal flame� throughout available recorded history, and which may have burnt naturally for many hundreds or even thousands of years. This remarkable flame marks a natural gas macroseep of dominantly thermogenic origin. Gas emanates directly from deep shale source rocks, probably the Rhinestreet Shale of the Upper Devonian West Falls Group, which makes this a rare case in contrast to most petroleum seepage systems where gas derives from conventional reservoirs. The main flaming seep releases about 1 kg of methane per day and seems to feature the highest ethane and propane concentration ever reported for a natural gas (~35 vol. %). The same gas is also released to the atmosphere from the ground through nearby invisible and diffuse seepages. The comparison of our chemical and stable isotope data with available gas-geochemical data of reservoir gases in the region and the stratigraphy of underlying shales suggests that the thermogenic gas originates from Upper Devonian shales without intermediation of a conventional reservoir.A burning seep near Clarington, Pennsylvania, also releases thermogenic gas, but may not represent a natural seep. Instead, the gas likely derives from a conventional reservoir in Venango sandstone (Devonian) and is transmitted to the surface through an abandoned and improperly sealed gas or oil well.

Origin of natural gas-fed �eternal flames� in the northern Appalachian Basin, USA

246th National Meeting (2013)

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