The Middle Devonian Marcellus shale in the US Appalachian basin contains 84 tcf of gas and 3.4 billion bbl of natural gas liquids, the US Geological Survey said Aug. 23.
The assessment, couched as undiscovered, technically recoverable hydrocarbons, is far above the 2 tcf and 10 million bbl the agency gave the formation in its 2002 assessment.
The USGS said the increase is due to new geologic information and engineering data on the unconventional play.
“Since the 1930s, almost every well drilled through the Marcellus found noticeable quantities of natural gas,” USGS said. “However, in late 2004, the Marcellus was recognized as a potential reservoir rock, instead of just a regional source rock, meaning that the gas could be produced from it instead of just being a source for the gas.”
USGS estimated that there is a 95% chance that the Marcellus holds at least 43 tcf of gas and a 5% possibility that it contains as much as 144.1 tcf. The mean is 84 tcf. There are no conventional petroleum resources assessed in the Marcellus shale.
The agency said the new estimates are for technically recoverable oil and gas resources, which are those quantities of oil and gas producible using available technology and industry practices, regardless of economic or accessibility considerations. As such, it said, the estimates include resources beneath both onshore and offshore areas such as Lake Erie and beneath areas where accessibility may be limited by policy and regulations imposed by land managers and regulatory agencies.
The assessment covered areas in Kentucky, Maryland, New York, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia. About 96% of the resource lies in the Interior Marcellus Assessment Unit, which extends from near Woodstock, NY, to Charleston, W.Va.
USGS worked with Pennsylvania, West Virginia, and Ohio geological surveys and representatives from the oil and gas industry and academia in developing the assessment.