Approximately 84 Tcf of undiscovered, technically recoverable natural gas and 3.4 billion bbl of undiscovered, technically recoverable natural gas liquids (NGL) are contained in the Marcellus Shale, according to a new assessment by the U.S. Geological Survey (USGS).

This latest USGS estimate which puts the Marcellus Shale on the map follows on one nearly ten years ago when shale gas was not even a blip on the horizon. Production and technological development in the intervening years has yielded geologic information and engineering data prompting USGS to significantly increase the estimate compared with its 2002 assessment, which indicated about 2 Tcf of gas and 10 million bbl of NGLs.

The assessment is an estimate of continuous gas and NGL accumulations in the Middle Devonian Marcellus Shale of the Appalachian Basin. The USGS estimates of technically recoverable oil and gas — quantities producible using currently available technology and industry practices regardless of economic or accessibility considerations — include oil and gas beneath both onshore and offshore areas (including Lake Erie) and beneath areas where accessibility may be limited by policy and regulations.

More than 81 Tcf (96%) of the estimated oil and gas resides within the Interior Marcellus, which is the central extent of the trend and west of the Appalachian Structural Front (ASF), USGS said. Another 2 Tcf is in the Western Margin Marcellus, which encompasses the western extent of the formation and is west of the ASF, and about 0.77 Tcf is in the Foldbelt Marcellus, which is east of the ASF, according to the report.

The USGS Marcellus Shale assessment was undertaken as part of a nationwide project assessing domestic petroleum basins using standardized methodology and protocol. USGS said it worked with the Pennsylvania Geological Survey, the West Virginia Geological and Economic Survey, the Ohio Geological Survey and representatives from the oil and gas industry and academia to develop an improved geologic understanding of the Marcellus.