Marcellus Assessment

WASHINGTON–The Marcellus Shale and Point Pleasant-Utica Shale formations of the Appalachian Basin contain an estimated mean of 214 trillion cubic feet of undiscovered, technically recoverable continuous resources of natural gas, indicate new assessments by the U.S. Geological Survey.

The Middle Devonian Marcellus Shale formation of the Appalachian Basin contains an estimated mean of 96.5 trillion cubic feet of undiscovered, technically recoverable continuous (or unconventional) resources of natural gas, while the basin’s Upper Ordovician Point Pleasant Formation and Utica Shale hold 1.8 billion barrels of oil and 117.2 Tcf of gas, USGS says in an Oct. 3. release.

The assessed area of the Middle Devonian comprises parts of Kentucky, Maryland, New York, Ohio, Pennsylvania, Tennessee, Virginia and West Virginia, while the Upper Ordovician lies in parts of Maryland, New York, Ohio, Pennsylvania, Virginia and West Virginia.

In 2011, the USGS estimated a mean of 84 Tcf of natural gas in the Marcellus Shale, and in 2012, it estimated the Utica Shale held 38 Tcf. The survey explains the gas in the formations is classified as continuous because it is spread through the assessed rock layers instead of being concentrated in discrete accumulations. Production techniques such as directional drilling and hydraulic fracturing are used to produce these resources, it says.

The survey adds its Middle Devonian assessment estimates the Marcellus also contains 1.5 billion barrels of natural gas liquids, while the Point Pleasant-Utica Shale holds 1.8 billion barrels of oil and 985 million barrels of NGLs.

“Since our assessments in 2011 and 2012, industry has improved its development techniques for continuous resources like the shale gas in the Appalachian Basin,” says Walter Guidroz, program coordinator for the USGS Energy Resources Program. “That technological advancement, plus all of the geological information we have gained from the past several years of production, have allowed us to expand our understanding of these formations.”

The latest assessment is based on the geologic elements of the Devonian Shale-Middle and Upper Paleozoic Total Petroleum System (TPS), USGS says, and includes hydrocarbon source rocks, reservoir rock types and reservoir traps and seals. The assessed Marcellus Shale primarily is organic-rich marine mudrock, and contained petroleum resources are self-sourced based mostly on levels of thermal maturation in petroleum productive areas, the survey describes.

Using this geologic framework, USGS says it defined and quantitively estimated undiscovered, technically recoverable gas and natural gas liquids resources for six continuous assessment units (AUs).

Current productive wells for the Middle Devonian/Geneseo Shale member of the Genesee Formation and Burket Shale produce gas and NGLs from less than 100 wells in the Appalachian Basin, USGS notes, adding those wells closely overlie the Marcellus Shale. Primarily for those reasons, the survey says the Geneseo and Burket Shales were not assessed separately but are included as a minor part of Marcellus Shale resources.

According to the assessment, the extent of potential Marcellus Shale resources is based mainly on depths to the base of the mudrock of greater than 1,000 feet, a vitrinite reflectance equivalent of 0.5% and greater, and 25 feet and greater thickness of organic-rich and brittle lithofacies.

Upper Ordovician

The USGS assessment of the Upper Ordovician Point Pleasant Formation included its correlative units, the Antes Shale and Indian Castle member of the Utica Shale. According to the survey, the strata containing oil-prone Type II kerogen are preserved within the Upper Ordovician Point Pleasant Formation, Utica Shale and correlative units.

The assessed Upper Ordovician strata primarily consists of organic-rich mudstones, calcareous shales and argillaceous limestones deposited in a marine environment. USGS notes thermal maturation in hydrocarbon productive areas indicates that the hydrocarbon resources are self-sourced.

Using this geologic framework, USGS says it defined five continuous AUs within the Ordovician Point Pleasant/Utica-Lower Paleozoic TPS and quantitatively estimated undiscovered, technically recoverable oil, gas and NGLs for two of them. The survey reports the Point Pleasant-Utica Foldbelt Gas AU, Logana Shale Oil AU and Logana Shale Gas AU were not assessed because of insufficient evidence of movable oil or gas in those shale.

“Watching our estimates for the Marcellus rise from 2 trillion to 84 trillion to 97 trillion in under 20 years demonstrates the effects American ingenuity and new technology can have. Knowing where these resources are located and how much exists is crucial to ensuring our nation’s energy independence,” says USGS Director Jim Reilly.