The grande dame of tight gas: long-established tight-gas plays still yield drilling opportunities in the gas-rich Appalachian Basin, while an emerging resource play offers intriguing new possibilities.(APPALACHIAN BASIN)

Publication: Oil and Gas Investor

Publication Date: 01-MAR-06

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COPYRIGHT 2006 Hart Publications, Inc.

The Appalachian Basin is the matriarch of the oil patch. More than a million wells have been drilled into its Paleozoic sediments, which have yielded more than 70 trillion cubic feet (Tcf) of gas equivalent. Despite its old-line pedigree, the Appalachians remain an essential player in the nation's gas supply and a home where independent operators can thrive because of favorable finding costs, sturdy rates of return and low-risk drilling.

The first commercial attempt to drill for natural gas was in 1821, when entrepreneur William Hart drilled a well to the depth of 70 feet in the Devonian Dunkirk Shale in Fredonia, New York. Gas discoveries followed in 1860 in Pennsylvania, 1861 in Ohio and 1863 in Kentucky.

In the decades since, through manifold booms and busts, people have been drilling wells in Appalachia, the largest onshore basin in the U.S. Today, more than 147,000 active wells are producing 680 billion cubic feet (Bcf) of gas a year.

While the Appalachian Basin spans an immense area with myriad geologic plays, tight-gas reservoirs are an integral part of its remaining resource base. From the top down, major tight-gas plays occur in Mississippian sandstones and carbonates in Ohio, West Virginia and Kentucky; Upper Devonian sandstones and shales in Pennsylvania, West Virginia and Kentucky; and Silurian sandstones in New York, Pennsylvania and Ohio.

Mississippian reservoirs

The youngest tight-gas reservoirs in Appalachia are found in the Mississippian section, divided among sandstones and carbonates.

A major Mississippian reservoir is Ohio and West Virginia's Berea sandstone. In the Buckeye State, more than 12,400 wells have been drilled into the Berea, which consists of shallow marine sands found at depths down to 6,000 feet....

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