Big Sandy: Kentucky's Big Sandy Field remains a locus of exploration activity, more than 90 years after its discovery.(FIELD REJUVENATION)(NGas's production )

Publication: Oil and Gas Investor

Publication Date: 01-AUG-05

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COPYRIGHT 2005 Hart Publications, Inc.

Kentucky's Ohio Shale is far and away the Most prolific producer among the Upper Devonian shales that extend along the western margin of the Appalachian Basin. The main shale-gas area is 3,000-square-mile Big Sandy Field in Martin, Pike, Floyd, Knott and Perry counties.

Big Sandy, which sits on the eastern flank of the Cincinnati Arch, started as a bevy of separate shale-gas fields in several counties and eventually coalesced into one regional accumulation. Since its discovery in 1914, the field has produced 2.5 trillion cubic feet (Tcf) of gas from more than 10,000 wells.

The greater Big Sandy area, which extends into western West Virginia, features up to 500 net feet of kerogen-rich black shale at depths to 5,000 feet. According to the U.S. Geological Survey (USGS), the shale is thermally mature and contains total organic carbon between 2% to 3%. In Pike County, Kentucky, gas contents range from 60 to 100 standard cubic feet per ton, and the gas in place stands between 5--and 10 billion cubic feet (Bcf) per section.

In addition to hosting thick, mature shale, the Big Sandy area has a third element that is crucial to its productivity: it has a well-developed secondary porosity network. During several episodes of tectonic stress, joints and fractures developed within the shale, according to researchers. The Pine Mountain fault, which runs some 130 miles through eastern Kentucky from the West Virginia border to the Tennessee line, lies along the southeastern side of the gas accumulation. It is the most distal thrust of the Alleghanian orogeny, a major tectonic event that folded, faulted and thrust sediments westward during Pennsylvanian and Permian times. In eastern Kentucky, this activity intensely fractured the Devonian shales.

Furthermore, part of Big Sandy overlies the Rome Trough,...

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