The Middle Devonian Hamilton Group Shales in the Northern Appalachian Basin: Production and Potential
John P. Martin, New York State Energy Research and Development Authority, 17 Columbia Circle, Albany, NY 12203-6399
The rocks of the Hamilton Group are the oldest strata of the Devonian gas shale sequence. The black and gray shale found in the Hamilton Group mark the first terrigenous sediment deposited by the erosion of the Acadian Mountains. The group overlies the Onondaga Limestone, and consists of black and dark gray shales in the lower part, and limestone, light gray shale and mudstone in the upper part. The Hamilton Group outcrops in New York State along the northern and eastern margins of the Allegheny Plateau. The group thickens from 250 feet near Lake Erie to over 2,500 feet in Ulster and Green counties. Formation depths range from outcrop to 8,000 feet in Sullivan County (southeastern New York). The Hamilton has been subdivided into four units: the Marcellus, Skaneateles, Ludlowville, and Moscow. The basal unit of the Hamilton is the Marcellus Shale, the primary exploration target. As the lowest most unit, the Marcellus formation is regionally extensive, covering most of the northern Appalachian Basin.
Measured total organic content of the Marcellus Formation ranges from less than 1% to over 11%. Thermal maturity is geographically-controlled. In the eastern reaches of New York and Pennsylvania, these shales are in the dry gas window. To the west, the shale is more likely in the oil window. Kerogen has been measured as either Type II or Type III.
Since 1900, fewer than 100 Hamilton shale wells have been drilled in New York State. Recently, a flurry of test wells has been permitted in the area surrounding Watkins Glen. These new wells show promise and the application of new methods may make the Hamilton Group the next big shale play.