THE MARCELLUS SHALE IN WEST VIRGINIA AND PENNSYLVANIA: GEOLOGY, RECENT DRILLING ACTIVITY AND GAS PRODUCTION

The Middle Devonian Marcellus Shale has long been recognized as a source of much of the gas which has been produced in the Appalachian Basin in the last 150 years. The introduction of new technology for drilling (horizontally) and completion (large volume slick water fracturing) which was developed in other shale basins (i.e. the Barnett in Texas) has led to new drilling and production focused in West Virginia and Pennsylvania.

The Marcellus thins to the south and west across WV and is not present in southwestern WV, where a regional unconformity results in younger and younger rocks overlying progressively older rocks. The Marcellus is less thermally mature in northwestern WV and southwestern PA, and significant quantities of liquid hydrocarbons, in addition to natural gas, are being produced in this part of the play. More than 3100 wells in WV and more than 5400 in PA have been permitted, targeting the Marcellus. Horizontal wells, which cost several million dollars to drill, have reported estimated ultimate recoveries of several billion cubic feet (Bcf) of gas. The potential resource has attracted large multinational exploration and production companies to acquire acreage positions within the Marcellus play in keeping with worldwide focus on shale and other unconventional reservoirs. In WV, more than 61 Bcf of gas has been reported as produced from the Marcellus from 2005-2009. From July 1, 2009 to June 30, 2010, almost 200 Bcf of gas was reported as produced from almost 1100 PA Marcellus wells.