The Marcellus natural gas trend is a large geographic area of prolific shale gas extraction from the Marcellus Shale or Marcellus Formation, of Devonian age, in the eastern United States. The shale play encompasses 104,000 square miles and stretches across Pennsylvania and West Virginia, and into eastern Ohio and western New York. In 2012, it was the largest source of natural gas in the United States, and production was still growing rapidly in 2013. The natural gas is trapped in low-permeability shale, and requires the well completion method of hydraulic fracturing to allow the gas to flow to the well bore. The surge in drilling activity in the Marcellus Shale since 2008 has generated both economic benefits and considerable controversy.
Although before 2008 the Marcellus Shale was considered to have inconsequential natural gas potential, it is now believed to hold the largest volume of recoverable natural gas in the United States. In 2011, the U.S. Geological Survey estimated that the Marcellus Shale contained 42.954 to 144.145 trillion cubic feet (TCF) of undiscovered, technically recoverable natural gas; the USGS upgraded its estimate to 214 TCF in 2019. The speculated total volume of the Marcellus field is even greater; Chesapeake Energy places its estimate at 410 TCF of shale gas. In September 2012, the Marcellus Shale overtook the Haynesville Shale of northwest Louisiana as the leading producer of both shale gas and overall natural gas in the United States. In February 2014, Marcellus gas wells produced 14.0 billion cubic feet per day (BFCD), a 42 percent increase over the year previous, and comprising 21 percent of all the dry gas produced that month in the United States; this increased to 14.4 BCFD and 36% of all shale gas nationwide in 2015. By 2018, production had grown further from an average of 19.4 BCFD and reached more than 21 BCFD in December 2018. This increase in production, from the most productive basin in the U.S., has been a major contributor to the significant decline in price for natural gas but continued investment of production appears to be waning in the face of price weakness
Geological formation
The impervious limestone layers of the Onondaga directly below the Marcellus, and the Tully Limestone at the top of the Hamilton Group, have trapped valuable natural gas reserves in this formation. The gas is produced by thermogenic decomposition of organic materials in the sediments under the high temperature and pressure generated after the formation was buried deep below the surface of the earth. The rock holds most of the gas in the pore spaces of the shale, with vertical fractures or joints providing additional storage as well as pathways for the gas to flow; gas is also adsorbed on mineral grains, and the carbon in the shale.
Development history
The industry was long aware there was gas in the Marcellus, but it "occurred in pockets and flows that could not be sustained to make a well." Before 2000, some low production gas wells were completed to the Marcellus, but these had a low rate of return and a relatively long capital recovery period. There are wells in Tioga and Broome County, New York which are 50 years old or more.
From 1976 to 1992, the U.S. Department of Energy funded the Eastern Gas Shales Project, which studied many eastern shale formations. The project drilled and cored five wells in the Marcellus in Pennsylvania. The cores established that there were enormous amounts of gas in the Marcellus, and defined fracture directions that were used in later Marcellus well drilling. Although the great volumes of trapped gas found by the project in the Marcellus and other eastern shales created excitement, the project was less successful at finding ways to recover the gas economically during the low gas prices of the 1980s.
Range Resources drilled an unsuccessful well to the Oriskany Sandstone in 2003. Hoping to save some value by finding producible gas in the shallower formations in the wellbore, Range geologists noted that the Marcellus Formation had some of the same properties as the Barnett Shale of North Texas, which was a prolific source of gas. In late 2004 Range completed the well in the Marcellus, using hydraulic fracturing techniques developed for the Barnett, and started producing the well in 2005.