Penn Future - - Citizens for Pennsylvania's Future: Working to Protect Pennsylvania's Environment and Economy

History of drilling in Pennsylvania

Marcellus Shale is one of the largest natural gas fields in the U.S.

The Marcellus Shale is a geologic formation that lies 5,000 - 7,000 feet below most of Pennsylvania and stretches north and west of the Allegheny Front, which is roughly the western edge of the Appalacian Mountains. It continues north into New York, west into Ohio and south into West Virginia and contains one of the largest deposits of natural gas in the world.

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This map, adapted from a PA DEP graphic, shows the Pennsylvania location of the Marcellus shale formation.

In 2005, a drilling company confirmed that a well drilled in 2003 in Washington County, Pennsylvania used a relatively new drilling technique — hydrofracturing (or "hydraulic fracturing," or simply "fracking") — to cost-effectively produce commercially significant quantities of natural gas from the Marcellus Shale formation.

Geologists and drillers have known about natural gas in the Marcellus Shale for a long time.

However, until success with fracking technology, it wasn't economically feasible to drill for it. Now the Marcellus Shale is estimated to hold as much as 500 trillion cubic feet of natural gas. Between 10 and 20 percent of it — enough to meet the natural gas demand for the entire United States for three to seven years — is thought to be recoverable.

Although the Marcellus Shale formation is the current hot spot, natural gas is also trapped in a number of other deep shale formations that occur under Pennsylvania, including the Utica and Trenton/Black River shales. The horizontal drilling and hydrofracturing techniques used to extract gas from Marcellus Shale might make it economical for drillers to extract gas from these formations too. This could potentially bring large-scale gas production to most parts of the Commonwealth, with the exception of Philadelphia and its surrounding counties.

Drilling before Marcellus

Pennsylvania is popularly credited with the world's first commercially successful oil well, which was drilled by Colonel Edwin Drake near Titusville in 1859. Drake's success touched off the state's first oil rush and the Petroleum Age.

At least 350,000 oil and gas wells have been drilled in Pennsylvania since 1859 and at least 60,000 are currently operational, but Pennsylvania hasn't been considered a primary focus of the oil and gas industry for a long time. Recent successes drilling in the Marcellus Shale has drastically changed that situation.