Marcellus Shale

What is Marcellus Shale?

The Marcellus Shale forms the bottom or basal part of a thick sequence of Devonian age, sedimentary rocks in the Appalachian Basin. This sediment was deposited by an ancient river delta, the remains of which now form the Catskill Mountains in New York. The basin floor subsided under the weight of the sediment, resulting in a wedge-shaped deposit that is thicker in the east and thins to the west. The eastern, thicker part of the sediment wedge is composed of sandstone, siltstone, and shale, whereas the thinner sediments to the west consist of finer-grained, organic-rich black shale, interblended with organic-lean gray shale. The Marcellus Shale was deposited as an organic-rich mud across the Appalachian Basin before the influx of the majority of the younger Devonian sediments, and was buried beneath them.2

Where is it?

This formation underlies much of the Mid-Atlantic and Northeastern regions of the United States, including portions of New York, Pennsylvania, Ohio, Maryland, West Virginia and Virginia. The Marcellus Shale is a rock formation found at a depth of 5,000 to 8,000 feet.

How big is it?

The Marcellus Shale layer consists of little more than approximately 90,000 square miles (300 x 300 miles).

What does the Marcellus Shale offer?

It is believed to hold trillions of cubic feet of natural gas which have remained largely untapped to date due to the expense associated with extracting it. Recent advances in drilling technologies, including hydraulic fracturing, have made the Marcellus shale layer more accessible. This combined with the proximity of the shale layer to eastern energy markets has resulted in new interest in the formation. Natural gas, as we use it, is almost entirely methane. Natural gas as we find it underground, however, can come associated with a variety of other compounds and gases, as well as oil and water, which must be removed. Natural gas transported through pipelines must meet purity specifications to be allowed in, so most natural gas processing occurs near the well.

How much is there?

Estimates vary, but many geologists believe the Marcellus Shale formation could contain between 168 trillion to 516 trillion cubic feet of natural gas, though it is not currently known how much of this gas is recoverable. Some geologists believe that the gas stored in the Marcellus Shale formation could meet the energy needs of the entire United States for over twenty years. The annual average for natural gas usage in the United States is 23 tcf. If the infrastructure and use of natural gas increases we could see this annual average increase considerably. Currently at 516 tcf, (which some industry representatives say is low for recoverable gas) divided by 23 tcf annually then the expectation is that we will obtain about 23 years of natural gas usage.

Library & Links

Mountain Watershed Association – Visual Assessment Manual

PA DEP Marcellus Shale Face Sheet

Gas Well Information Links

Certified Water Testing Laboratories