Marcellus shale
From Wikimarcellus
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The Marcellus shale formation is a marine sedimentary layer of black shale rock found deep underground in an area stretching roughly 600 miles from southwestern New York to West Virginia and includes parts of Maryland, Kentucky, Ohio and Virginia. The thickest portion of the formation is located in Pennsylvania. It is named for an outcropping near Marcellus, N.Y. The gas is found in pores in the rock formation so tight that gas is released very slowly or the gas tightly adheres to the rock. Both conditions may be true.
It has been known for decades that this layer contained gas, but until recently it was not believed economical to extract. Recent improvements in technology such as horizontal drilling and hydraulic fracturing of the shale have changed the economics somewhat. When these developments are combined with recent comparatively high prices of natural gas, it makes the endeavor profitable for all of the participants.
Recent estimates indicate that there are 50 trillion cubic feet of recoverable natural gas in the Marcellus shale. This is twice the amount consumed during 2007 in the U.S.
In some areas of the formation, natural gas fractions are also present auch as butane, ethane, and propane.
Pennsylvania has around one half of the proven U.S. natural gas reserves. The proximity of most of the deposits to the natural gas consuming cities of the east coast make the Marcellus an especially attractive target for exploration.
The Marcellus shale formation is usually found at a depth of 5,000 to 8,000 feet, but can run as deep as 9,000 feet.
The production of a typical shale gas well drops off significantly after the initial year or two and then slowly declines after that over its full lifetime.
In the industry, it is known as an “unconventional deposit.”
One method of prospecting for gas, not only in shale formations but also for gas found within deeper structures below, is to use seismic waves to map out the underground location of deposits.