More than 350 million years ago, much of Pennsylvania was covered by a large ocean. It's waters teemed with microscopic plankton, tiny plants
and animals that provided food for prehistoric fish and other creatures. As plankton sank to the sea floor, they were covered with sediment (sand
and soil) and began to decay. Compressed under the weight of the water and sediments above, the decaying plankton was transformed into natural gas,
filling the many cracks and fractures that naturally occurred in the shale rock.
The Marcellus Shale natural gas deposits are the remnants of this long forgotten ocean floor. Today, that shale formation lies in a 50 to 200 foot thick band that is between 4,500 and 8,000 feet (about 1 mile) beneath the surface of the land. The formation spans 95,000 sq. miles across parts of six states including: Pennsylvania, New York, West Virginia, and Maryland. (See map at right for full geographic extent.)
Which country has the largest natural gas reserves in the world? If you answered Iran, try again! The graph (right) shows that Russia tops the list
with 1,688 TCF (trillion cubic feet). The U.S. has the fifth largest reserves in the world with about 273 TCF in proven (recoverable) reserves.
Comparing natural gas reserves across geographic regions of the world (Figure 69., below right), North America (the U.S. and Canada) again has the fifth largest reserves of any geographic region in the world. While this sounds like a lot of gas, this represents only about 10% of the amount of natural gas lying beneath the Middle East!
As such, the Marcellus Shale has the potential to significantly decrease our reliance on natural gas imports from foreign countries long-term. Current estimates for the amount of natural gas in the Marcellus Shale range from 50 trillion to 500 trillion cubic feet (TCF) (Lash and Engelder, U.S. Dept of Energy Primer, USGS Water Resources fact sheet). Scientists estimate about 50% of the natural gas can be extracted using current drilling technologies. Considering that the U.S. uses an average of 25 TCF of natural gas in 2013, the Marcellus Shale alone could provide enough gas to supply residential, commercial, and industrial consumers for the next 10 to 20 years!
Although geologists have known about the Marcellus Shale natural gas deposit for more than 75 years, removing natural gas from the fractures in the Marcellus shale didn’t make sense until recently. Other sources of natural gas and oil (oil is a substitute for natural gas) were plentiful and could be delivered to consumers at relatively low prices. In contrast, the depth of the Marcellus deposit and the difficulties associated with extracting natural gas from shale made it very costly to deliver to U.S. markets. Rising market prices combined with the recent development of new drilling methods has made extracting gas from the Marcellus Shale more practical.