The Marcellus Shale is a natural gas-bearing rock found beneath the surface of the Earth in parts of Pennsylvania, Ohio, West Virginia, and New York. It was deposited in a shallow sea that covered these states nearly 400 million years ago.
Shale is a type of sedimentary rock formed from very tiny, flat grains packed together like decks of cards
strewn across a table. Grains found in the Marcellus Shale accumulated together as muds–along with a large
quantity of organic material–in the shallow sea. Some of the organic material trapped in the mud has matured (changed chemically with heat and pressure) into natural gas. The natural gas now present in the Marcellus Shale remains mostly trappedbetween the grains and in natural fractures already present in the shale. Economically extracting the natural gas tightly trapped by the shale grains requires a process called hydraulic fracturing. There are various
types of hydraulic fracturing technology, but all hydraulic fracture jobs aim to create or extend a network of
joints, or fractures, in the shale that allows the trapped natural gas to flow into a natural gas well.