What is Marcellus shale?
Marcellus shale is a sedimentary rock which has exposure in eastern North America. It is found in the Appalachian basin where black shale of Devonian period called Marcellus shale. The name Marcellus is from the nearby village named Marcellus, New York, United States. This formation is extended into much of the Appalachian basin. These shales were discovered to be the containing most abundant gas reserves which is estimated to be about 1.9 trillion cubic feet of gas. It is alot of gas reserves but is spread at large geographical area.
Stratigraphical position of Marcellus formation
Marcellus formation is the lowest unit of the Devonian age Hamilton group and is divided into several sub units. As it is shale so is dominant by black shales but it also has limestone interbedded and lighter shales which are the result of sea level variations at the time of its deposition.
Production of gas from Marcellus
Marcellus shales has production of gas which is in trillion cubic feet and many wells are drilled in this formation. These shales yields gas production which occurs not for a long time when its production is declined gradually but some wells sustained which produced for decades.
How gas can be produced more from Marcellus shales?
Marcellus shales as wells declines with time so new technology and techniques can help produce large amount of gas from Marcellus shales. A vertical well drilled in these shales will gradually decline the production so in order to a sustained well, Horizontal drilling and hydraulic fracturing technique should be used which in some new wells produced over a million cubic feet of gas per day.
Gas occurring in the Marcellus shalesGas in Marcellus shales occurs in three ways
- Within pore spaces of the shales.
- Within vertical fractures of the shales.
- Adsorbed on mineral grains.
Most recoverable gas is present in the pore spaces of the shales. Gas has difficulty in escaping the pores because of the tiny spaces and poorly interconnection of the pores. Therefore a vertical well in these shales would be expected to intersect few fractures within the shales therefore a horizontal drilling will intersect maximum number of fractures which in turn will produce maximum amount of gas from these shales.
Hydraulic fracturing is another technique that can be used in Marcellus shales to enhance the production. Hydraulic fracturing uses high pressure water or gel which is inserted in the formation and it fractures the formation. To remain the formation open after releasing the pressure of the water or gel, sands or other propant is induced into the formation which allows the fractures to remain open.