A geologic formation known as Marcellus Shale lies 300-6,000 feet underground and covers 95,000 square miles, running from the Southern Tier of New York, across Pennsylvania into Ohio and West Virginia. While the natural gas held deep underground in the Marcellus Shale has existed for millions of years, the technology to get it out of the ground economically was only developed within the past decade. This huge untapped reservior of natural gas represents tremendous opportunity for landowners and communities within the Twin Tiers.
What is shale?
Shale is a fine-grained sedimentary rock formed when quartz and clay minerals or mud are compacted by pressure over an extended period of time. Shale has a very compressed layer structure and such low permeability that it releases gas very slowly. It is rich in organic material and sufficiently brittle but rigid enough to maintain open fractures. Natural gas found in shale is held in natural fractures, pore spaces, and on the surface of the organic material. The gas in the fractures is produced immediately while the gas attached to organic material is released over time as the pressure in the shale decreases. Shale gas reservoirs in the United States may be hundreds of feet thick.
How is natural gas extracted from the shale?
After penetrating the shale, the rock must be hydraulically fractured, or "fraced", to maximize the production of natural gas from Marcellus Shale. A fracture stimulation fluid comprised of fresh water, sand, and additives is injected into the well under high pressure to enhance fractures in the rock and free more gas. These fractures start at the wellbore and extend as much as several feet into the reservoir rock.
Sand, a "propping agent", is pumped into the fractures to keep the rock from closing when the pumping pressure is released, allowing the natural gas to migrate from the rock pores to the surface wellbore. Along with the fresh water and sand, the fracture fluid contains three additives. A friction reducer, similar to cooking oil, which aids pumping and a bactericide, similar to Chlorine in a hot tub, that kills bacteria. These two additives respectively make up 0.5% and 0.025% of the total fluid composition. The fracture fluid also contains a 0.1% portion of a micro emulsion similar to those found in personal care products and cutting oils. This additive ensures coating of the formation and effective fracture fluid recovery.
