The Marcellus Shale, one of more than twenty natural gas shale deposits in the United States, is the largest on-shore natural gas reserve in the world. This shale rock formation lies a mile or more underneath several states in the Northeastern United States, including parts of Pennsylvania, Ohio, New York, and West Virginia.
Unconventional oil and gas development (UOGD, which is commonly called “fracking”) is the process by which energy companies extract oil and natural gas from these shale deposits and deliver it to consumers. While companies have been extracting oil and gas from underground for many years, today’s process is called unconventional because it uses newer methods like horizontal drilling and hydraulic fracturing to reach previously inaccessible resources trapped in deep shale rock formations.
STAGES OF UOGD PROCESS
The complex process used to reach this trapped oil and gas includes many different stages that take place over a period of years.
- Initial exploration: Energy companies search for underground reservoirs of oil or natural gas using mapping, geological clues, seismic testing, and other methods. This process can take weeks to months.
- Leasing and permitting: After an energy company determines that a locality has enough resources to explore, leases are purchased from mineral rights owners (where applicable), and permits are issued by the state. This can take anywhere from months to 2 years.
- Well development & drilling: Once it is determined that an adequate amount of oil and/or gas deposits can likely be extracted from underground, access roads are constructed and development of the well site proceeds. The first step in developing the site is building a well pad, which is the large structural platform surrounding the drilling operations. A well pad is typically 3 to 7 acres in size, and may be the location for several wells. The well pad holds the drilling rig, storage tanks, and other machinery and equipment.
Next, the energy company uses the drilling rig to drill the well(s). A typical well is drilled 5,000 to 9,000 feet vertically and up to 10,000 feet horizontally. (Often, an initial exploratory well is drilled to confirm that the site will be productive; the findings from this initial drilling determine if an energy company will move forward with the project.) Developing the site can take 2-5 years.
- Production: After the well has been drilled, the drilling rig is removed and the well is ready for hydraulic fracturing. As the picture below explains, the hydraulic fracturing process (commonly called “fracking”) uses high-pressure machinery to inject water, chemicals, and sand into underground wells. This process creates cracks or “fractures” in the rocks through which oil or natural gas can be released. After the gas or oil is accessed, it is processed and transported to consumers. Work activity near well sites generally slows at this point, though some wells are re-fracked periodically in an attempt to boost gas production from a site. A well can be productive from 10-50 years.
- Water use and disposal are important issues during the production stage. To “frack” a Marcellus Shale gas well, millions of gallons of fresh water are hauled in or withdrawn from a local source. Chemicals are added to the water to allow the natural gas to flow more efficiently up the top of the well (called the wellhead), and sand is added to prop open fractures so the gas can escape from the rock. This mixture of water, chemicals, and sand is often called “fracking fluid.”
Two kinds of wastewater return to the surface during UOGD operations. One is flowback water, which contains the fracking fluid mentioned above. The other is produced water, which is water previously trapped in underground formations that was released by the hydraulic fracturing process. Produced water can contain naturally occurring materials that are present in the shale layer, such as radioactive compounds, toxic organic and inorganic chemicals, and heavy metals such as arsenic. The wastewater is held in pits or tanks at the well site until it is treated, recycled, or disposed of in an underground injection well.
- Site remediation involves plugging the well(s) and restoring the site when a well is done producing gas (or if an exploratory well does not produce an adequate amount of resources). The process of site restoration involves filling the well with cement, removing waste and equipment, and capping the well. Energy companies may also attempt to restore the original landscape as much as possible with plantings and other landscaping.
OTHER UOGD INFRASTRUCTURE
Many people think of well sites alone when considering the impact of UOGD in their homes and communities. However, the UOGD process involves many other activities and facilities that can affect those who live nearby (see graphic). For example, increased truck and train traffic can be disruptive in communities by creating road congestion, accidents, air pollution, and damage to local roads. Likewise, UOGD-associated infrastructure including pipelines, compressor stations, and processing plants all carry potential risks to health and environment. For additional information about each step of the process, please visit The FracTracker Alliance’s Virtual Oil & Gas Tour and visit EHP’s Health Issues section.
WANT TO LEARN MORE?
- Earthworks: Hydraulic Fracturing 101
- Earthworks: Oil and Gas at Your Door
- EPA: Hydraulic Fracturing
- FracTracker Alliance: Oil and Gas Drilling 101
- IEER: Drilling and Hydrofracking
- NAACHO: Community Health and Shale Development Guidebook
- NPR State Impact: PA Guide to Hydraulic Fracturing, or "Fracking"
- PA Environmental Council: Marcellus Shale Lease Guide