Chesapeake intends to use saltwater disposal wells for the disposal of produced water in New York once drilling and production activities commence. After produced water is separated from the gas, it will be returned deep within the earth from where it came using saltwater disposal wells. A type of EPA classified “Class II” injection well, saltwater disposal wells are highly regulated and commonly used by the oil and natural gas industry to dispose of water generated during production.
Saltwater disposal wells are a proven technology and the safest method of disposal today. The disposal of produced water through use of this technology is a monitored, safe and necessary practice which is overseen and inspected regularly by the U.S. Environmental Protection Agency (EPA).
“When wells are properly sited, constructed and operated, underground injection is an effective and environmentally safe method to dispose of wastes.” — EPA
The EPA, Region 2 and the New York Department of Environmental Conservation regulate disposal wells and their construction in New York. The EPA’s federal regulations are the industry standard. Chesapeake meets or exceeds these standards when constructing saltwater disposal wells, including multiple layers of protection to effectively isolate the injected water from surrounding drinking water aquifers1. These layers of protection include a number of factors such as:
- Surface casing is run 100 feet below the lowest usable source of underground drinking water
- A layer of cement holds the surface casing in place
- Production casing runs through approximately one to 1.5 miles of rock between the freshwater aquifers and the intended formation
- An additional layer of cement holds the production casing in place
- A packer is installed at a minimum of 3,000 feet below the deepest known freshwater zone
- Steel tubing is put in place down the entire length of the saltwater disposal well
- An internal plastic coating is added to the tubing to prevent corrosion
More than one mile of impervious rock typically exists between the injected water and the freshwater aquifers, making it virtually impossible for produced water to come into contact with these zones.
The mechanical integrity of a saltwater disposal well is tested regularly, and the pressure in the well is monitored continuously to ensure that all of the disposed water reaches the injecting formation.
The overwhelming majority of injected fluid is oilfield brine, which is also called produced water. Produced water comes up simultaneously with the production of natural gas. However, small quantities of substances used in the drilling, completion and production operations of a well may be mixed in with the produced water. Some of these materials include small amounts of drilling mud, fracture fluids and well treatment fluids. Also, since the produced water is associated with crude oil and natural gas, small amounts of naturally occuring hydrocarbons may also be found.
Strategically located saltwater disposal wells can reduce the miles trucks must travel in order to dispose of produced water. Since trucks must be used to transport produced water from wellsites to disposal locations, the number and location of saltwater disposal wells has a direct bearing on the number of vehicle miles traveled for natural gas production. Strategically located disposal wells would lessen truck traffic and reduce emissions, traffic noise, traffic congestion and road repairs. This would result in less impacts to air quality and increased road safety for the people of New York.
Recycling Technology
Most of the water generated from natural gas production contains too many naturally occurring minerals, such as salt, to be recycled effectively. There has been some success in recycling the first 5% of produced water during flowback operations. However, by the end of the first few days after fracing (and in some cases a few hours), salt content of the produced water can reach as high as 70,000 parts per million (ppm), more than twice the salinity of seawater (30,000 ppm). The majority (95%) of the produced water returned from the well, with its high salt content, is too saturated to make recycling currently economically viable2. Chesapeake and others in the industry are constantly evaluating opportunities to treat produced water, so that less of it will need to be injected into saltwater disposal wells.
Chesapeake is currently evaluating a number of water recycling technologies. One technology in particular is being pilot tested in the Barnett Shale in Fort Worth, Texas. This technology involves a water evaporation system as a potential way to reduce the amount of produced water being injected intosaltwater disposal wells. Using the heat generated by natural gas compressor stations — an energy source that would typically be wasted — the system filters and then evaporates a portion of the produced water. The clean water vapor is then released into the atmosphere, where it will eventually return to the earth in the form of rain. For more information on this technology, visit www.intevras.com/evras.html. Depending on the success of this pilot project, Chesapeake will evaluate the feasibly of using this and other technologies in the Marcellus Shale area.
Water Transportation Options
Produced water from wellsites is trucked to saltwater injection wells for disposal. Water trucks can transport between 3,000 to 5,000 gallons of water per load, depending on the size of the vehicle. Truck traffic, like the amount of water produced from wells, drops significantly in a relatively short amount of time.After three months of production, less than one truck per week per well is normally needed to carry water offsite and the volume of water continues to decline during the life of the well.
References
To learn more about the topics on this page, please contact the following organizations:
Section last updated July 17, 2009
Sourcing Reference:
1 “Hydraulic fracturing considerations for natural gas wells of the Marcellus Shale” Arthur, Bohm, et al presented to Groundwater Protection Council, September 2008. pg 15
2 US Department of Energy - “Modern Shale Gas Development in the United States. A Primer” – Page 70