Chesapeake uses saltwater disposal (SWD) wells for the disposal of produced water in the Haynesville Shale. After produced water is separated from the gas, it is returned deep within the earth to where it originated. A SWD well is considered a “Class II” injection well by the Environmental Protection Agency (EPA). SWD wells are highly regulated and commonly used by the oil and natural gas industry to dispose of water generated during production. Tank batteries are present at each drillsite for the storage of water resulting from natural gas production.
Tank batteries are present at each drillsite for the storage of water resulting from natural gas production.
The Railroad Commission of Texas (RRC) regulates disposal wells and their construction in the East Texas Haynesville Shale region. These regulations are the industry standard and are considered safe and effective. Still, Chesapeake exceeds the commission’s standards by constructing SWD wells with multiple layers of protective steel casing and cement that are specifically designed and installed to protect groundwater and to ensure that the producing zone is protected from overlying formations. The layers of protection are:
- Surface casing is run to a depth well below all freshwater aquifers, typically to a depth of 1,800 feet below the surface.
- A layer of cement holds the surface casing in place
- Production casing runs through several thousand feet of rock between the freshwater aquifer and the injecting formation
- A layer of cement holds the production casing in place
- A packer is installed deep within the casing to isolate the injection zone
- Steel tubing is put in place
- An internal plastic coating is added to the tubing to prevent corrosion
Thousands of feet of impervious rock exists between the injected water and the groundwater located in freshwater aquifers, making it virtually impossible for any produced water to come into contact with these zones.
The mechanical integrity of SWD wells is tested regularly, and the pressure in the well is monitored continuously to ensure that all of the disposed water reaches the intended formation.
SWD wells are a proven technology. The disposal of produced water through use of this method is a monitored, safe and necessary practice which is overseen and inspected regularly by the RRC in the Haynesville Shale East Texas region.
“When wells are properly sited, constructed and operated, underground injection is an effective and environmentally safe method to dispose of wastes.” — Environmental Protection Agency
The overwhelming majority of injected fluid is oilfield brine, which is also called produced water. This produced water comes up simultaneously with the production of oil and 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 minor 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 residual hydrocarbons may also be found the produced water.
Strategically located SWD wells can reduce the miles trucks must travel in order to dispose of produced water. Connecting water pipelines from gas wellsites to SWD sites would lessen truck traffic even more dramatically, reducing emissions, traffic noise, traffic congestion and road repairs. This would result in fewer emissions, improved air quality and increased safety in East Texas.
Recycling Technology
Most of the water generated from natural gas production is too highly concentrated with naturally occurring minerals, such as salt, to be recycled effectively. There has been some success in recycling the first 5% of returned water during flowback operations, which consists mostly of frac fluid or freshwater. However, by the end of the first few days (and in some cases a few hours) after fracing, salt content can reach as high as 70,000 parts per million (ppm), more than twice the salinity of seawater (30,000 ppm). At this time, the majority (95%) of the produced water returned from the well, with its high salt content, is too saturated to make recycling currently economically viable.1 Chesapeake and others in the industry are constantly evaluating opportunities to treat this produced water, so that less of it will need to be injected using 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 into SWD 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. Depending on the success of this pilot project, Chesapeake will evaluate the feasibly of using this and other technologies in the Haynesville Shale area.
Water Transportation Options
Water from natural gas wellsites is either trucked or piped to saltwater injection wells for disposal. Water trucks can transport between 3,000 - 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 day per well is needed to carry water to a SWD well and continues to decline over the life of a well.
The pipelines used to transport produced water are made of corrosion-resistant polyethylene and are nearly an inch thick. Pipeline segments are fused together to maximize leak protection, making the seams the strongest portion of the pipe. Sensors are installed at no less than every mile to monitor the flow of water through the pipeline, while state-of-the-art Supervisory Control and Data Acquisition (SCADA) controls can shut down the pipeline flow immediately from a remote location, should a change in flow be detected.
For more information about SWD wells, contact the following organizations:
- Clean Air Technology Hotline
919-541-0800
- Environmental Protection Agency
www.epa.gov
- National Response Center Hotline
800-424-8802
- Natural Gas Regulations
www.naturalgas.org / 202-326-9300
- Railroad Commission of Texas
www.rrc.state.tx.us / 877-228-5740
- U.S. Department of Energy
www.eia.doe.gov / 202-586-8800
- U.S. Department of Transportation
www.dot.gov / 202-366-4000
- U.S. Government Printing Office
202-512-0000
Sourcing Reference:
1 US Department of Energy - “Modern Shale Gas Development in the United States. A Primer” – Page 70