The role water plays in natural gas production is not widely understood. To better understand the need for saltwater disposal wells, it is important to examine how water is generated during the natural gas production process in the Barnett Shale. Many people do not realize that the majority of water generated from these operations originates far below the earth’s surface and that saltwater disposal wells are simply a means of safely returning this water back to where it originated.
Managing produced water through the use of saltwater disposal wells is a monitored, safe and necessary practice. Chesapeake is here to provide residents of the Barnett Shale with the facts about saltwater disposal and the methods and processes that make this a safe and highly effective way to dispose of the water generated by natural gas production. Advancing community-wide familiarity with saltwater management increases our ability to provide clean-burning natural gas that will fuel our local economy and the nation for years to come.
The entire amount of water used for all drilling and fracing operations in the Barnett Shale is between 0.5% and 2% of the total water used in this region. This data was acquired from a 2006 report from the Texas Water Board and a study conducted in 2007 by Dr. Peter Galusky of the environmental consulting firm, Texerra, and commissioned by the Gas Technology Institute. These water-use figures have been confirmed by various city water departments, as well as the Tarrant Regional Water District, a major water supplier in the area.
The sources for water in Barnett Shale vary. Much of the water used in drilling operations comes from rivers, creeks, lakes, discharge water from industrial or city wastewater treatment plants and groundwater. All water must be metered and purchased regardless of the source. Water can be purchased from the city when drilling inside city limits and delivered through existing conduits, such as fire hydrants.
The public can rest assured that the natural gas industry would not use any community’s water supply to the point that it would cause hardship for local citizens, nor would they be allowed to do so by the local governing authority. During periods of water restrictions, the delivery of municipal water to gas companies would be curtailed more quickly than it would be to residential users.
A technique known as hydraulic fracturing, commonly referred to as fracing, is a necessary part of natural gas production in the Barnett Shale area. Fracing is used to create small fissures in the shale, allowing natural gas to flow. It involves the pumping of a mixture of more than 99% water and sand with a small amount of special-purpose additives into the ground under high pressure to form the hairline cracks. The newly created fractures are “propped” open by the sand, which allows the natural gas to flow into the wellbore and be collected at the surface. Normally a hydraulic fracturing operation is only performed once in the life of a well.
During fracing, water and sand are pumped at a high pressure into the rock formation,
creating tiny cracks in the shale and allowing natural gas to escape.
Without the recent and significant technological advancements made in horizontal drilling and in hydraulic fracturing, the natural gas found in deep shale formations would be, uneconomic and unrecoverable. The fracing process allows the natural gas trapped within the very dense rock formation to flow through the wellbore so that it can be collected at the surface.
For a typical natural gas well in the Barnett Shale, Chesapeake uses about 3.5 million gallons of water during fracing operations. The 3.5 million gallons of water needed to drill and fracture a typical deep shale gas well is equivalent to the amount of water consumed by:
- New York City in approximately five minutes
- A 1,000 megawatt coal-fired power plant in 8.75 hours
- A golf course in eight days
- Six acres of corn in a season
While these represent continuing consumption, the water used for a gas well is a one-time use.
In addition to water and sand, other additives are used in fracturing fluids to allow fracturing to be performed in a safe and effective manner. Additives used in hydraulic fracturing fluids include a number of compounds found in common consumer products.
Example of Typical Deep Shale Fracturing Mixture Makeup
A representation showing the percent by volume composition of typical deep shale gas hydraulic fracture components (see graphic) reveals that more than 99% of the fracturing mixture is comprised of freshwater and sand. This mixture is injected into deep shale gas formations and is typically confined by many thousands of feet of rock layers.
Fracturing Ingredients
| Product Category |
Main Ingredient |
Purpose |
Other Common Uses |
| Water |
99.5%
water & sand |
Expand fracture and deliver sand |
Landscaping and manufacturing |
| Sand |
Allows the fractures to remain open so the gas can escape |
Drinking water filtration, play sand, concrete and brick mortar |
| Other |
approximately 0.5% |
| Acid |
Hydrochloric acid or muriatic acid |
Helps dissolve minerals and initiate cracks in the rock |
Swimming pool chemical and cleaner |
| Antibacterial agent |
Glutaraldehyde |
Eliminates bacteria in the water that produces corrosive by-products |
Disinfectant; Sterilizer for medical and dental equipment |
| Breaker |
Ammonium persulfate |
Allows a delayed break down of the gel |
Used in hair coloring, as a disinfectant, and in the manufacture of common household plastics |
| Corrosion inhibitor |
n,n-dimethyl formamide |
Prevents the corrosion of the pipe |
Used in pharmaceuticals, acrylic fibers and plastics |
| Crosslinker |
Borate salts |
Maintains fluid viscosity as temperature increases |
Used in laundry detergents, hand soaps and cosmetics |
| Friction reducer |
Petroleum distillate |
“Slicks” the water to minimize friction |
Used in cosmetics including hair, make-up, nail and skin products |
| Gel |
Guar gum or hydroxyethyl cellulose |
Thickens the water in order to suspend the sand |
Thickener used in cosmetics, baked goods, ice cream, toothpaste, sauces and salad dressings |
| Iron control |
Citric acid |
Prevents precipitation of metal oxides |
Food additive; food and beverages; lemon juice ~7% citric acid |
| Clay stabilizer |
Potassium chloride |
Creates a brine carrier fluid |
Used in low-sodium table salt substitute, medicines and IV fluids |
| pH adjusting agent |
Sodium or potassium carbonate |
Maintains the effectiveness of other components, such as crosslinkers |
Used in laundry detergents, soap, water softener and dishwasher detergents |
| Scale inhibitor |
Ethylene glycol |
Prevents scale deposits in the pipe |
Used in household cleansers, de-icer, paints and caulk |
| Surfactant |
Isopropanol |
Used to increase the viscosity of the fracture fluid |
Used in glass cleaner, multi-surface cleansers, antiperspirant, deodorants and hair color |
For more information about hydraulic fracturing, visit www.hydraulicfracturing.com.
Saltwater Disposal
All water returned from the well is called produced water. Initially, about the first 5% of the produced water that is returned is relatively low in salt content, but the salinity increases as the water continues to flow. As the gas begins to rise to the surface, the water that travels with it includes the already-existing geologic saltwater that was trapped with the gas inside the rock formation deep within the earth. In the Barnett Shale, this water, which represents the remaining 95% of the water generated from a well, can be more than three times the salinity of seawater. Produced water continues to flow with the natural gas throughout the life of the well.
In the Barnett Shale, once produced water is separated from natural gas, it is returned deep within the earth from where it came using saltwater disposal (SWD) wells, a type of Class II injection well used by the oil and gas industry. SWD wells are licensed and regulated for the disposal of water generated from the production of oil and natural gas. There are currently more than 50,000 Class II injection wells and more than 11,700 active SWD wells operating in Texas. Barnett Shale SWD wells are drilled into the Ellenburger formation, located more than 1.5 miles below the surface, for the disposal of water generated from natural gas operations.
Tank batteries are present at each drillsite for the storage of water resulting from natural gas production.
The Ellenburger is a porous rock formation which exists beneath the Barnett Shale. Located about 1.5 miles underneath the earth’s surface, this subsurface stratum already contains naturally occurring saltwater, making it an ideal location to inject produced water from the Barnett Shale operations. The span between the freshwater aquifers and the Ellenburger formation is made up of multiple layers of impervious rock, which prevent the injected water from migrating upward.
The Railroad Commission of Texas (RRC) regulates disposal wells and their construction in the Barnett 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 seven layers of protection to effectively isolate the water being injected from any drinking water aquifers. The seven layers of protections include:
- Surface casing, which runs 50 - 100 feet below the deepest drinking water aquifer
- A layer of cement to hold the surface casing in place
- Production casing, which runs through 1.5 miles of rock between the groundwater sands and the Ellenburger formation
- A layer of cement to hold the production casing in place
- A packer is installed at a level below the Barnett Shale (more than 7,000 feet below the surface)
- Steel tubing is put in place all the way down to the Ellenburger formation
- An internal plastic coating is added to the tubing to prevent corrosion
In addition, more than 1.5 miles of impervious rock exists between the injected water and the fresh water 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 Ellenburger formation.
Saltwater disposal 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 Barnett Shale 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 North Texas.
Natural gas pipeline is laid at DFW International Airport as planes fly overhead. To reduce the need for
water trucks, the wellsites at the airport are connected to saltwater disposal wells via water pipeline.
Recycling Technology
Present-day technology does not allow the majority of produced water to be recycled efficiently. Although the natural gas industry is testing the feasibility of recycling produced water that initially returns to the surface during the flowback process (because it contains less salt), it only amounts to five percent of the total water generated in the Barnett Shale production process. The remaining 95% of the water, with its high concentration of chlorides and other dissolved solids, is too saturated to make its recycling economically viable.
As a member of the Barnett Shale Water Conservation Management Committee, Chesapeake and other members of the North Texas oil and gas industry meet regularly to evaluate feasible recycling options for part or all of the produced water that is returned after the well begins to flow. To date, a number of different pilot recycling projects have been undertaken by various natural gas companies to advance the technology in order to make the process both more efficient and more economical.
As part of a joint pilot project with the City of Fort Worth, Chesapeake is studying water evaporation systems 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, as part of the earth’s hydrological cycle. For more information on this technology, visit www.intevras.com/evras.html.
This EVRAS system has the ability to evaporate a portion of the produced water from natural gas drilling,
ultimately reducing the amount of water needing to be injected into SWD wells.
Water Transportation Options
Water from natural gas wellsites is either trucked or piped to saltwater injection wells for disposal. Water trucks can transport between 5,000 to 6,300 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.
On average, water output drops about 47% in the second week of natural gas production and 72% after 60 days. This, in turn, greatly reduces the number of trucks needed to transport the water to a SWD well. 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.
Use of water pipeline systems can further reduce the amount of trucks needed to travel to and from natural gas wellsites. Formed from polyethylene pipe, these systems are corrosion-resistant and contain monitored sensors at every padsite. In addtion, these systems are located no less frequently than every mile along the water pipeline route to ensure an immediate response to potential leaks.
The pipeline used to transport produced water is made of corrosion-resistant polyethylene and is 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 no less frequently than every mile to monitor the flow of water throught the pipeline, while state-of-the-art 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:
- Barnett Shale Water Conservation & Management Committee
www.barnettshalewater.org
- 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