What are Saltwater Disposal Wells?
Posted on: Friday, January 20, 2012
Deposits of oil and natural gas can be found in porous rocks and shale, where saltwater is also found. The handling of the saltwater, or produced water, which brings the oil and gas up to the surface, can be done in different ways.
First of all, in certain situations, some of it can be recycled. Secondly, in the case of conventional reservoirs, it can be returned to the reservoir through fluid injection. Thirdly, as the Railroad Commission of Texas explains, it can be “Injected into underground porous rock formations not productive of oil or gas, and sealed above and below by unbroken, impermeable strata.” This last method is predominantly used by saltwater disposal wells to manage the saltwater, also referred to as oilfield brine.
In the case of the Barnett Shale natural gas wells, produced water is mixed with the water used to complete the wells, through the technique known as hydraulic fracturing or “frac’ing.” A significant portion of this hydraulic fracturing fluid returns to the surface (called flow-back water) containing sand, clay, polymers, oil, salt and a variety of dissolved solids.
Recycling usually involves some type of evaporation or distillation technique, but there are limitations to the process. In order for recycling to be economically feasible, there must be a sufficient quantity and constant flow of water that permits the equipment to operate continuously at its maximum flow rate. This is best accomplished in areas where there are a number of producing wells so the saltwater can be moved to the recycling equipment by saltwater pipelines. However, recycling does not produce a 100% return, so disposal of saltwater and solids must still take place.
The Railroad Commission of Texas is responsible for the regulation of saltwater disposal wells in Texas. There are specific programs in place to ensure the proper disposal of saltwater and the Railroad Commission of Texas details these regulations on their website:
Operators are required to follow the Railroad Commission disposal regulations administered by the agency’s Technical Permitting Section-Underground Injection Control Program. Underground Injection Control is a program that is federally delegated by the U.S. Environmental Protection Agency to Texas, and it follows national guidelines under the federal Safe Drinking Water Act for surface and groundwater protection. The EPA awarded the Railroad Commission “primary enforcement responsibility” over oil and gas injection and disposal wells on April 23, 1982.
The Railroad Commission of Texas also implements certain rules and requirements to protect groundwater. The construction of disposal wells requires “multiple layers of cement and steel to ensure that shallow, usable quality water is not impacted.” In addition, disposal wells “inject saltwater into underground formations, sometimes over a mile in depth, into fields that are already full of naturally occurring saltwater.” In the Barnett Shale, saltwater disposal wells are drilled into the Ellenburger formation to depths of almost 2 miles. The Railroad Commission of Texas points out that in comparison to saltwater wells, fresh water wells “usually are no deeper than a few hundred feet.”
In order to further protect the groundwater, there are “disposal well construction standards” in place that bolster the disposal wells with three layers of casing. The Railroad Commission of Texas’ website lists them as follows:
The first protection layer is surface casing—steel pipe that is encased in cement that reaches from the ground surface to below the deepest usable quality groundwater level. Surface casing acts as a protective sleeve through which deeper drilling occurs. The second protection layer is the production casing—a pipe placed in the wellbore to the well’s total depth and permanently cemented in place. The third protection layer is the injection tubing string and packer that conducts the injected water down through the injection tubing string and production casing to perforations at the bottom of the well to inject the water into an underground formation. With this well construction, all three protection layers must fail at the same time to impact groundwater.
It should also be noted that the Railroad Commission “inspects commercial disposal wells (wells that take produced water from various operators for a fee) at least once per year.”
There are approximately 50,000 permitted saltwater disposal wells in Texas. Ten of these permitted saltwater disposal wells are in Tarrant County, and 14 are in surrounding counties. However, none of these disposal wells have ever had a problem with groundwater contamination. The Railroad Commission states on their website: “There are no known instances of ongoing groundwater contamination as a result of saltwater disposal activities in the Barnett Shale play—the state’s largest natural gas plan that has been actively producing natural gas since 1997.”
For more information, visit the FAQ page of the Railroad Commission of Texas.