Fracturing Fluid Management
Fluid Storage – “Pits”
From the time the first oil and gas wells were drilled, “pits” have been used to hold drilling fluids and wastes. Pits can be excavated holes in the ground, or they can be above ground containment systems such as steel tanks. Pits are used for storage of produced water, for emergency overflow, temporary storage of oil, burn off of waste oil, and for temporary storage of the fluids used to complete and treat the well.
The containment of fluids within a pit is the most critical element in the prevention of contamination of shallow ground water. The failure of a tank, pit liner, or the line carrying fluid (“flowline”) can result in a release of contaminated materials directly into surface water and shallow ground water. Environmental clean-up of these accidentally released materials can be a costly and time consuming process. Therefore, prevention of releases is vitally important.
For pits constructed from ground excavation, pit lining may be necessary to prevent infiltration of fluids into the subsurface of the ground, depending upon the fluids being placed in the pit, the duration of the storage and the soil conditions. Typically, pit liners are constructed of compacted clay or synthetic materials like polyethylene or treated fabric that can be joined using special equipment.
Depending on the state, there are a number of other rules regarding pits and the protection of surface and ground water. In addition to liners, some states also require pits used for long term storage of fluids to be placed a minimum distance from surface water to minimize the chances of surface water contamination should there be an accidental discharge from the pits. In California, for example, pits may not be placed in areas considered “natural drainage channels”. Some states also explicitly either prohibit or restrict the use of pits that intersect the water table.
New systems have been developed that avoid the use of pits. One technology that is becoming more common is closed loop fluid handling systems. These systems avoid the use of pits by keeping fluids within a series of pipes and tanks throughout the entire fluid storage process. Since fluid is never placed into contact with the ground, the likelihood of groundwater contamination is minimized.
Fluid Handling and Disposition
Following hydraulic fracturing, fluids returned to the surface within a specified length of time are referred to as flowback. Flowback can be comprised of as little as 3% and as much as 80% or more of the total amount of water and other material used to fracture the well. Besides the original fluid used for fracturing, flowback can also contain fluids and minerals that were in the fractured formation. Obviously, flowback water should be managed in a responsible manner.
The responsibility for regulating wastes such as flowback fluid lies with one or more state regulatory agencies, depending on the state. In at least 9 states, the jurisdiction over waste management for oil and gas exploration and production activity involves more than one agency.
Proper disposal of flowback fluids is critically important to the protection of both surface and ground water. The vast majority of flowback fluids are disposed of in underground injection wells. Injection of flowback fluids is conducted in a Class II injection well. Underground injection of flowback is regulated by either the U.S. Environmental Protection Agency’s (EPA) Underground Injection Control (UIC) program or by a state granted primary UIC enforcement authority by the EPA. At present there are 39 states, 2 tribes and 3 territories that have delegated authority from the EPA for the Class II (oil and gas related) injection well program. The remaining Class II UIC programs are managed by EPA regional offices.
While proper disposal of flowback fluids into permitted and monitored injection wells is currently the most effective means of safely isolating these fluids from the near-surface environment, the required specific geological conditions that are required for such wells do not exist in all areas. Depending upon where these areas are located, there may be other methods of handling flowback fluids such as treatment and discharge. Treatment of flowback can be conducted on-site or in centralized treatment facilities. If discharge is allowed under state or federal law, it must be done under strict controls which would typically require the issuance of a National Pollutant Discharge Elimination System (NPDES) permit from a state or the federal environmental protection agency.
Advances in flowback fluid treatment technology offer the promise of using flowback fluid for other purposes, rather than simply disposing of it. The use of filtration, reverse osmosis, decomposition in constructed wetlands, ion exchange and other technologies may eventually result in the widespread practice of using flowback fluids for such things as managed irrigation and land application. One practice in use today is the recycling of flowback fluids for their reuse in other hydraulic fracturing jobs, which saves water. This technology is being used by companies like Devon Energy in the Barnett shale area around Ft. Worth, Texas. Several companies also use this technology in the Marcellus shale play in Pennsylvania.
The chart below shows the typical flowback water handling options used in various shale gas regions throughout the U.S.