Horizontal drilling and hydraulic fracturing come with various environmental risks that must be prevented or mitigated, such as groundwater contamination, induced seismicity, and well integrity issues. One of the greatest challenges associated with hydraulic fracturing is the generation of co-produced water, including flowback of hydraulic fracturing fluids at the surface.1Blogs, E. D. F. (2018, February 2). Six ways oil and gas development can contaminate land and water (and what to do about it). Energy Exchange. http://blogs.edf.org/energyexchange/2017/12/29/six-ways-oil-and-gas-development-can-contaminate-land-and-water-and-what-to-do-about-it/. Let’s define a couple of terms we will be using for our discussions in the rest of this lesson.
Flowback water refers to fluids that return to the surface from the well following a treatment. For example, water and chemicals used to hydraulically fracture a shale formation are recovered from the well at the surface and we refer to those fluids as flowback water.
Produced water refers to water co-produced with oil and gas from a wellbore that is not a treatment fluid, and the term includes naturally occurring water that comes from the deep reservoir during production of oil and gas. This water is often described as brine and typically has a high salt content and other chemical components that can be hazardous to health and the environment if not properly treated and disposed of.
*Some studies use produced water to refer to both flowback and produced water and it is generally very difficult to distinguish them. Some studies suggest that flowback is minimal and produced water dominates fluid production. Thus, it is important to know how these terms are strictly defined, and also how they may be used in reported data.
What is the difference between flowback and produced water?
Storage of Produced Water at the Wellsite
Pits or tanks at the surface where produced water is first stored after reaching the surface must be well constructed, with no leaks or integrity issues.2Blogs, E. D. F. (2018, February 2). Six ways oil and gas development can contaminate land and water (and what to do about it). Energy Exchange. http://blogs.edf.org/energyexchange/2017/12/29/six-ways-oil-and-gas-development-can-contaminate-land-and-water-and-what-to-do-about-it/. Leakage of produced water from pits or tanks could cause disastrous issues to the nearby land, surface water bodies, or underlying aquifers.
Once produced water is properly stored at the surface it must then be carefully managed for disposal, the dominant practice, or reuse and recycling, to optimize management and minimize adverse impacts related to contamination or induced seismicity. We will take a closer look at the processes involved in disposal, treatment, and reuse/recycling of produced water. But first, let’s look at some of the environmental challenges related to produced water.
Chemical Composition of Produced Water
Produced water is highly saline and can be referred to as brine because it often contains more dissolved inorganic salt than typical seawater. If you’ve ever been to the ocean you might have noticed how salty water tasted. Let’s compare that to produced water from oil and gas formations. Previous studies in the Permian Basin indicate that the salinity of produced water ranges from slightly less than that of seawater to about four times that of seawater.3Nicot, J.-P., Darvari, R., Eichhubl, P. , Scanlon, B. R., Elliott, B. A. , Bryndzia, L. T. , Gale, J. F. W. & Fall, A. (2020). Origin of low salinity, high volume produced waters in the Wolfcamp Shale (Permian), Delaware Basin, USA. Applied Geochemistry. 122, 104771.4Engle, M. A., Reyes, F. R., Varonka, M. S., Orem, W. H., Ma, L., Lanno, A. J., Schell, T. M., Xu, P. & Carroll, K. C. (2016). Geochemistry of formation waters from the Wolfcamp and “Cline” shales: Insights into brine origin, reservoir connectivity, and fluid flow in the Permian Basin, USA. Chemical Geology. 425, 76-92. In addition to the high salinity in produced water, other harmful chemicals may be present, such as zinc, lead, manganese, iron, barium, radionuclides, and many different organics. Flowback fluids typically contain chemicals that were initially added to the wellbore for stimulation of the formation. Drilling fluids are also returned and must be managed.
Potential Biological Toxicity and Landscape Impacts
If produced water were to leak into the nearby landscape and water bodies, the chemical composition would mostly likely be toxic for land and marine organisms. Furthermore, the chemicals in the produced water could contaminate sources where humans extract water for municipal purposes such as drinking water, or waters used for agricultural irrigation. The high salinity alone can cause crops to dry out, if the produced water infiltrates the soil, causing dispersion and swelling of soil particles and limiting water infiltration within both soil and vegetation.5Meehan, Sedivec, DeSutter, Augustin, & Daigh. (2017, June). North Dakota State University. Environmental Impacts of Brine (Produced Water) – Publications. https://www.ag.ndsu.edu/publications/environment-natural-resources/environmental-impacts-of-brine-produced-water. Depending on the quality of produced water, the amount of Total Dissolved Solids (TDS) varies greatly. Some standard terms used to describe the produced water are:6Mantell, M. (2011, March 10-11). Produced Water Reuse and Recycling Challenges and Opportunities Across Major Shale Plays. EPA Hydraulic Fracturing Study Technical Workshop #4Water Resources Management https://www.epa.gov/sites/production/files/documents/09_Mantell_-_Reuse_508.pdf
- Brackish is 1,000 to 10,000 ppm TDS
- Saline is 10,000 to 35,000 ppm TDS
(Seawater averages 35,000 ppm TDS)
- Brine is ≥35,000 ppm TDS
If a produced water spill were to occur, the exceedingly large amount of dissolved solids would have intense effects on the landscape, ecosystems, and water resources.
Management of produced water includes proper planning, monitoring, and established remediation protocols set in place in the case of contamination. The process of treating and disposing of produced water is strictly regulated, and it is important that companies abide by these regulations. Failure to comply will not only negatively affect the environment and health of humans and organisms nearby, it can also be financially burdensome for the company and various stakeholders.
Image Credits: U.S. Department of Energy