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Introduction

Produced water—water from underground formations that is brought to the surface during oil and gas production—is the greatest volume byproduct associated with oil and gas production (Veil, 2015; see also EPA [2015] and DOE [2004] for definitions of produced water). It is managed by some combination of underground injection, treatment, and subsequent use, treatment, and discharge, or evaporation, subject to compliance with state and federal regulations (NRC, 2010). Management of these waters is challenging not only for industry and regulators, but also for landowners and the public because of differences in the quality and quantity of produced water, varying infrastructure needs, costs, and environmental considerations associated with produced water disposal, storage, and transport (e.g., NRC, 2010).

Unconventional oil and gas development involves technologies that combine horizontal drilling with the practice of hydraulic fracturing. Hydraulic fracturing is a controlled, high-pressure injection of fluid and proppant into a well to generate fractures in the rock formation containing the oil or gas. These fractures allow the oil and gas to move from the formation into the well. “Proppant” refers to sand or ceramics that help keep the fractures open after the fluid injection is completed. The injected fluid can comprise a combination of water and small amounts of chemical additives that reduce friction in the pipe and help to carry the proppant into the fractures (King, 2012; NRC, 2013, 2014). After the hydraulic fracture procedure is completed, the injected fluid is allowed to flow back into the well, leaving the proppant in the newly created fractures. As a result, a portion of the injected water returns to the surface and this water is called “flowback water,” which initially may mix with the naturally occurring produced water from the formation. The chemistry and volume of water returning to the surface from unconventional oil and gas operations thus changes during the lifetime of the well due to the amount of fluid used in the initial stage of well development, the amount of water naturally occurring in the geologic formation, the original water and rock chemistry, the type of hydrocarbon being produced, and the way production is conducted (Veil, 2015). The volume and composition of flowback and produced waters vary with geography, time, and site-specific factors (EPA, 2015). Hereafter, in this Proceedings of a Workshop, both flowback and produced water are referred to as “produced water” without differentiating the proportions of flowback versus formation water that may be present.

The challenge of managing produced water from these kinds of operations relates both to the water quantity—use of surface and groundwater for hydraulic fracturing that may be permanently removed from the water cycle through deep injection in disposal wells—and water quality in terms of understanding the chemical characteristics of produced waters that could otherwise have a potential, alternative use if treated to an appropriate standard. Produced water quantity and quality also have bearing on mitigating concerns about spills or leaks to the environment when the waters are either temporarily stored or transported. Although disposal wells are the primary management practice for produced water from unconventional wells that use hydraulic fracturing (EPA, 2015), alternative management approaches can include opportunities to use produced water. Options for the potential use of produced water may include reuse in oil and gas fields, in a range of different industrial settings, and for agriculture after appropriate treatment. Evidence suggests, however, that the amount of produced water that is used for these or other types of beneficial purposes is low: less than 1 percent (Veil, 2015). With increased concerns about water resource management, including water availability, interest exists in considering produced water as a potential resource rather than predominantly as a byproduct of oil and gas production.¹

WORKSHOP OVERVIEW AND ORGANIZATION OF THE PROCEEDINGS

This workshop (agenda in Appendix A) was conducted under the auspices of the National Academies of Sciences, Engineering, and Medicine’s (National Academies’) Roundtable on Unconventional Hydrocarbon Development to highlight the challenges and opportunities associated in managing produced water from unconventional hydrocarbon development, and particularly in the area of potential beneficial uses for these waters (see Appendix B for the list of Roundtable members). The workshop was organized by a planning committee assembled for the purpose of developing the workshop program and convening the event, which was held on May 25 and 26, 2016, at the National Academies Keck Center (500 Fifth Street NW, Washington, DC) (see Appendix C). The biographies of the workshop moderators and presenters are in Appendix D.

The workshop was organized around the topical areas noted in the statement of task (see Box 1.1) with participants from universities, the private sector, federal and state government agencies, and nongovernmental organizations. One hundred and five people attended in person and 123 people participated via webcast (see Appendix E).² A glossary of terms is included in Appendix F.

Following welcoming remarks from Dr. Gregory Symmes, the Executive Director of the National Academies’ Division on Earth and Life Studies, and from the Roundtable co-chairs, Dr. David Dzombak and Dr. Wendy Harrison, three keynote presentations were provided to frame topics and concerns associated with potential beneficial uses of produced water. The remainder of the workshop focused on four panel discussions. The meeting concluded in plenary session with time provided for questions and comment from participants on the overarching themes raised during the workshop and identification of some next steps.

Chapter 2 summarizes keynote presentations on the energy water nexus, a description of flowback and produced waters, and an industry perspective on approaches to manage, treat, and transport produced water. Chapters 3 through 6 summarize panel presentations and the moderated discussions. Chapter 3 focuses on regional perspectives of using produced waters in an environmental and regulatory context. Chapter 4 covers technologies for managing flowback and produced

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¹ We note that, during the workshop, contributors variably employed the words “use,” “reuse,” and “recycle” with respect to potential applications of produced water but without necessarily defining specifically how they employed those terms. To the degree possible, we simply employed the word “use” or “uses” in this Proceedings of a Workshop when referring to subsequent potential or actual applications of produced water unless the meaning of the speaker would be altered through such a simplification.

² The webcasts are available at http://nas-sites.org/uhroundtable/meetings (accessed September 21, 2016).

waters. Chapter 5 describes characteristics of produced waters for potential use. Chapter 6 discusses research and technology, while Chapter 7 is a facilitated discussion on what is known about the technologies and characteristics of produced water, what is not known, and how to fill the gaps. Supporting material is provided in the references and appendixes.

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