Can we beneficially reuse produced water from oil and gas extraction in the U.S.?

Journal Pre-proof Can we beneficially reuse produced water from oil and gas extraction in the U.S.?

Bridget R. Scanlon, Robert C. Reedy, Pei Xu, Mark Engle, J.P. Nicot, David Yoxtheimer, Qian Yang, Svetlana Ikonnikova PII:

S0048-9697(20)30595-7

DOI:

https://doi.org/10.1016/j.scitotenv.2020.137085

Reference:

STOTEN 137085

To appear in:

Science of the Total Environment

Received date:

20 December 2019

Revised date:

31 January 2020

Accepted date:

1 February 2020

Please cite this article as: B.R. Scanlon, R.C. Reedy, P. Xu, et al., Can we beneficially reuse produced water from oil and gas extraction in the U.S.?, Science of the Total Environment (2020), https://doi.org/10.1016/j.scitotenv.2020.137085

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2020 Published by Elsevier.

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Can we Beneficially Reuse Produced Water from Oil and Gas Extraction in the U.S.?

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Bridget R. Scanlon, Robert C. Reedy, Pei Xu*, Mark Engle**, J.P. Nicot, David Yoxtheimer***, Qian Yang, and Svetlana Ikonnikova

Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin *New Mexico State University, Civil Engineering Department, Las Cruces, NM **Dept. of Geological Sciences, University of Texas at El Paso, TX ***Earth and Environmental Systems Institute, College of Earth and Mineral Science, Penn State Univ., PA

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Abstract

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There is increasing interest in beneficial uses of large volumes of wastewater co-produced with oil and gas extraction (produced water, PW) because of water scarcity, potential subsurface disposal limitations, and regional linkages to induced seismicity. Here we quantified PW volumes relative to water demand in different sectors and PW quality relative to treatment and reuse options for the major U.S. shale oil and gas plays. PW volumes from these plays totaled ~600 billion liters (BL, 160 billion gallons, Bgal) in 2017. One year of PW is equal to ~60% of one day of freshwater use in the U.S. For these plays, the total irrigation demand exceeded PW volumes by ~5× whereas municipal demand exceeded PW by ~2×. If PW is reused for hydraulic fracturing (HF) within the energy sector, there would be no excess PW in about half of the plays because HF water demand exceeds PW volumes in those plays. PW quality can be highly saline with median total dissolved solids up to 255 g/L in the Bakken play, ~7× seawater. Intensive water treatment required for PW from most unconventional plays would further reduce PW volumes by at least 2×. Desalination would also result in large volumes of salt concentrates, equivalent to ~3,000 Olympic swimming pools in the Permian Delaware Basin in 2017. While water demands outside the energy sector could accommodate PW volumes, much lower PW volumes relative to water demand in most regions would not substantially alleviate water scarcity. However, large projected PW volumes relative to HF water demand over the life of the play in the Permian Delaware Basin may provide a substantial new water source for beneficial use in the future. Large knowledge gaps in PW quality, lack of appropriate regulations, and economic factors currently preclude beneficial uses outside the energy sector in most regions.

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1.0 Introduction

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Co-production of large volumes of waste water or produced water (PW) with the expansion of energy production from shale or unconventional oil and gas (UOG) plays within the past decade is becoming an important topic because these plays are located mostly in the semiarid western U.S. where water scarcity is a critical issue (Fig. 1) (Huang et al., 2012; Reig et al., 2014; Scanlon et al., 2012). Water is also produced when coal beds are dewatered to mobilize methane, often termed coal bed methane (CBM) (NASEM, 2010). Previous analysis estimated the total PW volumes in the U.S. to be ~3.4 trillion liters (TL; 3.4 km3 ~0.9 trillion gallons, Tgal) in 2012 (Veil, 2015), similar to previous estimates from 2007 (Clark and Veil, 2009). Most PW is injected into the subsurface, with almost half of the 2012 volume injected into high permeability conventional reservoirs, mostly for pressure maintenance and enhanced oil recovery (EOR). In contrast, PW from UOG reservoirs cannot be managed by disposal into the shale and tight rock reservoirs because of the low permeability, but instead is injected into intervals that do not produce oil and gas using salt-water disposal (SWD) wells. This process affects the subsurface water budget, resulting in increased pressures and has been linked to seismicity, particularly if disposal is adjacent to basement rocks (Scanlon et al., 2019; Walsh and Zoback, 2015). Regulations were promulgated in Oklahoma and New Mexico, restricting disposal of PW in certain units, such as the Arbuckle in Oklahoma near the basement and its geological equivalent in New Mexico, the Ellenburger to reduce actual or potential induced seismicity (Lemons et al., 2019; Scanlon et al., 2019). Additional adverse impacts of subsurface disposal include contamination with a recent analysis suggesting that disposal wells may impact overlying aquifers in some basins (Ferguson et al., 2018). Previous studies address a variety of risks related to PW management, including pollution from spills and leaks and casing failures (Meng, 2017; Torres et al., 2016).

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Various PW management approaches have been suggested to reduce adverse environmental impacts, such as water scarcity, induced seismicity, and contamination. The most obvious approach is to reuse or recycle PW within the energy sector for hydraulic fracturing (HF) of new wells in shale or tight oil plays. PW reuse would reduce water sourcing to support HF. A recent analysis compared PW supplies relative to HF water demand in major U.S. plays, showing that PW reuse should alleviate many of the adverse impacts of subsurface disposal; however, some plays have PW volumes that exceed HF water demands (Scanlon et al., in rev.). PW reuse for HF was facilitated by advances in fracturing-fluid chemistry that shifted water-quality requirements for HF from freshwater during the early years of UOG development to use of “clean brines” with minimal treatment in many regions (Barnes et al., 2015; McMahon et al., 2015; Nichols et al., 2017). Although a large percentage of PW is reused for HF in the Marcellus and Fayetteville plays (Greaves et al., 2017; Rassenfoss, 2011), the total volumes of PW in these plays are low and can more readily be accommodated through reuse for HF than in plays with much larger PW volumes, such as the Permian Basin (Scanlon et al., 2017). New Mexico has changed its regulations precluding landowners from requiring operators to purchase water for HF when PW is available (New Mexico House Bill 0546). However, even in shale gas plays with low PW volumes, downturns in drilling can temporarily limit the potential for reuse for HF, as seen in the Fayetteville play (Greaves et al., 2017). Lack of reporting requirements for PW reuse/recycling volumes makes it difficult to assess the extent of PW reuse within the energy sector. Another approach for managing PW is to reuse PW outside of the energy sector, such as in irrigation, municipal, and industrial sectors or to discharge treated PW to surface water or to recharge groundwater. The feasibility of using PW for irrigation was evaluated for Colorado (Dolan et al., 2018). A recent study by the U.S. Groundwater Protection Council (GWPC) evaluated the potential for beneficial 3

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use within and outside the energy sector, focusing on legal and regulatory issues and research needed to ensure safe use of PW in other sectors (GWPC, 2019). New Mexico developed a Memorandum of Understanding with the U.S. Environmental Protection Agency (EPA) to assess regulatory frameworks for PW reuse within and outside the energy sector, including discharge to surface water (Danforth et al., 2019; USEPA, 2018). Beneficial uses of PW outside the energy sector will require much more intensive water treatment than that required to support HF where minimal treatment (clean brine) is sufficient. However, characterizing all of the constituents in PW, including flowback water from HF, is complicated because of difficulties with analytical techniques, problems with high salinity matrices, and lack of appropriate reference materials (Oetjen et al., 2017; Tasker et al., 2019). Less than a quarter of the ~1200 chemicals identified in PW have an approved analytical technique (Danforth et al., 2020). There is a lack of toxicological information for the majority of chemicals found in PW (Danforth et al., 2020). Treatment technologies for PW are continually advancing and selection of appropriate technologies will depend on the PW quality, water-quality requirements for reuse options, and treatment economics. To optimize PW reuse, fit-for-purpose treatment will be essential to minimize costs. Total Dissolved Solids (TDS) of PW from many UOG reservoirs may be too high (i.e. ≥~40 g/L) for traditional reverse osmosis (RO) approaches and more complex thermal distillation approaches may be required. Management of concentrates is also an important issue and can greatly increase treatment costs. Current water quality standards for different sectors, including irrigation and public water supplies, are insufficient for assessing the feasibility of using PW in these sectors because the standards did not consider many of the constituents present in PW (GWPC, 2019). For example, the standards for public water supplies only include 90 contaminants in the EPA primary list with most contaminants listed more than 20 years ago. The limited understanding of the toxicity of PW constituents underscores the risks and hazards to humans and the environment from reuse outside of the energy sector (Danforth et al., 2019). Projected exponential increases in PW from tight oil plays (Scanlon et al., in rev. ) raise the question about the adequacy of subsurface disposal capacity to accommodate the PW increases. Recent projections of PW over the life of the plays range from 1.1 TL (0.3 Tgal) in the Eagle Ford to 49 TL (13 Tgal) in the Permian Basin (Scanlon et al., in rev.). The projected PW volumes in the Permian represent ~3× water use in the state of Texas in 2017 (17 TL, 4.6 Tgal). Therefore, potential water scarcity, groundwater contamination, and induced seismicity concerns underscore the need to assess the potential to develop beneficial uses for PW to partially mitigate these issues.  

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The objectives of this study are to address the following questions: What is the potential for beneficially using PW from UOG reservoirs outside the energy sector based on volumetric water budgets? How feasible is beneficial use of PW considering water quality issues?

This study builds on a previous analysis that focused on reuse of PW from UOG reservoirs within the energy sector (Scanlon et al., in rev.). In the current study we examined a variety of potential beneficial uses for PW outside of the energy sector (Fig. 2). We quantified PW volumes relative to water demand for different sectors, including irrigation, municipal, livestock, and industrial uses. We briefly discussed issues with discharge to surface water and recharge to groundwater. The analysis covers the major UOG and CBM plays in the U.S., leveraging off of previous studies that quantified different components of the system in various regions (Graham et al., 2015; Horner et al., 2016; Kondash et al., 2017; Nicot et al., 2014; Scanlon et al., 2017). We do not consider PW from conventional reservoirs because this is mostly reinjected into the high permeability reservoirs with minimal adverse environmental impacts. However, we recognize that if incentives are created to reuse PW, operators may also consider PW from conventional reservoirs which could greatly increase the volumes of PW for reuse. For example, PW 4

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volumes from the Permian conventional reservoirs were ~ 10× greater than those from unconventional reservoirs (2005 – 2015) (Scanlon et al., 2017). We also evaluated the lifespan of PW from selected plays (Bakken, Eagle Ford, Marcellus and Permian plays) based on projected PW volumes, which is important for evaluating the reliability of PW feedstock for developing treatment options. This study complements the recent GWPC report assessing the feasibility of beneficial use of PW in different sectors by providing quantitative data on the relevant water volumes (GWPC, 2019). PW quality was evaluated using existing data from the USGS Produced Waters database (Blondes et al., 2017) and literature studies. Treatment options for PW reuse were examined and salt concentrate management was evaluated. The quantitative data provided in this assessment will be valuable to regulators and policy makers evaluating different options for managing PW.

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2.0 Materials and Methods The primary emphasis of this study was on major shale oil and gas plays within the U.S., often referred to as tight oil and shale gas (Fig. 1). The UOG plays evaluated include the Oklahoma Area of Interest (AOI in terms of high seismicity), Bakken, Barnett, Eagle Ford, Fayetteville, Haynesville, Marcellus, and Permian (Midland and Delaware Basins) plays. Water issues related to selected CBM plays were also examined, focusing on the Black Warrior, Powder River, Uinta, and San Juan plays. CBM plays were evaluated because they have a long history of PW management and they represent an end member in terms of TDS because the PW TDS is generally much lower than that from UOG reservoirs.

2.1 Volumetric Water Budgets

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The potential for beneficial use of PW depends on synergy between PW supplies and sectoral water demands and alignment of PW quality relative to quality requirements for different sectors. Data on PW volumes are available for ~100,000 UOG wells in the U.S. from state records and commercial databases (IHS Enerdeq). These data do not consider any reuse of PW for HF. Data on PW from 2017 were used in the analysis because PW reporting lags by at least one year in many of the plays (Texas plays: Barnett, Eagle Ford, Permian, and Haynesville). PW volumes in excess of HF water demand in 2017 were also calculated for the scenario with maximum reuse of PW for HF within the energy sector prior to considering reuse outside the energy sector. Water demand for different sectors—including irrigation, municipal, and industrial sectors—was obtained from the U.S. Geological Survey (USGS) compilation using the most recent data from 2015 (Dieter et al., 2018). PW volumes (2017) were compared to water demands for various sectors (2015) at the play level and also at the county level, the lowest spatial unit included in the USGS water use database. Projections of PW were compared with projections of HF water demand based on previous analysis of technically recoverable resource assessment over the life of the play assuming all potential wells will be drilled using current technology (Scanlon et al., in rev.). Data on projections are available for the Bakken, Eagle Ford, Permian, and Marcellus plays.

2.2 Produced Water Quality

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Data on PW quality were obtained from the USGS Produced Waters database, which is based primarily on conventional oil and gas reservoirs and CBM plays (Blondes et al., 2017). Details related to the data used in this study, including numbers of samples, types of analyses (TDS, major and trace element chemistry), and time periods covered are provided in Table S37. Additional data were obtained from the literature based on field studies of sampling in selected UOG plays. Most focus was placed on total dissolved solids (TDS) to evaluate water treatment options and treatment goals; however, we recognize that the TDS data alone are insufficient for assessing PW reuse outside of the energy sector. In particular, organics can be toxic at low concentrations and analytical tools to determine presence and concentration of organics are limited. Data on major and trace element chemistry were also compiled and we included analyses that had charge balances within ±10%. We reviewed treatment technologies based on PW quality and water quality requirements for different sectors or for discharge to surface water or recharge to aquifers. Options for managing concentrates were also examined because they can greatly affect costs.

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3.0 Results and Discussion 3.1 Spatiotemporal Variability in Produced Water Supplies PW volumes totaled ~600 BL (0.6 km3; ~160 Bgal) in 2017 from eight major UOG reservoirs (Fig. 1, Table 1). These eight plays account for 88% of tight oil and 84% of shale gas production in the U.S. based on 2018 data. PW volumes were much higher in western unconventional oil plays than in eastern unconventional gas, with 50× higher PW in the Permian oil play relative to the Marcellus gas play in 2017. PW volumes were much lower from CBM plays, totaling 46 BL (12 Bgal) in 2017.

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Beneficial use of PW would require a reliable supply of PW or feedstock. The only play with continuously increasing total PW volumes over the past decade is the Permian Basin where PW volumes increased by ~20× from 2011 to 2017 (Fig. 3a). PW volumes are not reported in Oklahoma but are approximated by SWD volumes which have remained fairly stable over the past several years at ~250 BL/yr (~65 Bgal/yr). PW volumes in many of the plays peaked in 2011 or 2014 and generally declined since then with decreasing oil and gas prices or resource depletion (2011 peak: Barnett, Fayetteville; 2014 peak: Eagle Ford, Bakken). PW from CBM plays peaked in 2009 and generally declined since then because of the reduction of CBM production (Fig. 3b, Fig. S2). For example, volumes of PW in the Powder River Basin (Wyoming) peaked in 2008 and declined by ~80% in 2017. The Permian Basin seems to provide the most reliable long-term PW feedstock based on the increasing PW volumes.

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PW volumes available for beneficial use in other sectors decrease substantially if the PW is first reused within the energy sector for HF (Fig. 1, Table 1). Reuse within the energy sector should be maximized because it represents the lowest risks relative to reuse in other sectors. HF water volumes exceeded PW volumes in about half of the plays; therefore, PW reuse for HF could potentially use up all of the PW depending on logistics. In contrast, PW exceeded HF water use in the remaining half of the plays (Bakken, Barnett, Oklahoma, and Permian Delaware basins). For example, PW in the Permian Delaware Basin was almost 2× HF water use in 2017. However, lack of reporting of PW reuse for HF precludes quantification of the extent of reuse within the energy sector. Other factors work against PW reuse for HF, such as landowners and organizations requiring operators to purchase water from them as part of lease agreements in Texas. For example, HF water demand in the Permian would represent ~ $0.5 billion in 2017 based on local water charges (~ $2.2/1000 L; $0.35/barrel) (Scanlon et al., 2017). The previous analysis focused on PW data from 2017. Projections of PW and HF water are also important for assessing the potential for PW reuse in the future. These data are available for the Bakken, Eagle Ford, Permian and Marcellus plays (Scanlon et al., in rev.). The potential for reuse outside of energy is similar for the projections and 2017 data for most plays except for the Permian Delaware Basin where the ratio of PW/HF water doubles over the life of the play (ratio: 3.6) relative to 2017 (ratio: 1.8). The increase in the ratio is attributed to the age of the well population, which is young in 2017 but increases substantially over the life of the wells (~20 yr). Therefore, there should be increased opportunity for reuse of PW outside of HF water demand in the Permian Delaware Basin within the next couple of decades. How long will PW be available for beneficial use? The PW volumes are projected to last ~25 yr for the Bakken and Eagle Ford plays, ~50 yr for the Permian Midland Basin, and ~70 to 80 yr for the Permian Delaware and Marcellus plays (Table 1). These estimates are based on projected well inventory over the life of the plays (Scanlon et al., in rev.) divided by the historical maximum drilling rate. Therefore, PW supplies would provide the most reliable feedstock in the Permian Delaware Basin. 7

Journal Pre-proof Most of the PW from UOG reservoirs has been managed by subsurface injection using SWD wells. Although PW and SWD volumes are reported separately without any direct linkage between the two, the reported SWD volumes provide a check on PW volumes (Table 1). SWD volumes are high in the Permian Basin and Haynesville play but include PW from both unconventional and conventional reservoirs. Cumulative PW and SWD volumes are similar in the Bakken and Eagle Ford plays. PW from CBM plays has not been managed using subsurface disposal but mostly surface disposal in ponds, as described in a later section.

3.2 Assessing Water Demand in Different Sectors Relative to Produced Water Supplies 3.2a Irrigation Sector

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The sector with the largest water demand is irrigation (2015 data), exceeding PW volumes in UOG plays (2017 data) by ~5× and exceeding PW volumes from CBM plays by ~50× (Fig. 1). Irrigation is concentrated mostly in the western U.S. (Figs. 4, S3). Box plots of water use in different sectors are provided in Figs. S4 and S5 and Tables S4 through S13. The much higher irrigation volumes relative to PW volumes at the play level means that the irrigation sector should be able to accommodate the PW volumes. If PW is reused for HF within the energy sector, there would be no excess PW in about half of the plays because HF water demand exceeds PW volumes in those plays (Table 1). The irrigation to PW ratio is similar in the remaining plays (ratio: 5). Irrigation could accommodate excess PW volumes in these plays, including the Permian Delaware (irrigation/excess PW ratio: ~10×) and Bakken (ratio: 30×) plays but not in Oklahoma AOI (ratio: ~0.6). There is also a temporal disconnect between PW, which is generated throughout the year, and irrigation demand, mostly restricted to summer months.

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Irrigation at the play level was highest in the Niobrara (870 BL, 230 Bgal) and Permian Basin (~840 BL, ~220 Bgal) plays in 2015 (Table 1). Although most (96%) PW in the Niobrara is from a single county (Weld County), HF water use exceeds PW in this county by ~4× and could reuse all of the PW (Fig. S10, S19; Table S18). If PW was used for irrigation, it would contribute only ~1% to irrigation in this county, with little impact on water scarcity. These results are consistent with previous findings (Dolan et al., 2018; Walker et al., 2017). Irrigation exceeded PW volumes by ~3× in the Permian Midland and Delaware Basins (Table 1). The most intensive irrigation is generally north of the UOG development (~2,500 BL; 660 Bgal), ~ 3× irrigation in the Midland and Delaware Basins (Fig. 4). PW represented 1%, 12%, and 17% of irrigation demand in counties with the highest irrigation (Eddy, Lea, and Pecos counties (2017) in the Permian Delaware basin) (Fig. S6, Table S14). These percentages would decrease to <<1%, 5%, and 11% if PW was reused to meet HF water demand in these counties. Counties with large volumes of PW relative to irrigation (e.g. Midland County: PW/irrigation ~30) could support expansion of irrigation but PW in this county represents ~3% of irrigation in the Permian. Irrigation in the Eagle Ford exceeded PW volume by ~6× (Table 1) with most irrigation in a few counties where PW would contribute <1% to irrigation demand. However, HF water use exceeded PW in most counties by up to 2– 3×; therefore, reuse of PW for HF would eliminate the PW source for irrigation. Irrigation in the Bakken/Three Forks is mostly restricted to a few counties, with PW accounting for <1% of irrigation in most counties. Total irrigation in the Oklahoma AOI is less than the PW volume but varies spatially (Table 1). Irrigation is generally much higher than PW volumes in the western CBM plays, ~45× PW in the Powder River Basin (Table 1), with PW contributing <5% to irrigation in most counties (Fig. S14, Table S23). In summary, irrigation could accommodate PW volumes in various regions of western plays; however, the high ratios of irrigation to PW in many counties suggest that PW volumes would not substantially 8

Journal Pre-proof reduce water scarcity in these regions. In many cases, HF water demand exceeds PW volumes and would eliminate the PW source for irrigation if PW was reused within the energy sector. In the past water transfers generally occurred from the irrigation sector to the oil and gas sector for HF in some plays, e.g. Bakken/Three Forks, Niobrara, and Permian plays (Horner et al., 2016; Kurz et al., 2016; Scanlon et al., 2016; Shuh, 2010). However, lack of reporting of water sourcing for HF makes it difficult to track water transfers among sectoral users.

3.2b Municipal, Livestock, Industrial, and Mining Sectors

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Many of the UOG reservoirs are located in rural areas with minimal municipal water use. Total municipal water demand in 2015 in the area of UOG reservoirs exceeded PW volumes in 2017 by ~2× (Table 1). Municipal demand was highest in the Niobrara (30% of total water demand) and Oklahoma AOI (22%), followed by the Barnett, Eagle Ford, and Marcellus (11%– 13%). PW would represent <0.1% of municipal demand in Niobrara counties with high municipal demand (Fig. S10). About 50% of the municipal demand in Oklahoma AOI is in Oklahoma County where PW would constitute ~3% of the municipal demand (Fig. S7). Similarly in the Marcellus, municipal demand was highest in a couple of counties but PW would only represent ≤3% of this demand because of the low PW volumes in this play (Fig. S12). Municipal demand in CBM plays was ~5×PW volumes, mostly in the Alabama portion of the Black Warrior Basin (Table 1). PW would represent ≤8% of municipal demand in the Black Warrior Basin. In summary, PW would contribute minimally to municipal demand in most cases from a volumetric standpoint. In the past, water has generally been transferred from the municipal sector to UOG reservoirs for HF in the Barnett, Niobrara, and Permian plays, either from freshwater or treated municipal waste water (Nicot et al., 2014; Scanlon et al., 2017; Walker et al., 2017).

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Water use for livestock was ~25% of total PW volume in UOG reservoirs in 2017 and was highest in the Haynesville and Eagle Ford plays (Table 1). Counties with high livestock water demand generally did not coincide with relatively high PW volumes in these plays. Livestock water use was negligible in CBM plays.

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Total volumes for industrial water uses were generally low in UOG and CBM regions (Table S1). The industrial water use category refers to self-supplied withdrawals for the industrial sector (Dieter et al., 2018).

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Thermoelectric cooling for power plants requires large water withdrawals in once-through cooling systems but consumption equals only a few percent of withdrawal (Dieter et al., 2018). This study focused on the consumptive water use for recirculating cooling towers which have lower water withdrawals and similar rates of water consumption than once-through systems. Water use for recirculating cooling was low, ~20% of PW, highest in the Oklahoma AOI (Table S5). PW would represent 23%–45% of cooling water use in counties with the highest water demand for these plants (Noble and Oklahoma counties). The mining water use sector includes water use for extraction of rocks and minerals (e.g. coal, sand, and gravel) and fossil fuels (Table S1)(Dieter et al., 2018). However, the mining values are difficult to interpret because they do not seem to be internally consistent. The mining values should include HF water but are less than HF water in the Marcellus and Niobrara, are similar to HF water in the Bakken, and are similar to HF water + PW in Texas plays (Barnett, Eagle Ford, and Permian). Therefore, the mining sector does not seem to provide an opportunity for reuse of PW. There may be some local cases where PW could be used in another mining sector. For example, PW could be used for potash mining in New Mexico; however, the potash mines are currently selling water to UOG operators because potash prices are low (Hayden, 2017). 9

Journal Pre-proof In summary, the most obvious sector for reuse of PW from a volumetric perspective is irrigation. With irrigation greatly exceeding PW volumes, it can accommodate the PW volumes in semiarid oil plays where PW volumes are highest. However, the PW volumes represent a small percentage of irrigation demand in most counties, particularly if PW is first reused for HF; therefore, PW will not substantially help reduce water scarcity concerns in these plays.

3.3 Surface Water Discharge and Managed Aquifer Recharge

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Additional beneficial uses of PW include discharge to surface water and recharging groundwater. Most PW from CBM plays has been discharged at the surface into unlined impoundments in Wyoming (~4000 permits by 2007 (Healy et al., 2011) or discharged to rivers, such as the Black Warrior River in Alabama without any or with minimal treatment (e.g. settling ponds). Comparing PW volumes with flow in the Black Warrior River, which is in a humid region, suggests that river discharge exceeds rates of PW generation by ~50 times during low flows and up to 400 times during normal flows (SI, Section 1a). Treated PW has also been discharged to surface water in the Marcellus play; however, there were contamination issues during the early years (SI, Section 1b). Incentives in the form of a tax credit ($0.13/barrel; $0.01/L) were put forward by New Mexico to promote discharge of treated PW into the Pecos River (SI, Section 1c). However, PW discharge from oil and gas wells within a 50 km corridor of the Pecos River (arid setting) would exceed annual stream discharge mostly by factors of 4×–10× but up to 20× in dry years and by much greater values during extremely dry years (Fig. S30b). The natural water quality in the Pecos River is quite variable, with total dissolved solids ranging from 1.6 to 17 g/L in different gages along the river based on USGS data (https://waterdata.usgs.gov/nwis). In summary, river discharge in humid regions greatly exceeds PW volumes, increasing the assimilative capacity of the rivers for treated PW. In contrast, rivers in semiarid regions are mostly ephemeral and discharge is much less than the PW volumes, complicating discharge of treated PW.

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The feasibility of groundwater recharge and aquifer storage and recovery (ASR) is also being considered in some plays, such as the Permian Basin. However, the risks related to such a practice seem high and potential unintended consequences large. Storing excess PW in the subsurface would provide a means to resolve PW supply relative to water demands for different sectors. An alternative to aquifer storage would be to use deeper geologic units, currently used for salt water disposal, such as the Delaware Mountain Group in the Permian Delaware Basin or the San Andres Formation in the Permian Midland Basin (Lemons et al., 2019). Pumping water from these units to support HF would reduce overpressuring from SWD and potential contamination of overlying aquifers (Ertel and Bogdan, 2017; Landis et al., 2016).

3.4 General Quality of Produced Water Produced water can contain oil and grease droplets, suspended solids, major elements, transition metals, naturally occurring radioactive material (NORM), organic compounds, and microbes. Chemicals present in HF fluids as reported in FracFocus (FracFocus.org) may also be contained in PW, particularly during the early stages of production. Data on PW quality are dominated by analyses from conventional oil and gas reservoirs from the USGS PW database with limited data from UOG reservoirs (Blondes et al., 2017). TDS provide a general indication of the mineral content of the PW with implications for water treatment and for salt management. Median TDS is highest in Bakken tight oil (255 g/L), ~7× that of sea water (Figs. 5, 6). TDS is moderately high in the Permian tight oil play (median: 158 g/L) and the Appalachian (Marcellus) shale gas play (147 g/L) with a lower value in the Eagle Ford shale play (74 g/L). The Permian TDS data include PW from unconventional units, such as the Wolfcamp and Cline Shales along with wells specifically 10

Journal Pre-proof designated as unconventional in the USGS database. The highest TDS (99th percentile) in shale oil and gas plays generally ranges from 300 to 340 g/L, with lower value in the Eagle Ford play (~160 g/L). No systematic difference exists between TDS in conventional and unconventional reservoirs as seen from the USGS database. There can be substantial variability in TDS within plays, both areally and vertically (Fig. 5). Recent analysis of Permian data reveal highest TDS in shallower zones near salt deposits and decreasing TDS with depth (Chaudhary et al., 2019). In the Eagle Ford, a salinity reversal and freshening of PW with a factor of 10 reduction in TDS from ~200 g/L at 2.5 km depth (1.6 miles) to ~ 20 g/L at 3.5 km (2.2 miles) was noted and attributed to clay conversion from smectite to illite with release of interlayer water (Nicot et al., 2018). PW from CBM plays is generally much fresher than that from the shale oil and gas plays, with median TDS ranging from ~1 g/L in the Powder River Basin to ~ 11 g/L in the Uinta Basin (Fig. 5).

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PW from tight oil and shale gas plays is dominated by Na (median: 30–78 g/L) and Cl (median: 55–152 g/L) (Fig. S31), consistent with previous studies indicating that nearly all basinal waters >10 g/L TDS are dominated by Na–Cl, with other ions existing only as minor or trace constituents (Hanor, 1994). Levels of Ca are generally much lower (~2– 13 g/L). Sulfate levels are mostly low (median: 0.020–0.430 g/L). PW from CBM plays is dominated by Na and Cl in the Black Warrior, Uinta, and Piceance Basins but Na and HCO3 in the Powder River, San Juan, and Raton Basins, reflecting marine versus terrestrial depositional environments (Fig. S32). Low sulfate concentrations in PW from CBM plays are attributed to methanogenesis. Median sodium adsorption ratios (SARs), important for irrigation, are generally high in PW from CBM plays but are quite variable among the plays, with medians ranging from 0.1 to 14 in different basins (Fig. S33). SARs > 3 generally require freshwater to flush the salts in irrigated lands and SARs > 13 can degrade soil texture (SI, Section 1d).

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Data on minor or trace elements in PW are limited. Here we only mention naturally occurring radioactive materials (NORMs) in PW, which mostly consist of 226Ra (half life: 5.75 yr) and 228Ra (half life: 1600 yr), derived from U and Th in the reservoir (Guerra et al., 2011). Total Ra (226Ra +228Ra) levels greatly exceed the EPA regulatory limit of 5 pCi/L (pico curies/L) for drinking water but are higher in the Marcellus shale (median, 1,500 pCi/L) and in the Bakken (790 – 1700 pCi/L) than in the Permian (480 pCi/L) or Eagle Ford (300 pCi/L) (Fig. S31).

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Combinations of compositional and isotopic data provide significant insight into the origin of PW from oil and gas reservoirs. The presence of Cl as the dominant anion in nearly all PW with salinity >10 g/L and maximum TDS concentrations several times seawater (35 g/L TDS) suggest that the dominant source of PW and ions is evaporated seawater and/or dissolution of Cl-bearing evaporites. Studies of UOG plays, including the Bakken, Marcellus, and Permian Basin, conclude that these same solute and water sources also dominate most shale reservoirs (Engle et al., 2016; Lauer et al., 2016; Rowan et al., 2015). Black shale specific processes, such as hydrocarbon maturation, clay diagenesis, and water-clay interactions have also been shown to control the composition of PW from unconventional plays (Engle et al., 2016; Nicot et al., 2018; Phan et al., 2016; Stewart et al., 2015). Sources of water and solutes in CBM plays vary, depending on geologic history and depth. Low TDS (median: 2.9 mg/L) Na-Cl-type waters found in much of the Black Warrior Basin indicate a marine origin (Pashin et al., 2014) with even lower TDS (median ~1 g/L) Na-HCO3 rich water from the Powder River Basin reflecting meteoric water which has undergone a series of geochemical reactions within the coal beds from which they are produced (Brinck et al., 2008). 11

Journal Pre-proof 3.4b Evaluating Water Quality Requirements for Different Sectors Relative to Produced Water Quality

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There is a long history of assessments of potential reuse of PW from CBM plays for irrigation and surface water discharge (Arthur et al., 2005; Guerra et al., 2011). CBM PW discharges are managed outside of national programs and are subjected to local permitting requirements. PW from CBM plays is much higher quality than that from shale UOG plays, with median TDS values of 1 – 11 g/L (Fig. 6). In addition, CBM PW does not contain the chemicals from HF. However, CBM PW does contain polycyclic aromatic hydrocarbons from the associated coal (Orem et al., 2014). For example, PW in the Black Warrior Basin (median TDS, ~3 g/L) is discharged directly to the Black Warrior River in Alabama where it is diluted (SI, Section 1a). However, some issues related to use of CBM PW for irrigation include SAR and negative impacts on soil infiltration and other toxic constituents, such as boron etc (SI, Section 1d). Use of high quality PW from CBM for irrigation can leach salts from semiarid soils, resulting in poor quality water reaching underlying aquifers with up to 100 g/L TDS in groundwater near an impoundment in Wyoming (Healy et al., 2011). Water quality standards and regulations for water use in irrigation, livestock, and municipal sectors (drinking water maximum contaminant levels and irrigation and land application standards) do not consider many of the risks related to use of PW from UOG reservoirs and are not appropriate for assessing such use (GWPC, 2019). For example, the EPA primary drinking water regulations include ~65 contaminants within the chemical contaminant rules, including inorganics, and volatile and synthetic organics (https://www.epa.gov/dwreginfo/chemical-contaminant-rules). Assessing treatment of PW by comparing to drinking water standards is insufficient because the regulations were not designed to consider PW.

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Surface discharges of PW from UOG wells are regulated under the National Pollution Discharge Elimination System (NPDES) and related national effluent limitation guidelines or corresponding state regulations (GWPC, 2019). EPA prohibits discharge of PW from UOG plays to public owned treatment works but PW can be discharged to Centralized Water Treatment (CWT) facilities. Because of the large number of potential organic contaminants in PW and difficulties in analyzing many of these elements within the context of high salinity matrices (Danforth et al., 2019; Luek and Gonsior, 2017; Nelson et al., 2014; Oetjen et al., 2017), it seems infeasible to conduct a comprehensive evaluation of PW chemistry. Detailed risk assessment will be required to evaluate potential human health and environmental impacts of beneficial uses of PW outside of the energy sector. The GWPC report outlines many of the aspects of a suitable risk assessment, building on previous studies (NRC, 2009). Whole effluent toxicity (WET) assessment is proposed to address known and potential unknown contaminants (GWPC, 2019).

4.0 Treatment Options for Produced Water Reuse Applications Selection of the appropriate treatment technologies depends primarily on two factors: (1) the quality of the input water or feed water, particularly salinity and other inorganic and organic constituents and (2) the quality of the water that is generated relative to the requirements for beneficial use. Recovery efficiency and waste generation from treatment are also important factors.

4.1 Desalination of Produced Water for Industrial, Agricultural, and Potable Reuse Removal of dissolved solids (desalination) is required for applications that require high water quality. Two primary technologies currently used for water desalination include those based on (1) membrane 12

Journal Pre-proof technologies or on (2) thermal technologies (Fig. 7). Additional information on treatment technologies is provided in SI, Sections 2 and 3.

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Membrane technologies include electrodialysis (ED), electrodialysis reversal (EDR), nanofiltration (NF), and reverse osmosis (RO). NF and RO use high hydraulic pressure to diffuse pure water through a dense non-porous membrane and retain solutes on the feed water side of the membrane. In general, RO is capable of treating PW with TDS up to ~40 g/L due to the limitation of pressure vessels; however, RO becomes too energy intensive and expensive at much lower levels of TDS (~15 – 35 g/L). Water recovery varies with salinity, ranging from 30% to 60% for seawater (35 g/L) to 60% to 85% for brackish water (≤10 g/L) (Igunnu and Chen, 2014). RO treatment is effective in removing almost all inorganic contaminants, including NORM; however, additional analytical techniques are required to determine whether some organics remain in the treated water. To minimize membrane scaling and fouling, RO requires extensive pretreatment to remove sand, silt, clay, algae, microbes, colloidal particles and large molecular organics (e.g., petroleum hydrocarbons), and sparingly soluble salts. RO has been applied to PW from the Marcellus, Barnett, and Fayetteville plays (ALL, 2010).

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Thermal technologies (e.g., multiple-effect distillation [MED], mechanical vapor compression [MVC] and recompression [MVR]) are almost independent of source water salinity (Fig. 7). Thermal distillation technologies involve heating and evaporating feed water followed by condensation of pure water. Typical water recoveries range from 20% to 35% for MED to 40% for MVC (Igunnu and Chen, 2014). These low water recoveries result in large volumes of concentrate that need to be disposed of. Biocides are not required because of the elevated temperature. MVR has been applied to waters with up to 300 g/L TDS and can generate high quality water (Nasiri et al., 2017). MVR can be used as a crystallizer for systems with zero liquid discharge (ZLD). However, managing solids is often challenging; therefore, systems designed to generate a concentrated brine are often preferred (GWPC, 2019). Thermal approaches have high-energy requirements and are generally used where waste heat is available.

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In addition, emerging technologies are being developed to improve certain aspects of the performance of existing desalination processes (e.g., increasing recoveries, reducing fouling, decreasing energy consumption and capital and operating costs). These new technologies can be classified into three categories: thermal (membrane distillation, MD), physical (forward osmosis, FO), and chemical (capacitive deionization). MD uses a heat source to enhance mass transport through membranes. One of the advantages of this approach is its ability to use any level of TDS in the feed solution. Solutes, including Na, SiO2, B, and heavy metals, are rejected at nearly 100%. Water recovery can be improved when paired with crystallizer technologies. A research example based on treating PW with ~250 g/L TDS showed this approach to be cost competitive (Macedonio et al., 2014). Forward osmosis is an osmotic pressure driven membrane process (Hickenbottom et al., 2013; Xu et al., 2013). Water diffuses from a feed stream with low osmotic pressure through a semi-permeable membrane to a draw solution with high osmotic pressure. No external high pressure is required by an FO system. Other hybrid configurations are also being developed by different companies, such as the Veolia OPUSTM system. Development of cost-effective desalination technologies represents the new frontier of PW treatment research. Although these emerging technologies have shown promise in highly saline PW treatment, improvements in membrane properties, membrane design, and module hydrodynamics are expected to further increase system efficiency (Shaffer et al., 2013). A limited number of treatment plants have been developed for PW. Antero Resources built a large desalination plant (Antero Clearwater Facility) in the Marcellus to treat up to 10 million liters of PW/day (GWPC, 2019). The estimated cost was ~$300 million; however, the facility was recently closed for evaluation. Eureka Resources developed three centralized wastewater treatment facilities to generate 13

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water fit for discharge from PW in the Marcellus (Mueller, 2017). Treatments include mechanical vapor recompression distillation and crystallization. ALL Consulting provided a treatment technology tool that includes treatment types and vendors for specific basins: Marcellus, Fayetteville, Haynesville, Woodford, and Barnett; however, the information is generally applicable to other basins (http://www.allllc.com/projects/produced_water_tool/). Besides salts, PW and flowback water contain complex organic constituents such as oil and grease, BTEX (benzene, toluene, ethylbenzene and xylene), PAHs (polycyclic aromatic hydrocarbons), biopolymers, and humic substances (Danforth et al., 2020; Khan et al., 2016). These organic constituents in high salinity water present unique challenges to most technologies. Organic matter must be removed first to minimize fouling of membranes or other surfaces, and prevent environmental impacts during disposal or reuse. Biological processes have been successfully used to remediate water contaminated by petroleum hydrocarbons, solvents, and other dissolved organic chemicals commonly observed in PW. The effectiveness of biological processes varies depending on the properties of chemicals present and their respective concentrations, as well as the salinity level in PW. For example, organic compounds such as BTEX and PAHs are readily biodegradable in aerobic processes whereas halogenated organic compounds or highly chlorinated compounds are more refractory. Physico-chemical treatment, such as adsorption and advanced oxidation processes, can be used to remove organic contaminants. Because the treatment technologies may not be highly effective in removing contaminants, risk assessment should be conducted on the treated PW also to evaluate the impact of PW reuse on public health and environment. Limited information on concentrate management indicates that PW is often treated to a point where the residual is still sufficiently liquid to be injected into a SWD well. The low recoveries of thermal distillation techniques result in up to 80% concentrate that is generally injected into SWD wells. In some cases, the concentrate is solid (ZLD) and the products are either marketed (salts) or disposed of in landfills (Ertel and Bogdan, 2017). For example, PW from the Delaware Basin in 2017 (160 BL, 43 Bgal) would result in 16 ×109 kg of salt or 16 million tons assuming a TDS of ~ 100 g/L (SI, Section 3). This would correspond to a volume of solids approximating ~3,000 Olympic swimming pools. Disposal of solid wastes laden with contaminants transferred and concentrated from PW may be cost prohibitive, and may not be a viable option to reach ZLD or high water recovery for PW treatment.

4.2 Implications for Produced Water Management

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There is considerable interest in beneficially using PW outside of the energy sector because of the perception that PW represents huge water volumes and reuse would retain the water within the hydrologic cycle whereas subsurface disposal removes it from the active hydrologic cycle. The total volume of PW from UOG reservoirs in 2017 (~600 BL, ~160 Bgal) corresponds to ~ 60% of fresh water use in the U.S. in one day, excluding thermoelectric water use. However, most of the PW is generated in semiarid regions where water scarcity is a big concern. In gas plays (Haynesville, Marcellus) and some oil plays (Eagle Ford, Niobrara, and Permian Midland), HF water demand exceeds PW volumes; therefore, much of this PW could be reused within the energy sector and reduce water scarcity caused by pumping water to supply HF. Reuse within the energy sector represents much less risk with minimal treatment and related low costs and energy use than beneficial use of PW in other sectors. The most likely sector to reuse PW in semiarid western U.S. is irrigation. Irrigation exceeds PW volumes in many plays, except the Oklahoma AOI, Barnett play, and Permian Delaware Basin. If we assume that PW is first reused within the energy sector, only half of the plays would have excess PW relative to HF water demand. Considering water treatment requirements and recovery factors would further reduce the PW volumes. PW as a percent of irrigation would represent 2% of irrigation in the Bakken, 5% in the 14

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5.0 Conclusions

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Permian Delaware Basin, 63% in the Barnett, and 77% in Oklahoma AOI, assuming 50% recovery factors for treatment. The percentages are more variable at the county scale, showing counties with large potential in the Oklahoma AOI and Barnett. Some point to examples in California where PW is reused for irrigation; however, the water quality is quite high and treatment is minimal (SI, Section 4). Other sectoral uses represent more localized demands, such as municipal and industrial uses. Detailed site specific studies would be required before discharging PW to surface water or recharging groundwater would be considered. Therefore, it does not seem that PW reuse will mitigate water scarcity concerns in most regions. Water scarcity related to oil and gas development would be more readily addressed by reusing PW within the energy sector in different plays. Development of treatment plants for beneficial reuse of PW would require a reliable feedstock. Maintaining PW volumes requires continued drilling because of exponential declines in PW volumes with time from UOG and CBM plays (Fig. 8). Many factors currently do not support reuse of PW outside of the energy sector. From a volumetric perspective, reuse of PW within the energy sector would eliminate half of the plays because HF water demand exceeds PW in these plays. In the remaining plays, PW represents a small fraction of water demand for irrigation mostly at the play and county level. In the future, high projected PW volumes in the Permian Delaware Basin, exceeding projected HF water demand, would support PW reuse outside of energy in future decades. From a water quality perspective, the following limitations restrict the potential for PW reuse outside of energy: poor knowledge of PW chemistry, inability to accurately measure the PW quality because of high salinity matrix and interference issues, lack of acceptable measurement techniques, absence of suitable standards, and lack of regulations for various sectors to consider the complexity of PW. In addition, suitable treatment technologies, such as thermal distillation, are expensive and have high energy demands. The efficiency of different treatment technologies in removing certain contaminants, particularly those with a boiling point similar to water, for example, is also not known. Because of these many uncertainties, more emphasis is placed on risk assessment, whole effluent toxicity, and related factors. The risks and liabilities associated with PW reuse outside the energy sector are high and much more data are required to address uncertainties in this field before such reuse should be considered.

Although interest in beneficially reusing the large volumes of PW generated from UOG reservoirs is increasing in the U.S., quantitative analysis of the volumetric and water quality issues does not support reuse outside of the energy sector. PW volumes in 2017 totaled ~600 BL (160 Bgal) from UOG reservoirs, primarily from tight oil reservoirs in the semiarid western U.S., and ~45 BL (12 Bgal) from CBM reservoirs. Beneficial reuse outside of the energy sector would favor irrigation, the largest water user. Irrigation exceeds PW from UOG reservoirs by ~5× and PW from CBM reservoirs by ~50×. Reuse of PW for HF water demand within the energy sector would reduce the number of UOG plays with excess PW by about half. PW requires intensive treatment for reuse outside of energy. If we assume an average recovery factor from treatment of ~50%, then the ratio of irrigation to PW would be doubled. Considering all of these factors, plays with potential for PW reuse for irrigation include Oklahoma AOI, Barnett, and Permian Delaware Basin. PW volumes in the Permian Delaware Basin would represent ~5% of the irrigation demand. PW projections relative to HF water demand would double in the Permian over the life of the play. Other sectoral users may provide local potential for reuse, including municipal, livestock and industrial uses but are generally 15

Journal Pre-proof limited based on volumetric analysis. Discharging PW to surface water is also being considered but would not be substantially diluted in western streams. Recharging depleted aquifers is also a consideration; however, water quality issues may preclude this option.

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Variable TDS of PW from UOG reservoirs (median TDS≤ 255 g/L in the Bakken, up to 7× seawater), would mostly require thermal distillation approaches to treat the PW. PW from CBM reservoirs is much higher quality (median TDS: 1– 11g/L) and does not include HF water. Evaluation of PW from CBM plays provides an example of PW that can be considered for potential reuse outside the energy sector. It is difficult to characterize the PW quality from UOG reservoirs because of problems with measurements, interferences caused by the high salinity matrix, and lack of suitable standards resulting in many unknowns. Uncertainties in treatment efficiency and problems with contaminants leaking through the treatment process further increases risks of reuse. The current regulations for various sectoral uses and discharge requirements were not designed to address PW issues. Therefore, large uncertainties related to water quality issues currently preclude PW reuse outside of the energy sector.

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In summary, water scarcity issues are more readily addressed by reusing PW within the energy sector rather than beneficial use of PW outside of the energy sector. Much more research is required to safely reuse PW in other sectors or discharge to surface waters or recharge aquifers.

6.0 Acknowledgments

7.0 Supporting Information

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We are very grateful for financial support for this study from the Mitchell Foundation, Sloan Foundation, ExxonMobil, and Jackson School of Geosciences Endowment. We very much appreciate access to the IHS Enerdeq database.

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Raw data on water volumes and water quality used in study are archived in Mendeley Data (doi: 10.17632/jjy5mtfkfk.2) and described in an associated data article(Scanlon et al., submitted). Additional figures and tabulated data are provided in the Supporting Information.

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8.0 References

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ALL. Water treatment technology fact sheet: reverse osmosis. ALL Consulting. 2010. Arthur JD, Langhus BG, C. P. Technical summary of oil & gas produced water treatment technologies. Report Prepared by ALL Consulting for the National Energy Technology Lab. (NETL) and the Dept. of Energy (DOE). 2005. Barnes CM, Marshall R, Mason J, Skodack D, DeFosse G, Smigh DG, et al. The new reality of hydraulic fracturing: treating produced water is cheaper than using fresh. SPE-174956-MS, Society of Petroleum Engineering, 29 p. 2015. Blondes MS, Gans KD, Engle MA, Kharaka YF, Reidy ME, Sarraswathula V, et al. U.S. Geological Survey National Produced Waters Geochemical Database v2.3 (provisional), https://energy.usgs.gov/EnvironmentalAspects/EnvironmentalAspectsofEnergyProductionandU se/ProducedWaters.aspx#3822349-data. 2017. Brinck EL, Drever JI, Frost CD. The geochemical evolution of water coproduced with coalbed natural gas in the Powder River Basin, Wyoming. Environmental Geosciences 2008; 15: 153-171. Chaudhary BK, Sabie R, Engle MA, Xu P, Willman S, Carroll KC. Spatial variability of produced-water quality and alternative-source water analysis applied to the Permian Basin, USA. Hydrogeology Journal 2019; 27: 2889-2905. Clark C, Veil J. Produced water volumes and management practices in the United States. Rep. ANL/EVS/R-09/1, Argonne Natl. Lab., Argonne, Ill. 2009. Danforth C, Chiu WA, Rusyn I, Schultz K, Bolden A, Kwiatkowski C, et al. An integrative method for identification and prioritization of constituents of concern in produced water from onshore oil and gas extraction. Environment Intl. 2020; 134: 677-682. Danforth C, McPartland J, Blotevogel J, Coleman N, Devlin D, Olsgard M, et al. Alternative Management of Oil and Gas Produced Water Requires More Research on Its Hazards and Risks. Integrated Environmental Assessment and Management 2019; 15: 677-682. Dieter CA, Maupin MA, Caldwell RR, Harris MA, Ivahnenko TI, Lovelace JK, et al. Estimated use of water in the United States in 2015. U.S. Geological Survey Circular 1441, 65 p. 2018. Dolan FC, Cath TY, Hogue TS. Assessing the feasibility of using produced water for irrigation in Colorado. Science of the Total Environment 2018; 640: 619-628. Engle MA, Reyes FR, Varonka MS, Orem WH, Ma L, Lanno AJ, et al. 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 2016; 425: 76-92. Ertel DJ, Bogdan JJ. A sustainable choice for unconventional oil and gas wastewater management/treatemnt when options are limited. EM, August 2017, 2017: 17-23. Ferguson G, McIntosh JC, Perrone D, Jasechko S. Competition for shrinking window of low salinity groundwater. Environmental Research Letters 2018; 13. Graham EJS, Jakle AC, Martin FD. Reuse of oil and gas produced water in south-eastern New Mexico: resource assessment, treatment processes, and policy. Water International 2015; 40: 809-823. Greaves R, Hartstein R, Lincicome D, Beck P, Boothe M, Olson KE. Fresh Water Neutral: Managing Water Use and Giving Back to the Environment. SPE Annual Technical Conference and Exhibition. Society of Petroleum Engineers, San Antonio, Texas, USA, 2017, pp. 27. Guerra K, Dahm K, Dundorf S. Oil and Gas Produced Water Management and Beneficial Use in the Western United States. Bureau of Reclamation Science and Technology Report No. 157, 113 p. 2011. GWPC. Produced Water Report: Regulations, Current Practices, and Research Needs. Groundwater Protection Council (GWPC), 310 p. 2019.

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Scanlon BR, Weingarten MB, Murray KE, Reedy RC. Managing Basin-Scale Fluid Budgets to Reduce Injection-Induced Seismicity from the Recent U.S. Shale Oil Revolution. Seismological Research Letters 2019; 90: 171-182. Shaffer DL, Arias Chavez LH, Ben-Sasson M, Romero-Vargas Castrillon S, Yip NY, Elimelech M. Desalination and reuse of high-salinity shale gas produced water: drivers, technologies, and future directions. Environ Sci Technol 2013; 47: 9569-83. Shuh WM. Water appropriation requirements, current water use, & water availability for energy industries in North Dakota—a 2010 summary: Response to House Bill 1322, Section 2 of the 61st Legislative Assembly of North Dakota, Water Resources Investigation No. 49, North Dakota State Water Commission, August 2010, www.swc.state.nd.us/4dlink9/4dcgi/ GetContentPDF/PB1800/W&E%20RPT%20FinalR.pdf (accessed 2014). 2010. Stewart BW, Chapman EC, Capo RC, Johnson JD, Graney JR, Kirby CS, et al. Origin of brines, salts and carbonate from shales of the Marcellus Formation: Evidence from geochemical and Sr isotope study of sequentially extracted fluids. Applied Geochemistry 2015; 60: 78-88. Tasker TL, Burgos WD, Ajemigbitse MA, Lauer NE, Gusa AV, Kuatbek M, et al. Accuracy of methods for reporting inorganic element concentrations and radioactivity in oil and gas wastewaters from the Appalachian Basin, US based on an inter-laboratory comparison. Environmental ScienceProcesses & Impacts 2019; 21: 224-241. Torres L, Yadav OP, Khan E. A review on risk assessment techniques for hydraulic fracturing water and produced water management implemented in onshore unconventional oil and gas production. Science of the Total Environment 2016; 539: 478-493. USEPA. EPA signs MOU with New Mexico to explore wastewater reuse options in oil and natural gas industry. [accessed 2018 Jul 30]. https://www.epa.gov/newsreleases/ 2018. Veil J. U.S. Produced Water Volumes and Management Practices in 2012. Report prepared for the Groundwater Protection Council, April 2015. 2015. Walker EL, Anderson AM, Read LK, Hogue TS. Water Use for Hydraulic Fracturing of Oil and Gas in the South Platte River Basin, Colorado. Journal of the American Water Resources Association 2017; 53: 839-853. Walsh FR, Zoback MD. Oklahoma's recent earthquakes and saltwater disposal. Science Advances 2015; 1. Xu P, Cath TY, Robertson AP, Reinhard M, Leckie JO, Drewes JE. Critical review of desalination concentrate management, treatment and beneficial use. Environmental Engineering Science 2013; 30.

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Figure 1. Comparison of water demand for irrigation (2015), produced water volumes and hydraulic fracturing water demand (2017) for shale oil and gas reservoirs (Bakken, Niobrara, Permian (Midland and Delaware basins), Eagle Ford, Barnett, Oklahoma Area of Interest (AOI), Haynesville, Fayetteville, and Marcellus) and coal bed methane reservoirs (Powder River, San Juan, Uinta, and Black Warrior basins). See Fig. S1 for units in billion gallons. Figure 2. Beneficial use of produced water within the energy sector (hydraulic fracturing) and outside the energy sector (irrigation, municipal, industrial, livestock), surface water discharge (evaporation ponds, stream discharge) and groundwater recharge.

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Figure 3. Time series of Produced Water (PW) volumes for a) the major tight oil and shale gas plays and b) the coal bed methane plays. Data for Oklahoma represent statewide values. The data are tabulated in Tables S2 and S3.

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Figure 4. Distribution if irrigated lands in the US based on composite satellite images for 2002, 2007, and 2012 based on Moderate Resolution Imaging Spectroradiometer (MODIS) Irrigated Agriculture Dataset for the United States (MIrAD-US) (https://earlywarning.usgs.gov/USirrigation). The various play regions discussed in this study are highlighted. The area of focused unconventional oil and gas development located in a 19-county region of the Permian Basin is also outlined within the basin showing most intensive irrigation north of the UOG development.

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Figure 5. Total dissolved solids of produced water from the USGS Produced Waters database (version 2.3) with supplemental data for the New Mexico region of the Permian Basin provided by the New Mexico Institute of Mining and Technology (NMIMT) Petroleum Research and Recovery Center (PRRC), and data from the USGS in the Eagle Ford Play. Labeled values represent median produced water TDS concentrations within each play area of wells classified as either shale gas, tight oil, or coal bed methane, with the exception that the Permian value includes wells that are classified as conventional hydrocarbon wells that are completed in unconventional formations (i.e., Wolfcamp, Bone Spring, Cline, Spraberry, and Dean). Data are provided in Table S26.

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Figure 6. Total dissolved solids (TDS) for tight oil (TO) and shale gas (SG) reservoirs (unconventional oil and gas reservoirs), conventional oil and gas reservoirs (Conv), and coal bed methane (CBM) reservoirs. The Bakken unconventional tight oil includes the Bakken and underlying Three Forks units. Coal bed methane reservoirs include Powder River, Raton, Black Warrior, and Uinta basins. The numbers at the base refer to the number of analyses. For locations of reservoirs, see Fig. 1. The USGS data are provided in Table S26. Additional data were obtained from Nicot et al. (2018). Figure 7. Treatment technologies for produced water, including minimal treatment of PW for hydraulic fracturing (clean brine), desalination for beneficial uses in various sectors, surface water discharge and groundwater recharge, and posttreatment technologies. TDS: total dissolved solids; ED: electrodialysis; NF: Nanofiltration; BWRO: brackish water reverse osmosis; SWRO: seawater reverse osmosis; MED: multiple effect distillation; MVC: mechanical vapor compression; MVR: mechanical vapor recompression, emerging technologies including FO: Forward Osmosis; MD: membrane distillation. AOP: advanced oxidation processes.

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Figure 8. Produced water decline curves for the major Tight Oil (TO: Bakken, Midland, Delaware), Shale Gas (SG: Marcellus), mixed TO and SG, (Eagle Ford) plays and for the Powder River Basin coal bed methane play (PRB). Data represent the median monthly produced water volumes expressed as a percentage of first-month production for wells completed during 2015-2017, except the PRB (19892018) in which few wells produce longer than 10 years. Note that the Delaware and Marcellus declines are virtually identical.

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Journal Pre-proof Declaration of interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

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Journal Pre-proof Table 1. Volumes (109 L) of produced water (PW), saltwater disposal (SWD), and hydraulic fracturing (HF) water during 2017 compared with irrigation (Irrig) and municipal (Muni) water use during 2015 and projected remaining total PW volumes. Also listed are the remaining years of well completion activity based on the projected well inventory and historical annual maximum number of wells drilled per year for selected plays. For more details on the projections, see Scanlon et al., in rev. Data for additional sectors are provided in metric and English units in Table S1. The total irrigation volume over all of the unconventional oil and gas plays sums 2,824 BL which is 5× the PW volume summed over these plays. Total irrigation in CBM plays (2,376 BL) is ~ 50× the PW volume. 2017 Play name

Projections

2015

Projected HF Water

Proj. Well Invent.

Max. Wells per yr

49,300

18,200

320,000

5,000

64

39,400

10,800

207,000

2,600

80

9,900

7,400

113,000

2,400

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-

-

Projected PW

841.7

65.1

708.7

54.0

119.4

132.9

11.1

195.3

28.0

108.7

270.1

54.6

56.7

29.3

747.5

18.8

35.1

38.9

66.2

219.1

Niobrara

6.7

6.4

28.0

Barnett

42.5

42.5

HF

Irrig

Permian

264.4

378.6

210.2

Delaware

164.2

217.7

90.8

Midland

100.3

160.9

OK AOI

195.3

Bakken Eagle Ford

69,000

2,700

25

144.6

1,100

3,200

105,000

4,000

26

867.4

362.8

-

-

-

1.4

32.9

134.2

-

-

-

3.9

161.6

2,200

1,700

73

2.6

76.4

-

-

-

2824 1,172.5

1234 18.4

55100 -

-

-

-

103.8

7.3

-

-

-

-

855.5

36.5

-

-

-

-

16.9

171.7

-

-

-

-

227.6

9.9

-

-

-

2,376

243.8

3.6

606 26.1

763 -

393 -

Raton

7.8

-

San Juan

5.7

-

BW

4.9

-

Uinta

1.7

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46.2

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26.0

45.0

lP

-

2.2

na

5.3

-p

1,700

Haynes.

-

-

Rem. Years

2,500

Marcellus

PRB

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SWD

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Muni

PW

ur

Play Type

5,200

124,000

Haynes: Haynesville Play; PRB: Powder River Basin; BW, Black Warrior Basin; PW volumes are not reported for the Oklahoma AOI but are approximated by SWD volumes. PW and SWD volumes are assumed equal in the Barnett because of uncertainties in PW volumes. The Permian data represent the sum of data from the Midland and Delaware basins and do not include development outside of these basins.

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Highlights:  Irrigation demand exceeds produced water volumes by 5 times.  Produced water quality is variable with salinity up to 7× seawater.  Intensive treatment is required for produced water use outside of energy.  Produced water volumes would not substantially alleviate overall water scarcity.  Knowledge gaps related to produced water quality preclude reuse outside of energy.

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