![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.](https://www.researchgate.net/publication/338994684/figure/fig1/AS:873790682714117@1585339341814/Comparison-of-water-demand-for-irrigation-2015-produced-water-volumes-and-hydraulic_Q320.jpg)
Available via license: CC BY 4.0
Content may be subject to copyright.
Can we beneficially reuse produced water from oil and gas extraction in
the U.S.?
Bridget R. Scanlon
a,
⁎, Robert C. Reedy
a
,PeiXu
b
,MarkEngle
c
,J.P.Nicot
a
, David Yoxtheimer
d
,
Qian Yang
a
, Svetlana Ikonnikova
a
a
Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, TX, United States of America
b
New Mexico State University, Civil Engineering Department, Las Cruces, NM, United States of America
c
Dept. of Geological Sciences, The University of Texas at El Paso, TX, United States of America
d
Earth and Environmental Systems Institute, College of Earth and Mineral Science, Penn State Univ., PA, United States of America
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 pro-
duced 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.
GRAPHICAL ABSTRACT
abstractarticle info
Article history:
Received 20 December 2019
Received in revised form 31 January 2020
Accepted 1 February 2020
Available online 3 February 2020
Editor: Dr. Damia Barcelo
There is increasing interest in beneficialuses of large volumes of wastewaterco-produced with oil andgas extrac-
tion (produced water,PW) because of water scarcity, potential subsurface disposal limitations,and regional link-
ages to inducedseismicity. Here we quantified PW volumes relative to waterdemand in different sectorsand PW
quality relative to treatment and reuse options for the major U.S. shaleoil and gas plays. PW volumes from these
plays totaled ~600 billion liters (BL, 160 billion gallons, Bgal) in 2017. One year ofPW is equal to ~60% of one day
of freshwater use in the U.S. For these plays, the totalirrigation 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
~3000 Olympic swimming pools in the Permian Delaware Basin in 2017. While water demands outside the en-
ergy sectorcould accommodate PW volumes, much lowerPW volumes relative to water demand in most regions
would not substantially alleviate water scarcity. However, large projected PW volumes relative to HF water de-
mand over the life of the play in the Permian Delaware Basin may provide a substantial new water source for
Science of the Total Environment 717 (2020) 137085
⁎Corresponding author.
E-mail address: bridget.scanlon@beg.utexas.edu (B.R. Scanlon).
https://doi.org/10.1016/j.scitotenv.2020.137085
0048-9697/© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Contents lists available at ScienceDirect
Science of the Total Environment
journal homepage: www.elsevier.com/locate/scitotenv
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.
© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://
creativecommons.org/licenses/by/4.0/).
1. Introduction
Co-production of large volumes of waste water or produced water
(PW) with theexpansion of energy production from shale or unconven-
tional 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 pro-
duced when coal beds are dewatered to mobilize methane, often
termed coal bed methane (CBM) (NASEM, 2010). Previous analysis es-
timated the total PW volumes in the U.S. to be ~3.4 trillion liters (TL;
3.4 km
3
~0.9 trillion gallons, Tgal) in 2012 (Veil, 2015), similar to previ-
ous estimates from 2007 (Clark and Veil, 2009). Most PW is injectedinto
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 ad-
jacent 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 Okla-
homa 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).
Various PW management approaches have been suggested to re-
duce 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
sourcingto support HF. A recent analysis comparedPW 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., 2020). 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 per-
centage 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 regu-
lations precluding landowners from requiring operators to purchase
water for HFwhen PW is available (New Mexico House Bill 0546). How-
ever, even in shale gas plays with low PW volumes, downturns in dril-
ling 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.
Fig. 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.
2B.R. Scanlon et al. / Science of the Total Environment 717 (2020) 137085
Another approach for managing PW is to reuse it outside of the en-
ergy 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 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, includ-
ing 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, charac-
terizing 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 tech-
nique (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 selec-
tion 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 mini-
mize costs. Total Dissolved Solids (TDS) of PW from many UOG reser-
voirs 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 con-
stituents 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 N20 years ago. The limited under-
standing of the toxicity of PW constituents underscores the risks and
hazards to humans and the environment from reuse outside of the en-
ergy sector (Danforth et al., 2019).
Projected exponential increases in PW from tight oil plays (Scanlon
et al., 2020) raise the question about the adequacy of subsurface dis-
posal 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.,
2020). 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
concernsunderscore the need to assess the potentialto develop benefi-
cial uses for PW to partially mitigate these issues.
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., 2020). 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, mu-
nicipal, 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 previ-
ous studies that quantified different components of the system in vari-
ous 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 im-
pacts. However, we recognize that if incentives are created to reuse
PW, operators may also consider PW from conventional reservoirs
Fig. 2. Beneficial use of produced water withinthe energy sector (hydraulic fracturing) and outside the energy sector (irrigation, municipal, industrial, livestock), surface water discharge
(evaporation ponds, stream discharge) and groundwater recharge.
3B.R. Scanlon et al. / Science of the Total Environment 717 (2020) 137085
which could greatly increase the volumes of PW available for reuse. For
example, PW 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 se-
lected plays (Bakken, Eagle Ford, Marcellus and Permian plays) based
on projected PW volumes,which is important for evaluatingthe reliabil-
ity of PW feedstock for developing treatment options. This study com-
plements the recent GWPC report assessing the feasibility of beneficial
use of PW in different sectors by providing quantitative data on the rel-
evant 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 ex-
amined and salt concentrate management was evaluated. The quantita-
tive data provided in this assessment will be valuable to regulators and
policy makers evaluating different options for managing PW.
2. 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, Fayette-
ville, Haynesville, Marcellus, and Permian (Midland and Delaware Ba-
sins) 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 becausethey have a long his-
tory 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
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 vol-
umes 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 vol-
umes 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 in-
cluded in the USGS water use database. Projections of PW were com-
pared 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 tech-
nology (Scanlon et al., 2020). Data on projections are available for the
Bakken, Eagle Ford, Permian, and Marcellus plays.
2.2. Produced water quality
Data on PW quality were obtained from the USGS Produced Wa-
ters 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 S26. Additional data were obtained
fromtheliteraturebasedonfield 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 ±15%. We reviewed treat-
ment technologies based on PW quality and water quality require-
ments 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.
3. Results and discussion
3.1. Spatiotemporal variability in produced water supplies
PW volumes totaled ~600 BL (0.6 km
3
; ~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.
Beneficial use of PW would require a reliable supply of PW or feed-
stock. 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 de-
clined since then because of the reduction of CBM production (Fig. 3b,
Fig. S2). For example, volumes of PW in the Powder River Basin (Wyo-
ming) 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.
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 de-
pending on logistics. In contrast, PW exceeded HF water use in the re-
maining 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 land-
owners and organizations requiring operators to purchase water from
them as part of lease agreements in Texas. For example, HF water de-
mand 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., 2020). 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.
4B.R. Scanlon et al. / Science of the Total Environment 717 (2020) 137085
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 Dela-
ware and Marcellus plays (Table 1). These estimates are based on
projected well inventory over the life of the plays (Scanlon et al.,
2020) divided by the historical maximum drilling rate. Therefore, PW
supplies would provide the most reliable feedstock in the Permian Del-
aware Basin.
Most of the PW from UOG reservoirs has been managed by subsur-
face injection using SWD wells. Although PW and SWD volumes are re-
ported 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 plays but
include PW from both unconventional and conventional reservoirs. Cu-
mulativePW and SWD volumes aresimilar in the Bakkenand Eagle Ford
plays. PW from CBM plays has not been managed using subsurface dis-
posal butmostly surface disposalin ponds, as described in a latersection.
3.2. Assessing water demand in different sectors relative to produced water
supplies
3.2.1. Irrigation sector
The sector with the largest water demand is irrigation (2015 data),
exceedingPW 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 differ-
ent 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 accommo-
date 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 irriga-
tion 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.
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,
Table 1
Volumes (10
9
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 totalPW volumes. Also listed are the remaining yearsof well completion activity based on the projected well inventory and historical annual max-
imum numberof wells drilled per year forselected plays. For moredetails on the projections, see Scanlon et al., 2020.Data for additionalsectors are provided in metricand English units in
Table S1. County level data for each play are provided in Tables S4 and S5.
Play
Type
Play name 2017 2015 Projected
PW SWD HF Irrig Muni PW HF water Well invent. Max. wells
per yr
Rem. yrs
TO Permian 264.4 378.6 210.2 841.7 65.1 49,300 18,200 320,000 5,000 64
TO Delaware 164.2 217.7 90.8 708.7 54.0 39,400 10,800 207,000 2,600 80
TO Midland 100.3 160.9 119.4 132.9 11.1 9,900 7,400 113,000 2,400 47
TO OK AOI 195.3 195.3 28.0 108.7 270.1 –– – – –
TO Bakken 54.6 56.7 29.3 747.5 18.8 2,500 1,700 69,000 2,700 25
TO Eagle Ford 35.1 38.9 66.2 219.1 144.6 1,100 3,200 105,000 4,000 26
TO Niobrara 6.7 6.4 28.0 867.4 362.8 –– – – –
SG Barnett 42.5 42.5 1.4 32.9 134.2 –– – – –
SG Marcellus 5.3 –26.0 3.9 161.6 2,200 5,200 124,000 1,700 73
SG Haynes. 2.2 45.0 3.6 2.6 76.4 –– – – –
Total 606 763 393 2824 1234 55,100 –– – –
CBM PRB 26.1 ––1,172.5 18.4 –– – – –
CBM Raton 7.8 ––103.8 7.3 –– – – –
CBM San Juan 5.7 ––855.5 36.5 –– – – –
CBM BW 4.9 ––16.9 171.7 –– – – –
CBM Uinta 1.7 ––227.6 9.9 –– – – –
Total 46.2 ––2,376 243.8 –– – – –
TO: TightOil; SG: Shale Gas;CBM: Coal Bed Methane;Haynes: HaynesvillePlay; PRB: PowderRiver Basin; BW, BlackWarrior Basin;PW volumes are notreported for theOklahoma AOI but
are approximated bySWD volumes. PW and SWDvolumes are assumedequal in the Barnettbecause of uncertainties inPW volumes. The Permiandata representthe sum of data from the
Midland and Delaware basins and do not include development outside of these basins.
Fig. 3. Timeseries of produced water(PW) volumes fora) the major tight oil andshale gas
plays and b) the coal bed methane plays. Data for Oklahoma represent statewide values.
The data are tabulate d in Tables S2 a nd S3.
5B.R. Scanlon et al. / Science of the Total Environment 717 (2020) 137085
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 (~2500 BL; 660 Bgal), ~3× irrigation in the Midland
and Delaware Basins (Fig. 4). PW represented 1%, 12%, and 17% of irriga-
tion 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 bb1%, 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 irriga-
tion in a few counties where PW would contribute b1% to irrigation de-
mand. 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 b1% of irrigation in most
counties. Total irrigation in the Oklahoma AOI is less than the PW vol-
ume 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 b5% 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 re-
duce 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 dif-
ficult to track water transfers among sectoral users.
3.2.2. Municipal, livestock, industrial, and mining sectors
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 b0.1% of mu-
nicipal demand in Niobrara counties with high municipal demand
(Fig. S10). About 50% of the municipal demand in Oklahoma AOI is in
OklahomaCounty, where PW would constitute ~3% of the municipal de-
mand (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 volumesin this play (Fig. S12).Mu-
nicipal demand in CBM plays was ~5× PW volumes, mostly in the Ala-
bama portion of the Black Warrior Basin (Table 1). PW would
represent ≤8% of municipal demand in the Black Warrior Basin. In sum-
mary, 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).
Water use for livestock was ~25% of total PW volume in UOG reser-
voirs 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.
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).
Thermoelectric cooling for power plants requires large water with-
drawals in once-through cooling systems, but consumption equals
only a few percentof withdrawal (Dieter et al., 2018). This studyfocused
on the consumptive water use for recirculating cooling towers, which
Fig. 4. Distributionof irrigated landsin the U.S. based on composite satellite images for 2002,2007, and 2012 basedon 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.
6B.R. Scanlon et al. / Science of the Total Environment 717 (2020) 137085
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 op-
portunity 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).
In summary, the most obvious sector for reuse of PW from a volu-
metric 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 re-
duce water scarcity concerns in these plays.
3.3. Surface water discharge and managed aquifer recharge
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 mini-
mal 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 ex-
tremely 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 re-
gions 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.
The feasibility of groundwater recharge and aquifer storage and re-
covery (ASR) is also being considered in some plays, such as the Perm-
ian Basin. However, the risks related to such a practice seem high, and
potential unintended consequences large. Storing excess PW in the sub-
surface 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 re-
duce overpressuring from SWD and potential contamination of overly-
ing 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 radioac-
tive 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 aredominated 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
(244 g/L), ~7× that of sea water (Figs. 5, 6). TDS is moderately high in
the Permian tight oil play (median: 154 g/L) and the Appalachian (Mar-
cellus) shale gas play (166 g/L), with a lower value in the Eagle Ford
shale play (57 g/L). The Permian TDS data include PW from unconven-
tional units, such as the Wolfcamp and Cline Shales, along with wells
specifically designated as unconventional in the USGS database. The
highest TDS (99th percentile) in shale oil and gas plays ranges from
300 to 370 g/L, with a lower value in the Eagle Ford play (~180 g/L)
and Niobrara (95 g/L). No systematic difference exists between TDS in
conventional and unconventional reservoirs as seen from the USGS da-
tabase. There can be substantial variability in TDS within plays, bothar-
eally and vertically (Fig. 5). Recent analysis of Permian data reveals the
highest TDS in shallower zones near salt deposits and decreasing TDS
with depth (Chaudhary et al., 2019). Inthe Eagle Ford play, a salinity re-
versal and freshening of PW (a factor of 10 reduction in TDS from
~200 g/L at 2.5 km [1.6 m] depth to ~20 g/L at 3.5 km [2.2 m] depth)
was noted and attributed to clay conversion from smectite to illite
with interlayer water release (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).
PW from tight oil and shale gas plays is dominated by Na (median:
15–76 g/L) and Cl (median: 22–150 g/L) (Fig. S31), consistent with pre-
vious studies indicating that nearly all basinal waters N10 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
(~0.3–13 g/L). Sulfate levels are mostly low (median:
0.020–0.675 g/L). PW from CBM plays is dominated by Na and Cl in
the Black Warrior and Uinta Basins but Na and HCO
3
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 vary considerably among the plays studied,
with medians ranging from 7 to 294 in different basins (Fig. S33).
SARs N3 generally require freshwater to flush the salts in irrigated
lands, and SARs N13 can degrade soil texture (SI, Section 1d).
Data on minor or trace elements in PW are limited. Here we only
mention naturally occurring radioactive material (NORM) in PW,
which mostly consists of
226
Ra (half life: 5.75 yr) and
228
Ra (half life:
1600 yr) derived from U and Th in the reservoir (Guerra et al., 2011).
Total Ra (
226
Ra +
228
Ra) levels greatly exceed the EPA regulatory limit
of 5 pCi/L (pico curies/L) for drinking water but are higher in the Marcel-
lus shale (median: 1980 pCi/L) and the Bakken (1,200 pCi/L) than in the
Permian (535 pCi/L) or Eagle Ford (284 pCi/L) (Fig. S31).
3.4.1. Sources of produced water
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 N10 g/L and max-
imum 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
7B.R. Scanlon et al. / Science of the Total Environment 717 (2020) 137085
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 composi-
tion 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 geo-
logic 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-HCO
3
-
rich water from the Powder River Basin reflecting meteoric water that
has undergone a series of geochemical reactions within the coal beds
from which they are produced (Brinck et al., 2008).
3.4.2. Evaluating water quality requirements fordifferent sectors relative to
produced water quality
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 of 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: ~4 g/L) is discharged directly to the Black Warrior River
in Alabama where it is diluted (SI, Section 1a). However, some issues re-
lated 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
Fig. 5. Total dissolved solids (TDS) of produced water from the USGS Produced Waters database (version 2.3) with supplemental data for the New Mexico region of the Permian Basin
providedby the New Mexico Instituteof Mining and Technology(NMIMT) PetroleumResearch and Recovery Center (PRRC), and data fromthe USGS in the Eagle Ford Play. Labeled values
represent median produced water TDS concentrationswithin each play area of wells classified as eithershale gas, tight oil, or coal bed methane, with the exception of the Permian value,
which includes wells that are classified as conventional hydrocarbon wells completed in unconventional formations (i.e., Wolfcamp, Bone Spring, Cline, Spraberry, and Dean). Data are
provided in Table S26.
Fig. 6. Total dissolved solids (TDS) for tight oil (T O) 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 numb ers 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).
8B.R. Scanlon et al. / Science of the Total Environment 717 (2020) 137085
underlying aquifers, with up to100 g/L TDS in groundwater near an im-
poundment in Wyoming (Healy et al., 2011).
Water quality standards and regulations for water use in irrigation,
livestock, and municipal sectors (drinking water maximum contami-
nant levels and irrigation and land application standards) do not con-
sider 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 vola-
tile and synthetic organics (https://www.epa.gov/dwreginfo/chemical-
contaminant-rules). Assessing treatment of PW by comparing with
drinking water standards is insufficient because the regulations were
not designed to consider PW.
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 regula-
tions (GWPC, 2019). The 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 con-
text of high salinity matrices (Danforth et al., 2019;Luek and Gonsior,
2017;Nelson et al., 2014;Oetjen et al., 2017), it seems infeasible to con-
duct a comprehensive evaluation of PW chemistry. Detailed risk assess-
ment will be required to evaluate potential human health and
environmental impacts of beneficial PW reuse outside of the energy sec-
tor. The GWPC report outlines many of the aspects of a suitable risk as-
sessment, building on previous studies (NRC, 2009). Whole effluent
toxicity (WET) assessment is proposed to address known and potential
unknown contaminants (GWPC, 2019).
4. Treatment options for produced water reuse applications
Selection of the appropriate treatment technologies depends pri-
marily 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 require-
ments 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 technologies
or (2) thermal technologies (Fig. 7). Additional information on treatment
technologies is provided in SI, Sections 2 and 3.
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 ana-
lytical techniques are required to determine whether some organics re-
main in the treated water. To minimize membrane scaling and fouling,
RO requires extensive pretreatment to remove sand, silt, clay, algae, mi-
crobes, 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).
Thermal technologies (e.g., multiple-effect distillation [MED], me-
chanical vapor compression [MVC] and recompression [MVR]) are al-
most 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
Fig. 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 posttreatme nt technologies. TDS: total diss olved 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.
9B.R. Scanlon et al. / Science of the Total Environment 717 (2020) 137085
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). How-
ever, 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.
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 con-
sumption 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 deioni-
zation). 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, SiO
2
,B,and
heavy metals, are rejected at nearly 100%. Water recovery can be im-
proved 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 os-
motic 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 OPUS™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 mem-
brane 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 Fa-
cility) 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 central-
ized wastewater treatment facilities to generate water fit for discharge
from PW in the Marcellus (Mueller, 2017). Treatments include mechani-
cal 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.all-llc.com/projects/produced_water_tool/).
Besides salts, PW and flowback water contain complex organic con-
stituents 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 minimiz e
fouling of membranes or other surfaces, and to prevent environmental
impacts during disposal or reuse. Biological processes have been suc-
cessfully used to remediate water contaminated by petroleum hydro-
carbons, solvents, and other dissolved organic chemicals commonly
observedin PW. The effectiveness of biological processes varies depend-
ing on the properties of chemicals present and their respective concen-
trations, 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 chlori-
nated compounds are more refractory. Physico-chemical treatment,
such as adsorption and advanced oxidationprocesses, can be used to re-
move organic contaminants. Because the treatment technologies may
not be highly effective in removing contaminants, risk assessment
should also be conducted on the treated PW 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 × 10
9
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 ~3000 Olympic swimming pools.
Disposal of solid wastes laden with contaminants transferred and con-
centrated from PW may becost prohibitive and may not be a viable op-
tion to reach ZLD or high water recovery for PW treatment.
4.2. Implications for produced water management
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, Nio-
brara, 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
treatmentand related lower costs and energy usethan beneficial use of
PW in other sectors.
The most likely sector to reuse PW in semiarid western U.S. is irriga-
tion. Irrigation exceeds PW volumes in many plays, except the Okla-
homa 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 re-
duce the PW volumes. PW as a percent of irrigation would represent
2% of irrigation in the Bakken, 5% in the 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 largepotentialin 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 PWto surface water or recharging
groundwater would be considered. Therefore, it does not seem that PW
reuse will mitigate water scarcity concerns in mostregions. Water scar-
city related to oil and gas development would be more readily ad-
dressed 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 contin-
ued 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 theen-
ergy sector. From a volumetric perspective, reuse of PW within the en-
ergy 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 per-
spective, the following limitations restrict the potential for PW reuse
outside of energy: poor knowledge of PW chemistry, inability to accu-
rately measure the PW quality because ofhigh salinity matrix and inter-
ference issues, lack of acceptable measurement techniques, absence of
suitablestandards, and lack of regulations for various sectors to consider
10 B.R. Scanlon et al. / Science of the Total Environment 717 (2020) 137085
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.
5. Conclusions
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 reser-
voirs, 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. Irriga-
tion exceeds PW from UOG reservoirs by ~5× and PW from CBM reser-
voirs 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 the Permian Delaware Basin. PW volumes
in the Permian Delaware Basin would represent ~5% of the irrigation de-
mand. 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 limited based on volumetric analysis. Discharging
PW to surface water is also being considered, but the PW would not
be substantially diluted in western streams. Recharging depleted aqui-
fers is also aconsideration; however, water quality issues may preclude
this option.
VariableTDS of PW from UOG reservoirs (median TDS: 244 g/L inthe
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: 1–11 g/L) and does not include HF water. Evalua-
tion of PW from CBM plays provides an example of PW that can be con-
sidered 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. Uncer-
tainties in treatment efficiency and problems with contaminants
leaking through the treatment process further increase risks of reuse.
The current regulations for various sectoral uses and discharge require-
ments were not designed to address PW issues. Therefore, large uncer-
tainties related to water quality issues currently preclude PW reuse
outside of the energy sector.
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.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgments
We are very grateful for financial support for this study from the
MitchellFoundation, Sloan Foundation, ExxonMobil, and Jackson School
of Geosciences Endowment. We very much appreciate access to the IHS
Enerdeq database.
Appendix A. Supplemenary data and Information
Raw data on water volumes and water quality used in this study are
archived in Mendeley Data (10.17632/jjy5mtfkfk.2) and described in an
associated data article (Scanlon et al., submitted). Supplementary data
to this article can be found online at https://doi.org/10.1016/j.
scitotenv.2020.137085. Additional figures and tabulated data are pro-
vided in the Supporting Information.
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