# BAKKEN WATER OPPORTUNITIES

ASSESSMENT

– PHASE 2

EVALUATION OF BRACKISH GROUNDWATER

TREATMENT FOR USE IN HYDRAULIC FRACTURING OF THE BAKKEN PLAY,

NORTH DAKOTA

Final Report

Prepared for:

North Dakota Industrial Commission 600 East Boulevard Avenue, Department 405 State Capitol, 14th Floor Bismarck, ND 58505

- 0840

Prepared by:

Bethany A. Kurz

Daniel J. Stepan

John A. Harju

Brad G. Stevens

Robert M. Cowan

Energy & Environmental Research Center

University of North Dakota

15 North 23 rd Street, Stop 9018 Grand Forks, ND 58202

- 9018

2011

- EERC

- 12

- 05 December 2011DISCLAIMER

This report was prepared by the Energy & Environmental Research Center (EERC) pursuant to an agreement partially funded by th e Industrial Commission of North Dakota, and neither the EERC nor any of its subcontractor s nor the North Dakota Industrial Commission nor any person acting on behalf of either:

(A) Makes any warranty or repr esentation, express or impl ied, with respect to the accuracy, completeness, or usefulness of th e information contained in this report or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or

(B) Assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method, or process disclose d in this report.

Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not n ecessarily constitute or imply its endorsement, recommendation, or favoring by the North Da kota Industrial Commission. The views and opinions of authors expressed here in do not necessarily state or reflect those of the North Dakota

Industrial Commission.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United

States Government. Neither the United States G overnment, nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or re presents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not n ecessarily constitute or imply its endorsement, recommendation, or favoring by the United States G overnment or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

EERC DISCLAIMER

LEGAL NOTICE This research report was prepared by the EERC, an agency of the University of North Dakota, as an account of work sponsored by Industrial Commission of North

Dakota. Because of the research nature of the work performed, neither the EERC nor any of its employees makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or othe rwise does not necessarily consti tute or imply its endorsement or recommendation by the EERC.i TABLE OF CONTENTS

LIST OF FIGURES ............................................................................................................... ......... ii

LIST OF TABLES ................................................................................................................ ......... iv

PROJECT SUMMARY ............................................................................................................... .. vi

BACKGROUND .................................................................................................................... .........1

CURRENT WATER USE PRACTICES ........................................................................................2

BRACKISH GROUNDWATER RESOURCES .............................................................................5

DESALINATION TECHNOLOGIES ............................................................................................7

MEMBRANE TECHNOLOGY ....................................................................................................15

RO FEEDWATER PRETREATMENT ........................................................................................18

RO Pretreatment Goals ........................................................................................................ 18

Pretreatment Processes ........................................................................................................ 19

Permeate Tr eatment ............................................................................................................ . 20 Concentrate Disposal .......................................................................................................... . 20

PILOT PROJECT BACKGROUND .............................................................................................20 Site Description .............................................................................................................. ..... 20

CORROSION AND SCALE FO RMATION MODELING ..........................................................21 Dakota Aquifer Water Composition ................................................................................... 23 Scaling Tendency .............................................................................................................. .. 23

Corrosion Evaluation .......................................................................................................... . 24 Corrosion and Scaling Analysis for Anticipated RO Concentrate ...................................... 28

MOBILE RO TREATMENT SYSTEM .......................................................................................29

SITE PREPARATION .............................................................................................................. ....30

PILOT TEST OPERATION AND PERFORMANCE ..................................................................32

FIELD-BASED CORROSION TESTING ....................................................................................39

ECONOMIC EVALUATION .......................................................................................................45

Continued . . .ii TABLE OF CONTENTS

RO Treatment Plant Costs ................................................................................................... 45

Production Well Costs ......................................................................................................... 46 Brine Disposal Costs .......................................................................................................... . 46 Land Acquisition .............................................................................................................. ... 49 Permeate and Concentrate Storage ...................................................................................... 49

CONCLUSIONS ................................................................................................................... ........51

REFERENCES .................................................................................................................... ..........52

LIST OF FIGURES

1 The location of the Bakken Formation within the Williston Basin ....................................... 1

2 The location of the Missouri River system and Lake Sakakawea with respect to Bakken drilling locations ..................................................................................................... . 4

3 Stratigraphic column showing the age and rock units associated with each of the five aquifer systems within the Northern Great Plains A quifer System ...................................... 6

4 Approximate extent of the Lower Tertiary aquifer system ................................................... 8

5 Approximate extent of the Upper Cret aceous aquifer system and generalized

TDS concentrations ............................................................................................................ ... 9

6 Approximate extent of the Lower Cretaceous aquifer system and generalized

TDS concentrations ............................................................................................................ . 10

7 Approximate extent of the Upper Paleoz oic aquifer system and generalized

TDS concentrations ............................................................................................................ . 11

8 Approximate extent of the Lower Paleoz oic aquifer system and generalized

TDS concentrations ............................................................................................................ . 12

9 MSF distillation ............................................................................................................ ....... 13

10 Cumulative worldwide desalination capacity...................................................................... 14

11 Desalination feedwater sources in the desalination market................................................. 15

Continued . . .iii LIST OF FIGURES (continued)

12 Distribution of desa lination capacity ................................................................................... 16

13 Photo of RO treatment membranes used to desalinize water in El Paso, Texas ................. 17

14 Block diagram of RO system .............................................................................................. 18

15 Predicted corrosion rates of carbon steel (A221B), stainless steel (316), and Hastelloy C-276 by raw Dakota water ................................................................................ 25

16 Predicted corrosion of Ca rbon Steel A212B by Dakota water over a range of temperatures and flow velocities ......................................................................................... 26

17 Flow diagram with corrosi on test rack locations ................................................................ 31

18 Pilot-scale RO system flow rates ........................................................................................ 33

19 Pilot-scale RO system operating pressures ......................................................................... 33

20 Pilot-scale RO system permeate conductivity ..................................................................... 34

21 Pilot-scale RO system feedwater temperature .................................................................... 34

22 Treatment Train 2 feedwate r and permeate conductivity .................................................... 37

23 Treatment Train 2 flux versus time ..................................................................................... 37

24 Flux versus temperature .................................................................................................... .. 38

25 Flux versus pressure differential ......................................................................................... 38

26 Photograph showing the installati on of corrosion test Rack S-2 ........................................ 40

27 Comparison of measured and predicted corrosion rates ..................................................... 42

28 Profiler images of select stainless steel coupons ................................................................. 43

29 Profiler images of select stainless steel coupons ................................................................. 44

30 Profiler image of carbon steel coupon zoomed in to pitted area ......................................... 44iv LIST OF TABLES

1 Common Constituents of Frac Fluid Makeup ....................................................................... 3

2 Water-Handling Costs ........................................................................................................ ... 5

3 General Description of Each of the Fi ve Major Aquifer Units Comprising the Northern Great Plains Aquifer System .................................................................................. 7

4 Classification of Water Type Based on TDS Concentration .............................................. 13

5 Comparative RO and NF Species Rejection Rates ............................................................. 17

6 Water Chemistry Results for Dakota Aquifer Samples ...................................................... 22

7 Lab Analysis Values Entered into OLI Lab Analyzer Software and Values after Reconciling Charge Balan ce, pH and Alkalinity ................................................................ 23

8 Scaling Tendency Values for the Ten Mine rals Having the Highest Scaling Tendencies for Dakota Aquifer Water at 152°F and pH 8.2 .................................................................. 24

9 Range of Corrosion Rates Calculated fo r All 19 Metals and Alloys Studied ..................... 25

10 Quantitative Classification of Car bon Steel Corrosion Rates for Open Recirculating Cooling Water Systems ................................................................................ 27

11 Quantitative Classification of Carbon Steel Corrosion Rates for Closed Recirculating Cooling Water Systems ................................................................................ 27

12 General Classification of Metals and A lloys Based on the Calculated Corrosion

Rates With Dakota Water .................................................................................................... 27

13 RO Concentrate Water Anal ysis and Reconciliation .......................................................... 28

14 Scaling Tendency for RO Concentrate ................................................................................ 28

15 Range of Corrosion Rates Calculated fo r Carbon Steel A212B and S316 Stainless Steel by the Anticipated RO Concentrate ........................................................................... 29

16 Summary of Water Analysis Results .................................................................................. 36

17 Summary of Flux Calculations ............................................................................................ 37

Continued . . .v LIST OF TABLES (continued)

18 Corrosion Rack Description ................................................................................................ 39

19 Comparison of Measured and Predicted Corrosion Rates .................................................. 41

20 Cost Estimate Assumptions – 1.5-MGD RO Plant ............................................................. 47

21 Total Cost Summary – 1.5-MGD RO Plant with Truck Transportation Disposal .............. 50

22 Total Cost Summary – 1.5-MGD RO Plant with Dedicated Pipeline Disposal .................. 51vi EVALUATION OF BRACKISH GROUND WATER TREATMENT FOR USE IN

HYDRAULIC FRACTURING OF THE BAKKEN PLAY, NORTH DAKOTA

PROJECT SUMMARY

The Northern Great Plains Water Consortium ® (NGPWC) is a partnership between the Energy & Environmental Research Center (EERC), the U.S. De partment of Energy, and key stakeholders in the north-central region of the United States. The overall goal of the NGPWC is to assess, develop, and demonstrate technologies and methodologies that minimize water use and reduce impacted water discharges from a range of energy technologies. One of the NGPWC’s
current activities is to evaluate potential sources of water for us e in hydraulically fracturing the Bakken oil play of North Dakota. Because of the current high costs for acquisition and transportation of existing water resources in we stern North Dakota, treatment of nontraditional water supplies may be economically feasible.

To evaluate the feasibility of treating nonpotable groundwater as a means of providing a freshwater supply for hydrauli c fracturing in the Bakken play, the EERC teamed with Hess Corporation to conduct a pilot tr eatment project using reverse os mosis (RO) to treat brackish groundwater from an existing water well screen ed in the Dakota Formation at a depth of approximately 5500 feet. GE Water Process and Technologies (GE) was contracted to provide a mobile pretreatment and RO system. Agrekko heat exchangers were used to reduce groundwater temperature to desired levels before RO treatme nt. The project demonstrated greater than 70% treated water recovery and greater than 90% removal of major ions. Over 25 million gallons of brackish groundwater was treated during the de monstration, producing over 17.8 million gallons of high-quality freshwater fo r use in hydraulic fracturing.

Metal test coupons were instal led at various locations duri ng the pilot demonstration to assess corrosion of standard plumbing and h eat exchange material s of construction. The corrosion study suggested that stainless steel woul d be a superior material compared to carbon steel pipe commonly used in the oil field; however , more exotic metals and alloys would not be required.

The success of the pilot project has led Hess to partner with GE to build and operate a fullscale, 1- to 2-million-gallon/day (MGD) RO treatme nt plant. While the exact costs of the plant are not available to the public, the estimated costs to build and operate a 1.5-MGD (35,700 bpd) RO plant were compiled by the EERC with input from GE. Capital co sts associated with construction of the RO plant and associated buildings, land acquisition, well field and pipeline costs, water storage ponds, and co ncentrate disposal costs were also assessed. Annual operating and maintenance (O&M) costs were also included for the RO plant, well field, and concentrate disposal options. Given the relatively high vol ume of concentrate th at would be produced (15,300 bpd), two different options were considered for disposal: truck transport to an existing commercial injection site and pipeline transport to a dedicated injection site.

The total estimated capital costs for a 1.5-MGD RO plant with concentr ate disposal at an existing commercial site were $24.9 million, and O&M was approximately $22.8 million a year. The capital costs for the second op tion (a dedicated con centrate injection site ) were estimated at $38.2 million, and annual O&M was estimated at approximately $1.2 million. Depending on the economic assumptions used, per-barrel costs ra nged from $1.28 to $2.95 over a payback period of 3 years or less. When compared to traditiona l frac water makeup costs, this approach appears viable if the cost savings associated with lower transportation costs and reduced heating costs are taken into account. Given the current pace of Ba kken development, coupled with limited access to water, treatment of brackish groundwater sources for use in Bakken fracturing appears economically viable.1 EVALUATION OF BRACKISH GROUND WATER TREATMENT FOR USE IN

HYDRAULIC FRACTURING OF THE BAKKEN PLAY, NORTH DAKOTA

BACKGROUND

Water is the most critical limiting resource throughout the world. Sufficient quantities of good-quality water are needed fo r several competing uses, incl uding energy production, growing and processing high-value crops, industrial manufacturing, and expanding populations. The

Northern Great Plains Water Consortium ® (NGPWC) is a partnership between the Energy & Environmental Research Center (EERC), the U.S. Department of Energy (DOE), and key stakeholders representing oil and gas compan ies, power generation utilities, industry, municipalities, and other entities interested in addr essing critical water issues in the north-central United States. The primary goal of the NGPWC is to assess, develop, and demonstrate technologies and methodologies that minimize wate r use and reduce impact ed water discharges from a range of energy technologies, includ ing coal combustion, coal gasification, coalbed methane, and oil and natural gas production.

One of the NGPWC’s key activities is to eval uate potential sources of water for use in hydraulically fracturing the Bakken Formation (Ba kken), located in the Williston Basin of North Dakota, Montana, South Dakota, and Saskatchewan (Figure 1). The Bakken oil play is rapidly

Figure 1. The location of the Bakken Formation within the Williston Basin.2 emerging as an important source of domestic oil, with potentially recoverable reserve estimates ranging from 4 to 24 billion barrels (Oil and Gas Journal, 2011). While the hydrocarbon resource within the Bakken is tremendous, the formation is characterized by very low porosity and permeability, which necessitates fracturing to enha nce the flow and recovery of oil. Water volumes for fracturing the Bakken range from approximately 20,000 to 115,000 barrels (approximately 840,000 to 5 million gallons), depending on the number of stages in the frac, and, to a lesser extent, differences in varying fractu re techniques. More fracturing stages require greater volumes of water. While these volumes of water are not especially high when compared to those needed for municipal and agricultural use within the western portion of North Dakota,

there are a limited number of locations from wh ich to obtain the freshwater. For water haulers,

the lack of water resources tran slates to long transportation di stances and excessive amounts of time spent waiting in lines at water depots. As a result, water acquisition costs for Bakken oil producers in the region can be quite high. Given the current demand for wa ter resources and the high costs of acquisition and transportation, treat ment of nontraditional water supply sources may be economically viable.

One of the first projects conducted by the NGPWC was an assessmen t of the potential to recover, treat, and recycle fract uring (frac) flowback water from Bakken oil wells (Stepan et al., 2010). The EERC evaluated an array of water treat ment technologies, primarily mobile treatment systems that could utilize the high-Btu associat ed gas generated during the flowback operations to thermally treat frac flowback. However, extremely high dissolved salts in flowback water, combined with a relatively low recovery rate of the flowback water, makes recycling very challenging and, in most cases, economically unattractive.

As part of a continuing effort to evaluate water supply optio ns for oil producers and other industries in the region, the EE RC teamed with Hess Corporati on to conduct a p ilot treatment project using reverse osmosis (RO) to evaluate the technical and economic feasibility of treating brackish groundwater as a water supply source for fracturing. This effort was funded by Hess, DOE, and the North Dakota Industrial Commissi on Oil and Gas Research Council. The pilot system was in operation from July 2010 through mid-April 2011. The follo wing report discusses the current state of water use practices for Ba kken fracturing, summarizes the RO pilot project results, and discusses the feas ibility of brackish groundwater tr eatment for fracturing given the

current state of water availabi lity within North Dakota.

CURRENT WATER USE PRACTICES

Fracturing is increasingly bei ng employed by oil producers in western Nort h Dakota to produce the tremendous oil and gas resources of the Bakken Formation. Fracturing entails the injection of water, proppants, and various othe r chemical constituents at high pressures into reservoir rock in order to increase the permeability of the formation and e nhance the flow of oil. Common constituents of frac fluid makeup are shown in Table 1, with water and proppants typically comprising 99 .5% of the frac fluid makeup (U.S. Department of Energy, 2009). Frac fluid makeup water typically contains low total di ssolved solids (TDS), will be free of bacteria, and be of consistent quality to ensure the ability of individual producers to generate and replicate

the desired fracture results.3 Table 1. Common Constituents of Frac Fluid Makeup

Frac Fluid Component Purpose Freshwater The primary mechanism for delivering the desired proppants

and chemicals into the forma tion; usually high quality. Proppant Typically sand or ceramic b eads that help keep the fractures open upon release of pressure fr om the fracturing operation.

Biocides Reduces the risk of well souring from microbes. Friction-Reducing Agents Surfactants that promote frac fluid flow. Polymers Forms gels to keep proppants in suspension. Scale Inhibitors Reduces scale formation in pipes. Weak Acids Helps dissolves minerals that cement formation pore spaces.

In western North Dakota, common freshwater acquisition points for frac fluid makeup are existing water depots and munici palities; however, these have a limited capacity to supply the large demand for water. In response to the incr easing demand for freshwater, the North Dakota State Water Commission (SWC) has received nu merous permit applications for additional groundwater appropriation for wi thdrawals at existing water depots as well as permit applications for new water wells. Prescribed permitting procedures require a published public notice, followed by a 30-day comment period. Ne w permit applications are typically contested by environmental groups, which results in signifi cant delays in the overall permitting process. Permits that would normally be issued within a 70- to 90-day period are taking in excess of

9 months.

In addition, SWC is reluctant to permit new allocations from potable groundwater resources for use in the oil industry because of concerns over depleti on of the resources and declining hydraulic pressures of bedrock aqui fers. With the exception of the Missouri River system, most regional surface waters do not pr ovide a reliable supply of water because of

seasonal flow variations. Sufficie nt flows typically exist only in the spring of the year, during periods of snowmelt.

Given the concerns over mining of groundwater resources, groundwater-permitting issues,

and the relative lack of small surface water availability in ma ny areas of the state, SWC is encouraging the oil industry to seek withdraw als from the Missouri River system for use in Bakken development. The Missouri River system, specifically Lake Sakakawea, is a tremendous resource that is located adjacent to many of the Bakken drilling areas (Figure 2). However,

several issues arise related to using Lake Sakakawea water, ke y among them being access to the lake and looming fees for use of the resource. While SWC handles water appropriations from the lake, permission for an easement to a particular point of diversion must be granted by the U.S. Army Corps of Engineers (Corps). This crea tes additional delays in accessing the resource because having to obtain permission from multiple agencies can slow the permitting process. In addition, it is not yet clear where access to the lake may or may not be allowed so as not to disturb existing cultural sites and/or threatened and endangered species. While the Corps is4 Figure 2. The location of the Missouri River system and Lake Sakakawea with respect to Bakken drilling locations (Energy Info rmation Administration, 2011).

studying the potential impacts of in creased access to and water use from the lake (estimated to be a multiyear study), it agreed to allow a temporar y annual allocation of water from the lake for municipal and industrial (M&I) use for a fee. The Corps recommended that 100,000 acre-feet of water yield be made available from Lake Sakakawea for temporary M&I use over a period of 5 years for an annual fee of $20.91 per acre-foot of yield (U.S. Army Corps of Engineers, 2010).

While water depot and pipeline projects are in the works to improve the availability of freshwater resources for use in Bakken development, in the near-term, there are significant water access issues. The Missouri River system has more than enough water available for Bakken development, but access issues and potential f ees associated with this water use remain5 unresolved. In addition, the Miss ouri River and Lake Sakakawea ar e not always ad jacent to areas of Bakken drilling; therefore, the high costs as sociated with long transportation distances may diminish the appeal of the resource.

As part of the EERC study to evaluate the fe asibility of fracturing flowback recycling (Bakken Water Opportunities Assessment – Phas e 1), cost data for water acquisition were provided by several producers wo rking in North Dakota (Stepan a nd others, 2010). The reported costs of current water handling for hydraulic fracturing can vary si gnificantly, depending on acquisition and transportation costs (including wait time). Table 2 lists a range of water-handling

costs for Bakken frac water as of 2010. The cost to purchase raw water ranged from $0.25/barrel (bbl) up to $1.05/bbl ($5.95 to $25 pe r 1000 gallons), and the cost of transporting that water to the fracture location ranged from $0.63/bbl up to an estimated $5.00/bbl ($15 to $119.05 per 1000 gallons). Transportation costs represented the highest level of variability in water acquisition costs and depended on several factors, including trucking charges, haul distances, and wait time. Trucking charges were reported to ra nge from $110 to $150/hr, and the charges that are incurred during wait time are included in the overall transportation cost s. The costs for deep well injection ranged from $0.50/bbl to $1.75/ bbl ($11.90 to $41.66 per 1000 gallons). Again, transportation costs are the most significant cost for disposal, and the higher overall transportation costs were associated with l ong wait times to unload at a disposal facility.

Given the current need for water, coupled wi th high water acquisition, transportation, and disposal costs, nontraditional options for water supplies, such as desalination of brackish groundwater resources, are worthy of further investigation. As a result of the work conducted during Phase 1 of the Bakken Water Opport unities Assessment, th e EERC, with the encouragement of the project sponsor, decided to pur sue a pilot project to ev aluate the feasibility of treating brackish groundwater.

Table 2. Water-Handling Costs Cost, $/bbl Cost, $/1000 gallons Acquisition Costs
Raw Water $0.25–$1.05 $5.95–$25.00 Transportation $0.63–$5.00 $15.00–$119.05 Disposal Costs Transportation $0.63–$9.00 $15.00–$214.29 Deep Well Injection $0.50–$1.75 $11.90–$41.66

Total Costs $2.00–$16.80 $47.62–$400.00

BRACKISH GROUNDWATER RESOURCES

One advantage to utilizing brackish groundwater as a potential water supply is that the region is not limited by a lack of potential resources. Much of the region is underlain by what the U.S. Geological Survey has classified as the Northern Great Plains Aquifer System, a large (approximately 300,000 square miles) regional flow system comprising five major aquifers of6 varying quality. These aquifers include sandstones of Tertiary and Cretaceous age, carbonate rocks of Pennsylvanian and Mississippian age, and sandstones and carbonates of Cambrian and Ordovician age (Figure 3 and Table 3). The rock s that comprise these aquifer systems were formed by sediment erosion from mountains to the west and subsequent deposition to the east in

the Williston and Powder River Basins and adjacent areas (Downey and Dinwiddie, 1988).

Water movement through these systems genera lly occurs from recharge areas in the southwestern part of the region to the northeast. Rechar ge occurs where the rocks are exposed at or near the surface in areas that were uplifte d as part of the Lara mide Orogeny (Bachu and

Figure 3. Stratigraphic column showing the age and rock units associated with each of the five aquifer systems within the Northe rn Great Plains Aquifer System.7 Table 3. General Description of Each of th e Five Major Aquifer Units Comprising the Northern Great Plains Aquifer Syst em (adapted from Whitehead, 1996) Hydrogeologic System Age Unit General Composition

Lower Paleozoic (Basal Cambrian Aquifer) Cambrian,

Ordovician Sandstone, shale, limestone, and dolomite; formed in a shallow marine

environment. Upper Paleozoic (Madison Aquifer) Mississippian, Pennsylvanian Limestone and dolomite with lesser amounts of clay, chert, and anhydrite; deposited in a marine environment.

Lower Cretaceous (Dakota Aquifer) Lower Cretaceous Sandstone; fo rmed in marine, deltaic, and

fluvial environments. Upper Cretaceous Upper Cr etaceous Sandstone interb edded with siltstone, claystone, and local thin beds of coal or lignite; deposited in a continental

environment. Lower Tertiary Eocene, Paleocen e Interbedded sandstone, siltstone, claystone, and coal; deposited in a

continental environment.

Hitchon, 1996), including the Black Hills, Pryor Mountains, Bighorn Mountains, Beartooth Mountains, and Little Rocky Mountains (Iampen and Rostron, 2000). Because water within these systems moves along very long flow paths and remain s in contact with aquifer minerals for long periods of time (sometimes thousands of years [G erla, 1992]), the water is typically enriched in various chemical species, reflected by moderate to high TDS concentrations. In many parts of the system, TDS concentrations exceed the secondary drinking water maximum contaminant level of 500 mg/L established by the U.S. Environm ental Protection Agency (Whitehead, 1996). Figures 4–8 show the approximate extent of each of the five aquifer systems and generalized TDS concentrations of each (no TDS data were av ailable for Figure 4). As a general rule of the thumb, the TDS concentrations are lower adj acent to uplift areas (reflecting recharge of freshwater) and higher in the middle of the Williston and Powder River Basins.

While the quality of the water in many areas of these aquifers is unsuitable for drinking, at many locations it is of a quality suitable for cost-effective treatment. In fact, the water in many areas of the aquifers (mostly excluding the Williston Basin) could be classified as only moderately saline (Table 4). The suitability of any of these aquifers as a water supply source would require a site-specific evaluation, not only to assess water quality, but also to assess aquifer yield, depth, temper ature, and sustainability.

DESALINATION TECHNOLOGIES

While many options exist for treatment of brackish groundwater, recent and ongoing improvements in desalination technology have made this an increasingly viable water treatment8Figure 4. Approximate extent of the Lower Tertiary aquifer system.9Figure 5. Approximate extent of theUpper Cretaceous aquifer systemand generalized TDS concentrations (in mg/L).10Figure 6. Approximate extent of theLower Cretaceous aquifer systemand generalized TDS concentrations (in mg/L).11Figure 7. Approximate extent of theUpper Paleozoic aquifer systemand generalized TDS concentrations (in mg/L).12Figure 8. Approximate extent of theLower Paleozoic aquifer systemand generalized TDS concentrations (in mg/L).13 Table 4. Classification of Water Type Based on TDS Concentration (Downey and Armstrong, 1977)

Water Source TDS Concentration, mg/L

Fresh <1000 Slightly Saline 1000–3000 Moderately Saline 3000–10,000 Saline 10,000–35,000 Seawater >35,000

option around the world. Whereas desalination was limited by high costs in recent decades, it is now a cost-competitive option for many communities as available freshwater resources become

limited or nonexistent. Because de salination is capable of treating water with varying degrees of salinity, including seawater, brackish ground and su rface water, and wastewater, desalination has wide-scale applications across the globe. Si nce the early 1970s, desa lination has gained a

foothold in the United States as a practical source of high- quality water supply and is now providing high-quality water for municipal and industrial use.

Desalination can be defined in simple terms as a water treatment process that removes

dissolved minerals from water. There ar e two commonly employed water desalination technologies: thermal (distillati on) and membrane. Thermal technologies heat water and collect the condensed vapor to produce distilled wa ter. The most common thermal technology is multistage flash (MSF) distillation (Figure 9), which employs thermal heating and reduced pressure to flash liquid water to vapor in a series of stages, each of which is at a lower pressure.

Thermal desalination is most commonly practi ced in areas with abundant fossil fuels to capitalize on cogeneration of power and water, such as in the Mi ddle East. Rarely are thermal

Figure 9. MSF distillation (Miller, 2003).14 processes used to desalinate wate r with less than 10,000 mg/L of TD S; indeed, the vast majority of these applications use seawater as the feed source, which typi cally has a TDS concentration of 35,000 mg/L. Thermal technologies are generally not cost-effective for low-TDS waters.

Membrane technologies are much younger in development than thermal technologies. Membrane technologies were developed for co mmercial and municipal water supplies in the 1970s, while thermal technologies have been in pr actice for over a century. As the name implies,

membrane treatment removes dissolved minera ls from solution using filtration through a semiporous membrane. The three main types of me mbrane treatment for dissolved salts include RO, electrodialysis (ED), and nanofiltration (NF).

The International Desalination Associ ation’s (IDA) Desa lination Yearbook 2011–2012 (IDA, 2011) indicates the global capacity for desalination grew to 77.4 million m 3 /day (20.4 billion gallons/day) with 71.9 million m 3 /day (19.0 billion gallons/day) of this currently

online and 5.5 million m 3 /day (1.4 billion gallons/day) of cap acity under construction. Figure 10 illustrates that this capacity represents substantial growth over the last decade which is anticipated to continue well into the next. The in formation in the figure also reveals that while the capacity of thermal desalination plants cont inues to grow at a steady pace, membrane-based capacity is expanding at an accelerating pace.

The total global desalination output comes fr om approximately 16,000 desalination plants which vary in size from very small systems producing less than 0.365 million m 3 /year (96.4 million gallons/year) of product water to very large systems producing up to 321.2 million

m 3 /year (84.8 billion gallons/year) (IDA, 2011). The bulk of this capacity is for production of

Figure 10. Cumulative worldwide desa lination capacity (Birkett, 2010).15 municipal supplies. The primary source of feedwater is seawater followed by brackish water as illustrated in Figure 11. The distribution of desa lination capacity around the world is illustrated in Figure 12. The figure shows that greater that 53.4% of existing capacity is located in the Middle East, 17% in North America, 10.6% in Asia, and 10.1% in Europe. Africa, Central America, South America and Australi a together account for another 9%.

Within the United States, approximately 180 municipal and rural water systems use desalination for part or all of their water suppl y. Approximately 94% of this capacity is generated using membrane technology. Together, these pr ocessing facilities pr oduce over 787 MGD of water for municipal use. Historic ally, the source water for these de salination plants was seawater,

but with advances in RO treatment technol ogy, brackish surface or groundwater sources are increasingly being used.

MEMBRANE TECHNOLOGY

ED is one of the three common membrane proc esses in desalination an d is primarily used

to treat brackish water. ED involves the selective movement of ions through a membrane in response to a direct electric cu rrent. Electric energy is consumed in proportion to the quantity of salts to be removed. Economics usually limit it s application to feed waters of less than 10,000 mg/L TDS.

Figure 11. Desalination feedwater sources in the desalination market (DesalData.com, 2011).16 Figure 12. Distribution of desalination capacity (Tinos and Culligan, 2009).

The electrodialysis reversal (EDR) proces s is based on the sa me principles of electrochemistry as ED. The fundamental differen ce is that during the EDR process, the polarity of the cell is periodically reversed, usually 3 to 4 times per hour, to alter the flow of ions across the membrane. This action improves the toleran ce of the technology to treat scaling-prone or turbid feedwater. EDR has largely replaced ED in the United States and in some overseas markets. EDR has a permeate recovery capacity a nd a salt rejection rate of 90% (compared to RO’s 75%–85% permeate recovery capacity a nd 99% salt rejection rate). A significant disadvantage of EDR treatment is the cost, whic h is approximately twic e that of RO (Hanson, 2008).

NF is a membrane process that primarily removes multivalent salt ions (such as calcium, magnesium, and sulfate) from solution, not monovale nt ions (such as sodium and chloride), as seen in Table 5. As a result, NF is most comm only used for water soft ening and for nondesalting applications, such as removal of organi c compounds. Given the hi gh concentration of monovalent ions (such as sodium and chloride) in Dakota water, NF is not the best membrane treatment option for producing a low-TDS water.

RO is a membrane-based technology that employs dynamic pressure to overcome the osmotic pressure of the saline feedwater. RO us es thin, semipermeable me mbranes (Figure 13) to separate the feed stream into two streams of differing TDS c oncentration: a low-TDS product (permeate) and a high-TDS brine (concentrate). Pressure forces pure water through a membrane

that retains dissolved solids. The retained dissol ved solids are rejected from the system in the

concentrate stream. The concentrat e is disposed of either by in troduction into a receiving water Body (ocean), evaporation ponds, or deep well inj ection into a geologic formation. The permeate is collected as product for beneficial uses.17 Table 5. Comparative RO and NF Species Rejection Rates (Bisconer, 1998) Species RO, % NF, % Sodium Chloride, NaCl 99 0–50 Sodium Sulfate, Na 2 SO 4 99 99 Calcium Chloride, CaCl 2 99 0–60 Magnesium Sulfate, MgSO 4 >99 >99 Sulfuric Acid, H 2 SO 4 98 0 Hydrochloric Acid, HCl 90 0 Fructose, MW* 180 >99 >99 Sucrose, MW 360 >99 >99

Humic Acid >99 >99

Viruses 99.99 99.99

Proteins 99.99 99.99

Bacteria 99.99 99.99
* Molecular weight.

Figure 13. Photo of RO treatment membranes used to desalinize water in El Paso, Texas (Hutchinson, 2007).18 For the purposes of this study, RO was deemed the most appropriate and cost-effective technology for treatment of Dakota water. ED a nd EDR were not consider ed because of their reduced salt rejection rates and high system cost. As previously mentioned, NF was not considered because of its inability to rem ove monovalent ions. Figure 14 is a simplified schematic of an RO system.

RO FEEDWATER PRETREATMENT

Pretreatment of the feedwater for a RO plant is required to ensure that constituents present in the raw water supply do not cause plugging, fouling, or damage to the membranes, with a resulting loss of performance and a reduction in output of the facility.

RO Pretreatment Goals

 Biological activity and fouling – Biological fouling is generally not an issue with water from deep aquifers, such as the Dakota, that typica lly do not contain organic carbon at levels that support biological growth. However, given that the Dakota is a commonl y targeted zone for produced-water disposal, residual hydro carbons may create issues for treatment.

 Iron oxide fouling – Water from deep aquifers often contains dissolved ferrous iron (Fe 2+ ).

Reduced iron remains in solution and will be removed by RO membranes; however, if any air is inadvertently introduced into the system, insoluble iron oxide will be formed. Iron oxide will foul the membrane, which requires, at a minimum, system shutdown and cleaning.

Figure 14. Block diagram of RO system.19 There is a very real possibility that the iron fouling will destroy the permeability of the RO membrane, necessitating membrane replacement. Iron oxide formation is prevented by chlorine addition to induce iron precipitation, with subsequent filtration for iron removal prior to RO treatment. Excess free chlorine can damage membranes, so it is removed with the

addition of bisulfite.

 Mineral scale – CaCO 3 or CaSO 4 scale formation occurs when the solubility limit of these compounds is exceeded on the concentrate side of the RO membrane. These scales can foul the membrane, requiring costly cleaning or re placement of RO membranes. Scale prevention can be successfully accomplished by adding antiscaling chemicals to the feedwater after iron

removal.

 Silica precipitation – SiO 2 can precipitate out of the concentr ate and form scale deposits that are very difficult to remove and may irrevers ibly damage membranes. Scale prevention can be successfully accomplished by adding SiO 2 antiscaling chemicals to the feedwater.

 Colloidal and particulate fouling – Some particulates and colloids, such as colloidal silica, are effectively removed via sand, cartridge, or stainless steel mesh filtration systems.

Pretreatment Processes

Pretreatment processes appropriate for RO systems include chlorine injection to precipitate iron, a scale inhibitor injection sy stem to prevent scale formation, a fine filtration system to remove suspended solids and iron precipitate, and a cleaning system to periodically perform cleaning of the membranes and piping system.

 Iron oxidation system – Iron oxide formation is prevented by chlorine a ddition to induce iron precipitation, with subsequent filtration for ir on removal. If iron re moval is required, the chlorine additive step precedes the filtration step , and the precipitated iron is removed by the filtration system. Systems for storing and introducing these chemicals include bulk and day storage tanks, metering pumps, monitoring a nd control systems, and safety equipment.

 Fine filtration system – This usually involves the use of sand, cartridge, or stainless steel mesh filters with a 5–10-μm particle-size nominal retention. These filters are designed to prevent total suspended solids (TSS) from damagi ng either the feed pump or the membranes. Sometimes, the filters are located downstream of the feed pumps, in which case a fine mesh strainer would be included upstrea m to protect the pump from TSS.

 Scale control system – Most RO systems require adding a scale inhib itor and, perhaps, acid addition, for CaCO 3 or CaSO 4 scale control in the membrane array, since at least one constituent of the feedwater will often be supersaturated in the concentrate. Silica antiscalants may also be added as necessary. Systems for storing and introducing these chemicals include bulk and day storage tank s, metering pumps, monitoring and control systems, and safety equipment. The antiscalan t chemicals are added after the fine filtration

system.20  Cleaning system – It is good engineering prac tice to include a cleaning system in the requirements for a commercially sized RO system . A typical cleaning system consists of one or two tanks, a recirculation pump, a fine f iltration device, and control and monitoring

instrumentation.

Permeate Treatment

The permeate from RO plants is often blended with a portion of the feedwater to produce a

finished water that is less corrosive to metal components in the water system and to increase the finished water yield. The secondary drinking wate r standard for TDS is 500 mg/L and is often the target to which the blending is aimed, with consideration to concentrations of sulfate, sodium, and perhaps other constituents. Stabilization of the water may require pH adjustment to an 8.0–9.0 range and addition of a low concentrati on of lime (CaO). The permeate is bacteriaand virus-free and is suitable for distri bution after stabili zation chlorination.

Concentrate Disposal

The RO system concentrate contains elevated concentrations of the salts contained in the feedwater and must be disposed of in an environmen tally acceptable manner. Deep well injection is a common method for disposal of industrial, municipal, a nd liquid hazardous waste and is increasingly being considered as an option for di sposal of desalination plant concentrate (Glater and Cohen, 2003). This method is used quite extens ively in the western pa rt of North Dakota for disposal of water produced from oil production. While other methods of concentrate disposal are available, such as evaporation ponds, evaporation/ crystallization systems, and/or atomization/ land application, the most cost-effective method of concentrate disposal is likely through deep well injection.

PILOT PROJECT BACKGROUND

Site Description

This project was conducted near Tioga, Nort h Dakota, at an existing site where a groundwater well site is screened in the Dakota Formation (Dakota) at a depth of approximately 5500 feet. The Dakota is part of the Lower Cretace ous aquifer system and is one of the most widespread aquifers in North America. It is pr esent in most states of the Great Plains, from western Iowa to Montana and from the Arctic Circle to New Mexico (Kansas Geological Survey, 1996). In eastern North Dakota, gr oundwater from the Dakota has b een used as a water source for livestock since the beginning of the 20th centu ry, but because of its marginal quality and increased costs associated with treatment and pu mping, it has been marginalized as a municipal or industrial water source. However, recent developments in water treatment technologies, coupled with the current wate r acquisition costs of water fo r Bakken fracturing, made the

economic and technical evaluation of the Dakota’s potential as a water supply source for the oil industry a logical endeavor.21 The well at the Tioga location provides water that is used as part of a secondary oil recovery operation (waterflood) an d is capable of sustaining mode rate to high yields. The well has been pumped nearly continuously at a rate of 11,000 to 12,000 bbl per day (320 to 350 gallons per minute [gpm]) for several decade s with no measurable impacts to hydrostatic water levels (Hess Corporation, personal co mmunication, 2009); therefore, the additional pumping rate required for the relatively short dura tion of the pilot project was inconsequential.

Water samples collected from the well revealed that the water chemistry is predominantly sodium chloride in nature, with lesser amounts of sulfate and bicarbon ate. TDS average about 8500 mg/L. Specific information on water chemistry is listed in Table 6. Because the Dakota is at such a great depth beneath the surface, th e water exits the well at a temperature of approximately 155°F (68°C).

A key issue of concern related to treatmen t of brackish groundwater (especially when dealing with elevated temperat ures) is corrosion of piping, pump s, cooling system components,

and other materials that come in contact with the water. Because salinity levels of the formation water are elevated, corrosion coul d lead to costly equipment fa ilures and corresponding inability to produce permeate at a high rate. Corrosion can be affected by chemical composition, temperature, pH, degree of aer ation, flow velocity, and pressu re. System-specific testing is helpful to most accurately evaluate corrosi on potential. Therefore, the EERC conducted corrosion rate testing of the feedwater and c oncentrate streams to determine proper heat exchanger, piping, and valve material selection for a full-scale plant.

CORROSION AND SCALE FO RMATION MODELING

A two-step approach was used to evaluate the corrosion potential of Dakota water during the pilot study. The first step was to evaluate the corrosi on potential of various metals and alloys using computer modeling. The second step was to use the modeling results, coupled with an evaluation of materials likely to be used for a full-scale RO plan t, to select corrosion coupons for installation and testing in conjunction with the p ilot project. The following section describes the results of the corrosion analysis modeling, whic h also includes an eval uation of the scaling potential of the water. The results of the fi eld-based testing of me tal and alloy coupons are discussed later in this report.

The model-based evaluation of Dakota wate r was conducted using OLI Systems, Inc., Stream Analyzer and Corrosion Analyzer software to predict the potential for scale formation and corrosion based on the chemistry of the fo rmation water and the predicted RO concentrate chemistry (at 60% recovery). 1 Corrosion rates for 19 metals and alloys were calculated for a water composition representing raw Dakota Aquife r water. Corrosion rates for carbon steel (A212B) and 316 stainless steel were also mode led using water compositions representing RO

1 Dr. Robert Cowan wishes to acknowledge and thank OLI Systems, Inc., for allowing his use of the Lab Analyzer, Stream Analyzer, and Corrosion Analyzer software for this project. The software was provided free of charge as part

of a 3-month “Friends of OLI” license.22 Table 6. Water Chemistry Results for Dakota Aquifer Samples
Analyte Average Value Units
Ba 0.11 mg/L Ca 11.85 mg/L Cl 4220 mg/L F 3.9 mg/L Fe 0.17 mg/L Mg 2.4 mg/L Mn 0.04 mg/L

NO 3 <1 mg/L P, Total <0.1 mg/L

PO 4 0.94 mg/L K 14.4 mg/L Si 16.3 mg/L Na 3755 mg/L

SO 4 499.5 mg/L

HCO 3 1763 mg/L Al <0.1 mg/L Cu 0.0034 mg/L Hg <0.1 μg/L Pb 0.0024 mg/L Sr 0.9 mg/L Temperature (field) 152 °F pH (lab) 7.8 –

Conductivity (lab) 14.1 mS/cm Conductivity (field) 13.88 mS/cm TDS (measured) 8820 mg/L TDS (calculated) 10,339 mg/L TSS 14.0 mg/L Turbidity 2.2 NTU 1

Alkalinity (as CaCO 3 ) 1445 mg/L Hardness (as CaCO 3 ) 39 mg/L

1 Nephelometric turbidity units.

feed and RO reject brine based on water chem istry provided by Hess. The water chemistry was based on an RO recovery rate of 60%, slightly less than the 72% average recovery achieved during the pilot project; however, at the time that the modeli ng work was conducted, a target recovery had not yet been established for the pilo t. Scaling tendencies of all three waters were also calculated using the OLI Systems softwa re. All calculations were performed over a temperature range of 70° to 170°F.23 Dakota Aquifer Water Composition

The water chemistry shown in Table 6 was used as the basis for building the water chemistry conditions used in the corrosion calc ulations. The procedure used was to enter the Dakota Aquifer water analysis results in the OL I Systems Lab Analyzer software and reconcile the charge balance, pH, and alkalinity. The fi nal composition of the water used in corrosion modeling is shown in Table 7.

Scaling Tendency

Scaling tendency is a measure of the likelihood of a dissolved species to precipitate from solution as a solid-phase chemical species. The results of the scaling tendency analysis for Dakota Aquifer water at 152°F are shown in Ta ble 8. Only the 10 highest of the 128 scaling tendency values calculated are given. The results indicate that dissolved solids are likely to precipitate as a scale. A scaling tendency value of 1 indicates the water is supersaturated with respect to that mineral. A scaling tendency belo w 1 indicates mineral co mponents are present at concentrations below saturation, but at values near 1, scaling may still be of concern. The scaling

tendencies shown in Table 8 i ndicate that fluorapatite (Ca 5 [PO 4 ] 3 F) and four carbonates, siderite

Table 7. Lab Analysis Values Entered into OLI Lab Analyzer Software and Values after Reconciling Charge Balance, pH and Alkalinity (charge balance adjusted by addition of chloride ion; pH and alkalinity did not require adjustment) Input Calculated Units % Diff. Water 1.00E+06 9.94E+05 mg/L

− 0.62 Si 16.3 16.3 mg/L Ba 0.11 0.11 mg/L Ca 11.85 11.85 mg/L Fe 0.17 0.17 mg/L Mg 2.4 2.4 mg/L Mn 0.04 0.04 mg/L K 14.4 14.4 mg/L Na 3755 3755 mg/L Al 0 0 mg/L Cu 0.003 0.003 mg/L Hg 0 0 mg/L Pb 0.002 0.002 mg/L Sr 0.9 0.9 mg/L Cl 4220 4390 mg/L 4.03 F 3.9 3.9 mg/L NO 0 0 mg/L

PO 4 0.94 0.94 mg/L

SO 4 499.5 499.5 mg/L

HCO 3 1763 1763 mg/L24 Table 8. Scaling Tendency Values for the Ten Minerals Having the Highest Scaling Te ndencies for Dakota Aquifer Water at 152°F and pH 8.2 (results valid through full temperature range evaluated [70°–170°F]) Solids Within Temperature Range Scaling Tendency Fluorapatite, Ca 5 (PO 4 ) 3 F 1 Iron(II) Carbonate 1 Manganese(II) Carbonate 1

Strontium Carbonate 1 Calcium Carbonate (calcite) 1

Barium Sulfate 0.624 Copper(II) Hydroxide 0.014 Magnesium Carbonate 0.011

Strontium Sulfate 0.008 Iron(II) Hydroxide 0.007

(FeCO 3 ), magnesite (MgCO 3 ), strontianite (SrCO 3 ), and calcite (CaCO 3 ), will form a precipitate or scale unless the chemistry and/or temperatur e of the water is adjusted. Acid addition and

removal of CO 2 through aeration of the water should eliminate the potential for calcite precipitation. The use of othe r scale inhibitors may be required to prevent fluorapatite precipitation. The apparent molecular composition of the solution suggests that the dominant

solid formed would be calcium carbonate. The fact that the scaling tendency for barium sulfate is close to 1 is a potential concern. Barium sulfat e scales are often associated with naturally occurring radioactive material (NORM) that can cause difficulties with respect to maintenance, reuse, and disposal of pipes and process equi pment. The NORM issue arises because barium (and strontium) scales tend to c oprecipitate radioactive radium.

Corrosion Evaluation

The 19 metals and alloys selected to eval uate the corrosion pot ential upon exposure to

Dakota water are listed in Table 9. These include iron (two grades), carbon steel (four grades), stainless steel (four grades), alum inum alloys (two grades), nickel , and six other iron alloys (four

Inconel ® and two Hastelloy ® ). These are all of the metals a nd alloys available in the public database in OLI Systems Corrosion Analyzer so ftware. Unfortunately, there was no option to

evaluate titanium. Corrosion rate calculation s were performed for flowing water over the velocity range of 0 to 20 ft/s and for every 10 de grees of temperature from 70° to 170°F. Table 9 includes a summary of the corrosion rate range for all of the metals and alloys studied. The lowest rate is always for the condition of 70°C and 0 ft/s. The highest rate is always for 170°C

and 20 ft/s.

The results of the corrosion analyses were comp iled in plots showing the corrosion rate in mils per year (mpy) versus the water flow velo city. Figure 15 shows an example of the modelpredicted corrosion rate of carbon steel (212), stainless steel (316), and Hastelloy C-276. It should be noted that these are semi-log plots th at show corrosion rates over a range of four orders of magnitude. The carbon steel exhib ited a moderate corrosion rate and would be25 Table 9. Range of Corrosion Rates Calculat ed for All 19 Metals and Alloys Studied

Metal or Alloy Name Lowest Calculated Corrosion Rate (mpy) (velocity = 0 ft/s; temperature = 70°F) Highest Calculated Corrosion Rate (mpy) (velocity = 20 ft/s; temperature = 170°F) Fe (zone refined) 0.051 0.278 Fe (pure) 0.051 0.278

Carbon Steel A212B 0.102 2.799

Carbon Steel A216 0.102 2.799 Carbon Steel G10100 (generic) 0.102 2.709

Carbon Steel 1018 0.102 2.732

Stainless Steel 304 0.104 0.275

Stainless Steel 316 0.018 0.096 Stainless Steel Alloy 254SMO (alloy 254, vlx954) 0.011 0.075

10% Cr Stainless Steel 0.073 0.346 Aluminum 1199 (pure) 0.066 16.890

Aluminum 1100 0.065 16.811

Ni 0.021 0.230 Superalloy Inconel 600TM 0.005 0.019 Inconel Nickel Chromium Alloy 625 0.004 0.008 Superalloy Inconel 690TM 0.004 0.018 Incoloy 825 ® 0.004 0.009 Hastelloy Alloy C-276 0.004 0.008 Hastelloy C-22 0.004 0.008

Figure 15. Predicted corrosion rates of car bon steel (A221B), stai nless steel (316), and Hastelloy C-276 by raw Dakota water.26 acceptable for use under certain conditions. The stainl ess steel had a very low rate of corrosion and should be acceptable for use over the full ra nge of conditions for which calculations were performed. The Hastelloy C-276 alloy exhibited an even lower rate of corrosion and would certainly be suitable for use with Dakota water; however, the additional cost of the alloy over stainless steel may prohibit its use.

It is interesting to note that while the stai nless steel and Hastelloy C-276 (as well as most other alloys evaluated) showed ve ry little variation in the predic ted corrosion rate as a function of flow velocity, the carbon stee ls that were evaluated were highly influenced by the flow velocity over the range of temperatures evaluate d (Figure 16). This may be of significance if interest in using water from the Dakota increas es since carbon steel pipe s are commonly used in North Dakota’s oil and gas operations.

The acceptability of the calculated corrosi on rate depends on the material and the application. For example, to ev aluate the severity of the carbon steel corrosion ra tes calculated using the OLI software, a comparison of corrosion rates was made to guid elines developed by Boffardi (2010) and Puckorius (2003) for open a nd closed recirculating cooling water systems (Tables 10 and 11). The modeled corrosion rates for carbon steel ranged from negligible to severe, depending on the temperatur e, velocity, and application. More specifically, the lowest

rate of corrosion for Carbon Stee l A212B was found to be 0.102 mpy for a velocity of 0 ft/s and a temperature of 70°F. This is considered to be negligible corrosion for an open recirculating cooling water system and mild corrosion for a cl osed recirculating cooling water system. The highest rate of corrosion for Carbon Steel A212 B was found to be 2.799 mpy for a velocity of 20 ft/s and a temperature of 170°F. This is cons idered mild for open recirculating cooling water systems and severe for closed reci rculating cooling water systems.

Figure 16. Predicted corrosion of Carbon Steel A212B by Dakota water over a range of temperatures and flow velocities.27 Table 10. Quantitative Classifica tion of Carbon Steel Corrosion Rates for Open Recirculating Cooling Water Systems Description Corrosion Rate, mpy Negligible or Excellent Less than or equal to 1 Mild or Very Good 1 to 3

Good 3 to 5

Moderate to Fair 5 to 8

Poor 8 to 10 Very Poor to Severe >10

Table 11. Quantitative Classifica tion of Carbon Steel Corrosion Rates for Closed Recirculating Cooling Water Systems Description Corrosion Rate, mpy Excellent Less than or equal to 0.2

Good 0.2 to 0.5

Moderate 0.5 to 0.8

Poor 0.8 to 1 Very Poor to Severe Gr eater than or equal to 1

Within these systems, stainless steel corrosion is more simply classified in both systems as acceptable for rates less than 0.1 mpy or unaccepta ble for rates greater than 0.1 mpy. In these systems, pitting of any meta l is considered unacceptable.

Based on the results of the corrosion analyses and the corrosion rate classification of the various materials, the metals were ranked into five groups, as shown in Table 12. Corrosion rates vary over 4 orders of magnitude, with the lo west rates being <0.004 mpy for Alloys C-22, C276, 625, and 825 and the highest rates being ne ar 16.8 mpy for Aluminum 1100 and Aluminum

1199. It should be noted that the corrosion rates were calculated for an environment containing no dissolved oxygen.

Table 12. General Classification of Metals and Allo y s Based on the
Calculated Corrosion Rates with Dakota Water Excellent Alloys C-22, C-276, 625, and 825 Alloys 600 and 690

Ver y Goo d Allo y 254SMO an d Stainless Steel 316

Goo d Fe (pure), Fe (zone refi ned), Ni, Stainless Steel 304, and 13% Cr stainless steel

Fai r Carbon Steel 10100,1018, A216, and A212B

Ver y Poor/Unacceptable Aluminum 1100 an d 1199 (pure)28 These results, along with information on the price and availability of metals for use in heat exchangers, as well as knowledge on standard material use in the oil field were used to help guide in the selection of corrosion test co upons. Selected corrosion test coupons were subsequently installed at the RO treatment pilot project site for field te sting. Those results are discussed later in this report.

Corrosion and Scaling Analysis for Antici pated RO Concentrat e (at 60% recovery)

Additional corrosion calculations were performed based on a pr edicted brine (concentrate) composition of Dakota water after treatment with RO at 60% recovery. These data were much

less detailed than that used for the raw Dakota water analysis discussed above. No scaling or corrosion analyses were done for RO permeate.

The same methodology used to evaluate the ra w Dakota water was used to evaluate the anticipated RO concentrate. The water analysis results were entered into the OLI Systems software and reconciled with respect to elect roneutrality, pH, and alkalinity (Table 13). The scaling tendency values were also calculated and are shown in Table 14. The resulting apparent molecular composition of the wate r was obtained and used to calculate corrosion rates for two metals (316 stainless steel and Carbon Steel A212B) over the temp erature range of 70° to 170°F

and water velocities of 0 to 20 ft/s.

Table 13. RO Concentrate Water Analysis and Reconciliation
Input Calculated Unit % Diff.
Water 1.00E+06 9.91E+05 mg/L

− 0.88 Si 81 81 mg/L Ca 26.2 26.2 mg/L Mg 4.5 4.5 mg/L

K 22.5 22.5 mg/L

Na 6777 6777 mg/L Cl 7875 8203 mg/L 4.16

SO 4 972 972 mg/L

HCO 3 2772 2772 mg/L

Table 14. Scaling Tendency for RO Concentrate (minerals with 5 highest values) (values are valid over the temperature range evaluated [70°–170°F]) Tendency Scaling Calcium Carbonate (calcite) 1 Calcium Carbonate (aragonite) 0.514 Calcium Carbonate Monohydrate (vaterite) 0.130 Sodium Bicarbonate (nahcolite) 0.010 Calcium Sulfate Dehydrate (gypsum) 0.00329 The only reconciliation required for the RO c oncentrate was the addition of a small amount

of chloride ion in order to obt ain electroneutrality (Table 15). Scale formation with calcium

carbonate minerals in the concentr ate is possible even at the temp erature of the water analysis, 25°C, as evidenced by the scal ing indices given in Table 15. Because the simplified water analysis did not include strontium, barium, or fluoride, the analysis could not identify a potential

for the formation of the other scale minerals id entified for the more detailed Dakota Aquifer

water.

Table 15 contains the lowest and highest ca lculated corrosion rate s for both carbon steel and stainless steel. As would be expected, the re sults suggest that the RO concentrate would be

more corrosive to Carbon Steel A212B and 316 st ainless steel than the raw Dakota water. While

the corrosion rate of 316 stainl ess steel was very similar between the raw Dakota water and RO concentrate, the predicted corrosion rate of Carbon Steel A212B was c onsiderably higher with the RO concentrate, particularly with increasing fl ow rate and at higher temperatures. These rates suggest that Carbon Steel A212B would be unacceptable for use w ith the RO conc entrate except
at the lowest flow rate and temperature conditions. The rates predicted for 316 stainless steel suggest that it would be acceptable for use w ith the RO concentrate at 60% recovery.

MOBILE RO TREATMENT SYSTEM

After evaluating several mob ile technology treatment system providers, Hess selected General Electric (GE) Water and Process Technol ogies as the preferred pilot system provider.

GE’s MobileRO ® is a mobile RO water treatment syst em, consisting of two semitrailers and several skid-mounted components, including all the hardware and electronics necessary to monitor the system operation and performance. Given the quality of the feedwater at the pilot project site, GE estimated that, at full capac ity, the system would be capable of producing approximately 160 gpm of permeate at a 75% rec overy rate. Because the system contains two independently operated filter arrays, it could also be operated at reduced capacity, equivalent to approximately 80 gpm of permeate at a 75% recovery rate. The mobile system contained all necessary prefilters, the antiscalant trea tment system, controls, piping, valves, and instrumentation. All operations associated with th e mobile RO unit were the responsibility of GE personnel for the duration of the pilot test.

Table 15. Range of Corrosion Rates Calculated for Carbon Steel A212B and S316 Stainless Steel by the Anticipated RO Concentrate

Metal or Alloy Name/Water Lowest Calculated Corrosion Rate, mpy (velocity = 0 ft/s; temperature = 70°F) Highest Calculated Corrosion Rate, mpy (velocity = 20 ft/s; temperature = 170°F)

Carbon Steel A212B 0.184 7.919

316 Stainless Steel 0.018 0.09630 SITE PREPARATION

In order to prepare the site for the pilot pr oject, several activitie s were conducted, including the following:

• Installation of the RO treat ment and pretreatment units.

• Installation of the feedwater coo ling system and heat exchangers.

• Construction of a lined and covered pond for storage of the treated water (RO permeate).

• Installation of five 400-barrel tanks that are used to store the feedwater, excess permeate (if needed), and RO concentrat e (the RO concentrate tank is designed to meet saltwater storage standards).

• Installation of the neces sary piping to connect the system components.

• Installation of the el ectrical power supply and necessary connections.

• Construction of a truck-loading station that is used to transport the RO permeate to fracturing locations within the Bakken play.

• Installation of corrosion coupon test racks to evaluate the co rrosivity of the feedwater, permeate, and concentrate on va rious metals and metal/alloys.

One of the challenging aspects of the pilot pr oject was the cooling of the feedwater, which exited the production well at a te mperature of approximately 155° F (68°C), down to the required 90°F (32°C) prior to membrane treatment duri ng the summer months, when temperatures can exceed 90° or 100° and humidity can be high. In fact, the pilot project cooling system did not provide sufficient cooling capacity during a couple of the hottest days of the summer, resulting in system shutdown during the afternoon hours. Wh ile the high feedwater temperature was an inconvenience with resp ect to the RO membranes, the heat fr om the water can also be a potential resource, given that the desired temperature of the fracturing fluid pr ior to injection is approximately 80°F (27°C). During the winter months , the cost to heat the fracturing fluid prior to injection is considerable and can sometim es exceed $150,000 or more to heat the water required for one well fracturing (Hess Corpor ation, personal communication, 2010). Therefore, heat exchangers were installed by Aggreko at the pilot project site to partially cool the feedwater using the RO permeate, which exited the system at approximately 90°F (32°C), and, in turn, to heat the permeate prior to use as frac water makeup.

As previously mentioned, because of the pot ential corrosivity of the feedwater and RO concentrate, in situ corrosion te sting was conducted as part of the pilot test. A total of six test racks, each equipped to hold either three or five test coupons, were installed at various locations in the treatment train of the RO system. The loca tion of the test racks as well as a generalized layout of the pilot-scale RO system is depicted in Figur e 17. Groundwater from the Dakota31 Figure 17. Flow diagram with co rrosion test rack locations.

Aquifer was pumped from the well to a surge tank (pressure vessel). Water was routed from the surge tank to a 400-bbl feedwater tank where it was stored prior to entering the cooling, pretreatment, and RO systems. The first corros ion coupon test rack (S -1) was installed to evaluate feedwater corrosivity ju st prior to cooling. The first st ep in the cooling process was a tube-and-shell heat exchanger be tween the hot feedwater and th e RO permeate, followed by an air-cooled system with foggers. The temperature of the hot feedwa ter from the storage tank prior to cooling was approximately 125°–130°F. Afte r passing through the cooling system, the feedwater was lowered to a temperature of a pproximately 80° to 90°F. The second corrosion coupon test rack (S-2) was installed at this point in the system to evaluate the corrosivity of the cooled feedwater before undergoing pretreatment . Prior to entering the RO trains, the water underwent pretreatment via sand fi ltration and granulated activated carbon adsorption to remove suspended solids and dissolved organics, respec tively. It was very impor tant to remove any organic carbon from the feedwate r, since this can result in membrane fouling. The water was then routed through one of the two RO treatme nt trains. Upon exiting the RO membranes, the permeate was routed back through the heat exchangers to help cool the feedwater, prior to storage in the lined and covered pond. Corrosion te st racks were installed to evaluate the permeate upon exiting the system (S-3) and following heat exchange with the permeate (S-4). The concentrate was routed to a 400-bbl storage tank prior to blending wi th raw Dakota water for injection into existing waterflood operations. The corrosion potential of the concentrate just after exiting the RO system was evalua ted at location S-5. In addition to evaluating the corrosivity of the concentrate at 80° to 90°F, a titanium plate a nd frame heat exchanger was installed at the site and coupled with the feedwater to heat the concentrate up to appr oximately 115° to 120°F (S-6). This evaluation was conducted to assess the corrosivity of the concentrate in the event that it be used in a heat exchanger as part of th e cooling system for future applications.32 PILOT TEST OPERATION AND PERFORMANCE

The pilot project system began operation on July 21, 2010, at a permeate flow rate of 80 gpm and 50% permeate recovery. Higher permeat e recovery rates were not achievable until GE performed system modifications on Augus t 3, 2010, at which time the recovery rates increased to approximately 70%. GE continued to operate the RO system at a flow rate (80 gpm of permeate production) to be c onsistent with the truck hauli ng cycle demands and maintain a more constant, steady operation. The permeate produ ced from the system was used for fracturing the Bakken, and the concentrate wa s blended with the waterflood injection system feedwater.

The RO system continued to operate at a perm eate flow rate of 80 gpm with 70% permeate recovery until September of 2010, when the system was shut down to make alterations to the permeate holding pond, to address elect rical issues at the truck load ing station, and to winterize the site. Based on GE operational logs, from July 21, 2010, through September 6, 2010, a total of 6,084,700 gallons of groundwater was processed through the RO syst em, resulting in approximately 4.26 million gallons of permeat e and approximately 1.83 million gallons of concentrate. Although no flow measurements we re recorded during the shutdown period, GE did operate the RO system approximately 1 hour each day to prevent membrane fouling.

After the necessary system modifications we re made, GE began continuous operation of the RO system on November 29, 2010, and as of April 13, 2011, had processed approximately 19 million gallons of Dakota Aquifer water. C ontinuous operation of the system was only stopped during three short periods:

• January 1, 2011 • February 25, 2011, through February 28, 2011 • March 22, 2011, through March 25, 2011

GE personnel observed lower flow rates (Figure 18), lower operat ing pressures (Figure 19), and higher permeate conductivity (Figure 20) when operating RO Train 1. Because of those conditions, GE primarily operated RO Trai n 2 throughout the demonstration and only occasionally operated Train 1 in order to m itigate membrane scaling. The cause of the operational differences between the two tr ains is unknown. Trai n 1 was operated for approximately 39 days, resulting in the trea tment of 5.5 million gallons, and Train 2 was operated for approximately 88 days, resulting in the treatment of approximately 13.5 million gallons. Feed water temperature was monitored during operation and is shown in Figure 21. The feed water temperature ranged from 62° to 95.0°F and averaged 81.3°F during continuous operation (November 29, 2010, through April 13, 2011).

Feedwater flow rates were lower while Train 1 (103 gpm) was operate d compared to Train 2 (124 gpm). Resulting permeate flow rates were also impacted, averaging 73 gpm on Train 1 compared to 90 gpm on Train 2. Permeate conduc tivity also showed a difference, averaging 585 microseimens per centimeter (μS/cm) on Train 1 and 395 μS/cm on Train 2.33 Figure 18. Pilot-scale RO system flow rates.

Figure 19. Pilot-scale RO syst em operating pressures.34 Figure 20. Pilot-scale RO system permeate conductivity.

Figure 21. Pilot-scale RO system feedwater temperature.35 As expected, the RO permeate was very high quality, and all major chemical constituents, except iron (Fe), were below Environmental Protection Agency secondary drinking water

standards. As shown in Table 16, there was a 97% reduction in TDS concentration along with a 96% reduction in conductivity. Most major chemical constituents in the feedwater were reduced by greater than 90%. Alkalinity was reduced by 94%, and pH was measured at 6.06 in the permeate. Iron was measured at higher levels in the permeate than in the feedwater. However, the analytical techniques used to measure the iron concentrations are less susceptible to

interferences with clean water th an with the brackish feedwater, and one could argue that the data are inconclusive with resp ect to iron. RO treatm ent did not appear to remove any total organic carbon (TOC).

Given the issues with Train 1 operation, system performance was analyzed solely based on the operation of Train 2. Permeate recovery rate s remained relatively consistent, averaging nearly 72% over the current operating period. Throughout the testing pe riod, membrane cleaning was not deemed necessary, and no scaling was ob served. GE personnel credited the low-turbidity feedwater for the lack of membrane fouling. GE performed backwash operations on a once-aweek basis as preventive maintenance. Since pressu re readings did not indi cate the need for more frequent backwashing, this frequency appeared to be sufficient to maintain desired operational pressures. GE records also indicated that once the system was stabilized, the feedwater conductivity was consistently around 14,000 μS/cm, and the permeate averaged 700 μS/cm. Figure 22 is a plot of co nductivity of Train 2 duri ng continuous operations.

Each treatment train consisted of 30 RO elements, and each element was nominally 365 square feet of surface area. This equates to each treatment train consisting of 10,950 square feet of surface area. By dividing the daily flow rate by the surf ace area of the treatment train, a flux rate in gallons per square foot per day (gfd) was calculated. A summary of permeate flux is presented in Table 17 and graphically shown in Fi gure 23. A regression of this data indicates that the flux would likely stabilize at approximately 15 gfd.

Additionally, flux was plotted agai nst temperature and pressure differential as presented in Figures 24 and 25, respectively. As expected, the flux decreases with decreasing temperatures but not significantly over the range of temperatures experienced dur ing the pilot test. Differential pressure also did not greatly influence the syst em flux over the range from 5 to 15 psig. In both cases, the flux maintained nominally between 14 and 16 gfd for the observed range of temperature (60o to 95° F) and differential pressure (0 to 20 psi).36 Table 16. Summary of Water Analysis Results (uni ts in mg/L unless otherwise noted)

Analyte Feedwater (S-1) Permeate (S-4) Concentrate (S-5, S-6)* %

Reduction

Ca 15.8 3.0 44.4 81 Na 3300 103 10,750 97

K 9.9 <1 42.8 >90
Cl 3710 130 13,200 96

SO 4 456 <5 1460 >99

NO 3 <0.1 <0.1 0.14 –

HCO 3 1220 74 3820 94

Ba <0.5 <0.1 <1 –

F 3.57 0.14 12.8 96

Fe <0.5 0.66 <1 –
Mg 2.6 <1 7.9 >62

Mn <0.25 <0.05 <0.5 –
P, total <0.1 <0.1 0.96 –

Si 17.2 <1.1 56.3 >94

Cu <0.25 <0.05 <0.5 –

Sr 0.98 <0.1 2.92 >90
Temperature (field), °F 127 110 96, 118* pH (lab) 7.4 6.2 7.8
pH (field) 7.32 6.06 7.55
Conductivity (lab), μS/cm 13,600 568 37,700 96
Conductivity (field), μS/cm 15,400 610 41,500 96

Total Dissolved Solids (calculated) 8230 280 27,800 97

Alkalinity (as CaCO 3 ) 1220 74 3820 94
Hardness (as CaCO 3 ) 50.2 7.49 144 85
Total Organic Carbon 5.9 4.9 7.1 17
* Because the water chemistry results from Racks S-5 and S-6 were not significantly different, they were averaged in this column, with the exception of temperature, which is listed separately for Racks S-5 and S-6, respectively.37 Figure 22. Treatment Train 2 feedwater and permeate conductivity.

Table 17. Summary of Flux Calculations Treatment Train Minimum, gfd Maximum, gfd Average, gfd

Train 1 11.57 17.23 13.51

Train 2 14.73 17.75 16.29

Figure 23. Treatment Train 2 flux versus time.38 Figure 24. Flux versus temperature.

Figure 25. Flux versus pressure differential.39 FIELD-BASED CORROSION TESTING

Shortly after start-up of the sy stem, six corrosion test racks were installed at the subject site. Based on corrosion modeling results presen ted earlier, the test coupons selected for

evaluation included four standard materials: carbon steel (API 5LX42), stainless steel (316L), copper–nickel alloy (CDA706), and titanium (Ti), as well as a more exotic alloy, Hastelloy C276, that is a nickel–molybdenum–chromium wrought alloy characterized by versatile corrosion resistance. The coupon ra cks were constructe d of 3⁄4-inch Schedul e 80 PVC (polyvinyl chloride) pipe which has an internal diamet er of 0.722 inches. The type of test coupon and operating conditions for each rack are included in Table 18. The discharge from Racks S-1, 2, 3, and 4 were manifolded together and plumbed to discharge into the feed tank. Figure 26 is a photograph of Rack S-2, a five-pla ce corrosion test rack assemb ly. The discharge from Racks S5 and S-6 were plumbed to discharge into the re ject tank. During the inst allation and testing of the racks, EERC personnel were unable to atta in enough water flow through Racks S-3 and S-4

to maintain desired corrosion test conditions. Th is was caused by insufficient water pressure on the influent side of the rack to overcome the pre ssure at the discharge point. While the test racks could have been relocated, it would have enta iled shutting down the system. Since permeate corrosivity was expected to be minimal, no te st coupons were installed in Racks S-3 and S-4.

Table 18. Corrosion Rack Description

Rack No. Rack

Material Number of Coupons Coupon

Order Fluid Fluid Design Temperature Observed Temperature

S-1 CPVC 1 5 Ti

C276

316L

CDA706

API 5LX42 Feedwater 155°F (68°C) 127°F (53°C)

S-2 PVC 5 Ti

C276

316L

CDA706

API 5LX42 Feedwater 90°F (32°C) 80°F (27°C)

S-3 PVC 3 No coupons Permeate 90°F (32°C) – S-4 CPVC 3 No coupons Permeate 130°F (54°C) 110°F (43°C)

S-5 PVC 3 Ti

316L

API 5LX42 Concentrate 90°F (32°C) 96°F (36°C)

S-6 CPVC 3 Ti

316L

API 5LX42 Concentrate 155°F (68°C) 118°F (48°C)

1 Chlorinated PVC.40 Figure 26. Photograph showing the instal lation of corrosion test Rack S-2.

Following installation of the corrosion test racks, water was allowed to flow through the

racks for several weeks to flus h the system prior to coupon inst allation, as recommended by the test rack manufacturer. Sample flow rates thro ugh the coupon racks varied between 0 corrosion and 5 gallons per minute, corresponding to a flow velocity in the coup on racks between 0 and 3.92 ft/s (0 and 1.19 m/s).

The test coupons were installed in the rack s in the order shown in Table 19, which represents their anticipated resistance to co rrosion from most to least. This was done to minimize the potential of corrosion from one test coupon infl uencing the corrosion rate of subsequent test coupons. The only notable issue obs erved during coupon installation wa s the presence of a black residue on the Rack S-1 flowmeter and coupon holders . This residue was later determined to be a form of hydrocarbon, although detail ed testing to determine the ex act nature and source of the

residue was never conducted.

On November 9, 2010, the corrosion racks and a ssociated piping were retrieved to prevent any damage occurring from freezing temperatures . The corrosion coupons were removed from their respective racks, visua lly inspected, photographed, and allowed to dry overnight.

Upon retrieval, the corrosion c oupons from Rack S-1 (127°F f eedwater) were covered in the same black coating that appeared on the coupon holder and the flowmeter during the August 26, 2010, site visit. Coupons removed from Rack S-2 (80°F feedwater) also exhibited a slight black coating. The black residue was not observed in any of the other test racks. As previously mentioned, a sample of the black resi due was collected, and so me preliminary testing indicated that it was a type of hydrocarbon. Additional testing of the residue to determine its exact composition has not been conducted.41 Table 19. Comparison of Measured and Predicted Corrosion Rates

Rack Fluid Coupon Metal Measured

Corrosion Rate, mpy Predicted

Corrosion
Rate,

mpy Temperature

and Flow

Rate for

Predicted

Rate 2

S-1 Feedwater, 127°F Ti-2 Titanium 0.0968 NA

S-1 Feedwater, 127°F C276 Hastelloy 0.0472 0.0061 130°F, 4 ft/s

S-1 Feedwater, 127°F 316L Stainless steel 0.0724 0.0525 130°F, 4 ft/s

S-1 Feedwater, 127°F CDA706 Copper–nickel 0.7528 NA

S-1 Feedwater, 127°F API 5LX42 Carbon Steel 1.2684 0.631 130°F, 4 ft/s

S-2 Feedwater, 80°F Ti-2 Titanium 0.0639 NA

S-2 Feedwater, 80°F C276 Hastelloy 0.0402 0.00407 80°F, 4 ft/s

S-2 Feedwater, 80°F 316L Stainless steel 0.0590 0.0219 80°F, 4 ft/s

S-2 Feedwater, 80°F CDA706 Copper–nickel 2.2485 NA

S-2 Feedwater, 80°F API 5LX42 Carbon steel 1.9256 0.256 80°F, 4 ft/s

S-5 Concentrate, 96°F Ti-2 Titanium 0.0542 NA

S-5 Concentrate, 96°F 316L Stainless steel 0.0601 0.0319 100°F, 4 ft/s

S-5 Concentrate, 96°F API 5LX42 Carbon steel 2.0864 1.10 100°F, 4 ft/s

S-6 Concentrate, 118°F Ti-2 Titanium 0.0716 NA

S-6 Concentrate, 118°F 316L Stainless steel 0.0501 0.0449 120°F, 4 ft/s

S-6 Concentrate, 118°F API 5LX42 Carbon teel 2.0249 1.65 120°F, 4 ft/s

1 Corrosion rate units on the figures at mm/year. To convert mm/yr to mil/yr multiply by 39.37 mil/yr/mm/yr.

2 Figures only show values for every 20° of temperature ch ange but calculations were performed at 10° intervals.

N ot available – this metal was not available in the OLI Corrosion Analyzer public database.

An initial visual corrosion assessment reveal ed that, in each case , the carbon steel (API 5LX42) and the copper–nickel, if present, showed significant corrosion, while the stainless steel, Hastelloy (if present), and the titanium coupons did not show visible corrosion although a slight scale was present.

Once the coupons were dry, they were individua lly weighed (without cl eaning), placed in individual glass vials, and sent to the supplier of the corrosi on coupons, Metal Samples Company (MSC), for postexposure analysis. MSC cleaned and weighed the coupons in accordance with ASTM International Standard G-1, provided th e EERC with a corrosion analysis, and then returned the coupons upon completion of the an alysis. MSC results are shown in Table 19.

With an initial and final weight, the corrosi on rates for the respective metal coupons were calculated using the following equation:

CR = (K × W)/(A × T × D) [Eq. 1]42 Where:

CR = Corrosion rate (mils per year) K = Conversion constant (3.45 × 10 6 ) W = Mass loss (g) A = Surface area (cm 2 ) T = Exposure time (hours) D = Density (g/cm 3 )

Results from MSC (Table 19) clearly show that the carbon steel and copper–nickel coupons corroded significantly more than the tita nium, Hastelloy, or stai nless steel samples, although even the higher corro sion rates are not considered to be excessi ve by industry standards. Interestingly, it a ppears that the more susceptible metals (carbon steel and copper– nickel) were protected somewhat from corrosion by the black substance that was present in the feedwater and coated the coupons in Rack S-1 (127°F feedwater).

For comparison, the predicted corrosion rates, calc ulated at a flow velocity of 4 ft/s and fluid temperatures close to what was measured in the field, are also listed in Table 19 and shown graphically in Figure 27. While all of the predic ted corrosion rates were lower than the observed corrosion rates, the modeling calculations did a good job of predicting the observed corrosion

rates for both 316L stainless steel and API 5L X42 carbon steel. The modeling calculations substantially underpredicted th e observed corrosion rates for Hastelloy C276 for the two conditions tested, feedwater at 80° and 127°F. Fo r the hot feedwater (Rack S-1), this may again be a result of the black coating that formed on the test coupons.

Figure 27. Comparison of measured and predicted corrosion rates.43 A surface analysis of select coupons was performed at the EERC using a Nanovea PS-50 optical profilometer. The profilometer measures the height of the sample surface in relation to a fixed optical assembly, with a ho rizontal detection lim it of 0.1 μm and a ver tical detection limit of 5 nanometers. Six corrosion coupons were an alyzed for comparison: carbon steel and stainless steel coupons from Rack S-1 (127°F feedwater), carbon steel and stainless steel coupons from Rack S-6 (118°F concentrate), and unexposed carbon steel and stainl ess steel coupons. The resulting profilometer images provide a graphi cal comparison of corrosion between carbon steel

and stainless steel in different water streams and are shown in Fi gures 28 and 29, respectively. It should be noted that the color height scales as sociated with each coupon are specific to that coupon and do not represent a common datum. More clearly explained, the profilometer scans a sample, and the deepest measured point on that sa mple is assigned the zero datum, and all other heights measured are referenced to that sample-specific zero datum.

As seen in Figures 28 and 29, the carbon steel exhibited more pitting corrosion than did the stainless steel (especially in Coupon No. 10 fr om Rack S-1). Figure 30 shows a more detailed projection of a highly corrode d section of the carbon stee l coupon from Rack S-1 (Coupon No. 10), illustrating the high degree of p itting observed for the carbon steel coupon.

Of all materials tested, the carbon steel and copper–nickel coupons exhibited higher rates

of corrosion in all of the wate r streams than did the titanium , Hastelloy, and stainless steel coupons. With that said, the most severe corro sion observed for carbon st eel was around 2 mpy.

This corrosion rate may not be considered exces sive if it occurred ev enly on the surface of a material; however, that does not appear to be the case, as localized pitting was observed and may be of concern in a long-term application.

Figure 28. Profiler images of select stainless steel coupons.44 Figure 29. Profiler images of select stainless steel coupons.

Figure 30. Profiler image of carbon steel coupon zoomed in to pitted area.45 Corrosion results do indicate that stainless steel should withsta nd contact with the respective feedwater and concentrat e streams quite well. Therefore, investment in more exotic (and expensive) materials such as Hastelloy and titanium are likely not warranted for use in the full-scale facility.

ECONOMIC EVALUATION

As summarized in earlier sections, the pilo t-scale RO system was operated continuously from November 29, 2010, through April 13, 2011. Ov er this period, approximately 19 million gallons of Dakota Aquifer water was processed to produce approximately 13.6 million gallons of permeate (average 71.6% recovery ra te). Operation of the pilot sy stem was intended to continue throughout the summer of 2011 but because of several issues that hampered continuous operation, the system was not operated be yond April 2011, except to prevent scaling by periodically circulating permeate water.

Although the pilot RO system experienced periodic interrup tions, it provided valuable

technical and economic informati on regarding design and operation of a full-scale system. These included the operation of modular RO systems in extremely cold and hot climates, identification of water-handling issues, and issues of logi stical coordination with oil field operations.Unfortunately, the intermittent operation of the pilot system made it difficult to estimate fullscale operation and maintenance (O&M) co sts based on the pilot-scale operation.

Based on conversations with Hess personnel during operation of the pilot system, Hess was sufficiently confident in the technical and ec onomic viability of the RO system to proceed with the design and bidding of a full-scal e 1- to 2-MGD RO treatment facility.

A comparison of the estimated costs of freshw ater for frac makeup from three different sources was performed by Hess and included 1) wa ter from a 1-MGD RO pl ant (per barrel cost included capital and operating expenses); 2) wate r from existing municipal, commercial, or private sources; and 3) water from the planne d Western Area Water Supply (WAWS) system, a pipeline project coupled with expansion of Willis ton’s water treatment plant that is currently being constructed in northwestern North Dakota. Hess’s internal evaluation included costs for heating and transportation of the water.

Based on this internal evalua tion, Hess determined that the water produced from its own RO plant was cost-competitive and logistically favorable compared to the current means of acquiring frac make-up water. As a result, Hess, jo intly with GE, is proceeding with plans to construct a full-scale RO system. The economic deta ils of this contractual arrangement were not made available for inclusion in this report.

RO Treatment Plant Costs

In the absence of actual bid data, the EERC ma de an effort to quantify the capital and O&M costs associated with a full-scale RO plant similar in size to that being constructed by Hessand GE. Estimates for equipment-only capital cost and O&M were provided by GE for a fullscale RO plant producing up to 1.5 MGD of treated water for use as a frac make-up water.46 GE’s estimates of capital showed that an RO system with a treated water capacity of 1.5 MGD would have an equipmen t-only capital cost of approximately $3.5 million. This capital

cost does not include site construction or infrastr ucture development-related activities. A series of assumptions summarized in Table 20 were made to estimate the remaining costs to construct a 1.5-MGD RO plant. The methodology to calcula te each cost was based on an assumed percentage of the equipment-onl y capital cost. Using this method, the total cost to construct a 1.5-MGD RO plant is estimated at approximate ly $15.75 million, not incl uding land acquisition costs, the cost of providing f eed water to the RO system, a nd the cost of RO concentrate disposal.

The estimated annual O&M cost for operatin g the RO system, provided by GE, was approximately $1,000,000 not including the co st of RO concentrate disposal.

Production Well Costs

In addition to the capital costs for the RO pl ant, costs were estimated for the groundwater

extraction well field. Based on the EERC’s e xperience in groundwater extraction wells completed in the Dakota Aquifer, five wells comple ted to a depth of 5500 ft would be required to provide the RO plant demands. At an estimat ed cost of $1.5 million for each well ($7.5 million total) and assuming an additional 10% of the total well field cost for the pumps and associated infrastructure, the total estimated cost for the water extraction system to provide water to the RO plant would be approximately $8.25 million.

The O&M cost associated with the groundwater extraction operation was based primarily on the cost of electricity to run the pumps. Assuming a 30-kW pump in each of five wells operating for 7872 hours (328 days) a year and an el ectrical cost of $0. 08/kWh, the electricity cost would be approximately $95,000.

Brine Disposal Costs

Two different brine disposal options were considered:

1. Truck transportation to an existing commercial injection site

2. Pipeline transport to a dedicated injection site.

The cost for disposal of RO concentrate was based on personal communications with service companies in the Williston Basin that pr ovide injection and disposal services. Based on these conversations, the cost for disposal is estimated to be $1.75 per bbl. Assuming 1.5 MGD of RO permeate (at 70% RO recovery), the volume of RO concentrate for disposal would be approximately 643,000 gpd or 15,300 bbl/day, which equates to approximately 211 million gpy or 5 million bbl per year (assuming 90% plant availa bility). At the previously stated cost of $1.75 per bbl for injection, the annual injection-only cost would be $8.7 million a year.47Table 20.Cost Estimate Assumptions – 1.5-MGD RO PlantDescriptionDirect Labor as% of ProcessEquipmentMaterial as %of ProcessEquipment Labor CostMaterialCostTotal DirectCostProcess Equipment 10.0 100.0 $350,000 $3,500,000 $3,850,000Site Preparation (clearing, grading) 2.8 0.5 $96,250 $17,500 $113,750Site Improvement 10.0 15.0 $350,000 $525,000 $875,000Concrete 10.0 5.4 $350,000 $189,000 $539,000Structural Steel – Platforms, Racks and Supports 6.0 15.0 $210,000 $525,000 $735,000Building – Steel, Cladding, Interior and HVAC 5.0 10.0 $175,000 $350,000 $525,000Underground Piping 8.0 12.0 $280,000 $420,000 $700,000Aboveground Piping 8.0 12.0 $280,000 $420,000 $700,000Electrical – MCC, Wiring, Lighting 6.5 12.5 $227,500 $437,500 $665,000Instrumentation 5.5 12.7 $192,500 $444,500 $637,000Insulation 7.5 5.0 $262,500 $175,000 $437,500Painting 3.0 1.7 $105,000 $59,500 $164,500Proratables 8.0 2.0 $280,000 $70,000 $350,000Total Direct Costs$3,158,750 $7,133,000 $10,291,750Construction Equipment% of DirectLabor CostTotal IndirectCostRental or Purchase 10.0$315,875Service Labor 3.0$94,763Fuel, Oil, Supplies 10.0$315,875Overhead and IndirectsSalaried 10.0$315,875Contractor Profit 10.0$315,875Office Hourly 6.0$189,525Field Hourly 5.0$157,938Temporary Construction Facilities 5.0$157,938Payroll Burdens and Benefits 32.0$1,010,800Small Tools and Consumables 7.0$221,113Other Indirects 2.0$63,175Total Indirect Costs$3,158,750Continued . . .48Table 20. Cost Estimate Assumptions – 1.5-MGD RO Plant (continued)% of TotalDirect andIndirect CostsEngineering/Design Services 10.0$1,345,050Construction Engineering 1.0 134,505Project General Management 2.0 269,010Total Engineering and Management Services $1,748,565Escalation (material – 1 yr) 2.0 $142,660SummaryTotal Direct and Indirect Cost $13,450,500Total Engineering and Management Services $1,748,565Escalation $142,660Total Project Costs$15,341,72549 The total cost of disposal must also include the cost of trucking the RO concentrate to the injection facility. This cost was estimated to be approximately $11.9 million a year based on the following assumptions:

 30-mile one-way haul to the injection site

 Three hours per round trip at $150 an hour

 26,315 round trips annually (190 bbl hauled ea ch trip)

Using these volumes and costs, the annual tota l cost for RO concentrate disposal by the truck transport method is estimated to be approximately $20.7 million.

Given the cost of RO concentrate disposal by truck transport method, it is feasible that a dedicated pipeline and injection well field would be more cost -effective. Assuming a pipeline cost of $1 million dollars per mile and a distance of 10 miles to the injection well field, the cost of the pipeline would be approxi mately $10 million. Using the same per well cost stated in the groundwater extraction discussion of $1.5 milli on, assuming two injection wells, and adding 10% for injection pumps and infrastructure, the to tal estimated cost for an injection well field would be approximately $3.3 million. The total cost for a dedicated pipeline and injection well
field is then estimated to be $13.3 million. In this scenario, the $13.3 million cost would be added to the total capital cost, and the $20.7 m illion O&M cost for RO concentrate disposal would be reduced to the cost of operati ng the injection pumps (approximately $75,000).

The O&M cost for the dedicated pipeline s cenario was estimated based on the cost of electricity to run the pumps. Assuming a 60- kW pump in each of two wells operating for 7872 hours (328 days) a year and an electrical cost of $0.08/kWh, th e electricity cost would be approximately $75,500 per year.

Land Acquisition

Assuming that the site area is not currently owned a land acquisition cost was included and estimated based on the following assumptions:

 Required land area: 160 acres

 Price per acre of land: $1500

Using these assumptions the estimated co st for acquiring land for the site is $240,000.

Permeate and Concentrate Storage

It is necessary to also include storage facili ties for the permeate and concentrate produced during system operation. Each pond (permeate and concentrate) was sized with a 5-day capacity. This resulted in a permeate and concen trate pond volume of approximately 7,500,000 and 3,200,000 gallons, respectively. The following assumptions were made to calculate the estimated product storage capital costs.

 Excavation: 50,000 cubic yards at $2.00 per cubic yard50  Liner: 130,000 square feet at $4.00 per square foot

 Pond cover: 100,000 square feet at $1.50 per square foot

 Security fence: 1900 linear f eet at $25 per linear foot

 Contingency: 25% of total cost

Using these assumptions the estimated cost for the total storage facility (permeate and concentrate storage) was approximately $1,021,875.

Total costs associated with a 1.5-MGD RO plant, showing the two RO concentrate disposal options summarized in Tables 21 and 22. In addition to a summary of the estimated costs, a calculated cost per bbl of treated water for each component is provided. O&M costs per bbl were directly calculated by dividing the line item cost by the annual volume of treated water produced (11,714,192 bbls). Deriving a per bbl cost for the capital cost items required assumptions to be made regarding the financing of capital costs. For these calculations the entire capital cost is assumed to be borrowed and th e following financial a ssumptions were made:

 Interest rate: 5%

 Term: 3 years

As shown in Tables 21 and 22 the cost per bbl of treated water for the truck transportation disposal is $2.63 per bbl and the cost for the dedicated pipeline and injection well field is $1.28.

When compared to the average water acquisiti on costs for traditional sources (water depots and pipeline), which range from $0.63 to $1.26 (Hess, personal comm unication), the total estimated costs for option one during the first three years ($2.63/bbl) are high. However, when compared to the costs savings achieved from re duced transportation cost s and reduced heating costs as a result of heating the permeate, the costs become quite competitive (Hess, personal communication). The second option, at $1.28/bbl appears quite viable, even without accounting for the cost savings associated with reduced tr ansportation and heating co sts. In each instance, the water costs are reduced substantially af ter the 3-year capital costs payback period.

Table 21. Total Cost Summary – 1.5-MGD RO Plant with Truck Transportation Disposal Cost Cost per bbl

Ca p ital Costs

Land Acquisitio n $240,000 $0.01

Groundwater Extraction Well Fiel d $8,250,000 $0.25 RO Plant $15,750,000 $0.47

Permeate and Concentrate Stora g e $1,021,875 $0.03

Total Ca p ital Cost $24,853,600 $0.76

Annual O&M Costs

Groundwater Extraction $95,000/y r $0.01 RO Plant Operatio n $1,000,000/ yr $0.09 RO Concentrate Disposal $20,700,000/y r $1.77 Total Annual O&M Cost $21,795,000/ y r $1.8751 Table 22. Total Cost Summary – 1.5-MGD RO Plant with Dedicated Pipeline Disposal Cost Cost per bbl Capital Costs

Land Acquisition $240,000 $0.01 Groundwater Extraction $8,250,000 $0.25 RO Plant $15,341,725 $0.47 Permeate and Concentrate Storage $1,021,875 $0.03 RO Concentrate Disposal Well Field $13,300.000 $0.41 Total Capital Cost $38,153,600 $1.17

Annual O&M Costs

Groundwater Extraction $95,000/yr $0.01 RO Plant Operation $1,000,000/yr $0.09 RO Concentrate Disposal $75,000/yr $0.01 Total Annual O&M Cost $1,170,000/yr $0.11

The per-barrel costs determined above were based on an economic model most representative of the RO plant capital costs bei ng financed by a third part y. An alternate means of determining per-barrel costs was also consid ered. This alternative assumed producer-deployed capital and a 15% internal rate of return (IRR) over a 3-yr period. A simplistic spreadsheet model was used to determine the per barrel costs for both scenarios using the capital and O&M costs provided in Tables 21 and 22. A 40% income tax rate was used, and it was conservatively assumed that the plant and all associated equipm ent fully depreciated in 3 years. The resulting payback period was 2.3 years. Given these assumptions, the per-barrel value (or acquisition costs) of the water was $2.95/bbl for the co mmercial disposal well and $1.75/bbl for the dedicated pipeline and injection well field. While the costs ar e higher than those determined using a 5% interest rate, they are still economica lly competitive with other options when the cost savings associated with reduced tr ansport and lower heating costs are taken into account. As with the previous scenario, it appears economically advantageous to inve st in a dedicate d pipeline and injection well field.

CONCLUSIONS

While water resources in the western part of North Dakota are not necessarily scarce, especially considering the resources in Lake Sakakawea and the Missour i River system, current

access to water is limited. This creates a un ique environment where unconventional water acquisition methods, such as treatment of brac kish groundwater resources, are economically competitive with conventional approaches. This pr oject demonstrated an approach that may be economically competitive with water acquisition from traditional resour ces. Two of the factors driving the costs of frac makeup water are transporta tion, including the time that water haulers spend waiting in line at water depots, and costs of heating th e water to the desired 80°F temperature for fracturing. The demonstrated appr oach provided a substantial reduction in both transportation and heating costs by considering both a dedicated on- site water hauling station and52 by utilizing the relatively high -temperature groundwat er to preheat the permeate. When these costs were taken into account, this project demonstrated that RO treatment of groundwater from the Dakota Aquifer may be economically feas ible compared to existing approaches.

RO treatment of nonpotable groundwater was demons trated to be techni cally feasible with pretreatment to remove suspended solid and or ganic matter, coupled with the use of heat exchangers to reduce water temperature. One of the greatest expenses of this type of RO treatment system is associated with concentrate disposal, especially when a commercial disposal well is utilized. The economic assessment suggested that if a dedicated injection well field were constructed, the disposal costs could be reduced substantially and this approach would become economically competitive, even without accounti ng for the reduced transportation and heating

costs.

Given the high demand for frac makeup water in western North Dakota and the widespread nature of brackish groundwater formations, like the Dakota, this approach may be economically and technically feasible for other producers and/or other industries in th e region. While case-bycase assessments will likely be needed, it is encour aging to know that this resource is available and may be economically competitive.

REFERENCES

Bachu, S., and Hitchon, B., 1996, Regional-scale flow of formation waters in the Williston Basin: AAPG Bulletin, v. 80, p. 248–264.

Birkett, J., 2010, Desalination at a glance: International Desali nation Association, www.idadesal.org/pdf/IDA%20guide_we bonly.pdf (accessed November 2011).

Bisconer, I., 1998, Filters have si milar looks, different applicati ons: Clifton Water District –
Water Treatment Process, www. cliftonwaterdistrict.com/Tr eatment_Cycle.htm (accessed 2009).

Boffardi, B.P., 2010, Standards for corrosion ra tes: www.flozone.com/flozone/white_papers/ qc/Standards%20for%20Corrosion%20R ates.pdf (accessed December 2011).

California State University, Sacramento Center for Colla borative Policy, 2008, California desalination planning handbook: Prepared for the Californ ia Department of Water Resources, www.owue.water.ca.gov/recycle/doc s/Desal_Handbook.pdf (accessed February 2009).

DesalData.com, 2011, Defining de salination: www.desaldata. com/desalination-markets-2010 (accessed November 2011).

Downey, J.S., and Armstrong, C.A., 1977, Ground-wa ter resources of Griggs and Steele Counties, North Dakota: North Dakota St ate Water Commissi on County Ground-Water Studies 21, pt. III, and North Dakota Geologi cal Survey Bulletin 64, part III, 33 p.53 Downey, J.S., and Dinwiddie, G.A., 1988. The re gional aquifer system underlying the northern Great Plains in parts of Montana, North Dakota, South Dakota and Wyoming—Summary: U.S. Geological Survey Pr ofessional Paper 1402-A, 63.

Energy Information Administration, 2011, Bakken Formation producing wells, Williston Basin, North Dakota, Montana, Saskatchewan and Manitoba: www.eia.gov/o il_gas/rpd/shaleoil1. pdf (accessed December 2011).

Gerla, P.J., 1992, Path line to geochemical evol ution of ground water in a regional discharge area, Red River Valley, North Dakot a: Ground Water, v. 30, no. 5, p. 743–754.

Glater, J., and Cohen, Y., 2003, Brine disposal fr om land-based membrane desalination plants— a critical assessment: Prepared for the Metropo litan Water District of Southern California CEC PIER II – Contract No. 400-00-013, Desalina tion Research and Innovation Partnership, Improving Energy Usage, Water Supply Reliab ility, and Water Quality Using Advanced Water Treatment Processes, Subtask 2.3.1 – Evaluate Various Brine Minimization Technologies, www.polysep.ucla.edu/Publica tions/Papers_PDF/BRINE% 20DISPOSAL.pdf (accessed October 2009).

Hanson, E., 2008, GE Osmonics, personal communication.

Hess Corporation, 2009, pe rsonal communication.

Hutchinson, B., 2007, El Paso Desa lination Plant: PowerPoint pr esentation, www.ibwc.state.gov/ Files/ibwc080907.pdf (accessed October 2009).

Iampen, H.T., and Rostron, B. J., 2000. Hydrogeochemistry of pre-Mississippian brines, Williston Basin, Canada–USA: Journal of Geochemical Exploration, v. 69–70, p. 29–35.

IDA 2011, IDA Desalination Yearbook 2011 – 2012, Inte rnational Desalination Association: www.desalyearbook.com/market-profile/11-global -capacity (assessed November 2011).

Kansas Geological Survey, 1996, Dakota Aquifer program introduction—extent of the Dakota Aquifer, www.kgs.ku.edu/Dakota/vol1/intr o/extent.htm (accessed December 2011).

Miller, 2003, Review of water resources and desalination te chnologies: Sandia National Laboratories, Report Number SAND 2003-0800, www.sandia.gov/water/docs/Miller SAND2003_0800.pdf (accessed February 2009).

Oil and Gas Journal, 2011, www.ogj.com/index/artic le-display.articles.oil-gas-journal.volume109.issue-23.general-inte rest.focus-unconventional-oil-ga s-sliding-sleeve-fracs.html.html (accessed December 2011).

Puckorius, P., 2003, Cooling water system co rrosion guidelines, Part 1: www.processcooling.com/PCE/Home/Images/0703pc-waterwo rks-table2and3-lg.jpg (accessed December 2011).54 Stepan, D.J., Shockey, R.E., Kurz, B.A., Kalen ze, N.S., Cowan, R.M., Ziman, J.J., and Harju, J.A., 2010, Bakken water opportunities assessment— Phase 1: Grand Forks, North Dakota, Energy & Environmental Research Ce nter, Publication No. 2010-EERC-04-03.

Tinos, NTUA, and Culligan S.A., 2009, Report on the evaluation of existing methods on brine treatment and disposal practices, Sol-Brine: http://uest.ntua.gr/solbrine/uploads/files/ Deliverable_1.1.pdf (accessed October 2011).

U.S. Army Corps of Engineer s, 2010, Garrison Dam/Lake Sakakawea project, North Dakota: Draft surplus water report, www.nwo.usace.ar my.mil/html/pd-p/Sakakawea_SWR_Public _Draft.pdf (accessed December 2011).

U.S. Department of Energy, 2009, Modern shal e gas development in the United States—a primer: GWPC.

Whitehead, R.L., 1996, Ground water atlas of the United States—Montana, North Dakota, South Dakota, Wyoming: U.S. Geological Surv ey Publication HA 730-I, http://pubs. usgs.gov/ha/ha730/ch_i/I-text2.html (accessed December 2011).