26 Oilfield Review

Managing Water—From Waste to Resource

Richard ArnoldNew Mexico State UniversityAgricultural Research CenterFarmington, New Mexico, USA

David B. BurnettTexas A&M UniversityCollege Station, Texas, USA

Jon ElphickCambridge, England

Thomas J. Feeley, IIIUS Department of EnergyNational Energy Technology LaboratoryPittsburgh, Pennsylvania, USA

Michel GalbrunRio de Janeiro, Brazil

Mike HightowerSandia National LaboratoriesAlbuquerque, New Mexico

Zhizhuang JiangConocoPhillips Inc.Shekou, China

Moin KhanHouston, Texas

Matt LaveryPublic Service Company of New Mexico(PNM)Albuquerque, New Mexico

Fred LuffeyChevronTexacoBakersfield, California, USA

Paul VerbeekShell International Exploration and ProductionThe Hague, The Netherlands

In mature fields, water is often perceived as a necessary evil. While water often

drives primary production and assists in secondary recovery, excess produced water

represents a significant liability and cost to the oil and gas producer. Today, improved

water-management techniques are minimizing the amount of water brought to surface

and transforming excess water from waste into resource.

For help in preparation of this article, thanks to the researchstaff and oil company partners working with Richard Arnold,New Mexico State University, Farmington, New Mexico,USA; Michael DiFilippo, Berkeley, California, USA; FrancoisGroff, Houston, Texas; Greg Hardy, ChevronTexaco, Bakersfield, California; Amy Miller, PNM, Albuquerque, NewMexico; Sun Jian Ming, Shekou, China; and Wynand Hooger-brugge, Gatwick, England.adnVISION, arcVISION, CHFR (Cased Hole Formation Resistivity), ELANPlus, INFORM (Integrated Forward Modeling), NODAL, OFM, PowerDrive, PowerPulse andWaterCASE are marks of Schlumberger. TORR and RPA are marks of EARTH (Canada) Corporation. Solar Dew is atrademark of Solar Dew B.V.

Summer 2004 27

Most mature oil fields have one thing in common:produced water, and lots of it. Globally, at leastthree barrels of water are generated with everybarrel of oil. Although exact numbers are difficultto obtain, data compiled in 1999 indicate thatmore than 210 million barrels [33.4 million m3] ofwater were being produced by the explorationand production (E&P) industry each day.1 Inthe USA, produced water comprises 98% of allwaste generated by the E&P industry—on average 10 bbl [1.6 m3] of water are producedwith every barrel of oil in that country.2

Even with the best field-management techniques, water production may eventuallyincrease to the point that it represents morethan 90% of liquid volume brought to the sur-face. Surface-handling systems becomeoverloaded, impacting efficiency and productiv-ity. Eventually, the cost of dealing with producedwater precludes field profitability.

Modern field-evaluation techniques com-bined with management of the water cycle canimprove field economics, productivity and hydro-carbon recovery factor (right). A holisticapproach to water management in a mature oilfield includes reservoir analysis, assessment ofproduction and injection wells, evaluation offlooding or sweeping techniques, surface-sys-tems analysis, and implementation of a plan tobest use excess produced water.

Like oil and gas, fresh water is a limitedresource. Once referred to as the Great AmericanDesert, today the western USA is becoming evendrier, yet it is supporting increased waterdemands for agriculture, industry and personalconsumption (below right). Moreover, the population in the western United States is

H

Drought Impact Types

Delineates dominant impactsA = Agricultural (crops, pastures, grasslands)H = Hydrological (water)

Drought Intensity

Abnormally DryDrought–ModerateDrought–SevereDrought–ExtremeDrought–Exceptional

AH

AHH

AH

H

H

H

AH

HA

> Drier times ahead for some regions of the USA. Much of the western USA is experiencing extremedrought conditions (dark orange). Associated hydrological impact, or water shortages, are indicatedin most drought areas (H). The US Drought Monitor is a partnership between the National DroughtMitigation Center (NDMC), United States Department of Agriculture, and National Oceanic andAtmospheric Administration. (Map courtesy of NDMC and University of Nebraska at Lincoln, USA.)

Oila

ndw

ater

Oil a

ndw

ater

Water

Oil and waterare separated.

Water drives theproduction of oil.

Water is treatedprior to reinjectionor disposal.

A portion ofthe producedwater isreinjected forwaterflooding.

> The role of water in the oil-production process. Oil-bearing sands are sweptby water, displacing oil and generating oil flow. However, water becomes aproblem when the amount of oil produced to the surface decreases and surfacewater-treatment systems become overloaded. As more water is generated atthe surface than is required for reinjection, treatment and disposal of thisexcess produced water add to oil-production costs.

1. Veil JA, Puder M, Elcock D and Redweik R Jr: “A WhitePaper Describing Produced Water from Production ofCrude Oil, Natural Gas, and Coal Bed Methane,”http://www.ead.anl.gov/pub/dsp_detail.cfm?PrintVersion=true&PubID=1715 (accessed April 16, 2004).

2. Khatib Z and Verbeek P: “Water to Value–ProducedWater Management for Sustainable Field Development ofMature and Green Fields,” paper SPE 73853, presented atthe SPE International Conference on Health, Safety andEnvironment in Oil and Gas Exploration and Production,Kuala Lumpur, Malaysia, March 20–22, 2002.

10 times greater than it was 100 years ago.3 Apartial answer to the looming shortfall of freshwater in the USA and elsewhere may be found inthe reuse of produced water.

Modern techniques for mature-field evalua-tion, remediation and management offerpotential solutions for both the E&P industry andareas of the world where access to water isincreasingly limited. In this article, we discussthe problem of produced water from two differentperspectives. First we explore examples showinghow operators are managing water in maturefields. Then we see how E&P companies,researchers and governmental agencies are focus-ing on alternative uses for excess produced water.

Managing the Water SystemVirtually every oil reservoir is swept by water fromeither natural aquifer pressure or waterflooding.Eventually, water production is inevitable. Watermovement promotes oil displacement and affectsvertical and areal sweep, thereby determining afield’s oil recovery factor (above left). Althoughwater is often seen as a problem, good water iscritical to the oil-production process.4 Bad water,on the other hand, is water that brings little valueto the production operation, although it may findits way to reuse outside the E&P environment atsome future time.

The first step in water management is assess-ing and diagnosing the water system. Because ofthe complexity of the system, defining the prob-lem is often the most difficult part of the process(left).5 Today, engineers and geoscientists applya multistep process supported by a sophisticatedarray of techniques and tools to diagnose water-related problems. The process often begins withgathering reservoir, production-history and sur-face-facility information (next page, top). Usingpreviously acquired data, engineers evaluate thecurrent production system to identify economicbottlenecks and to gain an initial understandingof the water-flow mechanisms in the reservoir,wells and surface system.

Next, engineers and specialists from opera-tor and service companies work together todetermine whether any new data are required toproperly assess the production system. Forexample, flow tests of production and injectionwells, downhole fluid-flow profiles, wireline andcrosswell surveys, and time-lapse seismic acquisition are capable of defining oil and water movements within the reservoir (see“Time Will Tell: New Insights from Time-Lapse

28 Oilfield Review

600.50 1.51.0 2.5

Pore volumes of water injected2.0 3.53.0 4.0 5.04.5

70

80

Mov

able

oil

prod

uced

, % 90

100

> Use of water to promote oil recovery. In management of a mature oil field,the proportion of movable oil produced is often a function of water throughput.Thus, the oil recovery factor depends on the volume of water injected into thesystem. Injection rates for optimal production efficiency vary and must beadjusted on a case-by-case basis.

Facilities Optimization• Separation• Water treatment• Gas handling

Environment• Water-quality monitoring and control• Discharge

Separation Oil

Treatment to removesolids and other contaminants

such as hydrogen sulfide

Reuse orwaste disposal

Gas

Water

Watertreatment

Injector Performance• Water quality• Injection mechanism• Injection profile

Reservoir Management• Areal and vertical sweep• Voidage replacement

Producer Performance• Shut off unwanted water• Improve production profile• Optimize lift

Aquifer

Water

Oil

Waterinjectionsystem

> The complexity of the mature-field water system. Water is an integral and often necessary part ofthe production process. During production, oil is swept from the reservoir and replaced by natural orinjected water. The process is seldom uniform. Formation heterogeneity may lead to prematurebreakthrough and downhole water problems. Production and injection wells are monitored andmanaged to minimize the water/oil ratio, maximize vertical sweep efficiency and optimize oilproduction. Surface systems may be complex and must be designed to manage and treat the watervolumes entering and exiting the production system. The quality of water discharged to theenvironment, disposed by conventional methods or diverted for resuse in reservoir flooding andalternative applications, is monitored and controlled.

Summer 2004 29

Seismic Data,” page 6). Data from crosswell electromagnetic evaluation are sometimes used to provide reservoir water saturation levels.Flow dynamics in the downhole and surface sys-tems can be evaluated with multiphaseflowmeters, helping to fully characterize thewater system.

Reservoir compartmentalization, waterbreakthrough, sweep efficiency and voidagereplacement are defined using tools such asOFM well and reservoir analysis software.6 OFMsoftware displays production history along withother well and reservoir data. Careful data analysis often reveals a wealth of hidden infor-mation. Schlumberger uses a set of specificallydesigned OFM templates for water analysis,allowing rapid reservoir evaluation and diagno-sis of flow patterns and well problems.7 The OFMtechniques range from simple breakthroughtime maps to production diagnostic plots andheterogeneity plots that display problematicwells at a glance.8

Once water problems are identified, toolssuch as the WaterCASE software for analyzingproduced water helps engineers perform furtheranalysis and propose possible solutions (see“Problem Types and Solutions,” page 30).A case-based reasoning engine powers theWaterCASE software, helping engineers solveintricate water problems by linking identifiedproblems with historically successful solutions.The system examines information from allsources including production history, reservoirdescriptions and logging results, but makesallowances for missing data. This importantaspect allows engineers to perform water-systemanalysis with only existing and sometimesincomplete datasets. Solutions and methodolo-gies proposed by the WaterCASE software canhelp optimize all elements of the water cycle.

Once each element of the downhole and sur-face system has been thoroughly analyzed, keyperformance indicators (KPI), help identify bottlenecks and rank potential opportunities byfinancial impact (right).

Water-management solutions ultimatelyfocus on the economics and direct cost of managing water. Costs related to surface han-dling and disposal vary greatly, but estimatesranging from US$ 0.10 to US$ 2.00 per barrel arenot uncommon. Taking a nominal water-disposalcost of US$ 0.50/bbl, the E&P industry expendi-ture to manage 210 million barrels of water daily would be on the order of $38.3 billion per year.

3. Burnett DB and Veil JA: “Decision and Risk AnalysisStudy of the Injection of Desalination By-Products intoOil- and Gas-Producing Zones,” paper SPE 86526, presented at the SPE International Symposium and Exhibition on Formation Damage Control, Lafayette,Louisiana, USA, February 18–20, 2004.

4. Good water is defined as that produced below the eco-nomic limit of the water/oil ratio (WOR). Conversely, badwater is water produced above the economic limit of WOR.

5. For more on water-control problems and solutions: Bailey B, Crabtree M, Tyrie J, Elphick J, Kuchuk F,Romano C and Roodhart L: “Water Control,” OilfieldReview 12, no. 1 (Spring 2000): 30–51.

System assessment

Process ResultsInput

Water breakthrough map

4D seismic

Risk economics decision tree

Production data analysis

Logs

Identifies economicbottlenecks and

opportunitiesReservoir and facilitiesdiagnosis

Defines flow mechanicsand identifies targetwells for intervention

Well diagnosis

Identifies types ofwater problems

Solution identification

Defines all feasible solutionsand expected results

Solution selection based on risk economics

Optimal solutions defined

Develop detailed design,then execute and evaluate

Outcome

> A systematic process for water management. Production-systemassessment considers the entire water and production cycle to identifyeconomic bottlenecks. Subsequent analysis focuses on the most criticalproblems. Only after completing the reservoir and facilities analysis canengineers diagnose wells to determine specific problem types. Then, allfeasible solutions are identified. Expected results are determined usingNODAL production system analysis or simulation. Risk and economics areevaluated to arrive at an optimal solution. The last step is critical: properdesign must be followed by proper execution and evaluation to validate theapplied solution.

Key Performance Indicators Bottlenecks

Reduce water-handling cost

Reduce environmental impact

Increase oil productivity

Increase reserves

Water-handling cost per bbl

Water-production rate

Oil-production rate

Sweep efficiency

> Limitations to performance. Key performance indicators and the bottlenecks,or limitations, in the production system are linked and must be defined prior toimplementing an overall water-management program.

6. Voidage occurs as the result of production of oil from the reservoir. As oil is removed, it is often replaced bywater. Voidage-replacement calculations are used toensure that sufficient water is injected to maintain reservoir pressure.

7. OFM templates contain predefined calculations, maps,crossplots and trend plots designed specifically to assistin water analysis at the reservoir and well level.

8. Chan KS: “Water Control Diagnostic Plots,” paper SPE 30775, presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, USA, October 22–25, 1995.

(continued on page 32)

30 Oilfield Review

Ten specific types of water problems are shownby degree of complexity. Elevated water cut mayresult from one or more problem type. Alreadyavailable information should first be used todiagnose excess produced-water problems.Solving less complex problems first canreduce risk and decrease the time requiredfor payout.

(1) Tubing, casing or packer leak. Produc-tion logs such as temperature and spinnermay be sufficient to diagnose these problems.Solutions typically include squeezing shutofffluids and mechanical shutoff.

(2) Flow behind casing. Failed primarycementing or creation of a void space due tosand production may allow water to flowbehind casing in the annulus. Temperature or oxygen-activation logs can detect waterflow behind casing. Shutoff fluids may providea solution.

(3) Oil/water contact (OWC) moving up.Typically, this is associated with limited verti-cal permeability, usually less than 1 mD. Withhigher vertical permeabilities, coning (7) ismore likely. In vertical wells, the problem maybe solved by mechanically isolating the lowerpart of the wellbore. In horizontal wells, thereis no near-wellbore solution, and sidetrackingthe well may be required.

(4) High-permeability layer without cross-flow. A shale barrier above and below thelayer is usually the cause of this condition.The absence of crossflow makes this problemeasy to solve by applying rigid shutoff fluids ormechanical shutoff either in the injector or inthe producer.

(5) Fissures between injector and producer.Water can rapidly break through to productionwells in naturally fissured formations. Pressure-transient testing and interwell tracers canconfirm the problem. Applying a shutoff fluidat the water injector may be effective withoutadversely affecting the fissures that contributeto oil production.

(6) Fissures or fractures from a water layer(2D coning). Water is produced from anunderlying water zone through natural fis-sures. A similar problem results when hydraulicfractures penetrate vertically into a waterlayer. The application of shutoff fluids may beeffective for this problem.

Problem Types and Solutions

1. Tubing, casing or packer leak

Oil

Water

2. Flow behind casing

Oil

Water

3. Oil/water contact moving up

Water

Oil

Water

1. Tubing, casing or packer leak

Simple

Complex

2. Flow behind casing

3. Oil/water contact moving up

4. High-permeability layer without crossflow

5. Fissures between injector and producer

6. Fissures or fractures from a water layer

7. Coning or cusping

8. Poor areal sweep

9. Gravity-segregated layer

10. High-permeability layer with crossflow

Summer 2004 31

1. A dual drain involves perforating above and below theoil/water contact. Then, both oil and water zones are produced through separate completions at the sameflowing pressure. High volumes of water are pro-duced, although the produced oil often contains verylittle water.

(7) Coning or cusping. Production drawswater upward toward the wellbore. A layer ofgel placed above the cone may be effective inslowing the coning process. However, to beeffective, a gel-placement radius of at least 50feet [15 m] is typically required, often limitingthe economic viability of the treatment. As analternative to gel placement, a new lateralborehole may be located near the top of theformation, increasing the distance from theOWC and decreasing the drawdown, both of which reduce the coning effect. A dual-drain production technique may also be aneffective treatment.1

(8) Poor areal sweep. This problem is oftenassociated with poor areal permeability het-erogeneity or anisotropy; it is particularlysevere in depositions with sand channels. Onesolution is to divert injected water away fromthe already swept pore space. Another way toaccess unswept oil is by adding lateral bore-holes to existing wells, or by infill drilling.

(9) Gravity-segregated layer. In thick reser-voir layers with good vertical permeability,water, either from an aquifer or a waterflood,is segregated by gravity and sweeps only thelower part of the formation. Shutting off lowerperforations in injection or production wellsoften has only marginal effect; ultimately,gravity segregation dominates. If this occurs,production wells will experience coning. Geltreatments are unlikely to provide lastingresults. Additional lateral drainholes may beeffective in accessing the unswept oil. Foamedviscous-flood fluids, gas injection or alternat-ing between the two may also improve verticalsweep efficiency.

(10) High-permeability layer with crossflow.In contrast to the case without crossflow (4),the presence of crossflow precludes solutionsthat modify production or injection profilesonly near a wellbore. Deep-penetrating gelmay provide a partial solution.

4. High-permeability layer without crossflow

Injector Producer

5. Fissures between injector and producer

Injector

Producer

6. Fissures or fractures from a water layer

Oil

Water

7. Coning or cusping

Water

Gel layer

8. Poor areal sweep

Aquifer

9. Gravity-segregated layer

ProducerInjector

Water

10. High-permeability layer with crossflow

ProducerInjector

Water

In mature fields, profitability is based on theeconomic limit of the water/oil ratio (bottomleft). Producing a well with a water cut abovethe economic limit generates negative cash flow.If water-treatment costs increase, then the eco-nomic water-cut limit decreases. To maintainprofitability, a well may have to be abandonedand reserves lost.

Reducing water-management cost andimproving production in mature fields are notalways straightforward. Balancing the completeproduction system—injector wells, productionwells and the water-management system—isessential to maximizing field performance.

Water at the SurfaceSurface-system assessment is a critical step inthe water-management process. Assets must beviewed as a complete system; identifying reservoir-related opportunities without simulta-neously determining potential bottlenecks insurface-handling capacity could be fruitless.

The efficiency of a mature-field system isoften related to its capacity to deal with pro-duced water. The initial surface design oftenfails to account for escalating water cut withtime. As a field matures, water cut increases andits surface-handling system becomes overloaded.Whether in separation, transmission or disposal,a high water rate reduces oil-handling capacityand threatens the economic viability of the field.

Restrictions, or bottlenecks, in the surfacesystems are often complex and expensive to rectify. In the late 1990s, Petrobras engineerspredicted that oil production from the southernarea of the Campos basin, offshore Brazil, would exhibit a significant increase in water cutduring the next decade. Solving the loomingwater-handing problem presented significanttechnical challenges, but the economics of the

Campos basin demanded an early solution to the problem.

The 90-km [56-mile], 24-in. export pipelinehad been designed to flow 180,000 bbl[28,600 m3] of crude oil daily from the centralproduction platform to a shore-based refinery.Offshore water-management facilities at thecentral and satellite production platforms werelimited. As water cut approached 45%, oil-production targets and quality through thepipeline could not be sustained. As an interimmeasure, Petrobras began supplementing theexport pipeline with shuttle tankers, transport-ing the water-laden oil to shore.

Petrobras and Schlumberger engineers evaluated options for reducing water production,the choices being downhole intervention,improving surface-management systems, orboth. Ultimately the decision was made toincrease the capacity of surface-handling facili-ties. This avoided the pipeline bottleneck byseparating water from oil offshore.

Working in conjunction with Schlumberger,the Sedco 135D semisubmersible drilling rig wasconverted to a floating dewatering facility(below). Connected to the central productionplatform, the facility can process 169,000 B/D[27,000 m3/d] of high water-cut crude.

Water-laden crude is processed to removewater from oil and to reduce the oil concentra-tion in the produced water below 20 parts permillion (ppm). First, a degasser removes dis-solved gases and stabilizes the crude oil. Then,an electrostatic coalescer reduces the basic

sediment and water (BS&W) content of the oilphase to less than 1%, and it reduces the oil con-tent of the water phase to less than 1,000 ppm.This produced water enters a water surge drumand then a hydrocyclone, further reducing oilcontent to less than 40 ppm. Lastly, a sparger,which is an induced-gas flotation device,reduces oil content to less than 20 ppm.9

Dewatering efforts in the Campos basinresulted in an immediate 60,000-B/D [9,530-m3/d] increase in capacity of oil trans-ported to shore through the export pipeline. Asengineers and operators optimized the water-removal system on the 135D, oil productionincreased by 20,000 B/D [3,180 m3/d].

Optimizing oil removal from produced waterhas two primary effects: more oil is recovered,and a cleaner produced water is delivered fordisposal or reuse.

Improvements in Water-Treatment TechnologyA new process for produced water cleanup isnow being field-tested with promising results.The light water treatment unit (LWTU) uses coa-lescing and separation techniques to reduce theamount of oil-in-water to levels below 20 ppm atflow rates up to 3,000 B/D [477 m3/d].

The LWTU is based on the TORR Total OilRecovery and Remediation technology devel-oped by EARTH (Canada), a process in whichoil-laden water flows through a succession ofcoalescing beds loaded with RPA (reusablepetroleum absorbent) material (next page, topright).10 The dispersed oil droplets, varying in

32 Oilfield Review

WORe = Vo/Cw

= US$ 20/bbl oil/US$ 0.7/bbl water= 28.6 bbl water/bbl oil.

Water cut = WOR/(1+WOR)

= 28.6/(1+28.6)= 96.6% at economic limit.

> Economic limit. The water cut at the economiclimit can be determined from Vo, the value of abarrel of oil after tax and lifting cost, excludingwater handling, and Cw, the cost to manage theproduced water. In this case, the values areassumed to be US$ 20/bbl of oil for Vo andUS$ 0.7/bbl of water for Cw. Using these values,the economic limit of the water/oil ratio, WORe,is 28.6, and for water cut it is 96.6%.

> Dewatering offshore. The Sedco 135D semisubmersible dewatering facilitycan process up to 169,000 B/D [27,000 m3/d] of produced liquids. Oil volumesof up to 107,000 B/D [17,000 m3/d] are processed, reducing the basic sedimentand water (BS&W) concentration below 0.6%. Associated produced-watervolumes of up to 63,000 B/D [10,000 m3/d] are treated, reducing total oil andgrease (TOG) content of discharged water below 20 ppm.

Summer 2004 33

size down to 2 microns, adhere to the surface ofthe oleophilic RPA material where the dropletscoalesce and fill void areas.

As flow continues, the RPA beds becomesequentially saturated with oil. The continuingflow of fluid through the beds begins to strip thecoalesced oil from the saturated RPA surfaces inlarge droplets, several millimeters in diameter.The system forms a steady-state equilibrium ineach bed between the emulsion coalescing onthe saturated RPA surface and the flow strippinglarge oil droplets into the next tank section.

The behavior of the larger oil droplets is governed by Stokes law: the larger the oil-droplet diameter, the greater the tendency forthe oil to separate and float. The larger oildroplets aggregate at the upper interbed space,where they form a free-oil layer that is bled fromthe LWTU vessel (above left). Several RPA bedsare spaced along the length of the unit; eachsuccessive bed intercepts increasingly smalleroil droplets not removed in earlier stages of the process.

In August 2002, engineers field-tested a 750-B/D [120-m3/d] pilot unit on a productionlease in West Texas, USA. Production water fedfrom a field oil and gas separator delivered33,500 bbl [5,320 m3] of water to the LWTU. Atan average flow rate of 670 B/D [107 m3/d], oilconcentration was reduced from 300 to 10 ppm.

More recently, a test conducted in the North Sea with a larger prototype unit reducedoil from 200 to 300 ppm at the inlet to an aver-age of 19 ppm at the discharge (right).Technicians processed a total of 600 bbl [95 m3]

9. Induced-gas flotation is a process in which specificallysized gas bubbles are evenly dispersed throughout theproduced water. These gas bubbles interact withentrained oil and suspended solids causing them to separate and accumulate at the surface for removal.

Tanksection 1

RPAbed 1

RPAbed 2

Tanksection 2

Treated waterout < 20 ppm oil

Oil out

Largecoalescedoil droplets

Prefilteredoil-watermix input

Tanksection 3

> Deoiling through a coalescing process. Mixtures of up to 3% oil in waterenter the light water treatment unit (LWTU). The solution passes through RPA Bed 1, where tiny droplets of oil are stripped from the flow by the RPA(reusable petroleum absorbent). Once the RPA bed is loaded with oil,continuing fluid flow through the bed forces oil droplets out of the bed andinto Tank 2. The coalesced oil droplets are large and float to the surface,where oil collects and is removed. Successive sets of beds continue theprocess, ultimately reducing oil content to less than 20 ppm.

> A much clearer picture. Tiny dispersed oildroplets cause the inlet water turbidity, orcloudiness, seen in the bottle labeled INLET.After passing through only one coalescing bed, a significant portion of the oil is removed, asindicated by the clarity of the fluid in the bottlelabeled BED 1.

5,000-B/D LWTU

25,000-B/D LWTU

> Light water treatment unit (LWTU). Field tests were recently conducted inthe North Sea with this LWTU capable of treating 5,000 B/D [795 m3/d] (top).The 24-ft [7.3-m] long unit weighs 15 tons [13.6 metric tons] when dry. Alarger unit has been built for deployment in July of 2004 in the Campos basin,offshore Brazil, on the Sedco 135D dewatering unit (bottom). The larger unitis capable of processing 25,000 B/D [3,970 m3/d]; it is 34 ft [10 m] long andweighs about 32 tons [29 metric tons].

10. Le Foll P, Khan M, Akkawi EI and Parent J-P: “Field Trialsfor a Novel Water Deoiling Process for the Upstream Oil and Gas Industry,” paper SPE 86672, presented at the 7th SPE International Conference on Health, Safetyand Environment in Oil and Gas Exploration and Produc-tion, Calgary, Alberta, Canada, March 29–31, 2004.

of oil-water mixture at a rate of 3,000 B/D. InJuly of 2004, a 25,000-B/D [3,970-m3/d] unit isscheduled for installation on the Sedco 135Dcrude-dewatering installation.

Water at the WellboreWhile new water-treatment technologies, suchas the LWTU, help operators deal with water atthe surface, engineers are using novel loggingtechniques to look behind casing, identifyingsources of water and bypassed reserves.11

In mature oil fields located offshore in theSouth China Sea about 130 km [78 miles] south-east of Hong Kong, the China National OffshoreOil Corporation and its partners are using log-ging behind casing technology to minimizeproduced water and improve oil recovery.

Discovered in 1984 and commercial since1994, wells in the area produce from 44 stackedreservoir sands in the middle Miocene XH for-mation.12 The permeability in the sandstonestypically exceeds 1 darcy, and the reservoir has astrong aquifer waterdrive. Despite 10 years ofproduction, aquifer pressure has dropped byonly a few psi. This has provided excellent production pressure support, but permeabilityheterogeneity has led to early water break-through in many of the wells.

The average water cut in the field has risen to 84%. Total liquid-production volume is550,000 B/D [87,400 m3/d], close to the maximumsurface-handling capacity. Electrical submersiblepumps (ESPs) assist in production lifting opera-tions, but the high water cut makes this moredifficult. Most of the available platform well slotshave been used, so infill drilling cannot be usedto improve oil recovery. Lower than expected oil-production rates have led engineers to focus on awater-management solution.

Reservoir, drilling and service-company engi-neers began the process of field and systemsevaluation to formulate a water-managementplan. Weighing the economics of severalapproaches, engineers chose downhole interven-tion to improve hydrocarbon recovery.

Reservoir evaluation and modeling studiesbased on seismic data, log evaluation and production history helped identify remainingreserves in the field. Engineers established therepeatability of the CHFR Cased Hole FormationResistivity tool and correlated it to the originalopenhole resistivity logs (above right).

Resistivity data from behind the casing, pro-cessed with ELANPlus advanced multiminerallog analysis software, established promising oil-bearing zones. By comparing original log datawith new data from the CHFR logs, engineers

observed little resistivity change since produc-tion began and determined that the XH1 sandstill contained recoverable oil.

Well X13, a wellbore penetrating the XH1 sand, was chosen for intervention. Using acombination of real-time directional drilling tools,drillers sidetracked the well, traversing the XH1sand along a 300-m [984-ft] borehole at about a90-degree deviation, 3 m [10 ft] from the top ofthe sand. The combination of INFORM Integrated Forward Modeling software, arcVISION Array Resistivity Compensated tool,adnVISION Aximuthal Density Neutron tool, PowerDrive rotary steerable system and PowerPulse MWD telemetry system helpeddrillers place the borehole within a 1-m [3-ft] win-dow across 98% of the borehole path (next page).

The X13 sidetrack was completed using 61⁄2-in. expandable screens. An ESP was placed atthe bottom of the 31⁄2-in. upper completion toassist with lift. Prior to intervention, the X13 well was producing more than 90% water.

Initial production after sidetracking was 3,500 B/D [556 m3/d] with only 2% water cut.Once stabilized, production doubled to 7,000 B/D [1,112 m3/d] while maintaining low water cut.

Following the successful X13 water-management intervention, several other wellswere sidetracked with similar success. Overall,the sidetracked wells have helped achieve a 28%increase in field oil output while reducing waterproduction by more than 17,000 B/D [2,700 m3/d].The operator avoided major expenditures for afacilities upgrade, and continues to enjoy reducedcosts associated with produced water handling.

From Waste to ResourceDespite advances made by operators and servicecompanies in surface and downhole water management, produced water remains a neces-sary, if burdensome, by-product of oil and gasproduction.13 In mature fields around the world,operators dispose of 30% to 40% of produced

34 Oilfield Review

Measured Permeability

mD10,000 0.1Depth, m

X100

X090

Openhole Water Saturation

m3/m31 0

m3/m31 0

ELAN Fluid Analysis

m3/m31 0

Volumetric Analysis

vol/vol1 0

CHFR Water Saturation

Water Saturation

Gamma Ray

API0 200

Water from Cased Hole Log

m3/m30.5 0

Depletion

Oil

Water

Moved Hydrocarbon

Illite

Bound Water

Quartz

Orthoclase

Calcite

Oil

Water

Depletion

> Cased-hole log data showing oil in place. CHFR Cased Hole Formation Resistivity data identified asignificant amount of bypassed pay behind casing. The green shaded areas in Tracks 3 and 4 indicateoil in place. Light and dark blue shading in Tracks 2 and 3 shows a minimal level of water in the upperreservoir area, indicating only minor depletion.

Summer 2004 35

water. As demand for usable water increases insome areas, engineers and scientists look forways to convert this economic liability into aviable resource.

The path from waste to resource oftendepends on water chemistry and contaminantlevel. Produced-water quality varies with geol-ogy, geography, production techniques and thetype of hydrocarbons being produced. The watermay contain dispersed oil, light hydrocarbons,metals, salts and a wide variety of other organicand inorganic materials.

As with produced water, about 97% of Earth’swater is salty.14 Only 3% of available water isfresh—2% is locked in Earth’s polar ice caps,leaving only 1% for consumption by plant and

animal life. Although water is a renewableresource, in some areas, agricultural demand,population growth and climate changes haveresulted in fresh water being consumed fasterthan the resource can recover.

The World Health Organization and otheragencies suggest that severe regional watershortages affect over 400 million people todayand may affect 4 billion by 2050. In 1995, theUnited States Geological Survey reported that 17western states support 10 times more peoplethan they did 100 years ago. Over the next 50 years, demand for fresh water in the USA isexpected to increase 100%, potentially out-stripping groundwater supply in some areas.15

Agricultural usage accounts for at least two-thirds of global water consumption. Shortages ofwater for irrigation are either already occurringor projected to occur in major grain-growingregions of the world.16

Of the more than 210 million bbl of waterproduced daily from oil and gas operations, 30% to 40% is considered waste and disposed of.With treatment, these 73.5 million barrels [11.7 million m3] of water have the potential toplay a key role in relieving demand on naturalfreshwater systems.

The substantial availability of produced water,along with a need for less costly alternatives todisposal, leads researchers to study the reuse ofproduced water for irrigation, industrial use andother applications. With proper treatment, pro-duced water may find many uses while relievingpressure on the Earth’s freshwater supply.

From Well to RangelandApproximately 47% of the Earth’s terrestrial sur-face comprises rangelands. Left in its naturalstate, indigenous rangeland vegetation, primarilygrasses, manages itself through natural pro-cesses. Human movement into these delicatelybalanced ecosystems has left its mark. Amongother things, overgrazing, recreation andmechanical manipulation of marginal soils have led to desertification, a process wherebybiosystems decline in the absence of significantclimatic changes.17

Although considerable time may be required,desertification often naturally reverses in theabsence of commercial livestock operations.With much of the world’s rangelands in decline,scientists are exploring methods to assist thenatural revitalization process.

200160120

Gam

ma

Ray

8040

0

2.952.752.55

Dens

ity

2.352.151.95

0.450.330.21

Neu

tron

Gam

ma

Ray,

API

TVD,

m

50 150 250Drift along the section, m

350 450 550

0.09-0.03-0.15

X925

X930

X935

X940

X945

1,000

100

10Resi

stiv

ity

41.3463.7266.7668.7370.9074.7981.2195.96107.78123.28132.09140.16146.16153.78160.07

arcVISION Gamma RayModeled Gamma Ray

arcVISION Resistivity 34-in.Modeled 34-in. Resistivity

adnVISION Bottom Quadrant DensityModeled Bottom Quadrant Density

adnVISION Neutron PorosityModeled Neutron Porosity

Trajectory

> Directional drilling along the reservoir cap. Measurements-while-drilling (MWD) and logging-while-drilling (LWD) tools enabled engineers to place the borehole within meters of the reservoir cap,maximizing oil contact and minimizing water production. Drillers encountered a fault at around 360-meters [1,180-ft] horizontal displacement causing the borehole to briefly intersect the shalesection above (dark brown). The LWD response to the shale is clearly seen in the gamma ray,resistivity and density data (top three tracks).

11. Many of the basics of water treatment were discussed inBailey et al, reference 5.

12. Luo D, Jiang Z, Gutierrez J, Schwab K and Spotkaeff M:“Optimizing Oil Recovery of XJG Fields in South ChinaSea,” paper SPE 84861, presented at the SPE Interna-tional Improved Oil Recovery Conference in Asia Pacific,Kuala Lumpur, Malaysia, October 20–21, 2003.

13. For more on produced water as a by-product of hydro-carbon production: Veil et al, reference 1.

14. http://ga.water.usgs.gov/edu/waterdistribution.html(accessed May 21, 2004).

15. Burnett and Veil, reference 3.16. The United Nations: “World Water Development Report–

Executive Summary,” http://www.unu.edu/wwf/watercd/files/pdf/Ex_Summary.pdf (accessed June 20, 2004).

17. Burnett D and Fox WE: “Produced Water: An Oasis forArid and Semi-Arid Range Restoration,”http://www.gwpc.org/Meetings/PW2002/Papers-Abstracts.htm (accessed May 26, 2004).

Climate research studies conducted by theUniversity of Arizona, Tucson, USA, indicate thatthe state of New Mexico, located in the south-western USA, will continue to be drier over thenext 30 to 40 years.18 Today, researchers, oil andgas operators and government officials are tak-ing steps to prepare for the drier times ahead.

At New Mexico State University (NMSU), scientists are exploring revegetation of pipelineright-of-ways and wellsites using selectedgrasses irrigated by water produced from localcoalbed methane (CBM) wells.

Working in conjunction with several E&Pcompanies and the US Bureau of Land Management, researchers at NMSU selected sixsites for experiments to identify varieties ofgrass capable of sustained growth in the aridNew Mexico climate. These grasses would be supported only by limited natural rainfall andirrigation with CBM-produced water.

36 Oilfield Review

> Grass survival in a harsh environment. Planted in mid-2002, Hy-Crest crested wheatgrass shows promise after a year’s growthin the arid climate. Cages (center) are placed over sections of grass to isolate the new growth and allow scientists todifferentiate grazing damage from other causes of grass loss.

>Water treatment in the field. The Texas A&M mobile water-treatment unit isdesigned to evaluate treatment methods for oilfield brine. Produced water isconditioned, or pretreated, prior to reverse osmosis filtration. Intake capacityis approximately 15 gallons per minute (gal/min) [57 L/min]. Depending on thecharacteristics of the brine and the type of filters used, freshwater outputranges from 1 to 5 gal/min [4 to 19 L/min].

Summer 2004 37

Control plots of rangeland grass were estab-lished during April and October 2002 using 16 varieties of native and nonnative grasses withonly natural rainfall. After 12 to 15 months ofgrowth, grass stands were evaluated for estab-lishment, or survival. Several varieties showedpromise (previous page, top).

In late summer of 2003, Phase 2 of the pro-ject began with an identical set of grassesplanted at each site. During a 4- to 6-weekperiod after planting, two of the new test siteswere irrigated with CBM-produced water (bot-tom left). Quantities varied from 26,880 gal [102 m3] to 50,000 gal [189 m3] in three or fourapplications (left). Although final reports willnot be prepared by NMSU until later in the year,several species of rangeland grass showed adaptation to CBM-produced-water irrigation.19

At Texas A&M University, College Station,Texas, USA, a team of engineers and rangeland,soils, wildlife and irrigation specialists is takingthe produced-water rangeland irrigation processone step further. Working with the Texas WaterResearch Institute (TWRI), engineers have builta prototype mobile produced-water treatmentunit. Water can be treated on site to remove con-taminants and dissolved salts prior to rangelandirrigation (previous page, bottom).20

The process of converting produced water toirrigation quality may require several steps.First, the produced-water feed stream is sub-jected to pretreatment filtration to remove sandand larger particulates. Hydrocyclones andmicrofiltration units separate the majority of thedispersed oil from the produced water. Then,organoclay adsorbents remove the remainingoil.21 The essentially oil-free produced water is

Wellsite Date pH Total dissolvedsolids, meq/L

Sodiumabsorption ratio

Electricalconductivity, dS/m

Site 1

Site 2

Produced-Water Chemistry Analysis

9/17/039/19/038/12/038/20/039/16/03

8.08.58.38.48.1

10,6825,4404,1906,9808,126

122.471.151.4

105.2100.8

17.416.111.117.613.6

> CBM-produced-water chemistry. During the irrigation cycle, samples ofproduced water were taken at Sites 1 and 2 for analysis. Although most otherproperties are relatively stable, variability in total dissolved solids (TDS) isseen in Column 4.

>Watering with CBM-produced water. A 400-bbl [64-m3] tank holds produced water for irrigation(top). Grass plots received irrigation from this tank in August 2003 (bottom).

18. Ni F, Cavazos T, Hughes MK, Comrie AC and Funkhouser G:“Cool-Season Precipitation in the Southwestern USASince AD 1000: Comparison of Linear and NonlinearTechniques for Reconstruction,” International Journal ofClimatology, 22, no.13 (November 15, 2002): 1622–1645.

19. http://www.all-llc.com/CBM/pdf/CBMBU/CBM%20BU%20Screen_Chapter%206%20Case%20Studies.pdf (accessed May 5, 2004).

20. Burnett and Fox, reference 17.21. Organoclay, also known as organopolysilicate, is typi-

cally a kaolin or montmorillonite clay. Organic structuresare chemically bonded to the clay surface to facilitate binding, or adsorption, of organic radicals.

then passed through a reverse osmosis (RO) filtration unit, reducing total dissolved solids(TDS) below 500 ppm (left). The rejected brinestream from the RO process is disposed of byconventional methods such as injection intowaste-disposal wells.

The water-treatment technology being devel-oped by Texas A&M may provide operators witha cost-effective alternative to disposing of pro-duced water. Researchers estimate that morethan one-third of the produced water in Texashas TDS less than 20,000 ppm, a level suitablefor RO desalination and freshwater recovery.Field tests indicate that mobile unit water-processing cost is approximately US$ 0.80 perbarrel of produced water, a rate often half thatof conventional regional-disposal practices. Scientists are investigating alternative tech-niques for effluent disposal that might furtherreduce desalination cost.

Increasing numbers of operators areexpected to apply water-reuse technology in thecoming years. TWRI estimates that by the year2020, more than 10% of the water used in Texaswill come from recycled sources, representing asavings of as much as 40 million gallons per day[151,000 m3/d] in fresh water.22

Oil and gas operators, local communities andthe environment benefit from the conversion ofan oilfield waste to a rangeland resource. Signifi-cant quantities of agricultural-quality water canbe generated, helping to reclaim rangelands,supporting environmental initiatives and conserving freshwater resources while simulta-neously helping operators manage productionand disposal costs more effectively.

Sustaining AgricultureAs some parts of the world experience drier con-ditions, farmers must work harder to produceample food to support growing populations.Today, modern land-management techniquescoupled with irrigation produce ample food sup-plies. However, one cost of food production isconsumption of vast amounts of fresh water.Alternative sources of water are needed both toconserve potable water and to supply the growing demands of agricultural irrigation.

The San Joaquin Valley in California, USA,home to the giant Kern River oil field, has one ofthe largest produced-water reuse projects. Eachday, ChevronTexaco produces 100,000 bbl[15,900 m3] of oil along with 860,000 bbl[136,700 m3] of water from this mature field—a90% water cut. Of this water, 79,000 bbl[12,600 m3] are reused for waterflooding and

38 Oilfield Review

> Salt-tolerant reeds in the desert. As part of the produced water-treatment process, halophyte reedsand other salt-tolerant vegetation are grown in the desert of Oman. The plant growth provides anatural filtration process that removes metals and other organic materials from water.

BrineWater

Sludge from pretreatmentAgricultural-quality water

Pump

To disposal wellRO effluent

Backwash waters

RO membranes

> Removing salts and contaminants. During reverse osmosis (RO), prefilteredproduced water is forced by pressure to pass from an area of high-salt andcontaminant concentration to areas of low concentration. Because theprocess is osmotic and the RO membrane has no true pores, mostcontaminants cannot pass through the membrane.

22. Burnett D, Fox WE and Theodori GL: “Overview of TexasA&M’s Program for the Beneficial Use of Oil Field Pro-duced Water,” http://www.gwpc.org/Meetings/PW2002/Papers/David_Burnett_PWC2002.pdf (accessed May 26, 2004).

23. Cogeneration is the simultaneous production of electric-ity and heat using a single fuel such as natural gas. Theheat produced from the electricity generating process iscaptured and utilized to produce steam. In the Kern Riverfield, injecting steam into oil-bearing reservoir rockenhances oil production.

24. Brost DF: “Water Quality Monitoring at the Kern RiverField,” http://www.gwpc.org/Meetings/PW2002/Papers/Dale_Brost_PWC2002.pdf (accessed June 12, 2004).

25. Verbeek P, Straccia J, Zwijnenberg H, Potter M and Beek A: “Solar Dew®-The Prospect of Fresh Water in the Desert,” paper SPE 78551, presented at the 10th Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, UAE, October 13–16, 2002.

Summer 2004 39

other in-field operations; 345,000 bbl[54,800 m3] are treated and supplied to severalelectric power cogeneration facilities; and436,000 bbl [69,300 m3] are sent to the CaweloWater District.23

Treatment of produced water is oftenrequired prior to agricultural use. However,water from the Kern River field is of high qualityand contains minimal dissolved solids and met-als. The very low amounts of hydrocarbon

present are removed prior to use. ChevronTexacomaintains an intensive water-monitoring pro-gram to assure the quality of its produced water.24

In the absence of irrigation, the San JoaquinValley might be a desolate, barren environment.Today, the Valley produces a variety of cropsincluding grapes, citrus fruits, almonds and pis-tachios. To supplement freshwater supplies andmaintain 46,000 acres [18,600 hectares] of fertile, irrigated farmland, the Cawelo Water District manages produced-water storage andtransmission facilities, distributing more than400,000 bbl [63,600 m3] of irrigation-quality produced water daily (left).

Watering the Desert In the deserts of Oman, fresh water is a rarecommodity. Efforts by Petroleum DevelopmentOman (PDO) focus on converting producedwater into a usable resource through a combina-tion of biotreatment and biosaline agriculture.

Mature oil fields produce large volumes ofwater. For example, PDO produces more than200,000 m3 [53 million US gal] of water dailyfrom the Nimr oil field in southern Oman. Atcosts as high as US$ 15.00/m3 [US$ 2.40/bbl], theproduced water is reinjected as waste into adeep aquifer.25

PDO’s Greening the Desert project began inthe late 1990s. Experiments in south Omantested converting produced water into a usableresource in a desert environment at a cost lowerthan that of disposal. Ideally, access to this freshwater could convert a dry, inhospitable environ-ment into one of economic prosperity throughagriculture and other associated benefits. Byselecting special salt-tolerant crops and treesfor produced-water irrigation, growth can be sustained even in desert environments.

Typical separation techniques remove oil dis-persed in water to a concentration below200 ppm. After primary oil-water separation, theeffluent has salinity that is only 25% that of sea-water. This water irrigates a lined-bed plantedwith halophytes, reed-type plants that grow wellin saline environments (previous page, bottom).

Farming operations have demonstrated thatnatural processes in the reed beds degraderesidual oil, while the halophytes cleanse thewater of heavy metals. With most of the contami-nants removed, only dissolved salts preclude thewater’s use for conventional agriculture andother applications.

> Produced-water transformation. On a daily basis, more than 436,000 bbl [69,300 m3] of water areproduced in excess of that needed for field management or power production. This treated producedwater is received by the Cawelo Water District in holding ponds (top), then distributed through canalsand pipelines for irrigation (bottom).

Removing dissolved salts by common tech-niques, such as RO, is not always cost-efficient.A novel polymer engineered by Akzo Nobelallowed Solar Dew B.V., working with Shell andPDO, to develop an alternative membrane-basedwater-purification concept. By taking advantageof the arid climate and abundant sunlight, themostly oil-free produced water is passed throughspecial polymer tubes made by Solar Dew.Energy from the sun heats the water inside thetubes. Water molecules migrate to the outside ofthe semipermeable polymer tube, leaving saltsand impurities concentrated within.

The purified water evaporates, then condenses, on the underside of a rigid plate covering the apparatus and is channeled to andcaptured in holding tanks. Unlike more conven-tional techniques, the process requires nopressure or external energy other than that sup-plied by the sun (above left).

The novel produced-water treatment pro-cesses being developed by PDO exploit availableand renewable resources to produce usablewater from waste, potentially leading the way togreener environments, habitability andimproved economic sustainability for many aridoil-producing regions of the world.

Sandia National Laboratories in the USA isone group working on the next generation ofdesalination technology. The laboratory servesas an engineering and research center for theUS Department of Energy (DOE). Over 8,000 sci-entists and support personnel staff SandiaLaboratories, headquartered in Albuquerque,New Mexico.

In the past several years, Sandia has used itsexpertise to support federal produced-waterreuse initiatives. In 2002, Sandia, working withvarious federal agencies, developing a NationalDesalination and Water Purification TechnologyRoadmap.26 The roadmap outlines the water sup-ply challenges facing the USA and suggests areasof research and development that may lead totechnological solutions. The roadmap definescritical objectives and metrics for technologicalchanges required before desalination and water-reuse technologies can become affordable andwidely used. The treatment and utilization ofboth traditional and CBM-produced waters arespecifically identified and addressed in theroadmap because they have the potential to atleast partially address water-supply challengesin many areas of the United States.

Key to this research is an ion-sequestrationprocess. Natural zeolite materials are modifiedto create a matrix capable of capturing specificcations and anions (above right). In initial test-ing with brackish produced water containing10,000 ppm TDS, surface-modified zeolite materials sequestered a wide range of cationsand anions including sodium, calcium, chlorine, carbonate and sulfate, reducing the TDS to 2,000 ppm.

In most desalination processes, salts andother contaminants are removed and becomeconcentrated in a waste material. Because of itsunique structure, spent zeolite material may beusable as construction material or in roadbeds,thus turning another waste product into aresource. Sandia is currently conducting scale-up engineering and materials processing coststudies to further evaluate the potential of thispromising material.

Researchers at Sandia continue to studyother types of desalination processes, includingdirect-contact distillation, forward osmosis andhydrate desalination techniques.

40 Oilfield Review

> Capturing ions with surface-modified zeolitematerial. The molecular model shows the matrixstructure of a modified zeolite. The mesh-likematerial can be engineered to form a selective ionfilter. Charge sites are designed for ion exchangewith specific cations and anions common toproduced water. Passing through a series ofzeolite filters, brackish fluids are deionized.

> Field trials of the Solar Dew process. The three 100-m [328-ft] long collectors (right) producebetween 0.8 and 1.5 m3 [211 and 396 gal] of fresh water per day.

26. For more on the roadmap: http://www.usbr.gov/pmts/water/desalroadmap.html (accessed June 22, 2004).

27. Hutson SS, Barber NL, Kenny JF, Linsey KS, Lumia DSand Maupin MA: Estimated Use of Water in the UnitedStates in 2000. Reston Virginia, USA: US Geological Survey, Circular 1268 (2004).

Summer 2004 41

Coal and Water The global community is highly reliant on electri-cal energy. Power plants that provide thiselectricity rely on transmission lines, a fuel suchas natural gas or coal, and water for cooling.Ranked in 2000 just behind agriculture in wateruse, thermoelectric energy generation in the USAwithdraws 195 billion gallons [738 million m3] ofwater daily from the ecosystem, most of which isfresh water (below).27

Located in northwestern New Mexico, thecoal-fired Public Service Company of New Mexico (PNM) San Juan Generating Station(SJGS) is one of the state’s largest power gener-ating facilities, producing the majority of PNM’selectricity and withdrawing a significant amountof fresh water from the San Juan basin(bottom). While generating as much as 1,800megawatts of power, the facility withdraws400,000 to 500,000 bbl [63,560 to 79,450 m3] ofcooling water daily. All but 6% of this water evaporates to the environment.

The San Juan basin also has more than18,000 oil and gas wells, cumulatively producingmore than 62,000 bbl [9,852 m3] of water dailyacross a 3,200-square mile [8,287-km2] area. Astudy published in 2004 by the DOE in conjunc-tion with PNM examined the potential use ofproduced water for cooling at the SJGS.

Engineers concluded that the natural gastransmission infrastructure in the form of aban-doned, or limited-use, pipelines is capable ofdelivering as much as 43,000 B/D [6,800 m3/d] ofproduced water to the power plant—8 to 11% ofthe daily cooling intake at SJGS and representinga 10- to 20-year supplemental cooling-water supply.

Although some adaptation of power plantcooling systems may be required to useuntreated conventional and CBM-producedwater, the benefits outweigh modification costs.

The SJGS represents only one case in whichgovernmental agencies and power generatorsare working together to conserve a vital resourceby converting waste into a resource.

Managing Future ResourcesAdvances in water-management technologiesare allowing engineers to better analyze, opti-mize and manage water in the reservoir and atthe surface. At the same time, researchersaround the world are working to find alternativeuses for excess produced water.

Today, operators and services companies aremaking great efforts to minimize the amount ofwater produced to the surface. As regional cli-matic paradigms shift, supply and demand mayincrease the value of water produced by the E&Pindustry. What was once a waste and liabilitymay tomorrow be a valuable resource in agricul-ture, industrial applications and beyond. Eventhough oil and water are said not to mix, thefuture of each resource is becoming moreentwined. Managing our liquid resources, oil andwater alike, will play a crucial role in developingthe future. —DW

Year

Freshwater withdrawals

1995* % change1950

267.1 177%150.7US population in millions

40.2

134.0

190.0

43.8

408.0

287%

151%

475%

118%

227%

14

89

40

37

180

Public supply

Irrigation

Thermoelectric power use

Other

Total* Last complete data set

> Daily water withdrawals in the USA. From 1950 to 1995, the US populationnearly doubled. During the same time period, freshwater withdrawals fromthe ecosystem grew at a faster rate, with withdrawals for thermoelectricpower increasing by almost fivefold. (Adapted from Hutson et al, reference 27.)

> Coal-fired power in New Mexico, USA. The San Juan Generating Station near Farmington is capableof producing 1,800 megawatts of electrical power. Significant amounts of water are required to cooland condense water used in the thermoelectric generating process. In the future, produced watermay supplement the daily cooling-water demand.