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In many of the Middle East’s major oilfields, water production is rising. This,coupled with stringent newenvironmental regulations beingintroduced across the region, hasencouraged operating companies andtheir service partners to find imaginativesolutions to the problems of waste waterhandling.

The industry has responsibilities forwater management in all phases of itsoperations. From extraction for aninjection program to filtration and safedisposal of waste water, the oilfieldmanager must protect fresh waterresources and safeguard theenvironment.

In this article Fikri Kuchuk and MahmutSengul discuss the environmentalaspects of water management.

Environmentaleffects

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In many countries around half of alldrinking water is groundwater. Three-quarters of the world’s cities derive part

of their water supplies from undergroundsources. Given these figures it is obviousthat no oilfield water disposal system canbe al lowed to threaten the purity ofgroundwater supplies.

The oil industry’s water disposal wellsmust be designed to ensure that water iscontained below the depths where it might

enter drinking supply aquifers. Typicaldisposal wells (Figure 4.1) inject wastewater into a deep aquifer, with shallowformations being protected by acombination of mechanical (surface casing)and geological (sealing layer) barriers.

Waste water from oi l and gasoperations is usually a fairly complexmixture of solids, liquids and emulsions(Figure 4.2). Modern filtration processes(Figure 4.3) can deal with this complex

Bottom of casing

Injection zone

Perforations

Packer

TubingConfining zone

(shale)

Cement

Annular space(fluid filled)

Drilling mud

Bottom ofsurface casing

Base ofprotected water

Annuluspressuregauge

Injectedliquid

Valves

Annularaccess

Injectionpressuregauge

mixture, settling out solids and separatingl iquid phases to high levels of purity.Commercial filter systems can be verylarge and in recent years, efforts havebeen made to reduce their size (e.g., foruse of fshore) without a f fect ing theirperformance.

Produced water may contain traceres idues of product ion treatmentchemicals such as demulsifiers, defoamers,wax inhibi tors, corros ion or sca leinhibitors and hydrate-control additives.When this produced water is to bereinjected the operator must ensure thatthe chemicals used are compatible withthose a lready in the system. I f theproduced water is to be disposed ofoutside the production–injection loopthen its environmental impact must beconsidered very carefully.

Free oil

Emulsions Liquid - floatables

( + )

( – )

Dissolved

Water

Dissolved

Settleablesolids

Suspendedcolloidals

Settleables

Tertiary

Secondary

Primary

Primary

Secondary

Tertiary

Figure 4.1: A typical

waste water disposal

well, injecting unwanted

fluids to a deep horizon

Figure 4.2: Waste water from the oilfield contains a

range of solid and liquid components

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Egyptian experience In 1988 a major onshore production facilityin Egypt’s Western Desert was producingoil from eight formations in six fields. Twoof these formations contained active aquiferwater, and there was a water-injectionscheme to enhance recovery. KhaldaPetroleum Company (KPC) startedproduction from these fields in 1986. Atthat t ime the produced f luids wereprocessed to extract oil from the producedwater. The oil was reprocessed and thewater was transferred to a disposal pond inthe desert.

A water-injection plant set up in 1988caused a major increase in produced water(Figure 4.4). The water produced from theKPC fields contained a number of pollutants(including heavy metals, hydrocarbons,formation solids and hydrogen sulfide) thatposed environmental concerns. Changes inEgyptian legis lat ion and a growingawareness of environmental issues led KPCto commission an extensive study of waterdisposal options.

Three options were discussed: disposalwells, surface ponds and reinjection.

Disposal wells

Inject ion into disposal wells involvespumping the produced water to aformation for permanent disposal. This is asafe environmental option, but requirescareful design and monitoring of theinjection system and must be operatedunder pressure restrictions.

2 3 5 8 2 3 5 82 3 5 82 3 5 82 3 5 82000

30005000

8000200

300500

80020 30 50 80

Ionic range Molecular range Macro molecularrange

Micro particlerange Macro particle range

Scanning electron microscope Optical microscope Visible to naked eye

Carbon black Paint pigment Human hair

Pyrogen Yeast cells Beach sand

Metal ion Virus Bacteria Mist Free oils

Tobacco smoke Coal dust

Dissolved oils RedbloodcellsSugars Colloidal silica/particles Pollens

Atomic radii Albumin protein Emulsions

Sand filters APIReverse osmosis

(hyperfiltration) MicrofiltrationIGF

Ultrafiltration

Particle filtration

Carbon filters CPI

Micrometers(log scale)

Micrometers(log scale)

Relativesize of

commonmaterials

Unitprocess

forseparation

0.001 0.01 0.1 1.0 10 100 1000 10,000101 100 1000 104 105 106 107 108

Year

Water production

1989

1990

1991

1992

1993

1994

4000

6000

8000

10,000

12,000

14,000

16,000

BW

PD

18,000

1988

1987

Figure 4.3: This spectrum indicates the range of industrial filtration

processes currently available and their uses

Figure 4.4: In this

Egyptian example a

water-injection plant set

up in 1988 led to a major

increase in produced

water. The water

contained a number of

pollutants, including heavy

metals, hydrocarbons,

formation solids and

hydrogen sulfide

Surface ponds

The study showed that the surfaceformations in the area around the fieldswere too hard for cost-effective excavationof evaporation ponds. More importantly,dumping the produced water in this waywould result in the concentration of saltsand residual hydrocarbons post-evaporation. This could lead tocontamination of the ground water and soil;special l iners and precautions wouldtherefore be required.

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Reinjection

The study indicated that reinjection was themost appropriate option. A leading-edgereinjection process has been developed forthe field, combining chemical treatment,gas l iberation, sett l ing, f i l trat ion andinjection. This process reduces the overallvolumes of produced water for disposal,helps to increase total reserves, reservoirpressure and oi l production whileconserving underground water resources.Chemical treatment and careful monitoringare key elements in the success of thisenvironmentally responsible scheme. Theinjected water must:• be compatible with the formation water

under reservoir conditions (i.e., it shouldnot be susceptible to scale formation)

• not affect the pore or fracture systems inthe reservoir rock (i.e., it should notcause plugging).

Plant process

Produced water is treated to achieveinjected water quality. Any entrained gas isliberated before the water is sent to a skimtank. Here, internal distributors produce auniform flow pattern that allows most ofthe dispersed oil to separate under gravity.The oil/water level within the tank is set byan adjustable siphon leg that discharges the

treated water into the surge tank. The nextstep is to pump the water through the up-flow media filters and into the injectiontank. Centrifugal pumps draw water fromthis tank and boost the pressure to matchinjection pump requirements. The filteredproduced water is then pumped at highpressure to the injection manifold.

Chemical treatment

The performance of produced water as aninjection medium depends on a number ofchemicals. For example, treatments may berequired to control bacteria, scaling andcorrosion within the system. To achieve acceptable water quality forwaterflooding, the plant was provided withthe following chemical injection facilities:• reverse emulsion breaker• scale inhibitor• oxygen scavenger• iron chelating agent• biocide• polyelectrolyte• surfactant• corrosion inhibitor.

Since the production facilities and theproduced waterf lood plant faci l i t iesrepresent a closed system, free of oxygen,field applications indicated that there wasno need for either an oxygen scavenger orthe iron chelating agent.

Reading the signs

A systematic monitoring program wasestablished to control water quality. Thistracked concentrations of iron, suspendedsolids, hydrogen sulfide and oil. The programalso monitored physical properties such asturbidity and particle-size distribution.

An increase in iron content monitoringchanges within the system would indicatecorrosion while a decrease might suggest thatiron compounds were being deposited.

Rising values for suspended solids couldindicate corrosion, scale formation orbacterial activity. The solids should beanalyzed to determine the exact nature ofthe problem.• An increase in the concentration of

hydrogen sulfide could indicate thepresence of sulfate-reducing bacteriawhich would require chlorination ortreatment with another biocide.

• The oil content for the system is assessedfrom samples upstream and downstreamof the skim tank and filters to check theirefficiency.

• Increasing turbidity in the water wouldindicate the presence of plugging solids.

• Particle size distribution is probably themost important parameter for injectionwater quality. Samples taken upstreamand downstream of the filters are used toevaluate filter efficiency.

After reinjection Before reinjection

Lower BahariyaAlam El-Buib 3D

Ultimate recoverable reserves (MMSTB)

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Egypt

CairoSalamField

(1996) EE Farid and MH Nour, Subsurface brine

injection: Proactive approach to close the produced

water loop in the Western Desert of Egypt,

SPE 35875

Figure 4.5: Water

reinjection at the Salam

Alam El-Buib 3D

reservoir began in 1989.

The initial rate of 3200

BWPD was increased to

9500 BWPD in 1994

when a second reservoir

(Salam Lower Bahariya)

was introduced. The

program has

dramatically increased

recoverable reserves

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Performance

Injection of treated produced water wasstarted in 1989 at the Salam Alam El-Buib 3Dreservoir. The initial rate of 3200 BWPD wasmaintained until 1994 when it was increasedto 9500 BWPD with the introduction of asecond reservoir; Salam Lower Bahariya. Thewater reinjection program has brought aboutsignificant improvements in both reservoirs(Figure 4.5).

Downhole flow in theGulf of SuezConventional production logs (spinner,density, capacitance, temperature andpressure) are routinely used in Egypt’s Gulfof Suez for reservoir monitoring and for thediagnosis of production problems.

Unfortunately, these methods areunsuitable for some of the more complexproblems facing production engineers. Forexample, they cannot identify water entriesor exits in horizontal wells or assess waterflow behind casing in cement channels orbehind tubing in dual completion systems.

The WFL* Water Flow Log tool’soxygen activation technique can be used todiagnose these problems and guideworkover activities. The WFL system,unlike some tools, is unaffected by holeorientation and only reacts to flowing

*

Rahmi

Ramadan

GS-437

Izz El Urban

G. Zeit

Nazzazat

Ekma

Ras Gharra

G. Araba

Ras Shukeir

SINAIEGYPT

Assram

Sidki

Ras Gharib

Ras BudranGS-173

GS-160

FF-83

October

GG-83-2GG-83-3

GS-206GS-196

EPKEPH Wadi Feiran

HH-83 Belayim LandBelayim Marine

Abu DurbaRas Amer

GS-277EPG-IX Ras Bakr

Ras FanarW. Bark

KareemEl Uyun

South Belayim

GS-315Morgan

Gharib Marine

JulyAl KhaligUmm El Yusr

Kheir ShukheirMarine

Amal

GS-336GS-347

GS-365Gharra

GS-382-1GH-348-IBGH-376

GS-391Shoab Ali

N. October

Injection to lowKareem

(through tubin

Sealing format

Injection to uppKareem

(through annulu

300 ftof perforations

water. Consequently, stationary water andany of the other fluids that might be presentin a borehole will be ignored. Using anuclear technique the WFL can investigatewater movements beyond the wellbore.

In one central Gulf of Suez field (Figure4.6) water is injected into the upper Kareemthrough the annulus, and to the lowerKareem through the tubing (Figure 4.7). This

Figure 4.6: Many of Egypt’s major oil fields are located in the Gulf of Suez

Figure 4.7: In the

central Gulf of Suez

water is injected into the

upper Kareem zone

through the annulus and

into the lower Kareem

through the tubing

(1997) HN Minhas and MA Eissa, Selective downhole

flow measurement of water phase using oxygen

activation logs in Gulf of Suez wells, SPE 37737

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injection scheme was employed becausedifferences in the productivity indices andpressures in these zones precluded acommingled injection. A conventionalspinner flowmeter could determine flow inthe lower Kareem, but injection to themore important upper zone, with 300 ft ofperforations, could not be monitored thisway.

Oxygen activation log measurementswere taken inside the tubing, at a depthcorresponding to the upper Kareem zoneto determine the injection profile throughthe annulus. During this survey f lowthrough the tubing was stopped.Measurements were subsequently takenfrom depths corresponding to the lowerKareem zone, below the tubing. Theinjection rate through the tubing was8000 B/D and through the annulus thefigure was 10,000 B/D. The injection profilein the lower Kareem zone (Figure 4.8)shows that about 30% of injected watergoes to the perforation around 7435 ft,while the bottom section takes no water.The injection profile in the upper Kareemzone (gas cap) through the annulus isshown in Figure 4.9. This indicates thatmost of the water goes to the lowersection, with 60% going to the perforationsat 7160 ft.

Riding the wave of watermanagement Petroleum Development Oman (PDO)currently produces around 330,000 m3 ofwater every day. The volume of thisproduced water has risen steadily overtime and is predicted to rise to about650,000 m3 per day by 2005 (Figure 4.10).

The disposal of large volumes ofproduced water presents PDO withserious environmental and economicchallenges. To meet these challenges, thecompany developed a detai led watermanagement plan. This ensures that thequest for optimum disposal methods ateach PDO production site involves fullevaluation and testing to determine thebest technical solution. Over half of PDO’sreserves are in reservoirs with conditionswhich result in high water production.Around 37% of the water currentlyproduced by PDO operations is reinjected

Deoiling trials

From 1990 to 1994, PDO conducted anumber of tr ials to evaluate varioustechnologies for the removal of oil fromproduced water. The projects weremotivated by three basic considerations:• good environmental practice• clean water supply for injection• economic oil recovery.

Unfortunately, none of the availabletechnologies could provide water that metthe legal requirements for alternative uses.The small oi l droplet s izes typical lyencountered in PDO’s produced water (for

for reservoir pressure maintenance (mainlyinto the Yibal, Lekhwair and Saih Rawlfields in northern Oman). About 42% isdisposed of in shal low (150–400 m)formations at oilfield sites. The remaining21% is placed in deep formations at fieldsites in southern Oman.

While the subsurface disposal ofproduction water is an accepted practicewithin the oil industry, it is essential that thedisposed water is contained within theformations. It must be adequately sealedfrom other aquifer layers and preventedfrom breaking through to the surface.

Injection B/DInjection profile

10,000

8000

6000

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2000

0

DepthIn

ject

ion

(bbl

/d)

Inje

ctio

n (%

)

30

25

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0

7280

7328

7362

7388

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7328

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7388

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7455

7493

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Injection B/DInjection profile

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7059

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0

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25

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0

Inje

ctio

n (b

bl/d

)

Depth

Inje

ctio

n (b

bl/d

)

Inje

ctio

n (%

)

Figure 4.8: This injection profile for the lower Kareem shows that about 30% of injected water goes

to the perforation around 7435 ft, while the bottom section takes no water

Figure 4.9: Injection profile for the upper Kareem, where water is injected through the annulus.

About 60% of injected water goes to the perforations at 7160 ft

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Nimr and Marmul production centers alldroplets are less than 50 µ and half aresmaller than 10 µ) meant that the unit costfor oi l recovery using centri fuges,membranes, hydrocyclones or aflotation/filtration method would exceed$15/bbl.

Agricultural trials

In March 1991 field trials were carried outat the desert agricultural project nearMarmul, using untreated Nimr production

water for irrigation and for the germinationof indigenous tree species (Figure 4.11).The Nimr production water contained anumber of contaminants (oil at 50 mg/l,selenium 0.2 mg/l and total dissolved solidsof 7100 mg/l); the results of this trial werenot encouraging. Nimr water was muchless beneficial to plants and seeds than thepotable water from the Umm er Radhumaaquifer, which was used as a control.

From 1994 to 1995 consultants wereasked to investigate possible alternatives tosubsurface use or disposal of produced

water. The list of possibilities was a longone, but several were quickly rejected.

Evaporation was rejected as it wouldrequire ponds with an excessively largesurface area and residual salts would incuradditional disposal costs.

Infiltration was rejected because it hadthe same problems as evaporation with theadded problem of uncontrolled transfer ofpollutants to the soil.

Energy production through methanegenerated by algal growth was rejectedbecause it involved evaporation, and thevalue of any gas produced would be low.

Salt production (col lection andprocessing of post-evaporation residues)was rejected because it involvedevaporation, and the value of any saltproduced would be low.

Using produced water as an industrialutility was rejected due to the remotenessof production locations.

Four other options on the original listwere considered possibilities and examinedin greater detail. These were:• fresh water production: this was deemed

uneconomic with disposal costs of$0.9/m3

• aquaculture, harvesting fish in theevaporation ponds to provide a relativelyhigh-value fish crop, was the mostattractive of the evaporation pondoptions with disposal costs of $0.35/m3

800

600

400

200

0

North Oman South Oman

Year

1000

m3 /

day

1998

1996

2000

2002

2004

1996

1998

2000

2002

2004

Figure 4.10: Petroleum Development Oman (PDO)

currently produces around 330,000 m3 of water every

day. The volume of this produced water has risen

steadily over time and is predicted to rise to about

650,000 m3 per day by 2005

Figure 4.11: In some cases produced water can be a

valuable resource for farmers. Unfortunately, water

from the Nimr Field contained too many contaminants

for use in agricultural projects

(1997) A Al-Muscati, J Huijskes and DH Parker,

Production water management in Oman, SPE 37786

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at the desert agricultural project nearMarmul, using untreated Nimr productionwater for irrigation and for the germinationof indigenous tree species (Figure 4.11).The Nimr production water contained anumber of contaminants (oil at 50 mg/l,selenium 0.2 mg/l and total dissolved solidsof 7100 mg/l); the results of this trial werenot encouraging. Nimr water was muchless beneficial to plants and seeds than thepotable water from the Umm er Radhumaaquifer, which was used as a control.

From 1994 to 1995 consultants wereasked to investigate possible alternatives tosubsurface use or disposal of producedwater. The list of possibilities was a longone, but several were quickly rejected.

Evaporation was rejected as it wouldrequire ponds with an excessively largesurface area and residual salts would incuradditional disposal costs.

Infiltration was rejected because it hadthe same problems as evaporation with theadded problem of uncontrolled transfer ofpollutants to the soil.

Energy production through methanegenerated by algal growth was rejectedbecause it involved evaporation, and thevalue of any gas produced would be low.

Salt production (col lection andprocessing of post-evaporation residues)was rejected because it involvedevaporation, and the value of any saltproduced would be low.

Using produced water as an industrialutility was rejected due to the remotenessof production locations.

Four other options on the original listwere considered possibilities and examinedin greater detail. These were:• fresh water production: this was deemed

uneconomic with disposal costs of$0.9/m3

• aquaculture, harvesting fish in theevaporation ponds to provide a relativelyhigh-value fish crop, was the mostattractive of the evaporation pondoptions with disposal costs of $0.35/m3

• ocean discharge is practicedinternationally and involves pretreatmentto achieve an oil-in-water level of 5 ppmwith disposal costs of $0.22/m3.Unfortunately, there could be noguarantee that excess oil discharge couldbe avoided in the event of processingproblems and the ecological fragility ofOmani coastal waters made this optionless attractive

• irrigation of salt-tolerant crops avoids theworst of the environmental risks

Oil

GOR

WOR

Date-9

0-8

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eads

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om w

ellh

eads

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Ave

rage

BW

PD

/wel

l

Before workover

Before workover

Before workover

Figure 4.12: Deeper completions can help to lower water/oil ratios. These graphs show how performance in 16

wells improved after their completions had been deepened by an average of 42 ft

associated with ocean discharge and hasdisposal costs of $0.23/m3. After al l of these studies had been

completed it became apparent that themost cost-effective ($0.17/m3) andenvironmentally sound option for disposalof produced water was in deep disposal

wells. PDO’s deep water disposal planswere confirmed in 1994 and nearly all ofthe produced water in southern Oman isdisposed of in this way, with the remainderbeing used for pressure support inreservoirs.

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good design calls for water productivitysl ightly below well l imits. Oil can beproduced initially to monitor reductions inthe water–oil ratio in response to a rapidshift in fracture fluid saturation. Waterproductivity above the well l imits willproduce a long period of constant water-rate water production and, in the past,many of these production periods havebeen abandoned as failures before oil entrycould be achieved.

A summary of 16 completion deepeningoperations demonstrates the potential ofthe technique. The completions weredeepened by an average of 42 ft by addingperforations, drilling out casing shoes orextending open holes (none of the existingintervals was plugged off). Within threeweeks of deepening the average oil ratehad increased by 100 BOPD for each well.Over the same period total producingGOR fell from 4800 scf/BO to 2300 scf/BOand the WOR dropped from 3.8 BW/BOto 2.5 BW/BO. Figure 4.12 provides acomparison of performance that plots all ofthe wells from their workover date.

ConclusionsWater production is an unavoidableproblem, but can be minimized bypracticing sound reservoir management. Asthe oi l and gas industry faces t ighterenvironmental regulations there will be agreater emphasis on minimizing water cutand the good completion and managementpractices which will make this possible.

back or a chemical shutoff treatment thatreduces the well ’s connection to thereservoir and its remaining oil potential.Completion deepening provides a cost-effective alternative to productionrestriction.

Completions compared

In shallow completions (those at the top ofthe oil layer) increased drawdown at thewell increases gas and water production asoil saturation and cross-sectional flow areaare reduced in response to localized oildepletion.

In intermediate completions (those in theupper half of the oi l layer) increaseddrawdown at the well results in increasedgas and water saturation at the expense ofnear-well oil saturation and flow capacity.

Deep completions (those below theoil–water contact) produce in a verydifferent way. Low drawdown at the wellproduces only water. Increased drawdownis matched by an increase in oil saturationand flow capacity while water saturationand flow capacity fall. As the completion issituated far from the static fracture gas–oilcontact, substantial drawdown and liquidrate must be achieved before depleting theliquids in the completion and creating thecondit ions necessary for free-gasproduction. Deep completions conservereservoir energy during primary recoveryand improve the efficiency of pressure-maintenance projects.

Shallow and intermediate completionsare supported by complex completionplacement and stimulation/conformancetreatment efforts to balance the mutuallyexclusive objectives of maximumdrawdown and minimum associated-fluidproduction. These treatments oftenprovide encouraging but short-l ivedimprovements.

Deep completions, in contrast, aresupported by a predictable sequence ofsaturation changes that improve theperformance of the well with time andproduction. Optimum completionplacement is inf luenced by wellborel imitat ions (such as tubing or pumpcapacity) and completion productivity. A

EE Wadleigh CI Paulson and RP Stoltz

Deeper completions really lower water/oil ratios,

SPE 37763