Water and Gas Injection System

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Water Injection and Gas Injection aremost widely used secondary recoverymethods for pressure maintenance.

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What is pressure maintenance?a method to artificially maintain the reservoirpressure in order to sustain the natural drive

.

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A relatively low cost and efficient means ofimproving oil production from a depleting fieldand it is used widely.

Treated water is injected under pressure into theflanks of the oil bearing strata through proposedrilled wells.

Water displaces any remaining particles of oiland reduce free space, thus increases reservoirpressure.

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Water injection system will consist of coarsefiltration, fine filtration, deaeration and waterinjection pumps

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Sea WaterLift Pumps

CoarseFiltration

FineFiltration Deaeration

InjectionPump

Generic Process Flow DiagramGeneric Process Flow Diagram

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Firewater

ServicesBackwash


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Water must be cleaned in order to be used asinjection medium.Untreated water may cause clogging of reservoir,

thus causing high pumping pressure andinefficient of oil recovery.This could further damage on the structure of the

reservoir.

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Seawater Lift PumpSucking seawater for thesystemUsually equipped with dosing

yHypochlorinator is requiredas an anti-fouling to preventmarine growth anddiscourage microbiologicalactivity in side pumps, pipingand equipment

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Multistage centrifugal submersible pumpsInstalled within separate caissonsSea water will be drawn from depth of 20 meter

below sea water surfaceCasing material is Cu-NiImpeller material is Al-BronzeNormally 3 x 50 % pumps

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Coarse FiltersFine Filters

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2 x 100 % automatically backwashed verticalfiltersRemoval efficiency of these filters is 98 % ofparticles above 80 micron present in sea water

The filter elements are made of wedge wire screenBackwashing is automatic and controlled by timerbut over-ridden by differential pressure across thefilterFilter elements are sequentially backwashed thusmaintaining filtration during cleaning cycle

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Fine filters are vertical dual media filtersCapable of removing 98% of particles above 2micron

Two filters will be operating with one filter beingbackwashed or standbyBackwashing is carried out by sequential

operation controlled by DCS

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Deaeration is the process of removal of oxygenfrom water to avoid corrosion in pipes and toprevent bacteria growth which will plug thereservoir

Sea water deaeration tower where oxygen isstripped from sea water under vacuumVacuum deaeration is a combination of physicaland thermodynamic operationsVacuum deaeration system consists of adeaerator tower, vacuum pumps, ejector andvacuum vent tank

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Seawater

Vacuum

Vent

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Biocide

Antifoam

DeaaratorTower

Ejector

VacuumPump

Vent Tank

Drain

DeaeratedSeawater


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The first stage uses a spray nozzle to atomisewater to release oxygenRemoving oxygen from the mist generated bythe spray nozzle using vacuum

Structured packing is used in the strippingcolumn to provide mass transfer surfaceThe second and subsequent stages are packedbed type and packing is pall rings inpolypropyleneDeaeration will achieve 10 ppb of CO 2 level

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O

2liberated in the deaerator will be handled by

the duty vacuum pumpThe pump uses sea water as seal water at adesign temperature of 30 0C

The vacuum system is designed so that the threedeaerator stages operate at different pressuresThe higher pressure being stage 1, whichhandles much the greater part of the gas take-offstream

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The ejector assists to achieve pressuredifferential in each of stage 2 and 3 of deaeratortowerA compression process for the mixture takes

place in the venturi type tube so that the finalpressure is greater than suction pressure as themixture enters the vacuum pumpThe ejector also maintains a minimum air loadingon the pumps in order to prevent cavitation

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The discharged gases are vented toatmospheric from the vacuum vent tankThe water is partially re-circulated to thevacuum um au mented b a continuous

make-up supplyThe make-up water supply will keep theoperating temperature within the parameterSurplus water is rejected at the tank overflowconnection

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A simple vessel toprovide agitation to theseawater to assist in

excess hydrocarbongas.

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After deaeration system, the suction pressure of the

injection pump will be negative, thus available NPSHis inadequate for high pressure pumpBooster pumps are used to over come NPSH

The main sea water injection pump is to inject treatedseawater into the reservoirThe water injection pumps are electric motor driven

capable of generating water pressure ranging from3000 to 5000 psig (205 to 340 bar)

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Hypochlorinator is required as an anti-foulantto prevent marine growth in side pumps,piping and equipmentThe h ochlorinator acka e is re uired to

generate hypochlorite by electrolysis ofseawater for chlorination of seawater

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Water injection rate: 47500 bpdDischarge pressure: 7900 kpag / 1160 psig

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Water injection rate: 60000 bpdDischarge pressure: 10400 kpag


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What is Gas Injection ?Injection of natural gas into an oil reservoir to maintainits pressure, thereby assisting the oil production from

.

Gas is compressed prior to injection, in order toincrease the bottom hole pressure.

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Production WellHP SeparatorDeh dration

HP ScrubberGas CompressorInjection Well

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• A vessel forseparation of onesubstance from

are intimately mixed,such as removing oilfrom water and/orgas

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Separator is used to separate a mixture of twomaterials. Their separation is based on thedifference in specific mass between the two

.The greater the difference in specific mass, thequicker and easier the separation achieved andvice versa.

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Separator is provided with a submerged weirA vane pack is provided at the vapour outletA sand boot is provided to facilitate sandaccumu a on an san remova ac esSeparator will be insulated for heatconservation and personnel protection

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Use to remove/absorbwater from gas

A contacting tower inwhich natural gas isbrought into intimatecontact with lean glycol

The glycol absorbs mostof the water from the gas

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The mechanics of water vapor absorption in aliquid desiccant involve a driving force whichcauses the vapor to leave the gas and condenseDehydration is achieved by reducing thetendenc of a li uid to va orize or increases the

driving force which causes the vaporcondensationThe main driving force is the difference in the

partial pressure of water in the gas and partialpressure of water in the liquid phase

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Gas enters near the bottom of the contactor andrises through the column where intimatelycontacted by a lean glycol solution flowingdownward across bubble traysHere the as ives u its water va or to the

glycolLeaving the top tray, the gas passes through mistextractor elements sweeps the glycol-coolingcoils in the upper end of the contactor, andpasses to the outlet

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The lean glycol solution enters at the top of theabsorber and flows through coils where it is

cooled by the dehydrated gasFrom the cooling coils, the glycol is dischargedin intimate contact with the ascending gas; thisac on e y ra es e gas an u es eglycol at the same timeThe dilute solution collects in the base of thecontactor from which point it is discharged tothe reconcentrator or reboiler

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Use to remove water,hydrocarbon condensateand crude oil that come

along with the gas fromwell.Usually installed before a

compressor, to preventmoist gas enteringcompressor anddamaging it.

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Gas compressor is a mechanical device thatincreases the pressure of a gas by reducingits volumeLoosely related to pumps; both increase the

fluid through pipelineCompressors may vary in size from small belt-driven units in the order of 50 hp to very large

reciprocating or centrifugal units of 15,000 hpor more

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There are a variety of factors that influence theselection of one compressor unit over another.

Among these factors are the following.• Comparative Costs• Specific Horsepower Required Versus Size

Availabilit

• Degree of automation• Compression requirements• Future gas volume and pressure• Location of compressor• Matching Existing Units

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There are few typeof compressor used,

Reciprocatingcompressor

CentrifugalcompressorAxial flow compressor

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Injection Gas rate : 20 mmscfd (per completion)Discharge Pressure: 17300 kpag (at wellhead)

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Water and Gas Injection System

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