The advent of high power multiphase pumps is changing the world of oil production, in particular by allowing the ex-ploitation of fields nearing the end of their useful lives. This revolutionary technique has been operated since autumn 1999 on the Dunbar platform, in the UK sector of the North Sea.

CASE STUDY

Sulzer multiphase pumps• TheSulzerMPPrangeofpumpsareofthehelico-axial

designoriginallydevelopedinthe90’sbyInstitutFrançaisduPétrole(IFP)

• Suchpumpsareparticularlywellsuitedtohighcapacities.Currentinstallationsincludepumpswithatotalcapacityofover500,000bpd

The role of multiphase pumpingMultiphasepumpingisessentiallyameansofaddingenergytotheunprocessedeffluentwhichenablesgas/liquidmix-turestobetransportedoverlongerdistanceswithouttheneedforpriorphaseseparation.ThisalsoenablesthewellstoproduceatalowerWHFP(WellheadFlowingPressure)andconsequently:• Theproductionfromexistingfieldsandweakwellsis

increased• Ultimaterecoveryisincreased• Thelifeofafieldcanbeextended• Developmentcostsarereduced

The Dunbar and Alwyn field

Dunbar Field Life Extension Using Sulzer Multiphase Pumps

TheDunbardevelopmentisanexamplewhichdemonstrateshowthesebenefitshavebeenrealizedinthefield.

The Dunbar fieldTheDunbarfieldislocated120kmNorthEastoftheShet-landIslandsand440kmfromAberdeen.Dunbarisawell-headplatformwhichisoperatedasasatelliteoftheAlwynNorthPlatformlocated22kmtotheNorthEast.

Inthefirstphaseofproduction,thewellheadpressurewassufficientfortheeffluenttoflownaturallyfromDunbarfieldsalonga16”multiphasepipelinetotheAlwynplatform.

TheintroductionofmultiphasepumpsonDunbarforthesec-ondphasehasenabledproductiontocontinueinthefaceofdecliningwellheadpressure.

Umbilicals / cablesOilGasOil / gas3rd partyWater injection

A01

A02

Umbilical

6" / Oil / Gas

Power Cable No. 2

Power Cable No. 1

NAA

NAB

24" to Frigg Bypass Skid

Ellon

Alwyn

Dunbar

CBM

Alwyn Subsea Barrier

MeOH Umbilical

6" / Oil / Gas

Grant

GVM

Subsea Pressure Transducer (SPT)

SPT Cable

6" Grant spool

Dunbar to NuggetsManifold N1

12" & 3"

Umbilical

Nuggets

(Not in use) 16"/20” Oil / Gas

10" / W.I.16"/18” Oil / Gas

Dunbar multiphase

pump package

during Factory

Acceptance Test

(FAT)

Why multiphase pumpsThetwomainalternativesconsideredforthesecondproduc-tionphasewere:• Firstlyaconventionalsystem(fig.1)comprisingasepara-

toroperatedatlowpressurewiththeliquidspumpedandthegascompressedupstreamofthemultiphasepipeline.

• Secondlyaninnovativesystem(fig.2)usingmultiphasepumpstoboostthelowpressurewellsdirectlyintothemultiphasepipeline.

Multiphasepumpswereselectedinpreferencetoasepara-torbasedsolutionbecause:• Therewerenomajormodificationsrequiredtotheexisting

processfacilitiesotherthantie-ingintheMPPs• Theyprovidedamorecosteffectivesolutionbeing50%

lowerCAPEX• WeightandspacerestrictionsontheDunbarplatform

favoredthedesignoftheMPPcantileveredmoduleexten-sion.Thismodulewasover30%lighterthanaconven-tionalsystemandinstallingthepumpsverticallyminimizedthespacerequirements

• Operationalflexibilitywasprovidedbyimplementingawellsegregationscheme

Well segregation schemeThisschemeofthreeindependentproductionheaders(HighPressureHP,LowPressureLPandLowLowPressureLLP)makesmaximumuseofthenaturalenergyofthewellswhichmeansthatelectricalpowerrequirementsareminimized:• Highpressurewellsbypassthepumps• LowerpressurewellsareroutedtooneofthetwoMPPs

inordertomaximizeproduction.IntheearlyyearsofMPPoperationthisroutingwasbaseduponthewellheadpressures(seeLPandLLPwellsonfig.2).Inrecentyearsotherfactorssuchasgas-to-liquidratioandwaterpro-ductionhavealsoinfluencedtherouting

About20wellsareroutedtotheMPPsatpresentwithothersplannedinthefutureinordertoacceleratetheirproduction.

Pump packageThepumpsetpackagesweresuppliedbyaconsortiumbetweenSulzer,ABBandTotalFinaElf.Eachpumpsetcom-prisesthefollowingmainitems:• Processcooler• Buffertankatpumpsuction• Multiphasepump• Epicyclicgearbox• Lubeoilandsealoilsystems• Electricmotor• Frequencyconverter• Transformer• Anti-harmonicfilters

Fig. 2: Innovative concept using MPP

Oil + Gas

Oil + Gas

Oil + Gas

To Alwyn North

Gas

Oil

LP wells

LLP wells

MP wells

HP wells

HP wells

Oil + Gas

Oil + Gas

Oil + Gas

To Alwyn North

MPP

MPP

Gas

Oil

LP wells

LLP wells

MP wells

HP wells

HP wells

Fig. 1: Conventional concept

InstallationThetwopumpsetpackageswereincorporatedintoamoduleatthefabricationyard.Themoduleof12mx7.5mx19m(LxWxH)dimensionand650tonsweightwashookeduptotheplatforminthesummerof1999andthepumpscommis-sionedinNovemberofthesameyear.

Module on the

fabrication yard

Impact of the torque

control on the vibration

Pump design features• Helico-axialimpellersandsplitdiffusers• Verticalbarrelinstallation• Axiallysplitinnercasing• Twistlockdesigntofacilitatecartridgewithdrawal• Tiltingpadbearings• Balancepiston• SuperDuplexmetallurgy• SUMEPUMP™coatingsonallwearparts

Thesearethelargestmultiphasepumpsinstalledoffshoreworldwide.

Original rated conditions

Totalcapacity 180,000bpd

GVF 75%

Suctionpressure 50-70barg

Dischargepressure 125barg

Speedrange 3,500to6,000rpm

Motorrating 4500kW

Control and monitoringThepumpcaneitherberuninmanualorautomaticmode:• Inmanualmode,theoperatormanuallyadjuststhespeed

tomaximizetheproductionwhilemaintainingthepumpwithinitspreferredoperatingenvelope

• Inautomaticmode,atorquesetpointisdefinedbytheoperatorandthepumpspeedisautomaticallyadjustedtoreachthissetpoint.Automatictorquecontroldampensliquidslugsinordertominimizepumpvibration

Vertically arranged

multiphase pump

MPP A Process (14/1/11)

0

500

1000

1500

2000

2500

12:3

0:00

12:3

5:00

12:4

0:00

12:4

5:00

12:5

0:00

12:5

5:00

13:0

0:00

Torq

ue/1

0 (N

m*0

.1),

Mot

or S

peed

(rpm

), Su

ctio

n Fl

ow (a

ct.m

3 /hr)

0

10

20

30

40

50

60

70

80

90

100

Pres

sure

(bar

g), B

T Le

vel (

%),

Rec

ycle

Val

ve (%

))

MPP A Torque/10 (Nm*0.1) SI-37218A (rpm) MPP Inlet Flow FI-37216A (m3/hr)

PI-37205A (barg) FCV Position (%) ZI-37216A,VALUE DE Vibration (micron) ZI-37253A,VALUEBuffer Tank LI-37202A,VALUE

Constant speed: large slugsTorque control: still getting slugs from wells and test separator but significantly reduced

speed torque

Multiphase pump design upgradesThereducingDunbarwellheadpressuresovertimeincreasedtheratioofgas-to-liquidflowrates.Thispro-ducedliquidslugsthatcausedMPPinstability,particu-larlyincreasedsub-synchronousvibration,sometimescausingMPPtripsandlengthyplatformdowntime.

Balance drum liner design 1 Balance drum liner design 2

SulzerR&DcenterlocatedinWinterthur,Switzerlanddedicatesalotofeffortsondevelopingnewsolutionsformultiphasepumps.Thechartsbelowshowthereductioninsub-synchronousvibrationresultingfromarevisedbalancedrumdesign(design2iswithrevisedbalancedrum).

The Sulzer partnership GoodcollaborationbetweenSulzerandTotalhasal-lowedthisworktobesuccessfullyappliedtotheDun-barMPPsin2013toovercomeinstabilitiesresultingfromreducedwellheadpressures.Themodificationstothepumpinclude:• Re-designofthebalancedrumprovidingadditional

damping

Dunbar multiphase pump rotor on the balancing machine

• Significantchangestothehollowshaftmanufactur-ingprocessprovidingadditionalstiffnessandbetterpumprotordynamicbehavior

• InstallationofaSulzerpatenteddampingdeviceontheshafttoprovideadditionaldamping

ThesemodificationstogetherwithgoodmanagementofwellroutinghasallowedfurtherreductionofwellheadpressuresandincreasedMPPavailabilitytoover90%.

20 40 60 80 100 120 140 160 180 200

02.55

7.510

12.515

17.520

00.0050.010.0150.020.0250.030.0350.040.0450.05

Ampl

itude

0-p

k [m

m]

20 40 60 80 100 120 140 160 180 200

02.55

7.510

12.515

17.520

00.0050.010.0150.020.0250.030.0350.040.0450.05

Am

plitu

de 0

-pk

[mm

]

Evolution of process conditions from 1999 until 2015ThedepletionofDunbarwellshasledtoasignificantdecreaseofthewellheadpressure.Thesepressureshavereducedfromabout70bargin1999tolessthan30bargin2015.

Therequireddischargepressurehasalsoreduced,fromabout125bargtoabout70barg,duetolesspressuredropintheexportpipelinetoAlwynplatformatlowerproductionrates.Consequently,thepumppressurerisehasremainedconstantatbetween40and50bar.

However,theinletGasVolumeFraction(GVF)hasincreasedfrom77%intheearlydaysto90-92%.

Thankstothewiderangeofoperationofthehelico-axialhydraulics,thepumpisstillinoperationwiththesamehydraulicdesignasin1999.

Future Dunbar MPP operationTotalE&PUKandSulzerareconfidentthattheflexibilityoftheMPPswillhelpoptimizelate-lifeproductionfromtheDunbarreservoir.Wellheadpressuresof20bargandbelowarepossiblewithouttheneedforsignificantinvestment.

ThepresentfocusisonmaximizingMPPspeedasthepressureriseachievedforagiveninletpressureandinletgas-to-liquidratioincreasesrapidlywithspeed.

Apr.01 Jan.04 Oct.06 Jul.09 Apr.12 Dec.14

120

140

Pre

ssure

(barg

)

100

Suction pressure

Discharge pressure

80

60

40

20

0

Dunbar MPP G2100B

The Dunbar platform in the North Sea

www.sulzer.comA10165 en (8.2015), Copyright © SULZER Ltd. 2015This study is a general product presentation. It does not provide a warranty or guarantee of any kind. Please, contact us for a description of the warranties and guarantees offered with our products. Directions for use and safety will be given separately. All information herein is subject to change without notice.

AcknowledgmentsRichardTanner(TotalE&PUK)StevenMcGhie(TotalE&PUK)CliveWhilde(CWCSLtdonbehalfofTotalE&PUK)Pierre-JeanBibet(TotalE&P)RobertBrown(Sulzer)ThomasWelschinger(Sulzer)

Contactxavier.gaillard@sulzer.com

Applicable marketsOilandGas

Applicable productsMPPmultiphasepumps