case study dunbar field life extension using sulzer
TRANSCRIPT
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)
Applicable marketsOilandGas
Applicable productsMPPmultiphasepumps