Sucker-Rod Pumping Handbook: Production Engineering Fundamentals and Long-Stroke Rod Pumping

583 Pages·2015·37.55 MB·English

by  Gabor Takacs

Sucker-Rod
Pumping Handbook
Production Engineering Fundamentals
and Long-Stroke Rod Pumping
Gabor Takacs, PhD
Petroleum Engineering Department,
University of Miskolc,
Hungary
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Preface
Thisbookretainsthebasicstructureandapproachofmy“ModernSucker-RodPumping”publishedby
PennWellBooksin1993butisacompletelyupdatedandenlargedversionoftheoriginal.Sucker-rod
pumping,althougha150-year-oldtechnology,stillcontinuouslyevolves;newequipment,newproce-
dures,andnewoptimizationschemesappeareveryday,ofwhichpracticingengineersmustbeaware.
Iwantedtohelpanyoneinterestedinthistechnologybypresentingthestateoftheartofmodern-day
sucker-rodpumpingtheoriesandpractices.ForthisreasonIdiligentlyresearchedtheliteraturefornew
developmentsthroughouttheyearssothatnosignificantcontributiontoourindustrycouldescapemy
attention.Proofofthisisthetotalnumberofreferencescitedinthetext,whichamountstoalmost400.
Havingspentmostofmycareerinacademiaandregularlyteachingindustryshortcoursesonarti-
ficiallifttopics,Ifullyunderstandtheimportanceofhavingpropertextbooks.WhenIwaspreparing
thisvolume,oneofmyobjectiveswastoprovidethetraineeaswellastheexperiencedengineerwitha
comprehensive textbook. The book follows the systematic way of teaching new material: after
covering the fundamentals of production engineering the different components of the equipment
and their features are introduced, then basic design and selection procedures are covered. Advanced
topics like optimization and analysis are fully explained with worked examples. The book can be
usedattheundergraduateandgraduatelevels,aswellasinindustrialtrainingofbasicandadvanced
topics.
All phases of rod pumping are introduced by presenting the technical background first; then the
most significant technical and theoretical developments are fully covered. This approach ensures
that the book can serve as a complete reference to its topic. Since design of individual parts and of
the total pumping system iscovered as well, one can utilize the book for solving mostof the design
problems encounteredinpractice.
Newtechnological developmentsinthe last twentyyearshavesignificantlywidenedthe applica-
tionrangesofsucker-rodpumping,andtodaydeeperwellswithgreaterliquidratescanbeproduced
thaneverbefore.Inadditiontonewmaterialsandinnovativeequipmentcoveredinthebook,Ichoseto
presentlong-strokerodpumpinginaseparatechapter,neverpublishedbeforebyanyoneelse.Thetwo
maintypesoftechnologiesavailabletodayareintroducedandtheirtechnicalandoperationalfeatures
are described indetail.
April 2015
Gabor Takacs
xi
CHAPTER
1
INTRODUCTION TO
SUCKER-ROD PUMPING
CHAPTER OUTLINE
1.1 ArtificialLiftMethods.......................................................................................................................1
1.1.1 GasLifting...................................................................................................................2
1.1.2 Pumping......................................................................................................................2
1.1.3 ArtificialLiftPopulations..............................................................................................3
1.2 ComparisonofLiftMethods...............................................................................................................4
1.2.1 LiftingCapacities.........................................................................................................4
1.2.2 SystemEfficiencies......................................................................................................5
1.2.3 FurtherConsiderations..................................................................................................6
1.3 MainFeaturesofSucker-RodPumping...............................................................................................7
1.3.1 ShortHistory................................................................................................................7
1.3.2 Applications.................................................................................................................9
1.3.3 Advantages,Limitations..............................................................................................11
References............................................................................................................................................12
1.1 ARTIFICIAL LIFT METHODS
Usually,oilwellsintheearlystagesoftheirlivesflownaturallytothesurfaceandarecalledflowing
wells.Flowingproductionmeansthatthepressureatthewellbottomissufficienttoovercomethesum
ofpressurelossesoccurringalongtheflowpathtotheseparator.Whenthiscriterionisnotmet,natural
flowends andthewell dies. The two main reasonsfor awell’s dying are:
• itsflowing bottom hole pressure drops belowthe total pressure losses inthewell; or
• pressurelossesinthewellbecomegreaterthanthebottomholepressureneededformovingthe
well stream tothe surface.
Thefirstcaseoccursduetotheremovaloffluidsfromtheundergroundreservoir;thesecondcase
involves anincreasingflowresistance inthewell. This can becausedby:
• an increasein the density of the flowingfluidasa result of decreased gas production; or
• various mechanical problems likea small tubing size, downhole restrictions,etc.
Artificialliftingmethodsareusedtoproducefluidsfromwellsthatarealreadydeadortoincrease
theproductionratefromflowingwells.Theimportanceofartificialliftingisclearlyseenfromthetotal
1
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Copyright©2015ElsevierInc.Allrightsreserved.
2 CHAPTER 1 INTRODUCTION TO SUCKER-ROD PUMPING
number of installations: according to one estimate there are approximately two million oil wells
worldwide, of which about 50% are placed on some kind of artificial lift [1].
There are several lifting mechanisms available for the production engineer to choose from. One
widely used group of artificial lift methods uses some kind of a pump set below the liquid level to
increasethepressureofthewellstreamsoastoovercomethepressurelossesoccurringalongtheflow
path.Otherliftingmethodsusecompressedgas,injectedfromthesurfaceintothewelltubingtohelp
the lifting of well fluids tothe surface.
Although all artificial lift methods could be grouped based on the two basic mechanisms just
discussed, their traditional classification is somewhatdifferent, asdiscussed inthe following.
1.1.1 GAS LIFTING
Allversionsofgasliftingusehigh-pressuregas(inmostcasesnaturalgas,butothergaseslikeN or
2
CO canalsobeused)injectedinthewellstreamatsomedownholepoint.Incontinuous-flowgaslift,
2
a steady rate of gas is injected in thewell tubing, aerating the liquid and thus reducing the pressure
lossesoccurringalongtheflowpath.Duetothereductionofflowresistance,thewell’soriginalbottom
hole pressure becomes sufficient to move the gas/liquid mixture to the surface and thewell starts to
flow again. Therefore, continuous-flow gas lifting can be considered as the continuation of flowing
production.
In intermittent gas lift, gas is injected periodically into the tubing string whenever a sufficient
lengthofliquidhasaccumulatedatthewellbottom.Arelativelyhighvolumeofgasinjectedbelowthe
liquidcolumnpushesthatcolumntothesurfaceasaslug.Gasinjectionistheninterrupteduntilanew
liquidslugofthepropercolumnlengthbuildsupagain.Productionofwellliquids,therefore,isdone
bycycles.Theplunger-assistedversionofintermittentgaslift,a.k.a.plungerlift,usesaspecialfree
plunger traveling in the well tubing and inserted just below the accumulated liquid slug in order to
separatetheupward-movingliquidfromthegasbelowit.Theseversionsofgasliftphysicallydisplace
theaccumulatedliquidsfromthewell,amechanismtotallydifferentfromthatofcontinuous-flowgas
lifting.
1.1.2 PUMPING
Pumpinginvolvestheuse ofadownhole pump toincreasethepressureinthewelltoovercomethe
sumofflowingpressurelossesoccurringalongtheflowpathuptothesurface.Pumpingcanbefurther
classifiedusingseveraldifferentcriteria,e.g.,theoperationalprincipleofthepumpused.However,the
generallyacceptedclassificationisbasedonthewaythedownholepumpisdrivenanddistinguishes
between rodand rodless pumping.
Rodpumpingmethodsutilizeastringofmetalrodsconnectingthedownholepumptothesurface
driving mechanism which, depending on the type of pump used, generates an oscillating or rotating
movement. Historically, the first kinds of pumps to be applied in water and oil wells were of the
positive-displacementtype,requiringanalternatingverticalmovementtooperate.Thedominantand
oldesttypeofrodpumpingiswalking-beampumping,orsimplycalledsucker-rodpumping(SRP).
Itusesapositive-displacementplungerpumpanditsmostwell-knownsurfacefeatureisthepumping
unitfeaturinga pivotedwalkingbeam.
1.1 ARTIFICIAL LIFT METHODS 3
The need for producing deeper and deeper wells with increased liquid volumes necessitated the
evolution of long-stroke sucker-rod pumping. Different units were developed with the common
feature of using the same pumps and rod strings as in conventional sucker-rod pumping, but with
substantiallylongerpumpstrokelengths.Thedesiredlongstrokesdidnotpermittheuseofawalking
beam,andcompletelydifferentsurfacedrivingmechanismshadtobeinvented.Thebasictypesinthis
classaredistinguishedaccordingtothetypeofsurfacedriveused:pneumaticdrive,hydraulicdrive,or
mechanical drivelong-stroke pumping.
A newly emerged rod pumping system uses a progressing cavity pump that requires the rod
string to be rotated for its operation. This pump, like the plunger pumps used in other types of rod
pumping systems, also works on the principle of positive displacement, but does not contain any
valves.
Rodless pumping methods, as the name implies, do not utilize a rod string to operate the
downhole pump from the surface. Accordingly, other means (other than mechanical) are used to
provideenergytothedownholepump,suchaselectricorhydraulic.Avarietyofpumptypescanbe
utilized in rodless pumping installations, including centrifugal, positive displacement, or hydraulic
pumps.
Themostimportantkindofrodlesspumpingiselectricalsubmersiblepumping(ESP),utilizinga
multistage centrifugal pump driven by an electrical motor, both contained in a single package and
submerged below the fluid level in thewell. Power is supplied to the motor by an electric cable run
from the surface. Such unitsare ideallysuited toproduce high liquid volumes.
The other lifting systems in the rodless category all employ a high-pressure power fluid that is
pumped down the hole. Hydraulic pumping was the first method developed; such units have a
positive-displacementpumpdrivenbyahydraulicengine,containedinonedownholeunit.Theengine
or motor provides an alternating movement necessary to operate the pump section. The hydraulic
turbine-driven pumping unit consists of a multistage turbine and a multistage centrifugal pump
sectionconnected inseries.Theturbine issupplied with power fluidfromthe surface and drivesthe
centrifugal pump at high rotational speeds, which lifts well fluids tothe surface.
Jetpumping,althoughitisahydraulicallydrivenmethodoffluidlifting,completelydiffersfrom
the rodless pumping principles discussed so far. Its downhole equipment contains a nozzle through
whichthepowerfluidpumpedfromthesurfacecreatesahigh-velocityjetstream.Thekineticenergy
ofthisjetisconvertedintousefulworkbythejetpump,liftingthecommingledstreamofthepower
fluidandthewell’sproducedliquidstothesurface.Thedownholeunitofajetpumpinstallationisthe
only oil-well pumping equipment known today thatcontains no moving parts.
1.1.3 ARTIFICIAL LIFT POPULATIONS
Therearenoreliableestimatesonthedistributionofeachartificialliftmethodinthedifferentpartsof
theworld.Onegenerallyacceptedfactis,however,thatsucker-rodpumpinginstallationsarethemost
numerous worldwide; inthe UStherewere about 350,000 such installations in2007 [1].
The charts in Fig. 1.1, available from the Artificial Lift Research and Development Council
(ALRDC)webpage[2],presentestimatesonthenumberofdifferentinstallationsandtheirshareinthe
world’s total oil production. As seen, there is no correlation for most of the artificial lift methods
between the number ofinstallations andthe liquid volumesproduced.
4 CHAPTER 1 INTRODUCTION TO SUCKER-ROD PUMPING
FIGURE1.1
Estimatesonthenumberofdifferentoilwellinstallationsandtheirshareintheworld’stotaloilproduction.
1.2 COMPARISON OF LIFT METHODS
Althoughthereareothertypesofartificialliftsinadditiontothosediscussedsofar,theirimportanceis
negligible.Inanycase,thereisamultitudeofchoicesavailabletoanengineerforselectingthetypeof
lifttobeused.Althoughtheuseofmanyofthoseliftingmechanismsmayberestrictedorevenruled
out by actual field conditions, such as well depth, production rates desired, fluid properties, etc.,
usually more than one lift system turns out to be technically feasible. It is then the production engi-
neer’sresponsibilitytoselect thetypeofliftthatprovidesthemostprofitablewayofproducingthe
desired liquid volume from the given well(s). After a decision is made on the lifting method to be
applied, a complete design ofthe installation for initial and future conditions should follow.
1.2.1 LIFTING CAPACITIES
In order to provide a rough comparison of the available artificial lifting methods, two figures are
presented where approximate maximum liquid production rates of the different installations are
given in the function of lifting depth. The lifting capacities listed are estimates based on latest in-
formation, including data froma major equipment manufacturer [3].
Figure 1.2 shows three lifting mechanisms capable of producing exceptionally high liquid rates:
gas lifting, electrical submersible pumping, and jet pumping. As seen, gas lifting (continuous flow)
allowstheproductionofthegreatestamountsofliquidfrommediumtohighdepths.Inshallowwells
likethoseusedforwatersupply,however,electricalsubmersiblepumpingiscapabletoproducerates
inexcessof60,000bpd.
Figure 1.3, on the other hand, includes artificial lift methods of moderate liquid production
capacity: hydraulic pumping, progressive cavity pumping (PCP), rod pumping, and plunger lifting.
In most cases, lifting depth has a profound importance for the liquid volume lifted, and well rates
rapidlydecreaseindeeperwells.Itcanbenotedthatsucker-rodandPCPpumpsproduceverysimilar
rates from the lifting depth range of 3,000–6,000 ft; this fact, combined with the much lower in-
vestmentandproductioncostsofPCPinstallations,explainsthegreatpopularityofPCPpumpsover
rod-pumping applicationsin recent years.
1.2 COMPARISON OF LIFT METHODS 5
FIGURE1.2
Maximumliquidcapacitiesofhigh-capacityartificialliftinstallations.
FIGURE1.3
Maximumliquidcapacitiesofmoderate-capacityartificialliftinstallations.
1.2.2 SYSTEM EFFICIENCIES
Theartificialliftmethodsavailabletodayofferverydifferentenergyefficiencies.Thetotalefficiency
of an artificial lift installation is found from the total energy required to operate the system and the
hydraulicpowerspentonliftingthefluidstothesurface.Thisefficiencyistheproductoftheindividual
efficiencies of the system’s components. The decisive part of the overall efficiency is due to the
6 CHAPTER 1 INTRODUCTION TO SUCKER-ROD PUMPING
effectivenessoftheliftingmechanism,e.g.,theenergyefficiencyofthepumpused,butpowerlossesin
thewellandonthesurfacecanalsohaveagreatimpactonthefinalfigure.Thebasicprerequisitefor
high total energyefficiency,therefore, is the application ofa highly efficient lifting mechanism.
ThemostexcellentdeviceavailableforartificialliftingisthePCPpump,whichcanbemorethan
70%efficientinconvertingmechanicalenergytohydraulicwork.SincetheuseofPCPpumpsinoil
wellsrequiresrelativelysimplesurfaceanddownholeinstallationswithlowlevelsofenergylossesin
systemcomponents,PCPsystemsarethemostefficientamongtheartificialliftmethods.Nowonder
that, wherever well conditions fall in their application ranges, the number of PCP pumping
installations is growing veryfast.
Next in the line, as shown in Fig. 1.4, are sucker-rod pumping and ESP installations, with
maximumsystemefficienciesofabout60%.Althoughsucker-rodandESPpumpsalonecanhavequite
high energy efficiencies, both lifting methods are plagued by high downhole losses in their power
transmissionsystem.Inadditiontotheselosses,freegasenteringthepumpsdramaticallyreducestheir
hydraulic outputand,consequently, the overall system efficiency.
Hydraulic pumping installations utilizing positive displacement pumps usually have power effi-
ciencies around 50%. Jet pumping and continuous-flow gas lifting are relatively low-efficiency arti-
ficialliftmethods,withmaximumsaround30%.Intermittentgaslifthasthelowestenergyefficiency
among the availablelift methods.
1.2.3 FURTHER CONSIDERATIONS
Theselectionoftheproperliftingmethodforagivenwellorfieldrequiresmorethancomparingthe
production capabilities and efficiencies of the possible systems. Fluid properties, field conditions,
operating and investment cost estimates, and possible production problems are all to be considered
before a final decision is arrived at. Table 1.1 (modified after [3]) provides help for a preliminary
selectionofpossiblecandidatesandforeliminatingthosemethodsnotsuitableforactualconditions.
FIGURE1.4
Approximatesystemefficienciesofdifferentartificialliftmethods.
1.3 MAIN FEATURES OF SUCKER-ROD PUMPING 7
Table1.1 Mainfeaturesofartificialliftinstallations
Al Gas Hydraulic Jet Plunger
Method SRP lifting ESP PCP pumping pumping lift
Max. 16,000 18,000 15,000 12,000 17,000 15,000 19,000
operating
depth,ft
Max. 6,000 50,000 60,000 6,000 8,000 20,000 400
operating
rate,bpd
Max. 550(cid:1) 450(cid:1) 400(cid:1) 250(cid:1) 550(cid:1) 550(cid:1) 550(cid:1)
operating
temp.,F
Gas Fairto Excellent Fair Good Fair Good Excellent
handling good
Corrosion Goodto Goodto Good Fair Good Excellent Excellent
handling excellent excellent
Solids Fairto Good Fair Excellent Fair Good Fair
handling good
Fluid >8(cid:1) >15 >10(cid:1) <40(cid:1) >8(cid:1) >8(cid:1) >15(cid:1)
gravity,
API(cid:1)
Offshore Limited Excellent Excellent Limited Good Excellent N/A
application
1.3 MAIN FEATURES OF SUCKER-ROD PUMPING
1.3.1 SHORT HISTORY
Duringtheearlyhistoryofmankinddifferentmethodswereusedtodeliverdrinkingwaterfromrock
formationsclosetothesurface.Theseincludeddrillingandpumpingofshallowwells,probablyfirst
invented by the Chinese many centuries ago. Creating plunger pumps made of bamboo pipes and
valves carvedoutof stone, they used wooden rods tooperate the pump from the surface.
The history of artificial lifting of oil wells had begun shortly after the birth of the petroleum in-
dustry.Atthosetimes,insteadoftherotarydrillingtechniquepredominantlyusedtoday,cabletools
wereusedtodrillthewells;thistechnologyreliedonawoodenwalkingbeamthatliftedanddropped
thedrillingbithungonaropeorcable.Inearlytimes,thedrillingrigwasdrivenbyasteamengine.
Whenthewellceasedtoflow,itwasquitesimpletousetheexistingwalkingbeamtooperateabottom-
holeplungerpump.Itbecamecommonpracticetoleavethecable-tooldrillingrigonthewellsothatit
could later be used for pumping. The sucker-rod pumping system was born, and its operational
principles have notchanged since [4].
Although today’s sucker-rod pumping equipment does not rely on wooden materials and steam
power,itsbasicpartsarestillthesameastheywerebefore;seeFig.1.5Firstofall,thewalkingbeam,
the symbol of this pumping method, is still used to convert the prime mover’s rotary motion to the
alternatingmotionneededtodrivethepump.Thesecondbasicpartistherodstring,whichconnects