10 unidades de bombeo, instalación

8/2/2019 10 unidades de bombeo, instalacin

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Chapter 10Pumping Units and Prime Movers forPumping Units: Part l-Pumping UnitsFred D. Griffin, Lufkin Industries Inc. *

IntroductionWhen oil wells cease flowing, some means of artificiallift is required to produce the well. About 85 % of all theartificial production of oil is accomplished by the use ofsucker rods lifting the fluid. A relatively simple,reciprocating, plunger-type pump is attached to the lowerend of the sucker rod string. Oil is lifted by means of aplunger and a traveling valve being moved up and downinside a polished cylinder with a valve at the bottom. Thecylinder is called a working barrel. The plunger is at-tached to the string of sucker rods that extends to the sur-face. The upper end of the rod string is attached to apolished rod, which is moved up and down by a pump-ing unit. Pumping units are discussed here and primemovers for pumping units in Part 2 of this chapter.Pumping UnitsA pumping unit is a mechanism which impartsreciprocating motion to a polished rod, which in turn isattached to the sucker rod string below the wellhead stuff-ing box. Several types of pumping units are available to-day. The component parts of most of the units are basicallythe same but the arrangement of the parts differs. Selec-tion of the proper size and type of pumping unit for a par-ticular application is important. Like most othermachinery, pumping units must be properly installed,lubricated, and maintained. Built into the majority ofpumping units is some method of counterbalance, whichin most cases consists of adjustable weights on the rotatingcranks or air pressure pushing up on the walking beam.The counterbalance system, whichever type is used, op-poses the weight of the sucker rod string and a portionof the fluid to be lifted. The actual well load on a pump-ing unit should be measured and analyzed often to ensurethat the counterbalance is correct and that the load andtorque capacity of the unit has not been exceeded.Authors of the chapter on this topic in the 1962 edmn were the author and LALittle. F. Ben Elliott Jr., J. Tavlor Hood. and John H. Dav Jr.

TypesPumping units generally are typed according to the methodof counterbalance. This is true for beam balanced units,air balanced units, conventional crank balanced units, andspecial geometry (or Mark II) crank balanced units.In addition to the method of counterbalancing, thegeometric arrangements of the principal components aredistinguishing features. The beam balanced, the conven-tional crank balanced, and some special geometry unitsare classified as Class I lever systems because the Samsonpost bearing (pivot point for the walking beam) is locatedbetween the well load and the actuating force of the pitmanside members.The air balanced and the Mark II crank counterbalancedunits are classified as class III lever systems because thewalking beam hinge point is located at the rear of the unitand the actuating force of the pitman side members islocated between this pivot point and the well.

The type of pumping unit best suited for a particularpumping problem very often is a matter of personal prcfer-ence. The conventional crank balanced pumping unit isthe choice of many operators mainly because it has beenreadily accepted by field personnel for many years. Manyother operators choice is the Mark II special geometryunit with its capability of a more uniform torque patternon the gear reducer. Usually these special geometry unitswill require one size smaller gear box size than other typeunits for a particular application. The American Petrole-um Inst. (API) lists standard gear box sizes in their spec-ification API Spec 1lE. Other operators specify the airbalanced pumping unit, which is readily adaptable to plat-form or pier installations and other unstable substructures.This is because the inertia and shaking forces of airbalanced units are very low. Air-balance units also arecompact and light in weight compared with other typesof pumping units of the same structural and gear box rat-


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1o-2 PETROLEUM ENGINEERING HANDBOOK

/ H O R S E H L K

I W A LL I N EHANGER

I E Y E R ,

Fig. lO.l-Conventional pumping unit.

ing. The beam balanced pumping unit is manufacturedonly in the smaller sizes and economics is the prime fac-tor for selecting this unit type.Pumping Unit GeometryPumping units are manufactured in various geometric con-figurations in addition to methods of counterbalance. Asmentioned before, beam balanced and conventional crankbalanced units are Class I lever systems, and air balancedand Mark II units are Class III lever systems. Within thesetwo lever systems are variations effected by moving thegear reducer on the structural base with respect to theequalizer or cross yoke.In the case of the Mark II, the cross yoke is not locateddirectly above the slow speed shaft of the gear reducerbut shifted forward toward the horsehead. This shifting,accompanied by a specified direction of rotation of thecranks, results in a longer time interval for the upstrokeand a shorter time interval for the downstroke.Conventional Crank Balanced UnitsThe conventional crank balanced pumping unit is the typemost commonly used today, especially in the short andmedium stroke lengths. It adequately serves a wide varietyof field applications. Fig. 10.1 shows a conventional crankbalanced unit with the various parts labeled. The rotationof the cranks connected to the pitman side members causesthe walking beam to pivot about the center bearing,thereby causing the polished rod to move up and downthrough its connection to the wireline and horsehead. Theadjustable counterweights located on the cranks are heavymetal castings. Fig. 10.2 illustrates the mechanics of the

counterbalance system. Adjustment of the counterweightsand their effect at the polished rod are discussed later inthis section.

Fig. 10.2-Crank-counterbalanced diagram


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PUMPING UNITS & PRIME MOVERS FOR PUMPING UNITS 1o-3

LOAD (6) AND REDUCERTOROUE COMPRESSCOUNTERc%!LANCE AIRZER

\

5

lziil!!LOAD 1 51 AND REDUCERTCROUE COMPRESSCOUNTERBALLINCE AIR1OTTOM DEAD CENTER

0

DYNAMOMETER CARD

\ 4Iii!!OP DEAD CENTER

COUNTERBALANCE AIRPRESSURE HELPS LIFT(2iRLkTERS REDUCER

COUNTERBALANCE AIRPRESSURE HELPS LIF T(31,LOWERS REDUCERTORQUE

Fig. 10.3-Air-balanced pumping unit. Fig. 10.4-Air-counterbalance diagram.

Air Balanced UnitsThe air balanced pumping unit is basically the same asthe crank balanced unit in that the rotation of the crankscauses the walking beam to pivot and move the polishedrod up and down. Fig. 10.3 shows a typical field installa-tion of an air-balanced unit with the various parts labeled.The unit is compact and relatively light. The long cylin-drical tank at the front of the unit houses a piston and aircylinder. Force exerted by compressing air in the cylinderis used to partially counterbalance the well load. A specialsealing device is used to prevent air leaks between thepiston and cylinder. One of the features of the sealingdevice is a pool of oil on top of the piston acting as anair seal. Fig. 10.4 shows how the counterbalance forceworks to partially offset the well load. An auxiliary aircompressor is used to maintain the system air pressureat an optimal working level. The operation of the com-pressor normally is controlled automatically by a pressureswitch to maintain air pressure within a manually presetrange.

1. The cross yoke bearing which is actuated by the pit-man side members is moved forward and is located veryclose to the horsehead rather than directly above the gearreducer crankshaft.2. The cranks have a dogleg (angular offset) in themto produce an out-of-phase condition between the torqueon the gear reducer exerted by the well load and the torqueexerted by the counterbalance weights.With these two unique features and with the cranksallowed to rotate in one direction only, a more uniformtorque is applied to the crankshaft. The torque peaks, nor-mally more prominent in conventional crank balancedunits, are reduced in magnitude.

Beam Balanced UnitsFig. 10.5 shows a beam counterbalanced unit. This unitis very similar to the crank balanced unit except that thecounterweights are mounted on an extension of the walk-ing beam. In general, use of this type of unit has beenlimited to the smaller sizes. The primary reason for thisis that the pumping speed is limited. High pumping speedscan result in shaking forces, which can wreck the unitunless the pumping speed is reduced.Mark II UnitsFig. 10.6 shows the Mark II unit with the various partslabeled. This type unit has two unique features. Fig. 10.5-Beam-balanced pumping unit


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Fig. 10.6-Mark II pumping unit.

In most cases, this reduction in the torque peaks is suf-ficient to permit the use of one API size smaller gearreducer than would be used otherwise for a comparableconventional crank balanced unit. Fig. 10.7 illustrates howthe torque on the gear reducer follows a more uniformpattern under ideal field conditions.Crank Balanced Units (With Special Geometry)Some crank balanced units are manufactured with the gearreducer shifted from a position directly underneath theequalizer to a position on the structural base farther awayfrom the centerline of the well. This change from the con-ventional geometry causes a change in the torque factorson the upstrokes and downstrokes. This geometric changealso causes a change in the time interval between the up-and downstrokes.These type units usually have the out-of-phase systemof counterbalance described previously and usually requirea specific direction of rotation.

Fig. 10.7-Unitorque geometry.

Component PartsThe main parts of a pumping unit consist of structuralmembers, bearings, speed reducer, and drive. Since thecrank balanced pumping unit consists of parts typical formost units, the discussion is limited to this type.StructureThe main structural parts of a crank balanced pumpingunit are the base, Samson post, walking beam, horsehead,equalizer, and pitman side members.The structural base serves as a rigid member to whichthe Samson post, gear reducer, and prime mover are at-tached for the proper alignment to effect satisfactoryoperation.The Samson post normally is constructed from three orfour legs of rolled steel shapes. The Samson post mustbe sufficiently rigid and strong to support at least twicethe maximum polished rod load.

Centered on top of the Samson post is the center bearing,which supports the large structural beam called the walk-ing beam. The walking beam must be strong enough toresist bending caused by the well load at one end and theactuating force from the pitman side members at the other.API specifies the maximum allowable stresses and otherdesign criteria for walking beams in API Spec 1 IE.

The horsehead is attached to the well end of the walkingbeam and supports the polished rod through a wirelineand carrier bar assembly. The center of curvature of thehorsehead is the center bearing. Thus, the polished rodmoves in a straight line tangent to the arc of the horsehead.On the other end of the walking beam are the equalizerand pitman side members. The rotary motion of the cranksattached to the speed reducer slow speed shaft is trans-ferred to the walking beam by the equalizer and the pitmanside members. The equalizer usually is mounted on thebeam in such a manner that it can move and compensatefor some misalignment in manufacturing and erectiontolerances.Loading on the pitman side members is tension on con-ventional crank balanced units, compression on Mark IIunits, and alternating tension and compression on airbalanced units.Structural BearingsTrouble-free operation of a pumping unit depends on theproper functioning and design of the various structuralbearings. Some characteristics to consider for properselection of bearing design are the type and speed of thebearing as well as the direction and magnitude of load.On a conventional crank balanced pumping unit, the centerbearing and equalizer bearing support an oscillating loadwhile the crank pin shafts (and bearing inner races) rotatewith respect to the load.Various types of bearings and bearing materials havebeen used in these applications. High-lead bronze bearingswere used for many years in all three of these bearingpoints. Bronze bearings operate with little damage evenunder marginal conditions of lubrication. In recent years,bronze structural bearings generally have been replacedby straight roller, tapered roller, or spherical rollerantifriction bearings. These bearings can be greaselubricated and require less maintenance in general thando bronze bearings, which require oil lubrication.


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Pumping unit bearings should be designed or selectedvery conservatively because they are often subjected tosevere shock loads. Provision must be made for adequatelubrication and for protection from dirt and moisture.Gear teeth proportions. hardness, and many other vari-ables that affect the API torque rating are outlined in API

Specification for Pumping Units, API Spec I IE. ReducerA speed reducer is used to convert high-speed, low-torqueenergy into low-speed, high-torque energy. A reductionratio of about 30: 1 commonly is used. This means thatif the input speed is from 300 to 600 revimin, the outputspeed or pumping speed of the pumping unit will be 10to 20 strokes/min.The speed reduction is accomplished by means of her-ringbone or double helical gearing in most cases. Helicalgearing has been used in some instances; however, caremust be taken that thrust bearings inherently required withhelical gears must be adjusted properly to take the thrustfrom the frequently reversing loads of the pumping unit.Spur gearing and chain drives have also been used butto a much lesser extent. Pumping unit speed reducers mustbe sturdy and dependable. Reducer design should includeprovisions for adequate and proper distribution of oil.

Gear teeth proportions, hardnesses. and many othervariables that affect the API torque rating are outlined inAPI Spec 1lE. This publication also outlines design pa-rameters for chain reducers.DriveV-bolts are the most universal driving means between theprime mover and the pumping unit gear reducer. Theyare dependable means of transmitting power and providinga certain amount of cushioning effect between the primemover and gear reducer. This cushioning effect is highlydesirable with slow-speed, single-cylinder engines. Sheavesizes can be changed easily to adjust pumping speeds. Pro-visions must be made to adjust belt tension periodically.A belt cover or guard usually is provided to protect thebelts from the elements and for personnel safety (seeGuarding of Pumping Units).Pumping Unit LoadingThere are many variables that affect the loading on thesucker rod string and pumping unit. Some of thesevariables are listed in Table 10.1.Unfortunately, many of these variables are unknownwhen design calculations for sizing a pumping unit aremade. See Fig. 10.8 for a visual representation of someof these loads.Dynamometer Card AnalysisA dynamometer card is a continuous plot of polished rodload vs. polished rod displacement, or it may be a con-tinuous plot of polished rod load vs. time. A polished rodload plot can in some instances be useful in analyzingdownhole problems as well as identifying the resultingloads on the surface equipment.A typical dynamometer card is shown in Fig. 10.8.When pumping speed is elevated above zero, the cardtakes on a different shape. Some of the load values are

TABLE lO.l-VARIABLES THAT AFFECT SUCKER RODSTRING AND PUMPING UNIT LOADING

Polished rod loadPumping speedPump setting or depthPhysical characteristics of the rod stringDynamic characteristics of the rod stringPlunger diameter of the pumpSpecific gravityPump intake pressurePolished rod acceleration patternMechanical frictionFluid frictionPump submergenceCompressibility or gas interferencePumping unit inertiaPumping unit geometryCounterbalanceTorque characteristics of prime moverFlowline pressure

increased over the zero-pumping-speed card shown by thedotted lines and some values are decreased.While this section is not intended as a treatise on pol-ished rod dynamometer card interpretation, certain con-clusions can be drawn from the card and knowledge ofsubsurface conditions.As noted under Pumping Unit Loading (Table 10. l),there are many variables that affect loading on the polishedrod. Sometimes some of these variables nullify each other,sometimes they are additive, and sometimes they are

shifted time-wise because of rod string dynamics, mak-ing it virtually impossible to make a meaningful interpreta-tion of the dynamometer card shape. This is particularlytrue in deep wells with a relatively elastic sucker rodstring. At other times, certain type cards have a verydistinctive pattern and downhole problems can be iden-tified quite easily.Fig. 10.9 shows a dynamometer card that is particularlydetrimental to all surface and subsurface equipment. Thiscard depicts a severe fluid pound. The condition general-ly is caused by attempting to produce fluid at a greaterrate than the reservoir will give it up. The result is in-complete pump fillage and a fluid pound when the plungerhits the fluid on the downstroke. If the pound occurs verynear the top of the pumping unit stroke, or at a low plungerspeed, the effect is not so damaging; however, if the poundoccurs at high plunger speeds in the pumping cycle, a pro-gressively detrimental effect and equipment damage is

P Q J w E 0 R OD C . v i D F O RP J U P I N G S P E E D. N D

- T O P D F S T R D KE

Fig. 10.8-Basic loads on polished rod


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1O-6 PETROLEUM ENGINEERING HANDBOOK

BOTTOM OF STROKETOP OF STROKE4 - UP

B-t-2 w DOWNPOLISHED ROD POSITION

Fig. 10.9-Example of fluid pound.

generally the result. If a fluid pound does exist, theoperator should make every effort to correct this costlypractice by decreasing the displacement of the bottomholepump. This can be accomplished by either reducing thepumping speed, shortening the stroke length, or install-ing a smaller-bore bottomhole pump. Sometimes it isnecessary to try a combination of these remedies to pre-vent a decrease in production.Fig. 10.10 shows a group of representativedynamometer cards illustrating the effect of pumpingspeed, rod stretch, and polished rod load. The abscissa,F, Sk,,s a dimensionless factor representing sucker rodstretch and load. F, s the differential fluid load on thefull plunger area in pounds and Sk,s the load in poundsnecessary to stretch the sucker rod string in an amountequal to the polished rod stroke.The ordinate, H/N:, is a dimensionless pumping speedfactor, where N is the pumping speed in cycles/min andNd is the natural frequency of the tapered sucker rodstring in cycles/min.This family of dynamometer cards show the various ef-fects of nondimensional pumping speeds and nondimen-sional sucker rod stretch on the shape of dynamometercards. The dynamometer card on the upper left corneris a rather extreme example of an overtravel card. Over-travel cards have the distinct shape of sloping up fromright to left. Undertravel cards, illustrated by thedynamometer card in the lower right-hand corners, slopeup from left to right. While these two examples may beon the extreme ends of the spectrum, there are many otherexamples in between that reflect various combinations ofpumping speeds and rod stretch.As a general rule, most operators limit the pumpingspeed factor to 0.3 or 0.35 and the stretch factor to 0.5.Very often certain card shapes favor certain types ofgeometry pumping units. This means that a pumping unitwith a particular geometry, owing to its unique set oftorque factors and perhaps phasing of counterbalance, maybe able to lift the rod string with less average net torqueon the gear reducer than will a pumping unit with a dif-ferent geometry. In general, crank balanced units, prop-erly balanced, will usually produce less torque on wellswith undertravel cards, whereas Class III lever systemunits with phased counterbalance usually will show to anadvantage on wells with overtravel cards.

30 c,

A0

35

30N

N,.2

.20

.IS

.I0

.I 2 3 F. .4 .5 .6=,

Fig. 10.10-Representative dynamometer cards.

CounterbalanceOne of the most important aspects of torque loading ona gear reducer is the level of counterbalance. Impropercounterbalance, either too much or too little, is probablythe biggest single factor involved in overloading a pump-ing unit gear reducer.In general, the counterweights are positioned on thecranks so that their effect approximately balances out theweight of the sucker rod string and a portion of the fluidto be lifted.In some special geometry units such as the Mark II,the counterbalance torque on the gear reducer is out ofphase with the torque on the gear reducer exerted by thewell load. This means that when the pitman side membersgo over top and bottom dead center with respect to thereducer slow speed shaft, the reducer torque exerted bythe counterweights is either leading or lagging the wellload torque. This is accomplished by putting a dogleg inthe crank so that the counterweights do not go over topand bottom dead center of the reducer slow speed shaftat the same time as do the pitman side members. The neteffect of this combination of torque loading is illustratedin Fig. 10.7.Torque FactorsFor any position of the cranks there is a number, whenmultiplied by the polished rod load, that equals the torqueon the gear reducer caused by the well load. This numberis called a torque factor. As the cranks are rotatedthrough one complete stroke of the pumping unit, thetorque factor changes for every crank position.


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PUMPING UNITS & PRIME MOVERS FOR PUMPING UNITS

The pattern of torque factors around the pumping cycleis altered by the particular type geometry unit in question.This changing pattern of torque factors, in conjunctionwith phased counterbalance (see Counterbalance section),is used to an advantage in reducing the net torque on thegear reducer in some cases. Torque factors usually areexpressed in inches.Torque factors usually are available from the manufac-turer of the pumping unit or can be calculated as illus-trated in API Spec 11E if the geometry dimensions ofthe pumping unit are known.Polished Rod Velocities and AccelerationTorque factors also provide a useful tool for calculatingpolished rod velocities and accelerations.It can be shown that for any particular pumping speedof the pumping unit, the polished rod velocity at any CrankPosition 1 is

I/~,., =O.O0873F,, xN, . _. _. ..(I)where

Pr I = polished rod velocity at Crank Position 1.ftisec,Fl = torque factor at Crank Position 1, in.. andN = pumping speed, strokesimin.

In Eq. 1. if r,lr, is expressed in m/s, F, in millimeters,and N in strokes/s, then the constant 0100873 becomes0.0121,If the pumping speed is not constant around the pumpingcycle, the equation is still true if the instantaneous pump-ing speed at Crank Position 1 is used in the equation.Similarly, the average polished rod acceleration be-tween any two Crank Positions 1 and 2 can be expressed as

A,,r,O.O524N

whereA/w,> = average polished rod acceleration be-tween Crank Positions 1 and 2.

ftlsec? ,torque factors at Crank Positions 1 and

2, in..angle cranks rotate between Positions I

and 2, degrees, andpumping speed, strokes/min.

In Eq. 2. If A,,,! is expressed in m/s, F, , and F,, nmillimeters, 0, and $2 in rads, and N in strokesisec. thenthe constant 0.0524 becomes 0.0695.SizingOver the years there have been several methods ofcalculating the structural rating and the gear reducer ratingof a pumping unit; however, it should be emphasized thatthe sizing of pumping unit is not an exact science. Thisis true because in virtually every case many of thevariables previously outlined are unknown at the time thepumping unit is selected.

1o-7

The most commonly used method for siring pumpingunits today is outlined in API RP 1 IL that was devei-opcd from test results conducted by Midwest RcaearchInst.In those instances where the majority of the listed vari-ables are known, there are more exotic computer programs available that may result in a more accurate sizingof the unit in some instances.API RP 11L covers the conventional pumping unitonly; however, the manufacturer has modified this rec-ommended practice to include air balanced and Mark IIunits.The API, Midwest Research Inst.. and the author makeno guarantee as to the degree of accuracy of this sizingmethod when compared with measured field results anddo hereby expressly disclaim any liability or responsibil-ity for loss or damage resulting from its use.The method of sizing conventional pumping units thatis recommended by API RP I 1L and this same methodas modified by the manufacturer for air balanced and Mark11 units are listed on the following pages. Sample calcu-lations for a given set of typical well conditions are filledin and circled for each type unit in Figs. 10. I I throughIO. 13.InstallationAn improperly installed pumping unit can result in earlystructural and bearing failures and overall unsatisfactoryoperation. An adequate foundation must be provided, andthe unit must be properly erected.FoundationA reinforced concrete block is always the best type offoundation for a pumping unit. Concrete blocks may becast in place although very often they are precast andmoved to location for the installation of the unit. Hold-downs are provided in the concrete foundation in the formof anchor nuts or slotted pipes embedded in the concreteto receive hold-down clamp bolts.

The top of the concrete foundation should be level andsmooth to support the pumping unit structural base. If thestructural base members do not bear properly on the con-crete, they may deflect with each stroke of the unit. Thisrepeated deflection can result in ultimate failure of thestructural steel base or the concrete foundation or both.Other types of foundations are acceptable under cer-tain circumstances. Foundations of heavy timbers set onalternate layers of sand and gravel have been used suc-cessfully in some areas. This board mat type of founda-tion must be supervised closely during its preparation toprovide correct setting of the timbers. Usually, wide (port-able) bases are required when board mat foundations areused.Details for the design of the concrete foundation as wellas the design of the board mat foundation is outlined inthe API Recommended Practice for Lubrication of Pump-ing Unit Reducers, API RP 1lG.sAlways use a current certified foundation print providedby the manufacturer.Erection of the UnitBefore placing the structural base on the foundation, drawa chalk line from the center of the well along the centerof the foundation. Place the base on the foundation lining


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IO-8 PETROLEUM ENGINEERING HANDBOOK

Con*anv: Well Name. Date:Field. cou IV state:Reqd. Production: BBLSIDay -. Fluid GrawtyPlunger Daa.: 1 %

I.npm, D.pth&&Ft. -. Stroke Length &&-JncherInches - Tubing Sire Inches - RodSIre: 86 - PumpwgSpeed 7.6 SPM

ALL TYPES OF UNITS1. Fo = Depth x G x Fluid Load (fig. 10.12) = 8.650x1.0. I.041 - 9.0052 SKR = 1000 x Stroke+ [Er (fig. ,O.IZ) x Depth] = 1000x 168 +( DO07 x 8.650, = 27.7462 FofSKR - 9.005 * 27.746 = .3254. N/No = SPM x Depth i 246000 = 7.6 x 8.650 245.000 = .2685 N/No =(N/No) + Fe(~,g. = .268 + 1.164 =.230O.IZ)6. BP0 (100% eff.)=Pump Const. (Fig. ro.lz)xSPMxStrokexSP (Fig. 10.13)=.357 x 7.6 x 166 x .7fl = 3517. WRF = Rod Weight (Fig. 10.12) x Depth x [l - (.I28 x G)] = 2.185.9.6fi0, [1-(.lalxI)j - l6.4816. WRFISKR = 16.481 + 27.746 = .5949. TA=lt[%(Fig.10.13)x(E-.3)x10] =l j-.0075 )(( .594 -.3)x IO]= .970

CONVENTIONAL UNITS10. PPRL= WRF+[Fl(wg. 10.13,~ SKR]= 16.4J31 +( .497 x 27.746 I = 30.27011. MPRL = WRF- ]F2(Fig. 10.13) x SKR] = 16.481 -t .I77 x 27.746 I = I I.5709,00312. CEL = 1.06 x (WRF + Fe/Z) = 1.06~ ( 16.401 + 2 I = 22.24313. PT=T(Fig. l~.rs)xSKRrStroke/?xTA= .w x27,746x 84 .970 = 793.20014. Rod Stress=PPRL;Area 30.270 + .785 = Se:561Fig. 10.13)=

AIR BALANCED UNITS15. PPRL=WRF+Fo+.85x[F1(Fig.lo.ro)xSKR-Fo]= 16,48l tW .95 x ( A97 x 27.746 - 9.005 ) = 29.55316. MPRL= PPRL- [Fl(Fig. 10.13) + F2(Fig. IO.?~)] x SKR = 29,553-c-497 + * I77 IO.-2x 27.746 =17. CBL = 1.06 x (PPRL + MPRLILZ = 1 a6 x ( 29.553 + IO.852 1i2= 21.41519. PT =T(Fag. ,~.,a) x SKR x Stroke/P x TA x .96= .348 x 27.746 x 04 x .978 x .s= 761.50019. Rod Stress = PPRL i Area (Fig. 10.13) = 29.553 A .705 = 37.647

MARK II UNITSx). PPRL=WRF+FO+.~~X[F~(F,~.~O.~~)XSKR-FO]= 16.481 + 9.005 +.,sx( -497 xn;F4a9&05)= 29.07521. hlPRL= PPRL - [Fl(Fig. 10.q + F2(Fag. 10.13)] x SKR = 29.075 -t .497 + .I77 I x 27.74.6 = IO.37422. CEL-~.O~~~PPRL+~.~~~MPRLJ~~=~.O~X~ 29.075+ 1.25 x 10.374 I t2 = 21,06223. PT = IPPRL x .93- MPRL x 1.2) x Stroke-4= I 29.07% 93 - IQ374 x I 21 x 168 ~4=24. Rod Stress = PPRL + Area (Fig. ,~.a) = 29.075 + .785 = 37.03025. NOTE. 00 Not Use Less Than One SIZQ Smaller Reducer Than Required For Conventional Umt

Fig. 10.1 l-Pumping unit design calculations.


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B R A KE H O RS E P O WE R R E Q U I R E D B A S E D O N l O O KV O L UME T R I C E F F I C I E N C Y :

Ce n wn t i o r u l a n d Ai r 9 d wa d Un i t sF w d e w s p e d q i n m & h i g h s l i p u t r i c mo t o r sDa p t h &6 f j OF t r F I P D 351 - 5 4 B HP

5aoooF o r mu l t i y l i n d w m+ a 6 n o r ml s l i p u t r i c mo t o r s- &5 C ) F t . x E %P D 3 5 1 = 6 8 B HP

u . = QE X P L A N A T I O N O F S Y M BOL S

F o - F l u i d L o a d o n Fu l l P l u n w Am u u m a F b i d L a dS KR- L o d n s u i n d c o mr n c h t h r r o d mi n Ot o mr m ou n t ~ c u l l o ~ ~ ~ ~ Di . h p s r f t .F e / S K R - Pu wm o l t t m s t mk p k n s m wh i c h t h a f l u i d wd w i l l t m t c h t h e r o d t i n 6Nl N o - R a t i o o f S P M t o n a t u n l f n q wn c v o f s t &h t r o d s t r i n g l - 1 1 1 6 0 . 3 9 4N/ N o - R ~i o ~ ~ t o l u t u n l f n q wn y o t ~ r o d I b i ~ l - 1 1 4 0 . 6 3 19 P D - B s r d s p e r d my p r o d u c t i o n a t 1 9 6 % v o l u me t r i c d f i c i a n c y l-1R 0 . 7WR F - W- t o f r o d s l r i i i n f l u i d - m l - 3 / 4 . 0 4 1T A - T or q u e d j u s t mmt f o r P DF t o r q u . f o r v a l wr o f WR F/ S KR o t h u t h a n . 3

2 52.P P RL * P a k p d i i r o d l o e d , p a r n d s 2 - 1 1 4 1 . 7 2 1MP RL - Mi n i mu m p o l i i r o d l o t d , p o u n d s 2 - w 2 . 1 2 5CB L - Cwn t r b * n a n q u i r d . P o u n d s 2 3 / 4 2 . 5 7 1P T - P n k md u a r t o r q w , i n c h p o u n d s 3 3 1 4 4 . 7 6 1Wr = Awa g s Wa l g h t o f r o d s i n a i r , o u n d s p a f o o t 4 - 3 / 4 7 . 6 7 1G = s # c i f i c Gr a v i t y o f p o d ua d f l u i d ROD AND PUMP DATA

R o d W . E l a s t i c F n p U . WV R od S t r i m6 , %o f E a c h S i nRo d mu + l b . p m f t . Co n s t J n t F Ut wNO. Dh. W Ef F e 1 7 1 8 j / 4 w9u Al l 0 . 7 2 6 . 9 9 1 9 9 1 . 9 9 6 --54 1 . 0 6 0 . 9 9 6 . U Cl 6 7 1 . 1 3 854 1 . 2 5 0 . 9 2 9 . 9 9 1 6 3 1 . 1 4 654 1 . 5 0 0 . 9 5 7 . 9 9 1 5 6 1 . 1 3 754 1 . 7 5 0 . 8 9 0 . 0 0 1 5 3 1 . 1 2 254 2 . 9 9 1 . 9 2 7 Ml 4 6 1 . 0 6 6

----_-.--- ----------_

U. 6 5 5 . 44 9 . 5 5 0 . 55 5 . 4 U66 4 . 6 3 5 . 47 3 . 7 2 6 . 3

55 Al l 1 . 1 3 5 . 9 9 1 2 7 1 . 9 9 9 l o o . 064 1 . 9 6 1 . 1 6 4 . OOl W 1 . 2 2 964 1 . 2 5 1 . 2 1 1 . D 9 13 2 1 . 2 1 564 1 . 5 0 1 . 2 7 5 . W1 2 3 1 . 1 9 464 1 . 7 5 1 . 3 4 1 . w1 1 4 1 . 1 4 5

--- -----_.------_

----_-3 3 . 33 7 . 24 2 . 34 7 . 4

3 3 . 1z :4 5 . 2

55 1 . 0 5 1 . 3 0 7 . I 3 9 1 1 4 1 . 9 9 695 1 . 2 5 1 . 3 2 1 . w1 1 3 1 . 1 9 495 1 . 5 9 1 . 3 4 3 . W l l 1 . 1 1 055 1 . 7 5 1 . 3 6 6 ) . W i m 1 . 1 1 466 2 . 0 0 1 . 3 9 4 . w1 0 7 1 . 1 1 495 2 . 2 6 1 . 4 2 6 . w1 9 5 1 . 1 1 055 2 . 5 6 1 . 4 6 9 . w1 0 2 1 . 9 9 966 2 . 7 5 1 . 4 9 7 . o o o 9 9 1 . 9 6 2

-_-...

I-.._

---_

---- 3 4 . 4 6 5 . 6.---- 3 7 . 3 6 2 . 7-_--- 4 1 . 9 5 8 1-- 4 s . 9 5 3 . 1-_--_ 5 2 . 0 4 S . 0--__ 5 9 . 4 4 1 . 6--- 6 5 . 2 3 4 . 6--- 7 2 . 5 2 7 586 Al l 1 . 6 3 4 . mx t w 1 . 9 9 9 -_.- 1 w. o - -7 5 1 . 0 67 s 1 . 2 57 5 1 . 5 67 5 1 . 7 67 5 2 . 9 07 5 2 . 2 5

1 . 5 6 6: : i Z1 . 7 3 21 . 6 9 31 . 6 7 5

. W W. w9 9 7. w9 9 4. 9 0 9 69. 9 9 m5. 0 0 9 90

1 . 1 9 11 . 1 9 31 . 1 8 91 . 1 7 41 . 1 5 11 . 1 2 1

-.-----_----_.--._-----.-_.-.--._.-__.--.

2 7 . 0 2 7 . 4 4 5 . 6z : j i t : 3 i i l l3 7 . 6 3 7 . 0 2 5 . 14 2 . 4 4 1 . 3 1 6 . 34 6 . 9 4 6 . 6 7 . 2

7 6 1 . 0 6 1 a 0 2 x l 9 9 2 1 . 0 7 27 6 1 . 2 5 1 . 6 1 4 . 9 0 9 61 1 . 0 7 77 6 1 . 5 0 1 . 6 3 3 . o o o 8 0 1 . 9 9 27 6 1 . 7 5 1 . 6 5 5 . O OWO 1 . 9 9 97 6 2 . 0 0 1 a 6 0 a 9 9 7 9 1 . 9 9 37 6 2 . 2 6 1 . 8 0 8 a 9 7 7 1 . 9 9 67 6 2 . 5 0 1 . 9 3 4 . OW7 6 1 . 9 9 77 6 2 . 7 5 1 . 9 6 7 . o o o 75 1 . 9 9 47 5 3 . 2 5 2 . 0 3 9 . OOQ7 2 1 . 0 7 67 6 3 . 7 5 2 . 1 1 9 . o o o 69 1 a 4 7

2 6 . 5x l . 63 3 . 83 7 . 54 1 . 7: : I6 6 . 56 6 . 76 2 . 3

7 1 . 66 9 . 46 6 . 26 2 . 65 6 . 35 3 . 54 9 . 24 3 . 53 1 . 31 7 . 7

- -- -- - -- - -- . -- - _I -- - -

1 0 9 . 0

3 3 . 62 6 . 81 7 . 3

7 . 4

---

--_---_-.--_.-

---Abbrevlallons and nomenclature used here are lndtgenaus to this form

Fig. 10.12-Pumping unit design calculations.


10/37

10-10 PETROLEUM ENGINEERING HANDBOOK

Rod wt. E l a s t i c F W? l UW ~ R od S t r i n g . % o f E &I S i z eR o d P l u n 9 m I b . p r f t . c o n s t a n t F a C t O rNo . b i a . Wr E r F W l - 1 1 4 l - l / a 1 7 l 8 Y 4 5 m7 7 Al l 2 . 2 2 4 . OW8 5 1 . 0 9 0 -_-_.-. -.- -- l o o . 0 --6 5 1 . 0 6 1 . 8 8 3 . Om8 7 1 . 2 6 16 5 1 . 2 5 1 . 9 4 3 a 0 9 8 4 1 . 2 6 38 5 1 . 5 0 2 . 0 3 0 . o w7 9 1 . 2 3 26 5 1 . 7 5 2 . 1 3 8 . Om7 4 1 . 2 0 1

--... --- 2 2 . 2 2 2 . 4-.-. -.- 2 3 . B 2 4 . 2.._.-.. _-- 2 6 . 7 2 7 . 4. .-_._ -.--- 2 9 . 6 3 0 . 46 66 6

- - W8 66 66 6

1 . 0 61 . 2 51 . 5 01 . 7 52 . 0 02 . 2 52 . 5 02 . 7 5

2 . c f E . 8 . 0 0 0 7 42 . 0 8 7 a 9 7 3

1@

2 . 1 8 5 c &3. 4 7 . wo 6 82 . 3 1 5 . wo 6 62 . 3 8 5 B O O6 32 . 4 5 5 DO0 6 1

1 . 1 5 11 . 1 5 6

r " 31 . 1 6 41 . 1 11 . 1 5 31 . 1 3 81 . 1 1 9

-_---.---_-------_-

---.-_----.------------

2 2 . 6 2 3 . 02 4 . 3 2 4 . 52 6 . 8 2 7 . 0: : : 2 :3 8 . 9 3 S . 04 9 . 6 3 9 . 74 4 . 5 4 3 . 3

33.0El i 27626.8 1 9 : 22 9 . 5 1 0 . 55 4 . 3 -6 1 . 2 -4 6 . 3 -g xn . 1 -1 9 . 7 -1 2 . 2 -

6 7 1 . 5 0 2 . 4 1 3 B O O6 1 1 . 0 6 2 -_--- --6 7 1 . 7 5 2 . 4 3 0 . o o o 60 1 . 0 6 6 -_-_._ -I6 7 2 . 0 0 2 . 4 5 0 . wo 6 o 1 . 0 7 1 ----- -_--.6 7 2 . 2 5 2 . 4 7 2 DO9 5 9 1 . 0 7 5 -- ---6 7 2 . 5 0 2 . 4 9 6 .WO59 1 . 0 7 9 --_-- -.--8 7 2 . 7 5 2 . 5 2 3 .wo58 1 . 0 8 2 ---.... ---0 7 3 . 7 5 2 . 6 4 1 DO0 5 6 1 . 0 7 8 -.--. -._-6 7 4 . 7 5 2 . 7 9 3 B OO5 2 1 . 0 3 6 -_-.._ -.

2 7 . 7E : 2 "3 6 . 43 9 . 94 3 . 96 1 . 28 3 . 6

7 2 . 38 9 . 78 8 . 86 3 . 66 0 . 15 6 . 13 8 . 61 6 . 4

----I_ --- ------_ ---

8 8 Al l 2 . 9 0 4 . o o o 5 o 1 . 0 0 0 -.--. l o o . 0 --i i9 69 69 69 6

1 . 0 6 2 . 3 8 2 a 0 0 6 7 1 . 2 2 21 . 2 5 2 . 4 3 5 . o o o 6 8 1 . 2 2 41 . 6 0 2 . 6 1 1 . 0 0 9 6 3 1 . 2 2 31 . 7 5 2 . 6 0 7 . OC Q6 1 1 . 2 1 32 . 0 0 2 . 7 0 3 . OM5 8 1 . 1 9 62 . 2 5 2 . 8 0 6 . 0 0 9 5 5 1 . 1 7 2

_..__.-.. _._..-.--_..-.-._..-.---.

1 9 . 1 1 9 . 22 0 . 5 2 9 . 62 2 . 4 2 2 . 52 4 . 6 2 5 . 12 7 . 1 2 7 . 92 9 . 6 3 0 . 7

1 9 . 52 0 . 72 2 . 62 5 . 12 7 . 42 B8 . 65 4 . 55 0 . 44 5 . 74 0 . 43 4 . 42 8 . 6

4 2 . 3 -3 8 . 3 -3 2 . 3 -2 5 . 1 -1 7 . 6 -

9 . 6 -9 7 1 . 5 0 2 . 7 0 7 B OO5 6 1 . 1 3 19 7 1 . 7 5 2 . 7 5 1 B OO5 5 1 . 1 3 79 7 2 . 0 0 2 . 8 0 1 . 0 0 0 5 4 1 . 1 4 19 7 2 . 2 5 2 . 8 5 8 0 0 0 5 3 1 . 1 4 30 7 2 . 5 6 2 . 9 2 1 . 0 0 9 5 2 1 . 1 4 19 7 2 . 7 5 2 . 9 8 9 . 0 0 0 5 0 1 . 1 3 5

--_._-_.--.. 2 2 . 52 4 . 52 6 . 82 9 . 43 2 . 53 6 . 1

2 3 . 02 5 . 02 7 . 4: : :3 6 . 3

- -- ---------

:E s8 89 89 89 6

1 . 7 5 3 . 1 0 3 . o w4 7 1 . 0 5 12 . w 3 . 1 1 8 . 0 0 9 4 7 1 . 0 5 52 . 2 5 3 . 1 3 7 . 0 0 0 4 7 1 . 0 5 82 . 5 0 3 . 1 6 7 B OO4 6 1 . 0 6 22 . 7 5 3 . 1 8 0 B OO4 6 1 . 9 5 63 . 7 5 2 2 8 9 a 0 9 4 5 1 . 0 7 44 . 7 5 3 . 4 1 2 a 0 0 4 3 1 . 0 6 4

----_- 2 5 . 7..--.. ._ 2 7 . 7-_-_._ 3 0 . 1-..-._- 3 2 . 7- _.... 3 6 . 6-..-..- 4 9 . 7-_.-_... 6 6 . 7

7 4 . 37 2 . 369.96 7 . 36 4 . 45 0 . 33 4 . 3

- - _- _ . . -

--- ------------9 91 0 71 0 71 0 71 0 71 0 71 0 71 0 81 0 81 0 81 0 81 0 81 0 81 0 91 0 91 0 91 0 9

Al l 3 . 6 7 6 . o w 39 l . o o O ---_.- l o o . 0 - - - --1 . 5 0 3 . 0 8 5 BOO5 1 1 . 1 9 5 1 9 . 4 1 9 . 2 1 9 . 51 . 7 5 3 . 1 5 8 . o w4 9 1 . 1 9 7 2 1 . 0 2 1 . 0 2 1 . 22 . w 3 . 2 3 8 . wo 4 6 1 . 1 9 5 2 2 . 7 2 2 . 8 2 3 . 12 . 2 5 3 . 3 3 6 . 0 0 6 4 6 1 . 1 8 7 2 5 . 0 2 5 . 0 2 5 . 02 . 5 0 3 . 4 3 5 . OMl 4 5 1 . 1 7 4 2 6 . 9 2 7 . 7 2 7 . 12 . 7 5 3 . 5 3 7 B OO4 3 1 . 1 5 6 1 9 . 1 3 0 . 2 2 9 . 3

- - -

4 1 . 93 8 . 93 1 . 42 6 . 01 8 . 21 1 . 3

- --L-------

1 . 7 5 3 . 4 1 12 . 0 0 3 . 4 5 22 . 2 5 3 . 4 9 82 . 5 0 3 . 5 4 82 . 7 5 3 . 8 0 33 . 7 5 3 . 8 7 32 . 5 0 3 . 9 1 12 . 7 5 3 . 9 3 03 . 7 5 4 . 0 2 04 . 7 5 4 . 1 2 0

. o o o 4 4a 0 0 4 30 0 9 4 3. 0 0 0 4 2. 0 0 6 4 2. o o o 3 8. 0 0 0 3 7. 0 0 0 3 7. o o o 3 8. o w3 5

1 . 1 1 1 2 0 . 9 2 1 . 4 5 7 . 71 . 1 1 7 2 2 . 6 2 3 . 0 5 4 . 31 . 1 2 1 2 4 . 5 2 5 . 0 5 4 51 . 1 2 4 2 6 . 5 2 7 . 2 4 6 . 31 . 1 2 6 2 6 . 7 2 9 . 6 4 1 . 61 . 1 0 8 4 0 . 6 3 9 . 5 1 9 . 9

- - - -- - -- -

- -- _ -- -

- -

-- -------- ---1 . 0 4 8 2 7 . 21 . 0 5 1 2 9 . 41 . 0 6 3 3 9 . 91 . 0 6 6 5 1 . 5

7 2 . 87 0 . 6

-- --------

Fig. 10.12-Continued.


11/37

PUMPING UNITS & PRIME MOVERS FOR PUMPING UNITS I O - 1 1

1 5 5. 6

. 4 5

. 5. 5 5. 6

1 . 9 11 .Ol . 9 21 . 0 2 . 9 31 . 0 6 2 61 . 1 1 . 0 31 . 0 9 1 . 0 51 . 1 1 . 0 11.19 1 . 11.33 1 . 2 3

. 8 13 3. 6 5: Z. 8 9. 9 3

1 . 0 41 . 1 5

. 7 1 . 6 1

. 7 2 6 3. 7 5 . 6 6h-G--. 7 6 . 7 23 3 . 8 19 8 . 9 l

1 . 0 9 1 . 0 3

. 5 15 3I %

. 5 8. 6 6. 7 63 8. 9 6

. 4 1

. 4 3. 4 7. 4 7

-. 6. 6 8. 7 8. 8 7

1 . 4 8 1 . 3 7 1 . 2 7 1 . 2 1 1 . 1 3 1 . 0 5 9 91 . 8 1 . 5 1 . 4 1 . 3 3 1 . 2 4 1 . 1 5 1 . 0 71 . 7 1 . 6 1 1 . 5 2 1 . 4 4 1 . 3 7 1 . 2 6 1 . 1 6

Fl, PEAK POLISHED ROD LOAD La

. 0 2 . 1 2 . 2 3 3 3 . 4 3 . 5 3 . 6 3. 0 5 . 1 5 2 6 3 6 . 4 6 3 6 . 6 6. 0 8 . 1 8 2 9 3 9 . 4 9 . 5 9 . 6 9. 1 2 . 2 2 . 3 3 . 4 3 . 5 2 . 6 2 . 7 2. 1 7 . 2 - i . 3 7 . 4 6 . 5 5 . 6 5 . 7 5. 2 1 . 3 1. 2 7 3 62 4 . 4 2. 4 3 . 5 . 5 8 5 8 . 7 5 A3 .91. 5 5 . 6 2 . 8 8 . 7 8 3 3 . 9 3 8. 7 . 7 6 34 .93 .97 1 1.05. 8 3 . 9 39 1.06 1.1 1.13 1.16

1 5 004 .Ol ,015 ,019 ,015 .022 ,025. l ,016 .02S ,039 ,045 ,039 .05 , 0 5 5. 1 5 . 0 3 5 , 0 5 5 , 0 7 3 . 0 8 0 7 3 $8 3 , 0 8 5. 2 , 0 6 5 , 0 8 8 . 1 1 5 , 1 2 5 . 1 2 , 1 1 9 . 1 2

. 5 I 3 4 , 3 4 95 5 . 4 2 . 4 3 3. 6 . 4 9 . 4 9

, 1 5 4, 1 9 2. 2 2 8, 2 6 9, 3 1 6, 3 6 84 4 6

. 4 9

0. 0 5. l I

0. 0 5

.230 : : 59 ,

. 2N / N V : 3

. 3 5 s l 4 . 0 1 6 - . 0 0 5 - . 0 1 7 . 0 0 6 . 0 1 2 . 0 1 4

. 4 . 0 3 , 0 1 2 - . 0 0 5 - , 0 0 5 . O l l . 0 1 3 , 0 1 5. 4 5 . 0 2 . 0 1 3 0 0 0 5 , 0 1 1 , 0 1 4 , 0 2 5. 5 , 0 2 5 , 0 1 5 . W9 , 0 1 1 , 0 1 3 . 0 1 5 , 0 2 55 5 . 0 3 . M , 0 1 5 , 0 1 5 , 0 1 5 . 0 2 . 0 3. 6 : 0 3 . 0 2 . 0 2 , 0 1 5 . 0 2 . 0 3 . 0 5

0 , l . 1 . . 3 I / . 4 . 5 . 6. 0 6 . 0 8 . 1 4 . 1 9 . . 2 2 . 2 5 2 6. 0 6 . l . 1 8 . 2 1 . 2 5 . 2 8 2 9. 0 6 . l l . 1 9 . 2 4 2 8 . 3 . 3 1. l . 1 4 2 2 . 2 7 . 3 1 . 3 2 . 3 3. 1 3 . 1 8 2 6 . 3 3 3 3 4 2 4 5. 1 6. 2. 2 5. l 9 . 3 5 . 4 2 . 4 5 . 4 7 . 5 , 5 1 5. 3 4 . 4 A6 . 4 9 . 5 1 . 5 2 , 5 2 53 6 . 4 5 . 5 5 3 5 6 5 6 , 5 6 54 4 . 5 . 5 5 5 8 . 6 2 . 6 3 , 6 3 5. 4 9 . 5 5 . 6 6 4 . 6 7 6 6 . 6 8 5

. 1 8 . 1 2 , 0 6 5 . 0 4 . 0 1 5 ~0 0 5 - . 0 1 7

. 1 2 . 0 8 , 0 5 5 , 0 2 7 . 0 0 5 - . 0 1 7 - , 0 0 51 0 7 5 , 0 6 5 . 0 2 5 + . 0 0 5 - . 0 1 7 ~3 0 5 . O l l

ROD S!ZE VS. AREA

Rod Size1 1 2

S q . l n .0 . 1 9 6

5 ! 8 0 . 3 0 73 1 4 0 . 4 4 27 1 8 0 . 6 0 1

-1 l-l/8 s?l-1/4 1 . 2 2 7

F i g . 1 0 . 1 3 - P u mp i n g u n i t d e s i g n c a l c u l a t i o n s .


12/37


up the center of the base with the chalk line. The distancefrom the well to the front of the structural base shouldbe given on the certified print provided by themanufacturer.Follow the manufacturers instructions and assemble therest of the unit. Proper alignment of all working parts of

the mechanism is essential. This may be checked by useof a level, plumb bob, or a transit. Make necessary ad-justment to align the wireline hanger with the well.Tighten all bolts and nuts. Some pumping unit manufac-turers specify that all structural bolts be hammer-tight.After all other adjustments and inspection have beenmade and the unit is in operation, visually check align-ment of moving parts. This may be done by observingthe distance between the cranks and pitman side memberson each side of the unit. The distances should be approx-imately equal. Check the wireline to see if it is trackingthe horsehead properly. Objectionable noises or knocksusually indicate that some part of the unit is loose or outof alignment. All necessary adjustments should be madeat this time. Misalignment may result in excessive axialmotion of bearings which are designed primarily for radialload.Guarding of Pumping UnitsGuarding should be provided for all pumping units to pre-vent bodily injury or death from contacting moving partsof the unit by anyone inadvertently walking into the unit,falling, slipping, tripping, or any similar action. Guardsshould be provided around the V-belt drive as well asaround the entire pumping unit.

The type of guarding around the unit depends on thelocation. For remote locations, usually a rail type guard-in,e is considered satisfactory. For more populous areas,wire mesh guards several feet high are provided to en-sure a greater degree of safety to personnel. Details forguarding can be found in API RP 1 I ER.4LubricationPumping units should be given periodic lubrication andmaintenance checks. When they are subjected to heavyvariable loads, extreme temperature conditions, or adversemoisture or dust conditions, it might be necessary to in-crease the frequency of the checks.Structural BearingsAll the structural bearings (i.e., center bearings, equalizerbearings, crank pin bearings, etc.) require an adequateamount of the proper type of lubricant. A fluid lubricant

TABLE 10.2-VISCOSITY RECOMMENDATIONSFOR GEAR REDUCERSAppkatlon SAE Gear or

(OF) Transmission Oil AGMAt Oil0 to 140 90 EP 5 EP (IS0 VG 220)-30 to 110 80 EP 4 EP (IS0 VG 150)

Operating iemperature of 011n a gear reducer on a pumping unit normallyWI be lrom a,, fem!x?ra,re to 25OF above a,, temperature Thetemperatures shown I the table are Ihe l,m,t,ng values between wh,chsalisiaclory lubrlcallon can be expected

Sot of Automotive Engineers Inc 2 Pennsylvania Plaza. New York CityNY 10001tAmewan Gear Manufacturers Ass- 1330 Massachusetts Ave. NWWashIngtan. DC 20005

is more efficient in moving to the areas where the lubri-cant is most needed within the bearing housing; however,good quality grades of greases are recommended by mostmanufacturers for their particular bearings. In general,sleeve type beatings require oil as a lubricant and antifric-tion type bearings operate satisfactorily with greaselubrication.Gear ReducersLubrication procedures for gear reducer drives and chaindrives are recommended in accordance with API stan-dards. Temperature and viscosity ranges for gear reducersand chain reducers are tabulated in API RP 1 1G3 (alsosee Tables 10.2 and 10.3).

It is not possible to describe adequately suitablelubricants by brief specifications or by Sot . of AutomotiveEngineers (SAE) or Intl. Standards Organization (ISO)viscosity numbers alone. Adequate lubrication instructionscannot be condensed sufficiently to be placed on thenameplate because of the many variables in operating con-ditions to which pumping units are subjected.The proper oil for pumping unit gear reducers is bestchosen with the advice of a representative of a reputablesupplier of lubricants and should be based on the serviceconditions that are established by the design of the reducerand the service conditions of the particular installation.The areas in contact on gear teeth and on chains andsprockets are relatively small, and, therefore, the unitpressures produced in transmitting high torque loads arecorrespondingly high. These gears, chains, and sprocketsare designed to operate under these high unit pressuresprovided the lubricant used is also capable of withstandingthese unit pressures during the periods of peak loads.The temperature of the air in the vicinity of the reduceris of considerable importance in selecting oil of the properviscosity. For high-temperature operations, an oil witha higher SAE or IS0 viscosity number should be selected.For low-temperature operations, the oil should have suf-ficient fluidity to insure a free flow of oil through thelubricating channels.

The operating temperature of oil in pumping unit gearreducers normally would be at least 25F above ambienttemperature. The temperature increase in the oil will be

TABLE 10.3-VISCOSITYRECOMMENDATIONS FOR CHAINREDUCERSTemperature ofOil in ChainCase, OF-50 to + 50-20 to + 80

0 to +lOO+lO to +125+20 to +I35+30 to +155

SAE Viscositv NumberEngine Oil Gear Oil

5W **tow 75+2ow 8030 804050 so

Operating temperature 01 oil m a chain case on apumping nit normally ll be lrom air temperature to29 F above air temperature. The lemperatures shownin the table are he limiting alues etween whichsatisfactory lubrwzafion can be expected.SAE gear 011sare no! recommended to1 use I chainreducers for this range of temperatures

t SAE 75 gear 01 1 S not usually avadable.


13/37


14/37

Chapter 10Pumping Units and Prime Movers forPumping Units: Part 2-Prime Moversfor Pumping UnitsSam Curtis. SPE. Sargent 011 Well EquipmentErnest Showalter, SPE, Sargent Oil Well Equipment

IntroductionPumping units are driven by either electric motors orinternal-combustion engines. Each type of prime moverhas characteristics that make it more appropriate. depend-ing on field conditions and energy availability. Theseprime mover characteristics are covered in detail in theirrespective sections.In this section. wellsite is considered the area aroundthe well where the pumping unit and prime mover arelocated.Internal-Combustion EnginesThe availability and economics of the power source fre-quently dictate that internal-combustion engines be select-ed to drive pumping units. For the sake of brevity.internal-combustion engines arc simply called enginesthroughout this chapter. Basically, engines used on pump-ing units are divided into two speed classifications: slow-speed engines and high-speed engines.Slow-speed engines are those with one or two cylin-ders, which generally have a maximum crankshaft speedof 750 revimin or less. High-speed engines are mul-ticylinder (usually four or six cylinders) and have an aver-age speed of more than 750 but not more than 2.000revitnin.Generally. high-speed engines have less torque thancomparable horsepower, slow-speed engines. Therefore.high-speed engines will experience greater speed varia-tion on the cyclic load of a pumping unit. Considerablespeed variation at the prime mover has many benefits onvarious components of a sucker-rod-beam-type pumpingunit system. 5.b While governors tend to limit speed var-

iation. it will not be eliminated. Speed variations of upto 35%, with resulting reductions in cyclic loads. havebeen measured on high-speed engine-driven pumpingunits.

Two-Stroke CycleTwo-stroke cycle engines or two-cycle engines completetheir work in only two strokes of the piston, which is ac-complished with one revolution of the crankshaft. The twostrokes are compression and power. The process of fill-ing the cylinder with a fresh charge and exhausting theburned gases occurs almost simultaneously near the endof the power stroke. The horizontal sliding piston firstuncovers exhaust ports and then uncovers intake ports,which charges the cylinder and thereby flushes out theexhaust gases. Because some of the fuel is lost at thispoint, two-cycle engines, above about 40 hp, are equippedwith fuel in.jection systems that raise their fuel efficiencyclose to that of a four-cycle engine. Normally. a two-cycleengine. for a given displacement and speed. develops 1.6times the power of an equivalent four-cycle engine.The two-cycle engine normally is built as a crossheadtype. This construction uses a bore in the engine base.where a crosshead is mounted to take the angular thrustof the connecting rod, and places a seal between the cyl-inder and crankcase. Contamination of lubricating oil isthereby reduced. Lubrication of the cylinders is acconl-plished by using an auxiliary oiler that in,jccts a prescribedamount of oil into the cylinder/piston area.


15/37

PUMPING UNITS & PRIME MOVERS FOR PUMPING UNITS IO-15

Fig. 10.14-Slow-speed, four-stroke engine on a beam-type oilwell pumping unit.

Most two-cycle engines are the slow-speed variety.These are available with a single cylinder or multiple cyl-inders in sizes ranging from about 15 to 325 hp. Theseengines have twice the power strokes of four-cycle en-gines and, for that reason, a smaller flywheel is requiredand additional speed variation is possible.

To operate most efficiently, two-cycle engines shouldbe fairly well loaded. The proper size and length of ex-haust pipe is very critical on this engine. Actually, theexhaust system completes the scavenging system. Theproperly sized pipe then is fitted to the correct length, asrecommended by the manufacturer. This tuning of thepressure waves allows the engine to develop maximumefficiency and power. Incorrect exhaust-pipe length hasa detrimental effect on the life, power, and operation ofthe engine.

Ideally, this type of engine operates only on natural gasor liquid petroleum (LP) gas. Some sizes may be operat-ed on diesel fuel, but these engines must be derated.

Four-Stroke Cycle

An engine designed for four-stroke cycle or Otto cycleis called a four-cycle engine. The four-stroke cycle in-cludes intake, compression, power, and exhaust. Intakeand exhaust valves are mounted in the cylinder head orthe block and are actuated by cams and push rods. Thecrankcase is connected directly to the cylinder, and con-tamination of the lubricating oil occurs sooner than it doesin crosshead-type two-cycle engines.

The four-cycle engine is built in slow- and high-speedversions. Slow-speed engines usually have their cylinders

mounted horizontally, whereas high-speed engine cylin-ders are mounted vertically.

These engines use trunk pistons fastened to the crank-

shaft by connecting rods. Intake and exhaust valves aremounted in the cylinder head and actuated by cams andpush rods.

A slow-speed, four-cycle engine as shown in Fig. 10.14usually is built with a single horizontal cylinder. A largeunenclosed flywheel is provided to store energy anddeliver at a fairly constant speed to the pumping unit.

High-speed, four-cycle engines are multicylinder andcan operate at speeds up to approximately 2,000 rev/min.Normally, four- and six-cylinder engines are not operat-ed at more than 1,400 rev/min to maximize engine life.

A typical four-cycle, high-speed engine used as a primemover on a beam-type pumping unit is shown in Fig.10.15. This type of engine can operate on natural gas,

LP gases, or gasoline.

Diesel and Oil Engines

Some slow-speed, single-cylinder engines burn diesel orfuel oil by high-pressure injections into the cylinder. Thecompression is much greater than gas engines. Heat, de-veloped by compressing the air in the cylinder, ignitesthe fuel sprayed into the cylinder. These engines are divid-ed into two types: full diesels, which are cold-starting,and semidiesels, which require heating to start.

The cold-starting diesel has a compression ratio of 14:1,resulting in a pressure of approximately 500 psi. The semi-diesel has approximately 250 psi compression, which re-quires a hot tube heated by a torch or electric glow plug


16/37


Fig. 10.15-Typical four-cycle, high-speed engine used as primemover on a beam-type pumping unit.

to produce enough heat to ignite the charge. Once theseengines are started, enough heat is produced in the cylin-der to cause ignition of the fuel as it is injected into thecylinder.

High-speed, multicylinder diesel engines have been im-proved until they are now adaptable for oilwell pumping.These are not used commonly where gas is readily avail-

able. Diesel engines fill a need where other fuels are notreadily available.

Selection of Engine

Five factors should be considered when determining whichengine to purchase: fuel availability, equipment life andcost, engine safety controls, horsepower, and installation.

Fuel Availability. Natural gas is the logical choice. Takenfrom the wellhead casing annulus, it is called wet gasand is used most frequently. Where there is insufficientgas available at the wellhead, gas maybe piped to the en-

gine from the field separator. In either case, the gas mustbe scrubbed to remove oil and water. This is done in adouble compartment volume tank where gas pressure alsois reduced by a regulator. Gas from the separator will havemost of the moisture and oil removed and is considereda better fuel.

Sour gas is a natural gas that contains excessive sulfuror CO2 and is not considered a good fuel. Two percentsulfur is considered excessive. Where sour gas must beused, suitable treaters are required to improve the qualityof the fuel. Sour gas causes severe etching and wear ofengine parts as well as quick contamination of the lubri-cating oil in the four-cycle engines. Two-cycle enginesfare slightly better because of their construction.

Residue gas is natural gas that has had impurities re-moved at a refinery and then is piped back to the field.This is sometimes called dry gas.

LP gases, butane, and propane are excellent gases forinternal-combustion engines, if economically available.Such gases must be stored under pressure in suitable pres-sure tanks to keep them liquefied for transportation.

Vaporizers must be provided to turn the liquid into gasform for use in engines. On small engines, the vaporusually can be drawn off through a reducing regulator toprovide sufficient gas; however, on larger engines, thefuel must be vaporized before entering the engine. Bu-tane freezes to liquid at 0C, while propane does not reachthis state until -42C. A blend of butane/ propane is oftenused in mild climates.

Dual-fuel engines can use natural gas as long as it isavailable, but as soon as the pressure drops, the standbyfuel is fed automatically to the engine in sufficient quan-tity to keep the prime mover going continuously. Suchsystems are designed primarily for gaseous fuels, but simi-lar systems can switch from dry gases to gasoline or vice

versa. Dual-fuel installations should not be overlookedif there is a shortage of natural gas.

Diesel fuel specifications are supplied by manufacturersof diesel engines. These fuels must be free of moistureand in clean dirt-free containers. Filters must be used toensure that only clean fuel gets to the engine.

Some engines that are really semidiesel can burn crudeoil of light gravity, but this must be cleaned satisfactorily.The type of crude must meet the standard set by the en-gines manufacturer.

Equipment Life and Cost. The fact that the slow-speedengine may run at 400 rev/min and the high-speed en-gine may operate at 1,200 rev/min lends logic to the the-


17/37

PUMPING UNITS & PRIME MOVERS FOR PUMPING UNITS 10-17

ory that slow-speed engines generally outlast high-speedengines. Compared with high-speed engines, slow-speedengines have a longer life, are heavier, and cost moreinitially. A slow-speed engine requires fewer parts andis easier to repair; thus maintenance will cost more forthe high-speed engine. A slow-speed engines average lifebetween major overhauls is somewhere between 5 and 10years. whereas a high-speed engines life is 2 to 5 years;albeit, there are exceptions to these averages.Pumping unit and sucker rod life should be longer ifa high-speed (lower-torque) engine is used because ofgreater speed variation.

2. Deduct 1% of the standard brake horsepower foreach 6C rise in temperature above 29C, or add I % foreach 6C fall in temperature below 29C.Information concerning these corrections for turbo-charged engines should be secured from the manufacturer.

Calculations. Sizing prime movers to drive pumping unitswas discussed as part of the pumping unit load calcula-tions in Part 1. The equation used to calculate brake horse-power, Ph, or slow-speed engines and high-slip NEMA(Natl. Electrical Manufacturers Assoc.) D motors* is:Longer-interval maintenance features are available onall engines to reduce costs and extend equipment life. qxDPh=-1. Low-tension ignition provides better ignition with 56,000 . . . . . . . . . . . .._ _...,longer life to magnetos and spark plugs.2. Extended service clutch requires lubrication only whereonce each 6 months. Pb = brake power, hp,3. Automatically filling the crankcase on the engines q = fluid flow rate, B/D, andfrom drums of oil ensures correct oil-level at all times.4. Water makeup condensers provide water for the radi-

D = depth (lift), ft.

(3)

ator automatically as required. The bhp equation given for high-speed engines andnormal-slip NEMA C motors** isEngine Safety Controls. Every oilfield engine should beprovided with reliable safety controls since the enginesin this type of service usually are unattended. Some en- qxDPb=- (4)gine manufacturers provide safety controls as standard

45,000, . . . .equipment. If not originally equipped, safety controls areavailable from supply companies. These equations are empirical and result from modifi-Safety controls usually ground the magneto, and will cations of the basic horsepower equations.shut off the fuel to stop the engine. Most desirable safety Hydraulic horsepower needed for actual lifting of thecontrols for engines are: (1) high water temperature, (2) fluid is only a small portion of the total power requiredlow oil pressure, (3) overspeed, and (4) pumping unit by the pumping system.vibration (to shut down the unit in case of sucker rodbreak)Horsepower. API 7B-1 IC covers the procedure for test-ing and rating of engines.Maximum standard brake horsepower for engine andpower unit (including accessories) is measured at vari-ous revimin for intermittent and continuous operation.Torque and fuel consumption measuring procedures alsoare outlined in the API specification.At any rotational speed, maximum brake horsepowerwill be the greatest horsepower corrected to standard con-ditrons [29.4C and 29.38 in. of mercury] as outlined un-der Test Procedures.The manufacturer usually shows rating curves belowthe API curve, which is based on the power that the en-gine can produce for various conditions of service. Ex-perience has shown that, for the cyclic load of oilwellpumping, high-speed engines must be derated more than

P/l qxDxW33,ooox24x6o, . .

wherePi, hydraulic power, hp,q = fluid flow rate, B/D,

W = weight of barrel of fluid, Ibm,D = depth (lift), ft, and

33,000 = conversion factor, ft-lbf/min.

For a fluid with 1.0 specific gravity

Ph= qxDx42x8.335633,000x24x60

(3

slow-speed engines to provide a margin of safety to standup in continuous service. Normal oilfield horsepower rat-ings for continuous duty. at the speed the engine will beoperated. are (1) slow-speed engine (API) = maximumstandard bhp x0.80, and (2) high-speed engine(API)=maximum standard bhpx0.65.Altitude and temperature corrections (approximate) for

qxDx350= 47,520,OOO

qxD=- 135,735, . . . . . . . . . . . . . . . . . . . . . . . . .._ (6)altitude and temperature for naturally aspirated enginesmay be made as follows. HKJhllPmotorsredefinedere s NEMA510 ?h lipThe mng ,IfraiTgh-I. Deduct 3% of the standard brake horsepower for slip motms Wlfh wer 13% shp 15presented I Ihe eiectr,c mo,ot porllon 0, ,h,S secmneach I .OO@ft rise in altitude above sea level. Normal-slop motors are deimed as NEMA C . 3 10 5% sltp


18/37


where 42 = conversion factor, gal/bbl, and8.3356 = conversion factor, lbmigal.Additional power is required to offset the frictional loss-es in the subsurface system.Frictional horsepower has been defined empirically bySlonneger.9 (This may be low for extremely viscouscrudes, such as those of lOAP1 gravity encountered inthe Boscan field in Venezuela.)

9r= j/,W,X2SXN, .3.000 (7)wherePf = pnwer to overcome subsurface friction, hp

W,. = weight of rods, lbm,S = polished-rod stroke, ft. andN = strokes per minute,

Frictional horsepower added to hydraulic horsepowerequals polished-rod horsepower. The power required atthe prime mover can be calculated by assuming a surfaceefficiency of 75 to 93 70, depending on geometry and typeof bearings in the pumping unit.Example Problem 1. A well of 6,000-ft depth. produc-ing 200 B/D of 1 O specific gravity fluid using a 64.in.stroke unit, a pump with a 1 %-in. bore, %-in. rods (I .64Ibmift, 14.4 strokesimin, and anchored tubing beingassumed), can have its hydraulic and frictional horsepow-ers calculated as follows:

qxDPI,=------135,735200~6,000

= 135.735=8.84

andp .= %W,.2SxN.i 33,000

= )/,(l.64~6,000)2(~~,)~ 14.433.000

(1.230)(10,666)x14.433,000

=5.72. p = yxD' 56,000The horsepower required at the polished rod, P,,,sP,"=P,,+Pf . (8)

=8.84+5.72= 14.56.

The horsepower required at the prime mover, P,,,, as-suming a pumping unit with an efficiency of 85% isPPpm=L . ..(9)85%14.560.85

=17.13.Because of the cyclic nature of pumping unit loads andthe fact that the preceding calculations reflect averagehorsepower, a factor must be applied in sizing to ensurethat there is adequate horsepower available to handle peakloads.Both high-speed engines and 3- to 5 %-slip electric mo-tors have limited torque available and should be derated

35% to handle peak loading. Generally, slow-speed en-gines, with higher torque capabilities, and NEMA D elec-tric motors do not require more than 20% derating.When using the cyclic load derating factor, F,.,, of 0.8in the equation, the following prime mover horsepowerwill be required.Slow-speed engine or NEMA D motor horsepower:

P P/l pfP')l-EpirF,., . . . .

8.84+5.72= 0.85x0.80=21.41,

(10)

where E,, pumping unit efficiency and F,.,cyclic loadderating factor.High-speed engine and NEMA C horsepower:

8.84t5.72P""= 0.85x0.65=26.35

The results of this method of horsepower calculationscompare favorably with the results of the abbreviatedmethod of Eqs. 3 and 4 as follows.Slow-speed engine horsepower:

200x6.000=56.000

=21.43.


19/37

PUMPING UNITS 8 PRIME MOVERS FOR PUMPING UNITS 10-19

High-speed engine horsepower:YXDP,,=-45,000200x6.000= 45.000

=26.66Under most conditions, the use of the illustrated methodshould provide adequately sized prime movers. Sizingprime movers for viscous crude may require additionalfrictional horsepower. In this case. experience is the bestguide.A rule commonly used in sizing high-speed engines forlong life on pumping units is: 10% of engines cubic-inchdisplacement as available brake horsepower. Hence. anengine with 817 cu in. of displacement can be relied onto handle an 81.7-hp pumping load.A prime movers minimum operating speed alwaysshould bc greater than its speed at maximum torque out-put. This will ensure that. as the torque requirement ofthe pumping unit increases and the prime mover speeddecrcaaes. adequate torque capacity will be av,ailable. Thisis extremely important on high-speed engine drives.

installationThe prime mover must be installed correctly to ensuregood results. Most pump installations use a V-belt drivefrom prime mover to pumping unit. Slide rail motormounts or some means of adjustment is necessary to pro-vide for installation and proper tension that allows forpower to be transmitted with minimal loss through beltslippage. When the prime mover is installed, the beltsshould be aligned and tightened properly but not over-tightened. Overtightening will overload the prime moversshaft and bearings.Slow-speed engines require sturdy foundations such asa steel base set on concrete or set directly on rails em-bedded in concrete. The slide rails should be set in linewith the cylinder because of the horizontal moving forces.Cross rails, sometimes called universal rails, should beused only on small engines. Most manufacturers provideprime movers with properly designed slide rail assemblies.Multicylinder or vertical engines, in which the forcesare in a vertical plane, can be set on much lighter foun-dations. Cross rails on such installations are the preferredmethod.Provisions must be made for exhaust and fuel lines tothe engine. The manufacturer furnishes specifications fortheir installation. Usually, four-cycle engines comeequipped with both a small silencer and a short exhaustpipe. Two-cycle engines arc not equipped with such equip-ment unless specifically ordered by the customer.The gas line is brought to a scrubber, then through aregulator to reduce the gas pressure to a few ounces be-fore entering the volume tank. Normally, l-in. pipe is thesmallest size recommended from the volume tank to theengine. Larger engines may require larger lines. The pur-pose of the volume tank is to prevent fluctuations of gaspressure. It should have a volume of at least five timesthe cylinder displacement of the engine.

The gas regulator must be fitted with a properly sizedorifice to maintain the proper gas flow. A regulator withtoo large an orifice will cause surges. whereas too smallan orifice will not supply enough fuel to product the powerrequired.Suitable cutoffs are required between the source lintand volume tank, and the volume tank and engine. Thesecutoffs assist with draining the scrubber and volume tank.and also servicmg of the reducing regulator.For engine starting. many types of starters are used.Electric starters were put in automobiles, and soon wereadapted to multicylinder oilfield engines. Formerly, slow-speed engines were started by manually turning the largeflywheel. Some manufacturers provide electric or otherbuilt-in starters as optional equipment. Examples of start-ers include the following.1. For electric starter motors requiring from 6- to 24-Vdirect current, power is furnished by batteries.2. 1 lo- to 440-V AC power and lighting circuits alsoare used for starter motors.3. Air or gas motor starters in which a small vane-typeair motor turns the engine through reduction gears anda Bendix-type engaging mechanism. This type of starterrequires from 20 to 50 psi of gas or air pressure to operate.4. Friction wheel starters for slow-speed engines USCa small gasoline motor or an electric motor to turn a fric-tion wheel, which engages the engine flywheel and turnsthe engine.

5. High-pressure air starting is somctimcs applied toslow-speed engines, in which a valve admits air cant-pressed from 125 to 200 psi into one or more cylindersto cause the engine to rotate. Usually a small engine-drivencompressor is connected to a tank. which is used as a com-pressed air storage tank.6. Diaphragm gas starters in which a rather large rubberdiaphragm is expanded by 20. to 50-psi gas pressure causea rack to turn a pinion attached to the engine crankshaft.7. Gasoline-driven engine starters mounted on the en-gine can be used to provide power through reduction gearsto start an engine.The electric motor starter of 6 to 24 V is probably themost widely used of all starters on small engines. The bat-tery can be located near the engine and charged by anengine-mounted generator. Portable cables from the en-gine can be attached easily to the batteries in trucks orautomobiles. In this case, only one set of batteries wouldbc required for starting several engines.

Large slow-speed engines are best started by using high-pressure air supplied by a small compressor and storagetank assembly. This system is simple and foolproof. Theair compressor also can be used for cleaning or spraypainting around the installation. Compressor units mount-cd on pickup trucks will accommodate starting a largenumber of engines and reduce the installation expense.API RP 7C-11F is a good guide for engine operators. aThis publication should supplement the manufacturersrecommendations for installation, maintenance, and op-eration of internal-combustion engines.Electric Motors for Oilwell PumpingDesign StandardsThree-phase induction motors generally are classified byNEMA as being either B. C, or D. Ultrahigh-slip motorsare classified by NEMA as a special purpose motor. The


20/37


SLIP

0 20 40 60 80 100PWcEm SYN SPED

ULTRI HIGI: SLIP M7iY3FS

440400360

g 320E 2805 240

ii200160

i120

!8 8640

I I I 1 I I I I \0 20 40 60 80 100

PExcm?TSrn SPEED

Fig. 10.16-Typical ratings for horsepower rated motors andultrahigh-slip motors.

following is a portion of the NEMA specifications forthese classified motors (Fig. 10.16).NEMA B. Normal slip no greater than 3 % , and normalstarting breakaway torque 100 to 175% of full-loadtorque.NEMA C. Normal slip no greater than 5 % , and startingtorque 200 to 250% of full-load torque.NEMA D. High slip 5 to 8 % , and starting torque 275 %of full-load torque.NJXMAD Special. High slip 8 to 13%) and starting torque275% of full-load torque.Ultrahigh-slip motors, which have greater than 13 % slipin high-torque mode, fall into an area not standardized

by NEMA. This motor, classified as a special purposemotor, is manufactured exclusively for the beam-type oil-well pumping unit. Designed with ultrahigh slip, the re-sulting wide speed variations produce benefits for themechanical loading on the pumping unit. Fig. 10.16 il-lustrates typical ratings for one size of a multiple-ratedultrahigh-slip pumping motor.High-Torque Mode. Maximum slip 17%) and high start-ing torque 410% of full-load torque.Medium-Torque Mode. Maximum slip 2 1 k, and start-ing torque 320% of full-load torque.Medium-Low-Torque Mode. Maximum slip 27 %, andstarting torque 260% of full-load torque.Low-Torque Mode. Maximum slip 32 % , and startingtorque 225% of full-load torque.Horsepower Ratings of MotorsThree-phase induction motors are available in a widerange of horsepower ratings: 1, 1 %, 2, 3,4, 5, 7 %, 10,15, 20, 25, 30,40, 50, 60, 75, 100, 125, 150, and 200.Most motors found on pumping units range from 10 to75 hp. These motors are available in synchronous speedsof 600, 720, 900, 1,200, 1,800, and 3,600 rev/min. Themajority of the three-phase 460-V induction motors usedon pumping units are 1,200 rev/min.

Multiple Horsepower Rated MotorsWhen a new well is completed, sizing is based on basicinformation provided by the depth of the pump and fluid,size of pump, stroke length, speed of pumping unit, andspecific gravity of the fluid. There are many variables incalculations that are not always considered and may af-fect the required motor size. Sometimes, overlooked vari-ables influencing loading on the motor are: actual fluidlevel, viscosity of fluid, deviation of hole, friction in thepump, friction in the stuffing box, excessive friction com-ing from the pumping unit, and quality of electric poweravailable. Because of the many variables involved, it issometimes difficult to size a motor accurately for new in-stallation on the first attempt. Sometimes multiple-ratedmotors are considered as pumping unit drivers.

Multiple horsepower rated motors usually have threedifferent modes available. Table 10.4 lists typical sizesavailable.

TABLE 10.4-TYPICAL SIZES (hp) OF MULTIPLE-HORSEPOWER-RATED MOTORSHP HP HP-T 3.5 210 7 415 9 620 14 825 14 1030 21 1240 26 1650 35 2975 52 30


21/37


Multiple Size Rated MotorsAn ultrahigh-slip motor is also a multiple-rated motor,usually being quadruple rated. The stator winding of thismotor has been designed for multiple connections. Theultrahigh-slip capability is a result of special design char-acteristics incorporated in its rotor. Fig. IO. 16 is twographs that show a comparison of ultrahigh-slip motorsto the horsepower rated motors. The first illustrationshows the horsepower rated motors with only one torquemode available. The second shows an ultrahigh-slip mo-tor with four-mode capability. For maximum benefits, theultrahigh-slip motor should be used in the lowest-torquemode possible without exceeding its thermal limit.Single-Phase MotorsSingle-phase (AC) motors are also found in the oilfieldin sizes up to 10 hp, although their use is limited. Thesesingle-phase motors are confined to shallow stripper wellsproducing in fields where three-phase power is notavailable.Single-phase motors initially cost more than their three-phase counterpart with like rating. These operate lessefficiently. To ensure high starting torque and low oper-ating current, single-phase motors of the capacitor-startcapacitor-run varieties should be used.DC MotorsDirect-current (DC) motors have a very limited use onthe beam-type pumping unit. DC voltage cannot bechanged by transformers, which make transmission anddistribution difficult without high line losses. Initial costsand maintenance for DC motors and controls are higherthan for induction motors. Power available from utilitiesis normally 60 Hz AC. and cannot be used for DC motors.Electric Generating SystemsWhere utility-furnished power is not available, genera-tors may be used to provide electrical power required foroperation of the pumping units. This system allows theoperator the benefits of electrification. When selectingequipment for the generating system, consider which typeof motor will most efficiently use generator power. Theultrahigh-slip motors, which use fewer kilovoltamps(kVA) than conventional horsepower rated motors, arevery popular. Distribution equipment for the generatorsystem would be the same as for utility power if it werefurnished. Generated voltage depends on the size of theelectrified field. The following considerations determinethe most desirable generated voltage.I. Where the system consists of a small number of wells(one to five) with short distances from generator to well-site. the generator voltage may be the same as the motorrated voltage.2. Where the field consists of many (5 to 50) wells, thedistribution voltage should be higher than the motor ratedvoltage to mimmize voltage drop. At each motor, a step-down transformer would be used. This system would beconsidered a moderately sized system with a generatorhaving a distribution of 2.300 or 4,160 V.3. In an exceptionally large field (50+ wells), thegenerator voltage would be stepped up to 7,200 or 13.800V for distribution. At each wellsite, a transformer wouldbe installed to drop the distribution voltage to motor rated

voltage. The generated voltage could be 2,300 or 4.160V. The higher voltage allows smaller conductors to car-ry the loads and lessen line drop voltage within accept-able limits.The procedure used in selecting primary and secondaryequipment should be the same as that used by the utilitycompanies. Protective devices and grounding proceduresoutlined in this chapter apply to either system.Selecting Motor SizeProper operation of the pumping unit depends mainly onproperly sizing the components. Too often motors areoversized because the operator does not want to risk un-derpowering equipment. Choosing a large enough motorwill ensure minimum motor failures and perhaps longevityof the motor. This does not take into consideration theeffects a too-large motor has on the mechanical loadingof the pumping system and the added cost in electricalpower consumption.

For sizing of horsepower rated motors, refer to primemover horsepower calculations shown in the enginesection.Proper use of the ultrahigh-slip motors requires that themotors not be oversized to obtain maximum speed varia-tion and resulting benefits. Ultrahigh-slip motor manufac-turers have established methods of sizing their motors forpumping units. It is important that the sizing method usedbe approved by the motor manufacturer. Motors havingdifferent characteristics require different considerationsfor sizing. Table 10.5 shows a method used by one man-ufacturer.

Voltage FrequencyInduction motors may be operated from utilities or gener-ators where frequency is other than the designed frequen-cy. It is a common practice to operate 60-Hz motors at50 Hz when certain conditions are met. If the V/Hz ratiois maintained as frequency is changed, the motors willoperate satisfactorily but with new characteristics.

F,.=Vif . .(ll)or

V=F,.f,

whereF,. = characteristics ratio, V/Hz,V = electrical potential, V, andf = frequency, Hz.

Example Problem 2. If a 460-V. 60-Hz motor is usedwhere a 50-Hz frequency is available,

460F,.=-60

=7.66


22/37


TABLE 10.5-ULTRAHIGH-SLIP-OPEN DRIP-PROOFSIZING DATA-460 V, 60 Hz

Size 1, 215 T framelye-in. shaft20-amp fuse

Size 2, 286 T frame17/~-in. shaft30-amp fuse

Size 3, 326 T frame2l/&in. shaft60-amp fuse

Size 4, 405 T frame27/8-in. shaftloo-amp fuse

Size 5, 445 T frame33&in. shaft125-amp fuse

Size 6, 445 T frame33/8-in. shaft175-amo fuse

Size 7, 509 T frame4-in. shaft300-amp fuse

ToraueModesIO W

medium lowmediumhigh

(amp) Required6.1 4.6

LoadCapacity5,9506,3006,0009,300

SpeedVariationW)50393224

lowmedium lowmediumhigh

11,500 5615,470 4719,350 3622,000 30lowmedium lowmediumhigh

7 5.39.1 6.911.3 8.612 915 1119 1422 1720 1523 1829 22


39,200 5348,205 4359,840 3671,590 29

lowmedium lowmediumhigh


37 283846 ;i57 4472 5544 3456 4371 5586 6564 4874 5692 70122 92

68,000 4980,000 40100,000 33130,000 29low 118 89 127,000 52medium low 136 103 151,000 43medium 170 129 190,000 35high 207 157 224,000 28

Full-Load MaximumCurrent kVA

Diameter Constant(in.) C1% 0.1321 /4 0.1821% 0.2621 a/4 0.3572 0.4662% 0.5902% 0.7282% 0.8813% 1.2313% 1.639

Speed FactorStrokes/Minute F,

20 0.27719 0.26818 0.25917 0.25016 0.23915 0.22814 0.21713 0.20512 0.19311 0.18010 0.1669 0.1528 0.1377 0.1226 0.1065 0.0904 0.073

SIZING INSTRUCTIONSLoad calculated = C x D x S x F, x 7,where C = a constant, the value of which is different for each

size of plunger as shown above,D = depth to fluid, ft,S = polished rod stroke, in.,

F, = a constant, the value of which is different for eachnumber of strokes per minute (see above), and

y = specific gravity of fluld being lifted.The load capacity must be greater than load calculated.Example: l%in. plunger, 120-in. polished-rod stroke, depth lofluid = 7,000 ft, 12 strokes/min., and specific gravity =0.97.Load calculated = 0.357 x 7,000 x 120 x 0.193 x 0.97 = 56.140.A size 4, medium-torque mode, load capacity = 59,840.Size 5, medium-low-torque mode, load capacity= 59,590.The Sire 5 MLT will have mole max,mm speed var,at,o ava,lable as

56,1404 MT = __ x 37% = 35% maximum SV59,84056.140

5 MLT= ~ x 45% = 42% maxlmm sv59,590


23/37


Fig. 10.17--Ultrahigh-slip motor used as prime mover on abeam-type pumping unit.

and

V=7.66x50

=383.

If the voltage changes to 383 V, the motor will operatesatisfactorily at the new ratings. The change in perform-ance should be obtained from the manufacturer. Approx-imations of changes in characteristics when using 60-Hzrated motors on 50-Hz power are: synchronous speed is/6 of 60-Hz rating, horsepower is /6 of 60-Hz rating,torque is approximately the same, motor amps are thesame as 60-Hz rating, and applied voltage is % of 60-Hzrating. A standard voltage in some countries is 415 at 50

Hz, which is 10% over the design voltage for 50 Hz. Themotor will operate satisfactorily but at different charac-teristics. Contact the motor manufacturer for the changein ratings and performance characteristics.

On either 50- or 60-Hz operation, control componentsso marked have dual rating. If the voltage is changed, asshown in the example for motors, the devices would oper-ate equally well at 50 or 60 Hz. Where control devicesare not marked for dual frequency, contact the manufac-turer to obtain their rating at the new frequency.

Motor Performance Factors

Electric motors have a wide variety of operating charac-teristics. When buying equipment for oilwell pumping

units, factors that contribute to the performance of the

electric motor must be understood. This section discuss-es terms that describe the operating characteristics of theelectric motor (see Fig. 10.17).

Motor Slip. Motor slip applies only to induction motors.Induction motors have a synchronous speed that is a func-tion of applied voltage frequency and the number of polesin the stator winding. Table 10.6 represents a relation be-tween the number of poles and synchronous rev/min for50 and 60 Hz.

The majority of oilwell units use the six-pole inductionmotor. Three-phase voltage, when applied to the statorwinding of an induction motor, causes a rotating mag-netic field at the synchronous speed shown in Table 10.6.

As a result of this voltage in the stator, there will be cur-rent and a magnetic field in the rotor. The interaction in

TABLE 10.6--INDUCTION MOTORPOLES VS. SYNCHRONOUS SPEEDS

FOR 50- AND 60-HZ FREQUENCY

Number Rev/Min Rev/Minof Poles at 60 Hz at 50 Hz

2 3,600 3,0004 1,800 1,500

6 1,200 1,000

8 900 750

10 720 600


24/37

1o-24

TABLE 10.7-FULL-LOAD SLIP FOR NEMA RATEDAND ULTRAHIGH-SLIP MOTORSNEMA RATEDNEMA 0:NEMA C:NEMA D:NEMA D:ULTRAHIGH-SLIP

no more than 3%no more than 5%5 to 8%(special) 8 to 13%

High mode 17Medium mode 21Medium-low mode 27Low mode 32

the stator between the rotor magnetic field and the rotat-ing magnetic field is responsible for the turning actionor torque ofthe electric motor. The difference in percentbetween the speed of the rotating magnetic field and therotor is the slip of the motor.

All motors have a design slip, which is the slip the mo-tor has when running full load. Published slip values formotors are based on full load rating.Table 10.7 illustrates the full-load slip for NEMA ratedand ultrahigh-slip motors (see Fig. 10.22).Slip is calculated by the following equation.

5- flF,,= ____________100, .(12)5where

Fs =v, =vfj =

motor slip factor, X,synchronous speed, revimin, andfull load speed, rev/min.

Example Problem 3. If a six-pole, 1,200-revimin syn-chronous induction motor has a full-load speed of 850revimin, the motor slip is 29.16%.1.200-850F., = Xl001,200

=29.16%.The design slip of the oilwell pumping motor is a veryimportant feature. The speed of the induction motor isreduced as more torque is required. In the case of thepumping motor, when large amounts of torque are re-

quired there will be a slowing down of the motors rotor.As the rotor slows down, less motor torque will be re-quired to drive the pumping unit.There are two different torque reductions to be consid-ered. (1) Torque resulting from polished-rod loading isreduced as a result of lower acceleration at peak torquemoments. 5 (2) Torque reduction is achieved because ofinertial effects of the changing speed of the pumpingunit. 6Fig. 10.18 shows a comparison of speed/torque curvesfor motors of various slip ratings. All motors on this charthave essentially equalull-load capacity on a beam-type

PETROLEUM ENGINEERING HANDBOOK

Fig. 10.18-Comparison of speed/torque curves for motors ofvarious slip ratings.

pumping system as a result of the derating factors neces-sary for cyclic load operation.The broken-line curve in Fig. 10.18 represents the max-imum torque and minimum speed under which each ofthese motors will operate on the same pumping load. Onewill see that the changing speed of the higher-slip motorswill have beneficial effects on the pumping equipment.

Motor Speed Variation. Motor speed variation dependson a maximum and minimum revimin of the motor. Mo-tor slip and motor speed variation are two different butrelated factors. Each is represented by a value in percentand all are calculated by very similar equations.Speed variation:VF,, max minx100, . . . . . .(13)V ox

whereF,, = speed variation factor, %,V ?lO.Xmaximum motor speed, rev/min, andVn~in minimum motor speed, revimin.

Example Problem 4. An oilwell pumping motor havinga maximum speed of 1,180 rev/min and a minimum speedof 690 rev/min will have a speed variation of 41.52% :

F,s,.1,180-690 x 1001,180=41.52%.

Speed variation on the cyclic load of the sucker rodpumping is considered beneficial. As torque demand ofthe system increases, motor speed decreases, therebyreducing acceleration. The force required to accomplish


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PUMPING UNITS & PRIME MOVERS FOR PUMPING UNITS 1O-25

work equals mass times acceleration; hence. a reductionin acceleration causes a reduction in force (F=Mxu).Another benefit of increased speed variation is increasedplunger overtravel, which occurs frequently. The instan-taneous speed of the pumping unit is significantly greaterat the top and bottom of the stroke where there is littleor no torque on the pumping unit and motor. At thesepoints, the induction motor will speed up toward its syn-chronous (no-load) speed, frequently increasing plungerovertravel.Motor Power Factor. Motor power factor, being a num-ber between zero and one, is a measure of the phase rela-tion between the volts applied to a motor and the ampsof the motor. In an induction motor, the motor currentwill lag the voltage by a certain amount of electricaldegrees. The cosine of this angle is the power factor. Incases where the current and voltage are in phase, the an-gle is zero; consequently the power factor is one. Theother extreme would be where the curren

10 unidades de bombeo, instalación

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