Post on 14-Apr-2018
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Sucker Rod Pump
Beam PumpDesign
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Beam Pump Surface Components
Prime Mover
Gear reducer
Pumping unit Polished rod
Transformer
Control BoxElectricMotor
Polished RodStuffing Box
Tubing
Sucker Rods
Pump
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Surface Components
Prime Mover Electric or internal combustion engine
Provides driving force as a rotary movement of themotor shaft
Gear reducer Reduces the high rotational speed of the motor to
the required pump speed Increases the torque (the ability of a force to
cause a body to rotate about a particular axis.)
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Surface Components
Pumping unit Transforms the rotational movement of the
gearbox shaft into a reciprocatingmovement at the tip of the walking beam.
Polished Rod
connects the walking beam with the suckerrod string and provides sealing surface atthe wellhead
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Downhole Components
Rod String Responsible for transmitting the reciprocating
movement of the polished rod to the downholepump.
Pump contains the traveling valve and the standing valve
admit fluids from the annulus to the pump barrel transfer momentum to the fluids to be produced
through the tubing
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Schematic of PumpSucker Rods
Plunger
Traveling Valve
Standing Valve
Upstroke Downstroke
Working Barrel
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Upstroke
Traveling valve closes due to thepressure of the fluids inside the tubing
The rising rod string pushes the plungerand fluids above it upwards.
Standing valve opens and casing fluids
enter.
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Downstroke
Increased pressure forces standingvalve shut.
Traveling valve opens allowing fluidabove the plunger.
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Design Methods
Simplified Method Developed for Shallow wells
Simple (reliable) equations for operationalparameters
API RP 11L Valid at increased depth where simplified
method fails Successfully used in the oil industry for
more than 20 years
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Beam Pump System Performance
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Reference
Gabor Takacs: Modern Sucker-Rod
Pumping- PenWell Books
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Schematic of a Beam Pump Unit
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Beam Pump Configurations
Conventional
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Beam Pump Configurations
Mark II
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Beam Pump Configurations
Air Balanced
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Beam Pump Configurations
Torque Master
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Pumping Unit Designations
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Design Methods
Mathematical solution for the movementof the sucker rod string
Most accurate method Requires the use of a numerical simulator
We will confine ourselves to API RP 11L www.api.org
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Design and Analysis
Prediction of the operating conditions isof vital importance for the design of new
installations and the analysis of existingones Polished rod loads
Downhole stroke length Torques
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Polished Rod Load
The weight of the rod string, Wr
The buoyant force
Mechanical and fluid frictionUsually neglected
Dynamics force on the string
The load of the fluid being produced
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Polished Rod Load
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Design Prequisites
Polished rod loads
Downhole stroke length
Torques
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Peak Polished Rod Load
(PPRL) Maximum
(downward) force on
beam Occurs when the
rod is moving upand lifting liquid
F
rW
TD
DD
DLF ,
ULF ,
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Loads neglecting acceleration
Simplified Model Weight of sucker rod string in air
Pressure force of fluid above plunger
Ap plunger area, ft2
Arod
area of thedeepest sucker rod, ft2
rW
c
rodpTL
D,Lg
AAgDF
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Upward force on plunger due topressure from casing fluid:
DD depth to dynamic fluid level, ft Measured using an Echometer
c
DTpL
U,Lg
DDgAF
Loads neglecting acceleration
Simplified Model
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Dynamic Load SimplifiedMethod
Mass of the rod times its acceleration
Concentrated point load
Acceleration factor of Mills (dimensionless)
S Polished rod stroke length, inches N pumping speed in SPM (strokes per minute)
70500
2NS
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Peak Polished Rod LoadSimplified Method For Conventional Units
In most texts, the last term is neglectedto compensate for unknown friction
losses Fluid Load:
c
TrodL
c
DpL
rg
DgA
g
DgAWPPRL
1
c
DpL
og
DgAF
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Minimum Polished Rod LoadMPRL
F
BrW ,
TD
DD
Occurs when rod ison the downstroke
Fluid flowing throughtraveling valve
Rod buoyed up bysurrounding fluid
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Force Balance - Downstroke
MPRL = Buoyant rod weight DynamicForces
Buoyant rod weight :
Dynamic Forces (Simplified method) :
rod
LrodrW
r
W
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Minimum Polished Rod Load
Simplified Method
SGW
WMPRL
r
rod
Lr
128.01
1
SGfluid specific gravity
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Example
Find the minimum and maximumpolished rod loads for a 5000 ft rod
string composed of 42.3% of , 40.4%of 5/8 and 17.3% of rods.Plunger
size is 1.5 and the fluid level is at 4800
ft. Pump speed is 10 spm, stroke lengthis 120 and the specific gravity of thefluid is 0.95.
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Solution
Determine the total rod weight,Wr From table,
Acceleration Factor
lbf6375
726.0173.0135.1404.0634.1423.05000
rW
17.0
70500
101202
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Table for rod properties
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Solution
Fluid load on Plunger
Peak Polished rod load
lbf3487
480024
5.1
4.6295.0
2
c
DpL
og
DgA
F
lbf10964
1
or FWPPRL
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Solution
Minimum Polished Rod Load
lbf4513
17.095.0128.016375128.01
SGWMPRL r
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Peak Torque Sizing Motor Crankshaft torque
Rod string requirements
Counterweight requirements
Assumptions Pumping unit balanced
MPRL and PPRL occur when the torque
factor maximum
in-lbf4
)(S
MPRLPPRLPT
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Plunger Stroke Length
Surface and downhole stroke lengthsdiffer considerably
Sucker rod string is elastic Tubing string is also elastic
Definition: Plunger stroke is the travel of
the pump plunger relative to thestanding valve. (Units: inches)
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Plunger Stroke Length Fluid load alternately
acts on the travelingvalve and on the
standing valve Upstroke traveling
valve
Downstroke standing
valve Additional stretch due
to acceleration
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Plunger Stroke Length
Low pumping speeds (negligibledynamic loads)
Unanchored tubing
Anchored tubing (no tubing stretch)
erand etare rod and tubing stretch in inches
trp eeSS
rp eSS
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Rod Stretch
Erelastic constant,(see Table)
L
length of the rodsection, ft
Fo- fluid load onplunger, lbf
orr LFEe
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Fiberglass Rods
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Tubing Stretch
Etelastic constant, (see Table) Ltlength of the tubing section, ft Fo- fluid load on plunger, lbf
ottt FLEe
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Dynamic Stretch (inch)
Due to inertial forces Maximal at the endpoints of the stroke
Cause an attritional elongation in therod string
Plunger Overtravel
Simplified model concentrated load
261036.1 Leo
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Total Stretch
Unanchored tubing
Anchored tubing
otrp eeeSS
orp eeSS
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Tapered rod/tubing
If the rod and/or tubing strings aretapered, we must sum the stretches on
each section
i
i
ioLEFe
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Example
Calculate the plunger stroke length for a5000 ft rod string composed of 42.3% of
, 40.4% of 5/8 and 17.3% of rods.Use the results from the previousexample for loads.
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Solution
Elongation of the rod Sum elongations over each section
inch4.21
173.01099.1404.01026.1423.010833.0
50003487
666
i
ririor LeFe
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Solution
Elongation of the tubing
Plunger overtravel
inch9.3
3487500010211.0 6
te
inch8.5
17.050001036.1 26
oe
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Solution
Plunger stroke
inch5.100
8.59.34.21120
pS
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Pump Displacement
From downhole stroke length, the dailyvolumetric pump displacement is given
by
PD pump displacement in RB/d
d plunger diameter (inch)
21166.0 dNSPD p
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Example
Calculate the pump displacement forthe previous example.
Solution
RB/d264
5.1105.1001166.0
1166.0
2
2
dNSPD p
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Question:Does a Sucker rod pump
produce fluid only on theupstroke?
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Rod string design
Should we use a single-diameter rod? Rods near the plunger carry the smallest
loads (the fluid weight) Rods near the surface carry the fluid
weight as well as the weight of all rodsbelow
Use a tapered string Rod diameter decreases with depth
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Ideal Tapered String
Tapered to have nostress hot spots Stress = load/area Want uniform stress
Rod strings come indiscrete diameters Uniform stress
unattainable
Equalize stressesin rod strings.
Ideal Tapered String
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Rod Size
At a given position, the minimumapplicable rod diameter must support
the maximum tensile stress at thatposition. Tensile stresses are cyclic.
Maximum on upstroke Minimum on downstroke
Must account for metal fatigue
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Tensile Strength For small loads, a metal rod will stretch an
amount proportional to an applied load, andreturn to its original dimensions when theload is removed. Hookes Law Applies until the elastic limit
Beyond the elastic limit, additional load willpull the rod apart.
Tensile Strength - The quantity of stressneeded to overcome a materials resistanceto structural failure.
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Metal Fatigue
Weakened condition induced inmetal parts of machines, vehicles,
or structures by repeated stressesor loadings, ultimately resulting infracture under a stress muchweaker
than that necessary tocause fracture in a singleapplication.
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Fatigue Endurance Limit
The maximum stress level at which theequipment will operate under cyclic
loading conditions for 10 millioncomplete cycles.
Affected by operating conditions Salt water
Hydrogen Sulfide
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Goodman Diagram
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Goodman Diagram
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Rod Stresses
Maximum Stress, psi
Minimum Stress, psi
2max
4rd
PPRLS
2min4
rd
MPRL
S
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Maximum Allowable Stress
To prevent rod breakage from metalfatigue, we need maximum allowable
stress
SF service factor T tensile strength of the rod
SFST
Sa
min5625.04
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Service Factors
Maximum tensile strength (T) for API grades C and D
are 90000 and 115000 psi respectively.
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Tapered String Design
Attempt to equalize stress distributionsin the rods
Several approaches available Simplified Method
Wests method
Neelys method/API Method
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Simplified Method
Goal Keep maximum rod stresses at avalue based on a percentage of the
tensile strength of the rod material. Set the maximum stress at the top of
each taper section equal.
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Example 7/8 6/8 - 5/8
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Simplified Method
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Simplified Method
Gives reasonable rod life for shallowwells.
Using this method, practically all rodbreaks are due to fatigue Still applied to high-strength E-rods
Maximum allowed stress is constantregardless of stress range (50,000 psi)
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Example
Design an API 65taper rod string usingE rods for a pump setting depth of 5000
ft and a pump size of 2.5 inch. Assumewe are pumping water.
Note: a API 65 refers to two strings, the
top with size 6/8 inch and the bottomwith 5/8 inch.API 64 will consist of 6/8, 5/8, 4/8 rods.
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Solution
From formulas
Length of 5/8 section: 1621 ft
Length of section: 3379 ft
%42.32
5.208.767.762
1
R
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Solution
Checking whether the rod design willmeet maximum allowable stress
requirements Weight of rod string:
lbf5521634.13379
lbf1840135.11621
86
85
W
W
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Solution
Fluid Load
Maximum stresses (neglectingacceleration)
lbf10625500024
5.2
4.62
2
oF
psi40690442.0/5521184010625
psi40600307.0/184010625
8/6max,
8/5max,
S
S
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Solution
Minimum stresses
Since E Rods are rated at a maximum
allowable stress of 50000 psi regardlessof stress range, the design is safe.
psi16650442.0/55211840
psi5990307.0/1840
8/6min,
8/5min,
S
S