session #1 virtual instructor led copyright
TRANSCRIPT
Session #1 Virtual Instructor Led
Reciprocating Rod PumpFundamentals
Module Contents
Reciprocating Rod Pump Components and Operational Principles
Pump Size / Pump Design
Rod Pump Surface Unit
Rod Pump Rod String
Rod Pump Downhole Pump
Dynamometer Analysis
Failures and Maintenance
Controllers
Summary
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Module Contents
Reciprocating Rod Pump Components and Operational Principles
Pump Size / Pump Design
Rod Pump Surface Unit
Rod Pump Rod String
Rod Pump Downhole Pump
Dynamometer Analysis
Failures and Maintenance
Controllers
Summary
Module Contents
Reciprocating Rod Pump Components and Operational Principles
Pump Size / Pump Design
Rod Pump Surface Unit
Rod Pump Rod String
Rod Pump Downhole Pump
Dynamometer Analysis
Failures and Maintenance
Controllers
Summary
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Rod Pump System Components
Rod Pumps are also Called Beam Pumps*
1. Surface Equipment2. Sucker Rods3. Downhole Pump
Analytical Techniques for:• Prime Mover System• Rods• Pump at Reservoir Depth
Reservoir inflow from producing zone
Group 2 Well Characteristics
Wells less than 4000 ft (1220 m) deep
AND
Have a pump diameter greater than 2 inches (5.08 cm)
Group 1 Well Characteristics
Wells greater than 4000 ft (1220 m) deep and any pump diameter,
OR
Wells less than 4000 ft and a pump diameter less than equal to 2 inches (5.08 cm)
Group 1 and Group 2 Rod Pump Wells
Each of the above groups has unique features
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Group 2 Well Characteristics
Fluid Inertiaeffects in large volume shallow
wells (lesser rod stretch to absorb load “shock”) is the most important diagnostic
consideration.
As a result, larger forces are required to accelerate fluid
loads beginning the upstroke which complicates rod pump
well diagnosis.
Group 1 Well Characteristics
Road Loading / Rod Stretcheffects in deeper wells is the
most important diagnostic consideration.
For shallower wells, minimal fluid inertia effects and minimal
rod stretch effects aids rod pump well diagnosis.
Group 1 and Group 2 Rod Pump Wells – Main Differences
Group 1 Well Features (> 4000 ft or < 4000 ft & Dpump < 2 in)
A majority of industry rod pumps world wide
Rod loading is the main restriction to increased rate due to greater well depth (must reduce pump size)
Surface polished rod dynamometer load shape analysis is a function of many factors:
• Pump depth
• Rod string material
• Rod string design
• Pump speed
• Pump unit type
• Pump fillage
• Prime mover type, etc.
Downhole calculated dynamometer load shape is a function of pump condition only
Rods act as “shock absorber” to limit fluid inertia forces; rod elongation / stretch is expected but it must remain within the elastic limit of the rods
Surface dynamometer shape is difficult to analyze
Calculated downhole dynamometer shape is necessary to analyze pump performance
(1220 m) (5 cm)
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Group 2 Well Features (< 4000 ft and Dpump > 2 in)
Much smaller percentage of rod pumped wells Larger pump used for greater productivity wells Large fluid inertia forces compared to Group 1 wells Large pump sizes, large rates, fast speeds Both surface and downhole dynamometer shape a function of:
• Pump condition • Pump depth• Pump speed• Pump size, etc.
Fluid inertia forces significant in high rate wells• Can double plunger load
Shallower depths (short rod string) so limited “shock absorber” effect of the rods
Less rod stretch Surface dynamometer shape difficult to analyze Calculated downhole dynamometer “predictive” shape is necessary
to analyze pump performance
(1220 m) (5 cm)
Analyzing Group 1 and Group 2 Rod Pump Wells
Dynamometer data and software programs are the primary diagnostic tools for modern rod pump wells
Surface diagnostic data measuring the load on the rod string as a function of position throughout the upstroke / downstroke rod pump cycle is used to predict downhole loads on the pump
Modern diagnostic analysis computer programs provide quantitative analysis to distinguish between mechanical pump problems (e.g., leaking or worn pump) and fluid issues (gas, low productivity zones, etc.)
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Analyzing Group 1 and Group 2 Rod Pump Wells
Question / Discussion:
Is the function of the dynamometer clear?
Analyzing Group 1 and Group 2 Rod Pump Wells
Question / Discussion:
Is the function of the dynamometer clear?
Rod pump animations follow...
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Module Contents
Reciprocating Rod Pump Components and Operational Principles
Pump Size / Pump Design
Rod Pump Surface Unit
Rod Pump Rod String
Rod Pump Downhole Pump
Dynamometer Analysis
Failures and Maintenance
Controllers
Summary
PBHP
Fluid Level
Gas
Pt
Pc
Rod Pump Design Starts with Inflow (Rate) Determination
Engineers use acoustic surveys to determine bottomhole pressures.
A remotely fired gas gun with a precision pressure transducer to measure casing pressure change as an acoustic signal measures the distance h' to the fluid level.
May be carried out for both flowing and shut-in rod pump wells.
from: Echometer
Pump
Oil + Gas
Liquid
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Knowing h, then:
h x fluid gradient = PBHP
PBHP - for both flowing and shut-in conditions
Knowing the distance to the liquid level for both flowing and shut in conditions allows engineers to determine the height of the fluid level above the pump h.
PBHP
Gas
Pt
Pc
Oil + Gas
Rod Pump Design Starts with Inflow (Rate) Determination
H
Pump
H - Distance to the producing zone
h' – From acoustic surveys
h = H – h'
h Fluid Level
Liquid
Knowing h, then:
h x fluid gradient = PBHP
PBHP - for both flowing and shut-in conditions
PBHP
Gas
Pt
Pc
Oil + Gas
Rod Pump Design Starts with Inflow (Rate) Determination
H
Pump
H - Distance to the producing zone
h' – From acoustic surveys
h = H – h'
h Fluid Level
Liquid
Question / Discussion:
Is It clear how well fluid inflow will determine pump capacity sizing?
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Module Contents
Reciprocating Rod Pump Components and Operational Principles
Pump Size / Pump Design
Rod Pump Surface Unit
Rod Pump Rod String
Rod Pump Downhole Pump
Dynamometer Analysis
Failures and Maintenance
Controllers
Summary
Rod Pumps are also Called Beam Pumps*
Analytical Techniques for:• Prime Mover System• Rods• Pump at Reservoir
Depth
Reservoir inflow from producing zone
The three major components of a rod pump system:
Sucker Rods
Downhole Pump
Surface Equipment
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Rod Pump Surface Unit Types
Rod Pump Surface Unit Types
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Conventional Rod Pump Units
Question / Discussion:
If a conventional unit can be operated in both a clockwise and counterclockwise direction, and if the gear box routinely suffers wear on the gears, assume that well #123 has been operating in the clockwise direction for several years.
What might be the reason for reversing the unit to operate in the counterclockwise direction?
Wellhead
Long stroke polished rod
Hydraulic cylinder actuator
RotoflexTM Unit
Long Stroke Polished Rod Pump
The Rotaflex has two sprockets connected by a large chain
On the front of the unit is a large, reinforced steel belt
• This connects to the polished rod in the well
Can produce significant rates [2,000–3,000 bbls/day (318 – 477 m3/d)] from a depth of about 3,000 ft. (914 m)
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Wellhead
Long stroke polished rod
Hydraulic cylinder actuator
RotoflexTM Unit
Long Stroke Polished Rod Pump
Question / Discussion:
What would the long stroke length of a Rotolex unit provide?
Conventional Unit• Usually lowest cost unit
• Can be set up to rotate clockwise or counter clockwise
• Works well with fiberglass rods
• Usually lower maintenance costs
• Less counterweight required compared to others
Mark II Unit• Usually more efficient than others
• Usually has lower torque requirements
• Often costs less
Air Balanced Unit• Compact, yet largest available size
of all units
• Least weight of all units
• Can be set up to rotate clockwise or counter clockwise
Most Common Units – Some Advantages and Disadvantages
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Conventional Unit• Gear reducer requirements often
large
• Less efficient than other units
Mark II Unit• Can only rotate counter clockwise
• Often not a fast as other units
• Cannot use fiberglass rods (due to potential rod compression possibilities)
Air Balanced Unit• More complex than others
(compressor, overall maintenance)
• Air cylinder water condensate build up possibilities, other)
Disad
vantag
esD
isadvan
tages
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Rotoflex Unit• Can achieve high production rates
due to long stroke
• System efficiency very high
• Much smaller prime mover required than other units
• Much lower gearbox loading
• Minimizes load reversal cycles due to long stroke length and low strokes per minute
• Easy to work on well by sliding unit away from well on its tracks
Hydraulic Units• Used for very deep wells
• Often has built in dynamometer
Most Common Units – Some Advantages and Disadvantages
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Rotoflex Unit• Costly
• Stroke lengths up to 300 in (7.6 m) require large, long pumps
Hydraulic Unit• Higher maintenance costs
• Complex hydraulics, therefore breakdown frequency
Disad
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BOTTOM OF DOWNSTROKE
TOP OF UPSTROKE
Rod Pump Operating
At the top of the upstroke, the unit has lifted well fluids one stroke length and the rods to the surface.
At the bottom of the downstroke, the unit has lowered the rods back into the well one stroke length.
One half rod pump cycle illustrated
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On the downstroke, the gearbox lifts the counterweight with the help of the rod load (to get the counterweight ready to help again on the upstroke).
On the upstroke, the counterweight releases energy to the gearbox and helps the gearbox by falling.
Rod Pump Operating
TOP OF UPSTROKE
BOTTOM OF DOWNSTROKE
Mark II Unit Crank
Conventional Unit Crank
Mark II Unit Rod Pump Offset Crank Angle
The Mark II unit offset (195o vs 180o) crank geometry effectively reduces rod acceleration at the beginning of the upstroke when load is greatest, thereby effecting a reduction in the polished rod load.
The maximum upstroke torque required (when lifting rods and fluid load) is reduced and the maximum downstroke torque (lowering rod load in fluid back into the well) is increased.
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C-228D-246-86
See API Specification 11E
Rod Pump Surface Unit API Designation
A – Air Balance
B – Beam Balance
C – Conventional
M – Mark II
LP – Low Profile
RM – Reverse Mark
Polished Rod Rating in
100s of LBFs (pounds force)
Maximum Stroke
Length in Inches
PK Torque Rating in
Thousands of IN-LBS
A “letter” indicating pump type is often placed in
front of the surface unit naming designation
168”(4.3 m)
Example: Rod Pump Surface Unit Identification
C-912D-365-168 Conventional UnitC-912D-365-168 Conventional Unit
Designate:• Well on right and the surface unit on the left• Counter Clock Wise (CCW) or Clock Wise (CW) rotation• Cranks fall towards Sampson Post is called positive rotation• Cranks fall away from Sampson Post called negative rotation
912,000 in-lbs.(10,507 m-kg)
36,500 lbs.(16,556 kg)
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Example: Rod Pump Surface Unit Identification
X-XXX-XXX-XXX UnitX-XXX-XXX-XXX Unit
Designate:• Well on right and the surface unit on the left• Counter Clock Wise (CCW) or Clock Wise (CW) rotation• Cranks fall towards Sampson Post is called positive rotation• Cranks fall away from Sampson Post called negative rotation
Question / Discussion:
Could you identify a rod pump based upon its API 11E spec ?
Sucker Rod Pump Design and Analysis
Operating loads are influences by several factors:• Deviated or crooked holes• Fluid viscosity• Specific gravity of the produced fluids• Pumping fluid levels
Diagnosis of actuator, pump, and rod performance is performed by a strain gauge tool called a dynamometer.
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Rod Pump Data Gathering and Design
Loads on the rod string as a function of the position of the rod string reciprocation and position of the rod are continuously measured for analysis.
A strain gauge on the polished rod measures these loads on the pump upstroke and downstroke.
The pictured tool which gathers this data is called a “dynamometer.”
Load vs. Position of Walking Beam and Rods
Rod Pump Idealized Dynamometer Card Analysis
Trav. Valve Closing Recoil
Rods & Fluid being lifted
Max LoadWalking Beam Decelerating
Polish Rod Up
Standing Valve Taking Over Load
Rods & Plunger Falling Through Fluid
Min Load
Walking Beam Decelerating
Load Increase
Polish Rod Down
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Sheaves and Gear Box
Typically beam pump motors are running 1200 or 1800 RPM (Revolutions Per Minute)
Need a method to reduce speed to get down to approximately 10 SPM (Strokes Per Minute)
Use ratio of sheaves and gearbox
Gear Reducer Box Illustration
Case Head Removed For Lubrication Maintenance
Reduces RPM by a factor of 30Increases torque as a function of 30
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1170x 12" / 47" = 298.7 RPM(119 cm / 31 cm)
RPM x DMS / DGB = ____ RPMRPM x DMS / DGB = ____ RPM
Sheaves / Gear Box Design and Strokes / Minute
How Sheaves and Gearbox Convert Motor RPM to Rods SPM
Gear Box Sheave47" diameter (119 cm)
298.7 RPM30.12 GB Ratio
= 9.92 SPM
Motor RPM1170 RPM
Motor Sheave12" diameter (31 cm)
Gear Box Ratio30.12
STEP (1)
STEP (2)
STEP (3)
Rod Pump Strokes Per Minute Exercise
The rod pump motor works with the gear box to convert the rotational rpm’s of the motor into the reciprocating motion required by the rod pump at the downhole pump.
• A rod pump has a motor sheave of 10" (25.4 cm) O.D.
• The gear-box sheave is 34" (86.4 cm) O.D.
• The gear box is a standard 30:1 ratio unit.
• The motor is a gas engine turning at 500 rpm average speed.
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Rod Pump Strokes Per Minute Exercise
10" / 34" =(25.4 cm / 86.4 cm) 10" / 34" =(25.4 cm / 86.4 cm)
RPM x 0.294 =500 x 0.294 =
147.1 RPM
RPM x 0.294 =500 x 0.294 =
147.1 RPM
147.1 RPB / 30 = 4.9 SPM
147.1 RPB / 30 = 4.9 SPM
0.294
The rod pump motor works with the gear box to convert the rotational rpm’s of the motor into the reciprocating motion required by the rod pump at the downhole pump.
• A rod pump has a motor sheave of 10" (25.4 cm) O.D.
• The gear-box sheave is 34" (86.4 cm) O.D.
• The gear box is a standard 30:1 ratio unit.
• The motor is a gas engine turning at 500 rpm average speed.
SLIP = (No-Load RPM – RPM Under Load) / (No-Load RPM)
Oil Field Rod Pump Motor Types
Type~ Efficiency
Full LoadSlip
Starting Torque
Application
NEMA B ~92+ 2 – 3% 100 – 175% Transfer Pumps
NEMA C ~90+ 4% 200 – 250%Positive
DisplacementInjection Pumps
NEMA D ~88% 8 – 13% 275%+ Beam Pumps
ULTRA HIGH SLIP’’
Lower 15 – 30% 275%+Special
Application Beam Pumps
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The motor provides external energy input to work with the gear box, crank arm, and counterweight to lift rods and fluids out of the well on the upstroke and lower rods back into the well on the downstroke… for each cycle.
Wrist Pin
Pitman Arms
Rod Pump Crankshaft / Counterweight
Counterweight
Gear Box
Crank Arm
Oil Field Rod Pump Motor Types
Balanced vs. Unbalanced Motor • Below are the torque (in-lbs or m-kg) or kW (power) signatures of an
electrically or mechanically unbalanced or balanced pumping unit
Balanced if the peak upstroke torque is equal to the peak downstroke torque
Balanced if the peak upstroke torque is equal to the peak downstroke torque
One Pump Cycle One Pump Cycle One Pump Cycle
Torq
ue/
Po
wer
Up DownUp DownUp Down
Rod Heavy Weight Heavy Corr. CB Moment
Mechanical/Electrical Unbalanced Balanced
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Module Contents
Reciprocating Rod Pump Components and Operational Principles
Pump Size / Pump Design
Rod Pump Surface Unit
Rod Pump Rod String
Rod Pump Downhole Pump
Dynamometer Analysis
Failures and Maintenance
Controllers
Summary
Major Rod Pump System Components
Surface pumping unit and prime mover
Rods run from surface to downhole pump• Rods are also referred to as “sucker rods”
Downhole pump
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The Rod String
The Rod String
Question / Discussion:
Have you been on site when rod pump rods were being pulled... or if tubing also was worn and also required replacement?
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C - 90,000 psi min. tensile (620,528 kPa)
K - 90,000 psi min. tensile(620,528 kPa)
D - 115,000 psi min. tensile(792,897 kPa)
High strength rods 140,000 psi in. tensile (965,266 kPa)
API Grade Rods
6 / 8
API 86 Rod String
Rods equally stressed
Rods designed with equal fatigue failure tendency
8 / 8Tapered String
The Rod String (Rod Pump Sucker Rods)
7 / 8
46.2%1.5" Pump –(3.8 cm)
26.8%, 27%,
Equal Stress
Rod Pump Rods
Grade C Sucker Rod Designed to be used with low and medium loads in non-corrosive or effectively
inhibited wells. Manufactured in 1530 Mod. steel.
D Carbon Sucker Rod Grade Designed for moderate loads in non-corrosive or effectively inhibited wells.
Manufactured in 1530 Mod. micro-alloy steel.
Grade K Sucker Rod Designed for low and medium loads in corrosive wells, which are recommended
to inhibit. Manufactured with AISI 4621 Mod. steel.
KD Special Grade Sucker Rod (Critical Service) Designed for moderate to heavy loads in corrosive wells, however an effective
inhibition program is recommended to minimize damaging effects. Manufactured in AISI 4320 Mod. steel.
D Alloy Grade Sucker Rod Designed for moderate to heavy loads in non-corrosive or effectively inhibited
wells. Manufactured with AISI 4142 Mod. steel.
Different grades and materials are offered, based on the load type and corrosive environment of the wells where they will be used.
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Stress Strain Curve
Rod Pump Rod Design
Rod Stress / Strain Curve • Sucker Rods should operate
in the linear portion of the stress vs. stain curve and never undergo permanent deformation.
• Rod Fatigue is, however, the main design consideration for continuous operation.
• Per API standard, when the difference between (range of) the maximum and minimum actual stress on rod string is great, the allowable rod stress is decreased. See the Modified Goodman Rod Design
Method Illustrated on the Following Slides
Tensile Strength
Yield Stress
Modulus of Elasticity
Rupture Stress
Permanent Deformation
Str
ess
(P
SI)
Strain (IN/IN)
Construction of Modified Goodman Diagram
Rod Pump Rod Design
SA = (T/4+ 0.5625(Smin)) (SF)
SA = SA – Smin
SA = Max allow stress psi
SA = Allow stress range
0.5625 = Slope of SA curve
SF = Service Factor
T = Min tensile strength
T
T
T/1.75
T/4SA
Sm
T
T
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Rod Pump Rod Design
Service Factors (SF) de-rate the allowable rod stress
Service Factor Guidelines• Use C grade rods to SF of 1.35
before using D grade rods• Use D grade rods to SF of 1.35
before going to hi strength rods• Inhibit well; do not use case
hardened rods• From failure control in rod pump
wells ‐ SWPSC
Service API-C (default)
API-D (default)
Non Corrosive
1.0 1.0
Salt Water 0.65 0.9
H2S 0.5 0.7
Note: At present, API is in the process of: (a) studies to justify increasing rod stress allowables (as most rod failures are related to other than stress related causes; i.e., failure due to corrosion, couplings, etc. failures), and (b) studies to justify changing the T/1.75 Modified Goodman variable to approximately T/1.28).T/1.75 T/1.28
Rod Pump Rod Design
Note: At present, API is in the process of: (a) studies to justify increasing rod stress allowables (as most rod failures are related to other than stress related causes; i.e., failure due to corrosion, couplings, etc. failures), and (b) studies to justify changing the T/1.75 Modified Goodman variable to approximately T/1.28).T/1.75 T/1.28
Question / Discussion:
What would be the effect of API changing the Modified Goodman variable as highlighted below?
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Rods Design Example: Get Surface Rod Loads from Dyno Card
Rod Area is .601 in2 (3.88 cm2)
Lo
ad,
lb.
Polished Rod Position
Pk Load = 17,900 lbs. (8,119 kg)
Stress = 29,768 psi (205 MPa)
Min Load = 9,100 lbs. (4,128 kg)
Stress = 15,141 psi (104 Mpa)
Dynamometer CardRod Diameter is .875 in
(2.22 cm)
(8,165)
(9,072)
(7,257)
(6,350)
(5,443)
(4,536)
(3,629)
(2,722)
(1,814)
(907)
(kg
)
Smin = 15,141 psi(104 Mpa)
Sucker Rod Design – Modified Goodman Diagram
T/1.75
T/4
0
115,000 psi (7,929 Mpa)
Pk Stress = 29,768 psi(205 MPa)
SA = (T/4+.5625(Smin))(SF)
= 37,267 psi(257 Mpa)
37,267 – 15,141
29,768 – 15,141
= 66%
Rod Loading
205 -104257 -104
S.F. = 1.0
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Smin = 15,141 psi(104 Mpa)
= 29,814 psi
Sucker Rod Design – Modified Goodman Diagram
SA = (T/4+.5625(Smin)) T/1.75
Pk Stress = 29,768 psi
0
S.F. =
SF = 0.8
T/4
(.8)
15,141 psi
0.8
37,267 – 15,141
29,768 – 15,141
= 66%
205 -104257 -10429,814
= 99.7%
115,000 psi (7,929 Mpa)
(205 MPa)
Rod Loading
At 99.7%, rods are at limit.
205 -104206 -104
(206 Mpa)
Sucker Rods: Co-Rod
From: Weatherford
Ad
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Disad
vantag
es
• cost possibly up to five times higher than comparable conventional rod
• service rig and welding unit must be available in the area for servicing
• connection to polished rod and pull rod critical
• no couplings• minimal pin and coupling failures• minimal rod and tubing wear • minimal torque and power
requirement• enhanced pump efficiency • simple, quick, installation and
field service
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Sucker Rods: Co-Rod
From: Weatherford
Ad
van
tag
esQuestion / Discussion:
Do you know if your organization has evaluated the use of COROD strings?
Module Contents
Reciprocating Rod Pump Components and Operational Principles
Pump Size / Pump Design
Rod Pump Surface Unit
Rod Pump Rod String
Rod Pump Downhole Pump
Dynamometer Analysis
Failures and Maintenance
Controllers
Summary
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Exercise: Rod Pump Design Variables
Assignments:
1. Review the videos and animations for rod pump wells.
2. Work the rod design exercises using the Modified Goodman method.
End of Virtual Session #1
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