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Chapter 7A.
Matrix StimulationPetroAcademy Module
Artificial Lift Introduction
Reciprocating Rod Pump Fundamentals
Artificial lift rod pump wellcompletions comprise thelargest number of wellmechanical completiondesigns in the industry
A broad web search of rodpump data leads to theconclusion that the world’spopulation of producing wellsis around 1,000,000• Of these wells, between 90%
and 94% of them are onartificial lift
• About 85% to 90% of theseare estimated to be rod pumptype completions
Why Take This Module?
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Artificial lift rod pump wellcompletions comprise thelargest number of wellmechanical completiondesigns in the industry
A broad web search of rodpump data leads to theconclusion that the world’spopulation of producing wellsis around 1,000,000• Of these wells, between 90%
and 94% of them are onartificial lift
• About 85% to 90% of theseare estimated to be rod pumptype completions
Why Take This Module?
Conventional Unit
Mark II Unit
Artificial lift rod pump wellcompletions comprise thelargest number of wellmechanical completiondesigns in the industry
A broad web search of rodpump data leads to theconclusion that the world’spopulation of producing wellsis around 1,000,000• Of these wells, between 90%
and 94% of them are onartificial lift
• About 85% to 90% of theseare estimated to be rod pumptype completions
Why Take This Module?
Air Balance Unit
Hydraulic Unit
Long Stroke Unit
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
This module reviews in detail,the design and operationengineering and principles ofa rod pump’s surface unit, rodstring, and downhole rodpump, the three primarycomponents of a rod pumpcompletion
The standard rod pumpperformance analysis tool, thesurface dynamometer, ispresented in detail
Why Take This Module?
Well site controller technologyis introduced as well ascorrosion control principles forrod pumps
Learning how an operationsengineer responsible for rodpumps can take advantage ofthe available analytical toolsto maximize production from arod pump while minimizingundue stresses on the surfaceunit, rod string, and downholepump components will resultin minimal pump failures andgreatly reduced operatingcosts and downtime
Controller
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Well site controller technologyis introduced as well ascorrosion control principles forrod pumps
Learning how an operationsengineer responsible for rodpumps can take advantage ofthe available analytical toolsto maximize production from arod pump while minimizingundue stresses on the surfaceunit, rod string, and downholepump components will resultin minimal pump failures andgreatly reduced operatingcosts and downtime
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Well and reservoir conditions• Low to medium producing rates
– Typically used at relatively low rates often with high water cut
• Low productivity conditions– Normally applied where lift has to be achieved entirely by the artificial
lift system
• Low producing bottomhole pressure• Low solution gas ratios
– Gas occupying space reduces the efficiency of a pump
– Important to be able to handle fluids with low solution gas ratios andalso be able to remove gas before gas enters the pump
• High temperature at producing depth• High viscosity produced fluids• Corrosive fluids and overall corrosive conditions• Low operating costs compared to other artificial lift techniques
Group 2 Well Characteristics
Wells less than 4000 ft(1220 m) deep and
Have a pump diametergreater than 2 inches(5.08 cm)
Group 1 Well Characteristics
Wells greater than 4000 ft(1220 m) deep and any pump diameter, or
Have a pump diameterless than or equal to 2inches (5.08 cm)
Group 1 and Group 2 Rod Pump Wells
Group 1 Group 2
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Have a pump diameter greater than 2 inches (50.8 mm)
Group 1 Well Characteristics
Wells greater than 4000 ft(1220 m) deep and anypump diameter, or
Have a pump diameter less than or equal to 2 inches (50.8 mm)
Group 1 and Group 2 Rod Pump Wells
Each of the above groups has unique features
Analyzing Group 1 and Group 2 Rod Pump Wells
Dynamometer data and softwareprograms are the primary diagnostictools for modern rod pump wells
Surface diagnostic data measuringthe load on the rod string as afunction of position throughout theupstroke / downstroke rod pumpcycle is used to predict downholeloads on the pump
Modern diagnostic analysiscomputer programs providequantitative analysis to distinguishbetween mechanical pumpproblems (e.g., leaking or wornpump) and fluid issues (gas, lowproductivity zones, etc.)
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Group 1 Well Features (> 4000 ft or <4000 ft and 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 manyfactors:
• 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 isexpected 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 pumpperformance
(1220 m) (1220 m) (50.8 mm)
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” effectof the rods
Less rod stretch Surface dynamometer shape difficult to analyze Calculated downhole dynamometer “predictive” shape is necessary
to analyze pump performance
(1220 m) (50.8 mm)
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Rod Pump Design Starts with Inflow (Rate) Determination
Engineers use acoustic surveys todetermine bottomhole pressures.
A remotely fired gas gun with a precisionpressure transducer to measure casingpressure change as an acoustic signalmeasures the distance h' to the fluid level.
May be carried out for both flowing andshut-in rod pump wells.
from: Echometer
Pump
Oil + Gas
Liquid
Knowing h, then:
h x fluid gradient = PBHP
PBHP - for both flowing and shut-in conditions
Knowing the distance to the liquid levelfor both flowing and shut in conditionsallows engineers to determine the heightof 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
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Leverage the skills you’ve learned by discussing the skill module objectives with your supervisor to develop a personalized plan to implement on the job. Some suggestions are provided.
Meet with a reservoir engineer or production engineer in your organization to review how inflow relationships are developed to properly size the capacity of your oil well rod pump completions.
Courtesy: Lufkin Industries
Determination of Pres, Pwf, estimated fluid rate, fluid level in well, etc.
(kPa)
(10,342)
(3,206)
(10,342)
(m3/day)
(31.8)
(7.95)
(39.8)
(m)
(3,048)
(3,048)
(392)
(566 kPa/m)
(kPa)
(3,206)
(1,276)
(36.9 m3/day)
(9.2 m3/day)
(46.2 m3/day)
(32 m3/day)
(8 m3/day)
(40 m3/day)
Typical Data Gathering and Rod Pump Planning Review
Production Potential Using Vogel Analysis Software
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Determination of Pres, Pwf, estimated fluid rate, fluid level in well, etc.
(kPa)
(10,342)
(3,206)
(10,342)
(m3/day)
(31.8)
(7.95)
(39.8)
(m)
(3,048)
(3,048)
(392)
(566 kPa/m)
(kPa)
(3,206)
(1,276)
(36.9 m3/day)
(9.2 m3/day)
(46.2 m3/day)
(32 m3/day)
(8 m3/day)
(40 m3/day)
Typical Data Gathering and Rod Pump Planning Review
Production Potential Using Vogel Analysis Software
KEY POINTS
These analyses provide a guide to inflow rateand therefore, accurate pump sizing
These analyses are regularly conducted aspart of routine surveillance activity
A rod pump artificial lift completion is being evaluated and the expected rate needs to be reviewed.
Use the Vogel Inflow relationship to assess the productive zone’s expected rate.
The oil bubble point pressure is 2881 psig (19863.8 kPa) based upon lab analysis.
A valid well test measurement is available where the well Pwf = 1602 psig (11045.4 kPa) with a flow rate of 403 bfpd (64.1 m3) and water cut of 20% and reservoir pressure = 2165 psig (14927.2 kPa).
Estimate the well inflow rate at a Pwf = 1000 psig (6894.8 kPa).
Scenario
Determine
Exercise: Estimate the Expected Inflow Rate Using Vogel IPR
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Leverage the skills you’ve learned by discussing the skill module objectives with your supervisor to develop a personalized plan to implement on the job. Some suggestions are provided.
Review the types of reciprocating rod pump units that are in service in your company’s oil well completions.
Analyze the reasons for each type.
Review your analysis with an experienced production engineer.
BOTTOM OF DOWNSTROKE
TOP OF UPSTROKE
Rod Pump Operating
At the top of the upstroke, the unithas lifted well fluids one strokelength and the rods to the surface.
At the bottom of the downstroke,the unit has lowered the rods backinto the well one stroke length.
One half rod pump cycle illustrated
Maximum load
occurs
Minimum load
occurs
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
On the downstroke, thegearbox lifts thecounterweight with the helpof the rod load (to get thecounterweight ready to helpagain on the upstroke).
On the upstroke, thecounterweight releasesenergy to the gearbox andhelps the gearbox by falling.
Rod Pump Operating
TOP OF UPSTROKE
BOTTOM OF DOWNSTROKE
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.
Conventional Unit Crank
Mark II Unit Rod Pump Offset Crank Angle
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.
Mark II Unit Crank
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
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)
Pause and Reflect
If the number “168” were replaced by the number “154” in the rod pump description C-912D-365-168, what would that
signify?
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
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 performedby a strain gauge tool called a dynamometer.
Rod Pump Data Gathering and Design
Loads on the rod string as a function of the position of the rod string reciprocationand position of the rod are continuously measured for analysis.
A strain gauge on the polished rod measures these loads on the pump upstrokeand downstroke.
The pictured tool which gathers this data is called a “dynamometer.”
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
The rod pump motor works with the gear box to convert therotational rpm’s of the motor into the reciprocating motionrequired by the rod pump at the downhole pump.
• A rod pump has a motor sheave of 10 in. (254 mm) O.D.
• The gear-box sheave is 34 in. (864 mm) O.D.
• The gear box is a standard 30:1 ratio unit.
• The motor is a gas engine turning at 500 rpm average speed.
Rod Pump Strokes Per Minute Exercise
10" / 34" =10" / 34" =
RPM x 0.294 =500 x 0.294 =
147.1 RPM
RPM x 0.294 =500 x 0.294 =
147.1 RPM
4.9 SPM4.9 SPM
0.294
The rod pump motor works with the gear box to convert therotational rpm’s of the motor into the reciprocating motionrequired by the rod pump at the downhole pump.
• A rod pump has a motor sheave of 10 in. (254 mm) O.D.
• The gear-box sheave is 34 in. (864 mm) O.D.
• The gear box is a standard 30:1 ratio unit.
• The motor is a gas engine turning at 500 rpm average speed.
(254 mm / 864 mm)
147.1 RPM / 30 =
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
The motor provides external energy input to work with the gearbox, crank arm, and counterweight to lift rods and fluids out of thewell on the upstroke and lower rods back into the well on thedownstroke… for each cycle.
Wrist Pin
Pitman Arms
Rod Pump Crankshaft / Counterweight
Counterweight
Gear Box
Crank Arm
Pause and Reflect
Can you explain the difference between a rod heavy and counterweight heavy unbalanced pump
cycle torque requirement?
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Leverage the skills you’ve learned by discussing the skill module objectives with your supervisor to develop a personalized plan to implement on the job. Some suggestions are provided.
Gather data regarding NEMA D electrical motor loads and determine if motor / gear box data indicate unbalanced torque conditions.
Review your analysis with an experienced production engineer.
Recommend rod pump set‐up changes if recorded motor load data illustrate an unbalanced torque condition.
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
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
This section will cover the following learning objectives:
Employ the steps necessary to design, maintain, and servicerod pump rod strings
Design a rod pump rod string using the Modified Goodmanmethod
Highlight the considerations and adjustments being reviewed byAPI regarding standards for proper consideration of rod fatigueand related corrosion effects upon rod string design
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Can you explain the stress/strain relationship of a rod string within the elastic limit of
the steel of the rod?
Does the rod string steel permanently
deform?
Stress Strain Curve
Rod Pump Rod Design
Rod Stress / Strain Curve• Sucker Rods should operate
in the linear portion of thestress vs. stain curve andnever undergo permanentdeformation.
• Rod Fatigue is, however, themain design consideration forcontinuous operation.
• Per API standard, when thedifference between (rangeof) the maximum andminimum actual stress onrod string is great, theallowable rod stress isdecreased. 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)
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Service Factors (SF) de-rate theallowable 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
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Rods Design Example: Get Surface Rod Loads from Dyno Card
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 Card Rod Area is .601 in2 (15.3 mm2)
Rod Diameter is .875 in(22.2 mm)
(8,165)
(9,072)
(7,257)
(6,350)
(5,443)
(4,536)
(3,629)
(2,722)
(1,814)
(907)
(kg
)
Back to Work Suggestions
Reciprocating Rod Pump Fundamentals
Leverage the skills you’ve learned by discussing the skill module objectives with your supervisor to develop a personalized plan to implement on the job. Some suggestions are provided.
Analyze the rod string design for a few typical wells in your area.
Review your analysis with an experienced production engineer.
Participate in developing/writing any required pulling unit or rig workover field programs to pull/run new rod strings (and possibly related tubing and downhole pump change outs).
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
These couplings are made of 8630 alloy steel and offer excellent resistance to hydrogen embrittlement. The base metal is prepared to a No. 1 finish per NACE TM0170 or TM0175 before spray weld coating is applied. This provides a strong metallurgical bond between base metal and the spray metal coating.
CO-HARD couplings incorporate a spray weld coating for maximum corrosion/abrasion resistance to hydrogen embrittlement. They are intended for use with rods where coupling abrasion wear or coupling corrosion is a problem.
Mechanical Properties
Tensile 100,000 psi (min) Hardness 56-62 HRA SM Coating Thickness 0.010” to 0.020” SM Coating Hardness 595 HV200(min).
From: Weatherford
Grade T Sucker Rod CouplingsGrade T Sucker Rod Couplings
These API Class T couplings are made of 8630 alloy steel and offer excellent resistance to hydrogen embrittlement. They are furnished with all Weatherford sucker rods unless otherwise specified.
Grade SM CO-HARD Sucker Rod CouplingsGrade SM CO-HARD Sucker Rod Couplings
Measured CircumferentialDisplacement
ScribedVertical
Line
Sucker Rod Makeup Torque
For Correct Make-Up, LubricateThreads Before Make-Up
For Correct Make-Up, LubricateThreads Before Make-Up
Leverage the skills you’ve learned by discussing the skill module objectives with your supervisor to develop a personalized plan to implement on the job. Some suggestions are provided.
Review the percentage of tubing pumps installed compared to the number of insert pumps.
Analyze the reasons for each.
Review your analysis with an experienced production engineer.
THTubing Pump
RWATop Hold
Down Pump
RHBBottom
Hold Down Pump
RWTTraveling
BarrelPump
Top Hold Down• RWA – Thin Wall• RHA – Heavy Wall
Bottom Hold Down• RWB – Thin Wall• RHB – Heavy Wall
Traveling Barrel• RWT – Thin Wall• RHT – Heavy Wall
Tubing Pumps
API Pump Classifications
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
BThis section will cover the following learning objectives:
Describe how a rod pump surface dynamometer gathers rodpump loading data over each pump cycle
Calculate maximum and minimum rod stress loading
Predict downhole pump performance
Select rod string taper sizing
Select motor horsepower required
Evaluate overall pump performance while identifying rod pumpproblems, all using a rod pump dynamometer, known as TheAnalytic and Predictive Tool for reciprocating rod pumps
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Reciprocating Rod Pump Components and Operational Principles Different elements of a pump, how they work, and why
Pump Size / Pump Design
Rod Pump Surface Unit Nomenclature, API specification, surface unit configuration
Rod Pump Rod String How rod string is designed, how stretch is incorporated and why
Rod Pump Downhole Pump Several types of downhole pumps, and their attributes and features
Dynamometer Analysis Dynamometer determines load on the pump at different positions
Failures and Maintenance Important to understand how and why failures occur and how to prevent them
Controllers Designed to manage performance of the surface unit
Summary
Dynamometer Analysis
The original dynamometer was a mechanical device that worked with fluidacoustic equipment
• Clamped onto the polished rod as it moved up and down
• A stylus moved across a drum and traced the polished rod load vs. the positionof the dynamometer on wax paper
• The resulting data was called a dynamometer card
Modern dynamometers are used to diagnose many different pumpingsystem problems
Before modern dynamometers, dynamometer cards were the primarymethod for diagnosing problems
• Individual operators needed much experience to compare data to typicalexamples and find issues
• Data histories are valuable in helping understand diagnostic problems or thecondition of the system
Today’s equipment and technologies are based on determining down hole,at-the-pump dynamometer data conducted using the wave equation, adifferential equation, and computer programs
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Typical Problems Identified by Dynamometer Analysis
* Each of the problems notedare illustrated on other slides.
Rod Pump Polished Rod
The polished rod is the connecting link betweenthe surface pumping unit and the downhole rodstring.
The polished rod’s exterior surface is ground toclose tolerances and has an extremely smoothsurface to provides a sealing surface for theelastomer seals (packing) that allow polish rodvertical movement.
Sucker Rod O.D.
5/8 in. (16 mm)
3/4 in. (19 mm)
7/8 in. (2.2 mm)
1 in. (25 mm)
Polished Rod O.D.
1-1/8 in. (29 mm)
1-1/8 in. (29 mm)
1-1/4 in. (32 mm)
1-1/2 in. (38 mm)
Recommended Polished Rod Sizes
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
3. Stop the unit on the downstroke(apply brake smoothly)
4. Hold for 10 seconds+
5. If the standing valve is holdingthe weight of the fluid load andremains constant (orincreases), then the travelingvalve will not be picking up aload if the standing valve wereleaking and the standing valveis thus in good condition. If thestanding valve load drops, thetraveling valve has not opened.
6. Repeat test
Pause and Reflect
Can you describe when the rod pump standingvalve opens?
Can you describe when the rod pump travelingvalve opens?
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Mills Method (1940s – manual calculations)• Clarified initial rod pump physics and geometry• Early attempts to understand pump and rod forces
API RP 11L (1950s – analog “average” model)• Assumes: pump full, anchored tubing, low slip motor, steel rods
only, no fluid acceleration, unit fully in balance, no downhole friction, no dynamic inertia effects, for wells > 2000 ft (610 m), etc.
Wave Equation (1960s)
Expert Wave Equation (1990s)
Computer based mathematics to solve the Wave Equation rod string model
Wave Equation
The Wave Equation is an important second-order linear partialdifferential equation for the description of waves as they occurin physics… such as sound waves, light waves and waterwaves.
Applicable to disciplines like acoustics, electromagnetics, andfluid dynamics.
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
For Modern State-of-the-Art ComputerBased Rod Pump Design
A partial differential equation that doesnot have an exact solution.
a - Velocity of sound in steel (ft/sec or m/sec)c - Damping coefficient (1/sec)t - Time (sec)x - Distance from polished rod (ft or m)u (x,t) - Displacement (ft or m)
Wave Equation
2 22
2 2
( , ) ( , ) ( , )u x t u x t u x tc
t x t
Use of computers in theiterative method ofsuggesting a solution andtesting it repeatedly allowsthe Wave Equation to beused because of the speedand capabilities of thecomputer application
Basic equation for rod pumpanalysis, and models theelastic behavior of the rodstring
Represents forces that areaxial along the rod, includingfriction
Friction due to fluid inertiadepends on relative velocitybetween rods moving andthe fluids
In Summary:• By reducing N (number of strokes per minute),• Increasing S (stroke length), and• Using a smaller sized pump with a therefore lesser load…
Movement away from the overtravel or undertravel extremes would put the dynamometer data more in the central portion of total range
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Leverage the skills you’ve learned by discussing the skill module objectives with your supervisor to develop a personalized plan to implement on the job. Some suggestions are provided.
Analyze dynamometer data from a few typical wells in your area and evaluate the range of identified rod pump problems observed from dyno data.
Review your findings with an experienced production engineer.
Visit several wells during dynamometer and controller installation and witness rod pump start up procedures/operations.
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
This section will cover the following learning objectives:
Outline the primary causes of rod failure and how the use of rodguides and other auxiliary equipment can mitigate failures, theeffect of gear box overload and how to prevent it, the properselection of rod metallurgy for corrosion conditions, and theneed for disciplined inspection of well tubing and rods tominimize failures
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
A key API study underway is recognizing that most rod pumpfailures are due to well corrosion environments rather thanfatigue stress which is the basis for most rod designs.
Rod parting and tubing failures are often related to sideloading and resultant tubing and rod wear in deviated holes.
Critical Factors to Minimize Pump Downtime
Inspection• Recommend inspection of
both new and used rods
Handling• Transport, pickup, running
(0.8 mm)
(0.1 mm)
(0.5 mm)
(0.4 mm)
(0.3 mm)
(0.2 mm)
ROD INSPECTION (API IIB (SPEC)
Threads:(Gauges)
End Cracks: (Magnaglow)
Parallelism:(Feeler Gauge)
End Finish:(Comparitor)
Stamping:(Pit Gauge)
UpsetSurface Finish:(Magnetic Flux Leakage)
BodySurface Finish:(Magnetic Flux Leakage)
DimensionalTolerances: (Micrometer)
Maximum Allow Bend in 1 FootBody – 0.130 in.Ends – 0.200 in.
(3.3 mm)
(5.1 mm)
Thread Dimensions CheckedWith Go–No–Go Gauges API
Check forImperfections and Cracks
No Gap Greater Than 0.003 in. (5.1 mm)
250 RMS
No Greater Than 0.031 in.
0.0625 in Imperfection (1.6 mm)
Traverse – 0.004 in.Longitudinal – 0.020 in.
Diameter – 0.016 in.+ 0.008 in.
Out of Round – 0.010 in.
(25 mm)Rod
Straightness:(Straight Edge
Gauges)
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Rod Guides• Use guides at wear locations such as dog-leg and locations just
above the pump to reduce wear due to fluid pound.• Molded guides tend to slip less than hand installed guides.• When dog-leg conditions are severe, guides are required for future
pump completions.
Pause and Reflect
Do you understand and can you describe the
purpose of rod string rod guides?
Reciprocating Rod Pump Fundamentals ═════════════════════════════════════════════════════════════════════════
Rod Rotators• Rod rotators are used in conjunction with
rod guides to remove paraffin deposition.
• A rod rotator should not be used when rodscan’t rotate freely. If the rods torque up,backlash could cause the rods to unscrew.
• A leveling plate should be installed on thecarrier bar to prevent misalignment thatcould cause side loads that could result ina polish rod failure.
• A rotating tubing hanger and anchorsystem is available that can be installed onwells that have severe wear problems.
• The entire tubing string can be slowlyrotated to distribute wear from rod contact,even if sides loads keep the rod string incontact with one side of the well. It isrelatively expensive but it can be justified ifit eliminates one tubing failure in a well.
• Use tubing rotator if tubing wears.
The rotator body rests on the cross bar and the polish rod clamp rests on the rotating body hub.
Fiberglass Sucker Rods
• Light weight, thereforereduced load on surfaceequipment.
• Due to elasticity, welldesigned rod stringscan have longer strokedownhole than surfacestroke over travel toincrease production.
This section will cover the following learning objectives:
Demonstrate how the use of modern instrumentation “smartwell” systems to control pump operation, gather data, andmanage pump functions results in optimum pump performanceand minimized costs
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Reciprocating Rod Pump Components and Operational Principles Different elements of a pump, how they work, and why
Pump Size / Pump Design
Rod Pump Surface Unit Nomenclature, API specification, surface unit configuration
Rod Pump Rod String How rod string is designed, how stretch is incorporated and why
Rod Pump Downhole Pump Several types of downhole pumps, and their attributes and features
Dynamometer Analysis Dynamometer determines load on the pump at different positions
Failures and Maintenance Important to understand how and why failures occur and how to prevent them
Controllers Designed to manage performance of the surface unit
Summary
Pump Off Controllers
Most common rod pump problem.
Pump overdesigned vs. well inflow.
Condition caused by incompletefilling of the fluid barrel on theupstroke which results in thedownstroke movement of pumphitting the partially filled barrel.
Detrimental to rods, pump, tubingand surface equipment.
Options include reducing pumpSPM, stroke length, install a smallerpump or a combination of the above.
Pump off controllers (POCs) turn offthe pump when reservoir inflow isinsufficient and fluid pound ensues.
Fluid Pound
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Modern microprocessor based multifunction systems:• Detect and control fluid pound• Adjust motor speed• Determine pump fill percentage• Acquire load / position data• Calculate gross fluid production• Manage set points for peak torque• Set and manage load limits• Detect, manage, and shut down on overload conditions• Other monitoring variables
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This section will cover the following learning objectives:
Develop engineering and operating skills to successfully design,properly set up, maintain, and provide overall service forimplementing and applying reciprocating rod pump artificial lifttechnology
Work several rod pump design exercises to assess maximumand minimum pump load, minimum and maximum rod stress,motor selection, strokes per minute, stroke length, and relatedoverall rod pump design parameter selection
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Production rates generally lower than other artificiallift types.
Production rate capability decreases rapidly withpump depth.
System not compatible with subsurface safety valve(SSSV).
Cannot be used on wells capable of flow.
Rods prevent measurement of flowing and staticpressures (but with proper tools to measure fluidlevel, can estimate both).
Gas in pump reduces efficiency dramatically.
Very large surface equipment.
Rod / tubing wear problems in deviated wells.
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Exercise: Rod Pump Design Variables
Work the rod pump design exercises using the Echometersoftware program provided.
• Initial data assumption variables are provided (well depth, strokelength, anchored tubing diameter, pump diameter, etc.).
• Evaluate the chosen pump by following the recommendedsequential steps in the exercise.
In the second synchronous review session,the module instructor will work / demonstratea complete design of several rod pumpconfigurations (surface unit, rod string,downhole pump, motor HP, and relatedparameters).
Exercises
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