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Diagnosis and Designof

Sucker Rod Pumping Systems

K.B. (Ken) Nolen

Lufkin Automation

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GOAL is to maximize profit by:

1. MAXIMIZING PRODUCTION Within Cost Restraints

2. MINIMIZING COSTS A) Reduce R&M Costs B) Reduce Power Costs

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Purpose of Well Analysis

1. WELL SURVEILLANCE Identify Wells With Additional Production

2. TROUBLESHOOTING Determine Causes for High Operating Costs

Equipment Failures High Energy Consumption

3. EQUIPMENT EVALUATION New Equipment Proper Application

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Performing On-site Well Analysis

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Diagnosis of Rod Pumping Systems

I. DIAG Program for Dynamometer Analysis A. Unit Structure Loading B. Gearbox Loading 1. Counterbalance Measurements 2. Torque Factor Analysis

a. Inertia Neglected (API Method)

b. Inertia Considered (UHS Motors) 3. Permissible Load Diagrams 4. Unit Balance

a. Counterbalance Existing b. Counterbalance for Ideal Balance c. Unit balance based on line current

C. Prime Mover Loading 1. Polished Rod Power 2. Cyclic Load Factor 3. Nameplate Power Requirement 4. RMS Current & Current Plots

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Diagnosis of Rod Pumping Systems (cont.)

I. DIAG Program for Dynamometer Analysis (cont.) D. Rod Loading Criteria

1. API Goodman Stress Range Diagram 2. Stress Range Diagrams for UHS Rods 3. Stress Range Diagrams for Fiberglass Rods

E. Rod Loading in Tapered Strings F. Sinker Bars G. Causes of Rod Compression H. Effects of Buoyancy I. Energy Losses Along Rod String

1. Drag Fiction a. Along Rod String b. Stuffing Box c. Pump

2. Fluid Friction 3. Fluid Inertia

J. Deviated Wells 1. Deviation Surveys and Well Bore Views 2. Side Loads and Drag Loads 3. Rod Guides and Placement

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Diagnosis of Rod Pumping Systems (cont.)

II. PIP Program for Analysis of Pump Cards A. Pump Intake Pressure B. Factors Affecting Displacement and Efficiency

1. Gas Interference 2. Over-displacement (Pounding Fluid) 3. Oil Shrinkage 4. Mechanical Leakage in BPD

a. Load Loss Method b. Polished Rod Velocity Method c. Pump Velocity Method

5. Inferred Producing Rate

C. Operating Conditions 1. Full Pump 2. Pounding 3. Gas Interference 4. Friction 5. Fouling 6. Hitting down or up 7. Unanchored Tubing Movement 8. Buoyancy 9. Many others

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Diagnosis of Rod Pumping Systems (cont.)

III. ELEC Program for Electrical Analysis (Electrical & Dynamometer Data Collected Simultaneously

A. Power Demand (Motor Input Power) B. Effects of Detent C. Power Factor and Correction D. Current, Power Factor & KW Plots E. Current & Voltage Measurements on all Three Phases F. Phase Balance, Voltage & Current G. RMS Current and Motor Loading H. Monthly Power Bill I. Lifting cost in $/bbl and $/bbl/1000 ft J. Surface Equipment Efficiency K. Rod String Efficiency L. Overall System Efficiency

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Diagnosis of Rod Pumping Systems (cont.)

IV. Supporting Programs A. PIVOG Program Determines Well Production

Potential 1. Vogel’s Method 2. Constant PI Method

B. CBAL Program Determines Counterbalance, Weight Selection and Placement of Weights for Ideal Balance

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Pump-off Controllers/Monitors/Managers

I. Primary Functions A. Sense pump-off B. Historical Data for Trends 1. Percent Run 2. Peak and Min Load 3. Polished Rod Horsepower

C. Malfunctions 1. Max/Min Load Violations 2. High Torque Violations

D. Dynamometer Analysis

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Pump-off Controllers/Monitors/Managers

II. Control Methods A. Load and Position B. Reference Load/Position on Downstroke C. Pump Fillage from Pump Card D. Motor Speed/Torque E. Change in Pumping Period F. Motor Power & Current G. Fluid Flow H. Downhole Producing Pressure/Fluid Level

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Pump-off Controllers/Monitors/Managers

III. Control with Speed Changes A. Variable Frequency Drives B. Eddy Current Clutches

IV. Economics A. Initial Costs B. Maintenance Costs C. Payout 1. Reduction in R&M, 25+% 2. Reduction in Power, 20+% 3. Increase in Production, 1-4+%

“Paying Attention Pays Off”

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Design of Rod Pumping Systems

I. SROD Program Models A. Unit Geometry

1. Conventional a. Standard B. Enhanced

2. Mark II 3. Air Balanced 4. Rotaflex 5. User Database

B. Prime Mover Torque/Speed/Efficiency 1. NEMA B, C & D 2. Ultra High Slip 3. User Database

C. Rod String 1. API Steel 2. Fiberglass 3. Corod 4. Sinker Bars 5. Viscous Friction

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Design of Rod Pumping Systems (cont.)

II. SROD Program Models (cont.) D. Pump

1. Full 2. Fluid Pound 3. Gas Interference 4. Tubing Movement

E. Deviated Wells – Requires Deviation Survey F. Shallow Wells/Big Bore Pumps – Fluid Inertia Effects

1. Tubing 2. Flowline

G. Electrical Analysis 1. Power Demand 2. Effects of Detent 3. Power Factor and Correction 4. Current Plot 5. RMS Current 6. Motor Loading 7. Monthly Power Bill 8. Surface Equipment Efficiency 9. Rod String Efficiency 10. Overall System Efficiency

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Design of Rod Pumping Systems (cont.)

II. SROD Program Output A. Surface and Pump Cards

SPM, Surface and Pump HP

B. Surface Equipment Analysis 1. Gearbox

a. Max & Min Torque b. Ideal Counterbalance c. Torque Plot d. Permissible Load Diagrams

2. Structure Max PR Load

3. Prime Mover a. Power Required b. Cyclic Load Factor c. RMS Current d. Speed Variation

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Design of Rod Pumping Systems (cont.)

II. SROD Program Output (cont.) C. Rod Analysis

1. Max & Min Stresses at Top of Each Rod Size 2. % Load Base on Stress Range Diagram & 3 Service Factors 3. Buckling Tendency Plot

D. Pump Analysis 1. Gross Displacement 2. Net Displacement

a. Fluid Pound b. Gas Interference C. Unanchored Tubing

3. Pump Simulation

E. Animation of Pumping System F. Overlay with DIAG G. Run with Variations

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Design of Rod Pumping Systems (cont.)

III. Program Output (Deviated Well) A. Views of Well Bore Path B. Plots of Axial, Side & Drag Loads C. Tabular Output of Side Loads for Placement of Guides

IV. Program Output (Shallow Wells/Big Bore Pumps) Surface and Pump Cards Display Effects of Fluid Inertia

V. Supporting Programs A. PUMPC Determines Pump Capacity Considering:

1. Free Gas 2. Oil Shrinkage 3. Pump Slippage

B. CBAL Determines Counterbalance, Weight Selection and Placement

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Running Deviated Hole SROD

Prompt ListStep 1 Create a .inp data fileStep 2 Create a .dev data fileStep 3 Proof .dev file by comparing dog leg severity with original deviation data and by

viewing bore pathsStep 4 Specify friction coefficients by selecting Run in the Deviation Survey Data Entry

ScreenStep 5 Run SROD and view results for possible changes in .inp fileStep 6 Run Downhole option and calculate Side loadsStep 7 Select Report and run Tabular Output. Select acceptable side load for bare rods

and side load for each molded guideStep 8 Print hard copy of Tabular OutputStep 9 Using hard copy of Tabular Output design rod guide installation with a

maximum of 10 rod sectionsStep 10 Modify rod design in .inp data file to include guides. Adjust rod weights and

select “Guides” in rod design table to change friction ratios if desired.Step 11 Run SROD to predict equipment loading, pump displacement, electrical

predictions, etc.Step 12 Print final Report

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Conclusions

Wave Equation Solutions Feasible for Deviated WellsRod Pumping Feasible for Highly Deviated Wells with Deviation Properly Controlled.Rod-Tubing Friction Can Be Inferred From Dynamometer Valve ChecksOptimum Borehole Paths ExistRod Tubing Friction Distorts Computed Pump Cards and Causes Error in Computed Pump StrokeShallow Doglegs Cause Greatest Problems in Deviated WellsMore Work Needed:

Coefficient of FrictionTolerable Side LoadsErosion-Corrosion ProcessesRole of Lubricity

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MiscellaneousIllustrations

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Pictorial Representation of a Mathematical Model of a Rod Pumping System

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Wave Equation for Vertical Wells

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Wave Equation for Non-Vertical Wells

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Forces on Rod Element

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Borehole Path of Unintentionally Deviated Well

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Measured & Computed Dynamometer Cards in Deviated Well

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Errors in Computed Pump Cards

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Performance Predictions for Different Paths to Same Target

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Borehole Path for Horizontal Well

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Simulation with Pump Set 80 Degrees from Vertical

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Identical Deviation Patterns at Different Depths

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“Paying Attention Pays Off”

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