ROD PUMPING DEVIATED WELLS ROD PUMPING DEVIATED WELLS

Jun Xu, Ken Nolen, Dennis Shipp, Andy Cordova, Sam Gibbs

Lufkin AutomationLufkin Automation

April 20, 2005April 20, 2005

CONTENTSCONTENTSCONTENTSCONTENTS Deviated Well Model

What Is the Key Factors in Deviated Well Design?

1. rod buckling

2. rod guide and sinker bar

3. side/drag load

4. dog leg severity

How to Design a Deviated Well?1. Case 1 – Rod Pumping Design in a Deviated Well

2. Case 2 – Optimized Wellbore Path

Deviated Well ModelDeviated Well Model

• Generalized 3-D Wave Equation Model (by S. Gibbs, in 1992)• vertical and deviated wells• consideration of 3-D wellbore

path• consideration of side load/drag

load and viscous friction• rod guide design• optimized well bore path design

• SROD and DIAG

r(s)

ds

x(north)

y(east)

z (down)

t1

SCHEMATIC OF ROD ELEMENT IN DEVIATED WELL

F

qnmgFf

dss

FF

FORCES ON ROD ELEMENT

SROD Mathematical Modeling Foundation

Key Factors in Deviated Well Design

1. side/drag loads

2. dog leg severity

3. rod buckling

4. rod guide and sinker bar

5. well bore path

6. rod pumping feasibility

7. overloaded rod, gear box or motor

8. design and optimization with whole system

Drag Friction (F), Side Load (Q)Drag Friction (F), Side Load (Q)

bare rod friction coefficient =0.2 ratio of guide friction to bare rod friction =1.5

guide

guide

Tubing

guide

¾”

rod

25’

Tubing

F

Q

F

Q

¾”

rrrod

guide

guide

Tubing

F

QQ =18 lbs/rod Q = 19 lbs/rod Q = 19 lbs/rod

F= 0.2X18 = 3.6 lbs/rod F = 0.2X1.5X19 = 5.7 lbs/rod F =0.2X1.5X19 = 5.7

Dogleg SeverityDogleg Severity• Dogleg severity, º/100 ft, – curvature of wellbore

• Dogleg severity is not directly used in calculation

A

c

Control Drag Loads

1. smaller pump size

2. pump depth

3. using rod guides

4. design sinker bar

5. tubing rotation

6. optimized wellbore design

Rod BucklingRod Buckling

Harmful consequences

• tubing wear/leaks

• rod parts

Root causes

1. downhole friction

2. faster pumping

3. pump-off condition

4. under-balanced units

5. unit geometry selections

6. any combinations

Fluid Level

Casing

Tubing

Upstroke Downstroke

Rod Buckling

Rod String

Pump

Buckling TendencyBuckling Tendency

What is buckling tendency?

• buoyancy ≠ buckling

• true load ≠ buckling tendency

• buckling tendency

Buckling criteria:

buckling tendency ≥ Pcr

Euler Loads and Measured Buckling LoadsFrom Scott W. Long, SPE 35214

Euler Loads and Measured Buckling LoadsFrom Scott W. Long, SPE 35214

Rod and Sinker bar Diameter

Euler Load (lbs)

(25 ft rod)

Measured Buckling

LoadsFixed Hinged

½” 41 10 N/A

5/8” 100 25 N/A

¾” 208 52 23

7/8” 385 96 162

1.0” 657 164 N/A

1-3/8” 2348 587 641

1-1/2” 3325 831 N/A

1-5/8” 4579 1145 N/A

1-3/4” 6160 1540 N/A

How to Control Rod Buckling ?How to Control Rod Buckling ?

Some most practical and effective ways

1. good pump fillage

2. smaller pump

3. slower speed

4. add sinker bar

5. rod guide design

6. selecting proper pumping unit and balance the unit

7. optimized wellbore design

Wellbore Deviation DataWellbore Deviation Data

• Input well deviation survey inclination azimuth

• SRPD designed wellbore true vertical depth horizontal departure kick-off depth build rate (º/100 ft) drop rate(º/100 ft) well bore type

Example 1 of Deviated Well DesignExample 1 of Deviated Well Design

System Performance for Existing DesignSystem Performance for Existing Design

92% 112%

115%

196 bpd

103%

pump depth : 11076’

pump diameter : 1 1/2”

stroke length : 216”

speed : 5.48 spm

rod : 3080’ (1”) (M)2980’ (7/8”) (M) 4410’ (3/4”) (M)600’ (7/8”) (M)

System Performance for Improved DesignSystem Performance for Improved Design

83% 78%

98%

219 bpd

92%

pump depth : 11076’

pump diameter : 1.25”

stroke length : 216”

speed : 6.83 spm

rod : 3080’ (1”) (W)

2980’ (7/8”) (M)

4410’ (3/4”) (M)

600’ (7/6”) (M)

Rod BucklingRod Buckling

6.8 SPM

Full Pump

6.8 SPM

Pump-off

(80%)

6.8 SPM

Pump-off

(80%)

Example 2 of Deviated Well Design

Problems for Existing WellProblems for Existing Well

92% 114%

100%

822 bpd

85%

pump depth : 6300’

tubing pump : 2 – 1/4”

tubing size “ 2 -7/8” (below KOP)

stroke length : 192”

speed : 9.1 spm

86 rod design : 2310’ (1”)

2400’ (7/8”)

1590’ (3/4”) (16 M.G.)

Proposed ModificationsProposed Modifications

74% 86%

80%

808 bpd

91%

pump depth : 6300’

insert pump : 2 1/4”

tubing size : 3 -1/2” (anchored 5000’)

stroke length : 168”

rod : 1800’ (1 -1/8” N-97)

2800’ (1” N-97)

400’ (1-5/8” grade C)

1300’ (7/8”) (N-97)

Rod Buckling and Drag LoadRod Buckling and Drag Load

Optimized Wellbore DesignOptimized Wellbore Design

Buildup-hold (KOP=5100’) Buildup-hold (KOP=2000’) Buildup-hold-drop (KOP=2000’)

Optimized Wellbore Design Optimized Wellbore Design

Existing Wellbore SROD Optimized Wellbore Path

existing modified buildup-hold-drop (2000 KOP)

buildup-hold (2000 KOP)

buildup-hold (5100 KOP)

power cost ($/m) 5447 4341 4963 4230 3901

production (bpd) 822 808 650 780 805

buckling tendency 1184 496 960 672 417

drag load 191 165 74 40 56

molded guides 16 12 3 3 4

motor loading 92 74 91 73 68

struct loading 85 91 95 84 81

reducer loading 114 86 124 94 81

rod loading 100 80 87 75 70

pump depth 6300 6300 7200 6600 6200

Optimized Wellbore DesignOptimized Wellbore Design

CONCLUSIONSCONCLUSIONS An accurate and comprehensive predictive program is

the only one tool for deviated well design and simulation.

Several options can be chosen to control rod buckling, that is, good pump fillage, smaller pump, slower speed, sinker bar, rod guides, and proper pumping unit.

Smaller bore pump can be effective used to reduce side/drag load.

Optimal wellbore paths exists that will reduce side/drag load, power cost and equipment loads and on-going R&M costs.