ESPCP Performance in West Sak Field, North Slope, Alaska

Ricardo Pardey - Baker Hughes CentriliftWalter Dinkins - Baker Hughes CentriliftJohn Patterson - ConocoPhillips CompanyJames Rodgers - ConocoPhillips Alaska, Inc.Hai Hunt - ConocoPhillips Alaska, Inc.Eric Hollar - ConocoPhillips Alaska, Inc.

Overview

Started but high amps

A26002.5Multi lobe3

Failure to start on install

B28001Single lobe2

Failure to start on install

B28001Single lobe1

CommentsElastomerPressure psi

Rate bfpd rpm

Pump Model

Well

Through Tubing Conveyed PCP systems (TTCCP)

Tear Down Evidences

noYes – very small amountnoSolids present

190low139Breakaway torque, ft-lbs

Did not PTFlowed water3000 psi, no flowPressure test

420333380Pulled pump torque*, ft-lbs

61%43%61%Pulled pump efficiency*

Anti-SeizeAnti-SeizeAnti-SeizeLubricant used at HB

456351381New pump torque*, ft-lbs

14.8%32%35%New pump efficiency*

170480WHP, psi when pulled

16201560Static BHP, psi

stuckstuckHard to turnRotation at pull

dieseldieselDiesel + 60/40 methanolFreeze protection

9813095Days between pull and testing

61045Total days in well

Yes – high amps SD after 20 min.NoNoPCP start?

255Days before start attempt

Well 3Well 2Well 1

Comparison Table of pumps evaluated

*At rated head and 300 RPM

Tear Down Evidences

• Pump evaluations could not reproduce the stuck pumps when the breakaway torque tests were conducted during the inspection three to four months after removing from the wells.

• In all cases, actual torque values were less than 200 ft-lb while the BHA is capable of delivering 1200 to 1500 ft-lbs.

• Pump performance tests revealed an increase in volumetric efficiency as compared to the original new pump test

• The root cause keeping these pumps from starting could not be identified. However, it was clear that the problem occurred down hole since each of these pumps could be rotated before installation, but not after being pulled.

Tear Down Evidences

Ideas on why these pumps would not turn down hole:

• Elastomer swelling, due to extended contact time with diesel at down hole static pressure, prevented the pump from turning.

• Change in rotor lubrication from a mineral oil (CL5) to an anti-seize grease. The grease may have degraded causing the pumps to lock up.

• The pump string pulled from each well could not be checked in its entirety because the flex shaft and pump eye were removed from each pump before testing. The pump eyes may have been bound up. Based onrestart of the pumps run in two wells, it is believed this was not an issue. These restarts also reduce likelihood that anti-seize lubricant is the culprit.

• Solids were not a factor in these installations as there were minimal to no solids found in any of the pumps.

Tear Down Evidences

• The most probable cause that prevented the pumps from running iselastomer swelling due to excessive contact with the freeze protection fluid over an extended period of time at down hole static pressure.

• Down hole soak times in the freeze protection fluid varied from two to five days before the pumps were ready to be started.

62DieselMulti Lobe “A”3

105DieselSingle Lobe/ “B”2

455Diesel + 60/40 methanol/water

Single Lobe /”B”1

Total days in well

Days before start attempt

Freeze Protection

Pump Model/ Elastomer

Well

Testing Objective

• Laboratory testing was initiated to investigate swelling behavior of elastomers commonly used in the Alaska West Sak field under simulated down hole conditions in order to:

– Identify root causes of the high amp conditions observed during start up procedures of three ESPCP systems installed in the field.

– Validate performance test criteria/rotor stator fit guidelines for West Sak applications.

– Recommend best practices in terms of permissible soaking times in any of the completion fluids utilized in the field.

Testing Methodology

• Elastomer Compatibility test: – Elastomers A, B, C (similar dimensions)

• Fluids:– Arctic diesel – 60/40 water/methanol mixture– West Sak Oil– Tabasco Oil

• Test conditions:– Pressurized cell (1600 psi)– Temperature: 75°F– Exposure time: 10 days

• Measurements:– Swelling Kinetics (mass, volume and hardness change)

• 1, 2, 3, 4, 5, and 10 days (progressive measurements)• Measurements conducted at atmospheric pressure

– Deswelling after exposure: 0, 4, 8, 24, 48, and 72 hrs at atmospheric pressure

ResultsArtic Diesel

0

1

2

3

4

5

6

7

8

9

0 50 100 150 200 250 300 350

Time (hrs)

Volu

me

Cha

nge

(%)

ABC

DeswellingSwelling

Arctic Diesel

ResultsArtic Diesel

-12

-10

-8

-6

-4

-2

00 50 100 150 200 250 300 350

Time (hrs)

Har

dnes

s C

hang

e (%

)

ABC

Arctic Diesel

Results60/40 Methanol Water Mixture

0

1

2

3

4

5

6

0 50 100 150 200 250 300 350

Time (hrs)

Volu

me

Cha

nge

(%)

ABC

DeswellingSwelling

Results60/40 Methanol/Water mixture

-16

-14

-12

-10

-8

-6

-4

-2

0

2

0 50 100 150 200 250 300 350

Time (hrs)

Har

dnes

s C

hang

e (%

)

ABC

DeswellingSwelling

ResultsWest Sak Oil

0

1

2

3

4

5

6

7

0 50 100 150 200 250 300 350

Time (hrs)

Volu

me

Cha

nge

(%)

ABC

Swelling Deswelling

ResultsWest Sak Oil

-12

-10

-8

-6

-4

-2

00 50 100 150 200 250 300 350

Time (hrs)

Har

dnes

s C

hang

e (%

)

ABc

Swelling Deswelling

ResultsTabasco Oil

0

1

2

3

4

5

6

0 50 100 150 200 250 300 350

Time (hrs)

Volu

me

Cha

nge

(%)

ABC

Swelling Deswelling

ResultsTabasco Oil

-12

-10

-8

-6

-4

-2

0

2

0 50 100 150 200 250 300 350

Time (hrs)

Har

dnes

s C

hang

e (%

)

ABC

Swelling Deswelling

Results

Equilibrium swelling values and hardness changes in Alaska fluids at 75°F and 1600 psi exposed for 10 days.

Fluid A B C Volume

Change (%) Hardness

change (%) Volume

Change (%) Hardness

Change (%) Volume

Change (%) Hardness

Change (%) West Sak Oil

5.8 -6.2 3.2 -5.3 4.1 -10.6

Tabasco Oil

4.2 -5.0 2.3 -6.9 4.4 -10.5

Artic Diesel

8.2 -10.9 3.0 -3.7 4.6 -9.6

60/40 Methanol water

4.1 -6.2 3.0 -7.3 4.5 -15.0

Arctic Diesel

Results

1.11.51.160/40 Methanol water

2.00.73.3Artic Diesel

2.21.11.7Tabasco Oil

2.01.52.6West Sak Oil

CBAFluid

Residual swelling (% volume change) after 72 hours post test

Arctic Diesel

Pump Efficiency Analysis

• Example for pump installed in well 3 • Diesel test • Expected increase in down hole efficiency due to soaking

in diesel.– 2 Days immersion in diesel:

• Measured volume change: 4.7%• Calculated increase in volumetric efficiency due to swelling: 87% at 300

rpm, rated P• Initial test bench volumetric efficiency: 14.8% at 300 rpm, rated P• Extrapolated down hole efficiency: 101.2% at 300 rpm, rated P

– 5 Days immersion in diesel:• Measured Volume Change: 5.6%• Calculated increase in volumetric efficiency due to swelling: 103% at 300

rpm, rated P• Initial test bench volumetric efficiency: 14.8% at 300 rpm, rated P• Extrapolated down hole vol. efficiency: 116.6% at 300 rpm, rated P

Rotor SizeStator Swelling

Performance Curve

Performance Curves

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0 1000 2000 3000 4000 5000

Lift (ft)

Vol.

Effic

ienc

y %

Rated P

FLUID SLIP

Performance CurveU.S. Customary Units

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1000 2000 3000 4000 5000

Lift (ft)

Vol.

Effic

ienc

y %

050100150200250300350400450500

EfficiencyTorque

Extrapolated BH Eff. swelling + thermal

5 days dieselSwelling

Pump Efficiency Analysis

Pump Efficiency Analysis

• Extrapolated efficiency values were above 100% after two days immersion in diesel revealing that the rotor stator interference would be too tight.

• Probability of locking up the system on high torque is very high. This explains why high amp readings were observed during the start upprocedure of well 3.

• Situation would be even more critical after five days soaking in diesel since the volume change increases causing the extrapolated down hole efficiency to also increase.

• Well 1: Elastomer “B” experiences lower swelling values in diesel. However, higher initial rotor stator interference in this case could lead to start up problems.

• Well 2: Elastomer “C” experienced a higher swelling degree than elastomer “B” indicating that start up problems would be expected if the stator is soaked over a prolonged period of time.

Pump Efficiency Analysis

Soaking times in diesel less than 24 hours seems to be permissible provided that:

– A similar arctic diesel is used. More aggressive diesel will reduce the permissible soaking time before causing start up problems since swelling behavior is very dependent on fluid composition and soaking time.

– Pump initial efficiency is kept similar. If original rotor stator fit is tighter, shorter soaking times would be required to avoid start up problems.

– If field practices necessitate long duration soaking times in completion fluid, the rotor stator fit should be loosened to compensate for the higher degree of swelling.

60/40 Methanol Water test– Extrapolated efficiency values are lower than those calculated

in diesel due to lower swelling power of the water methanol mixture. Under both scenarios (two and five days) the pump should operate with reasonable torque values in water methanol mixtures.

Pump Efficiency Analysis

Effect of Residual Swelling

• Test bench volumetric efficiency of pump installed in well 3 wasestimated based on the residual volume change measured from the immersion test in West Sak Oil.

– Residual volume change in West Sak oil: 2.7%– Estimated increase in efficiency due to residual swelling: 50%

(≈ 2 rotor sizes)– Initial test bench volumetric efficiency: 14.8% at 300 rpm, rated P– Estimated test bench efficiency with residual swelling: 64.8% at 300

rpm, rated P– Measured test bench volumetric efficiency (post run): 61% at 300

rpm, rated P– The degree of rotor stator interference resulting from the residual

swelling should not produce any problem with the pump torque. – High breakaway torques were not observed during the pump

evaluation in the test bench conducted several month after pulling.

Rotor Stator Fit Validation

Example:• Well: 3

• West Sak Oil

• Pump: Multi lobe – Displacement 2.5 bfpd/rpm

– Pressure rating: 3600 psi

– Elastomer “B”

• Reported volume change: 5.8% at 75° F, 1800 psi, 10 days

• Target test bench parameter designed to achieve 70% volumetric efficiency at BHT, rated P

• Reported degree of swelling +4.2 equivalent rotor sizes

• Recommended Test Bench parameter:

• -30+10% at 85°F, 300 rpm, rated P, or similarly

• 0% at 85°F, 300 rpm, 1475+200 psi

• Estimated rotor size: 2 under-size

Conclusions

• Experimental evidence leans toward stator swelling due to interaction with the completion fluid as the most probable cause of the inability to start the ESPCP systems installed in wells in Alaska West Sak field.

• Swelling values tend to increase with time until reaching a plateau value. Any variations in soaking times, especially at initial stages during swelling, could cause a significant increase in volume change.

• Even though swelling values of elastomer “B” in diesel are lower than for elastomer “A” or elastomer “C”, potential problems could exist, especially if the diesel composition is more aggressive than expected, longer soaking times occurred, or initial rotor stator fit is tight.

• Recommended practices were derived in terms of permissible soaking time in the completion fluid based on results obtained from these analyses. In the case of using diesel, soak time should not exceed 24 hours to avoid excessive swelling.

Conclusions

• Diesel seems to be more aggressive than the water/methanol mixtures in terms of swelling power. Therefore, soaking for shorter periods of time will tend to cause torque problems. In all cases, soaking time should not exceed five days.

• Both crude oils (West Sak and Tabasco) exhibit similar swelling power and they can be considered non aggressive.

• Rotor stator interference guidelines have been revised based on reported swelling values in West Sak oil.

• West Sak field application parameters are seemingly non-aggressive. Any one of the three elastomers analyzed in the report should perform satisfactorily in the field provided that the rotor stator fit is properly adjusted.

Recommendations

• As a field practice, avoid prolonged soaking times in diesel under down hole conditions to reduce the chances of locking up the system on high torque due to excessive elastomer swelling.

• Ideally, soaking times in diesel should not exceed 24 hours to minimize swelling. However, depending on the elastomer and the initial rotor stator interference, longer periods of soaking time could be permissible.

• Consider introducing the new fit guideline in trial wells and monitor torque, efficiency TDH, and run life. Increase rpms to obtain the desired well efficiency if rotor stator fit is slightly loose, particularly at initial stages during the operation untilequilibrium swelling is achieved.

Recommendations

• Consider conducting the following additional experiments to validate findings:

– Compositional analysis of diesel fluids utilized in the field. – Compatibility tests in new diesel samples to observed difference in

swelling power (duplicates). – Measurement of elastomer thickness variation “in situ” under

simulated down hole condition as a function of time (swelling kinetics) to avoid experimental errors associated to the cell depressurization process in conventional tests.

– Sequential swelling by exposing the elastomer first to diesel (defined period of time) and then to oil, until reaching equilibrium to better represent field practices

Recommendations

• Consider modifying start up procedures:– Start up speed: 5 Hz increments. – Pressure assisted reverse starts.

• Consider reusing short run pumps if:– Pump is inspected and no problems are found other than

elastomer swelling which is expected. – Retest with rerun acceptance criteria based on swelling tests.

Acknowledgements

• Authors thank the West Sak co-owners for allowing this report to be compiled with laboratory results they collected during elastomer testing.

• Following West Sak co-owners are gratefully thanked for permission to make this presentation:

– ConocoPhillips Alaska Inc.– BP Exploration (Alaska) Inc.– ChevronTexaco– ExxonMobil

• BACK UP

Well 1:

Well 2:

Well 3: