35th gas-lift workshop houston, texas, usa … of self lift concept offshore nigeria . ... downhole...

Feb. 6 - 10, 2012 2012 Gas-Lift Workshop 1

Application of Self Lift Concept Offshore Nigeria

Olawale Ayeni, Lucky Ishomo & Mike Johnson

ExxonMobil Production Company

35th Gas-Lift Workshop Houston, Texas, USA February 6 – 10, 2012

Presentation Outline

• Field / Reservoir Overview

• Description of Gaslift Operations Offshore Nigeria

• Self-lift Concept & Drivers

• Design Considerations

• Case Studies & Results

• Conclusion



• Whale Field located offshore Nigeria

• The Field was discovered in the late 1960’s at a water depth of 90ft.

• Comprised of 11 satellite platforms with 80 development wells.

Field Overview

Africa

Nigeria

Map Area

Nigeria


Gas/Oil -5355’

Qua Iboe Shale

160’ Oil Column

Oil/Water -5515’

Disturbed Biafra

Well 4A

Well 30B

Competent Biafra

Base Qua Iboe (BQI)

Present Gas/Oil - 5375’

Gas/Oil-5355’TVD

160’ Oil Column

Oil/Water-5515’ TVD

Reservoir Overview Reservoir Information • Large gas cap with weak aquifer support. • Initial Reservoir Pressure of 2464 psi ,

Current pressure ~1850psi @ ~400 scf/bbl GOR.

• Voidage replacement being practiced through gas injection.

• Full-field pressure communication. Well Hydraulics • Average PI 50 – 120 Bbls / PSI /day. • Average manifold pressure varies between

250 – 400psi. • Gaslift required on most wells to sustain

flow.

0 5 10 15 20 25 30X X X X X X X~ X X X X X X

~ X X X X X~ X X X X

~ X X~ X

~1950

Reservoir Pressure (psi)

y yWater cut %

165017001750180018501900

Parameters

~

Unstable flow

Stable Flow

X

No flow

Hydraulic Table

Reservoir Cartoon / Fluid Contacts

Analysis based on 3-1/2” Tubing (Standard Tubing Size in the Field)

Gaslift Strategy 1. Gas Source

– High Pressure Gas from compression plant

– Gas Cap Gas well (Mostly converted depleted Oil Producers with good stratigraphic gas section)

2. DownHole Set-up – Side Pocket Gaslift Mandrels (Most wells not completed with Gaslift

Mandrels)

– Thru Tubing Gaslift Operation (Provides a very cheap alternative when high pressure gas is available on the platform)

3. Surface Gaslift Facilities – Not available on most platforms

5 Feb. 6 - 10, 2012 2012 Gas-Lift Workshop

• Gas lifting the lower zone - oil producer with gas from the upper zone -gas well; via a mandrel below the shallowest packer.

• Gaslift mandrel is fitted with a Venturi valve. Venturi valves have the ability to deliver the required gas thru-put within the available pressure differential.

• No Well Integrity Issues associated with Self–Lift.(Offshore environment)

Drivers

Concept of Self-Lift Gas Lift

• Delays in installation of surface gaslift facilities on surface platforms.

• Provides immediate uplift pending installation and commissioning of surface gaslift facilities.

• Offsets pre-investment in converting wells to gas source wells prior to the commissioning of gas lift facilities.

• Reduces dependency of gas source well workovers on rig schedule.

• Provides opportunities to mitigate gaps in the rig schedule.

Self-lift Concept & Drivers


Self-Lift Gas Lift Design

• Design Considerations – Differential pressure at the gaslift Injection depth – Constant gas injection rate – Casing size and well deviation at gaslift mandrel depth

• Design Steps

– Determine gas lift mandrel depth at well deviation of about 55° – Run a nodal analysis to determine estimated liquid production rate

using target gas injection rate and gaslift mandrel depth. – Determine port size of Venturi valve using target gas injection rate.


Case Study 1 : Well A & B

Task • Re-complete Well A & B as a dual gas source and oil producer.

– Well A & B were initially single string oil producers • Gas arm of both wells were designed to produce ~7MMSCF/D at the

@1200psi WHP required for gaslift operations.

– Well A was an largely an Intermittent oil producer (0.2KBD). • ~ 16 months exposure between readiness of the gas source well and

complete implementation of the surface gaslift facilities.

– Well B was also an oil producer that has been shut-in since 2005 due to high water production i.e BS&W 50%. Last rate of ~ 0.5KBD

• ~ 20 months exposure between readiness of the gas source well and complete implementation of the surface gaslift facilities.

Opportunity – Complete both wells as a dual well gas source zone and a self-lift oil

producer Feb. 6 - 10, 2012 2012 Gas-Lift Workshop 8

Configuration of Well A & B

9

Perforation Interval 5630 – 5750’ MD (83' TVD)

5,500ft MD

5,600ft MD

5,700ft MD

5,800ft MD

5,900ft MD

GP packer @ 5540’MD

Sump packer @ 5760’MD

scssv SCSSV

R

F

2-7/

8" T

ubin

g

3-1/

2 Tu

bing

4600 Dual packer

2-3/

8" T

ubin

g Dual Tree

F

HZ Section 1,995'

Distance between Sump Packer and Top of predrilled liner ~416’ MD

4-1/2’’ Tubing

2-3/8" F- Nipple ID 1.875

182’ TVD

1850Psi @ 5540’TVD (Oil Zone)

1833Psi @ 5200’TVD (Gas Zone)

GLM Depth @ 5110’TVD Used 12/64” Venturi Valve

Orifice

Feb. 6 - 10, 2012 2012 Gas-Lift Workshop

10

Well Test Plot for Well A

WELL NAME

CHK (1/64'')

WHP (Psig) BOPD G0R

(Scf/STB) BS&W

Well A

48 1200 1281 2281 15

52 1200 1345 2566 16

68 1210 1125 2531 16

60 1225 1203 2860 16

64 1210 1231 2660 17

Sensitivity of choke changes

• Venturi- Valve designed for max injection rate of 1.5MMSCF/D • Cumulative production as result of self lift was ~ 300KBO (Discounting base

production of 0.2KBD prior to self-lift) • Limited sensitivity on choke changes • Significant gas production observed 2009

Results of Well A

~ 16 Months Production Cum’ed ~300KBO

Shut-in due to HGOR


11

Well A – Pictures of Pulled Venturi Valve

Observations - Well A was shut-in 2010 due excessive gas production.

- Valve was pulled in August 2011, An orifice valve was installed in the upper mandrel.

- Severe erosion observed on the Venturi valve. This is likely caused by wet gas injection; root cause still being investigated.

Broken off section of the Valve Cross section of the valve showing some Erosion


Well B Self-lift Performance

12

- Successfully restored production at an average rate of ~ 1200 BOPD - Cumulative production during 20 months was ~ 650KBO - Gas production spiked late 2009. Plan in place to pull valve and operate from

the upper mandrels.

Well B Production Plot ~ 20 Months Production

Cum’ed ~650KBO

Shut-in due to High Gas

Production


Case Study 2 : Well C

Task • Re-complete an intermittent single string oil well into a gas producer.

– Required gas rate for gaslift was ~ 15MMSCF/D for an uplift potential of 8.9KBOPD. – Gaslift facilities expected to be completed six months after the gas source well. – Last well test on the well was ~ 700BOPD @ 28% BS&W .

Opportunity • Re-completed Well C producer as single selective self-lifting oil / gas producer.

– Produce well as a self-lifted oil producer .

• Set-up well to be converted to a gas producer via a wireline operation once the Gaslift facilities have been completed.

Results • Restored sustained productivity of 3.5KBOPD (8KBLPD) to the well through self lift.

– Well production was cut back due to sand production issues to ~ 2.0KBOPD. • Gaslift facilities completed within 6 months of production.

13

Case Study 3 Continued

- Designed Ventri Valve for 1MMSCF/D. (Lessons learned from Well A&B) - Successfully converted the well to a gas producer via wireline operation

(Installed plug and opened the sliding sleeve) when surface facilities were completed.

R

SCSSV

4-1/

2’’ T

ubin

g

~200psi

Performance Curve for Venturi Valve (10/64” Port)


15

~ 6 Months Production Cumm’ed ~300KBO

- Successfully restored production at an average rate of ~ 1800 BOPD

- Cumulative production during 6 months was ~ 300KBO

Well C Self-lift Performance Well C Production Plot


Conclusion

• Application of self-lift concept has the potential of huge cost saving and benefits especially in offshore environment where several projects may not be synchronized.

• Potential of reducing gaslift project dependencies.

• Application of this concept has the potential of enhancing the economics for gaslift projects.


Feb. 6 – 10. 2012 2012 Gas-Lift Workshop 17

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Feb. 6 – 10, 2012 2012 Gas-Lift Workshop 18

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35th gas-lift workshop houston, texas, usa … of self lift concept offshore nigeria . ... downhole...

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