High Integrity / Reliability Gas Lift Valves for Subsea Applications

Alan Brodie PTC

Abstract

Session : Subsea Deep Water TLP

Presentation Title: New gas lift valve technology providing the reliability and performance required for deepwater applications

Author / Presenter: Alan Brodie PTC

Abstract:

This presentation will describe a new category of gas lift valves, which have been designed for the most challenging subsea applications, but which can also be technically and economically justified in more mainstream applications .

In addition to being rated to 10k psi, and thus significantly extending the envelope of deep water applications where gas lift can be deployed, the valves have also been accredited as fully fit for purpose as well barrier valves. Consequently, unlike their predecessors they don’t compromise the integrity of the production tubing string. The valves also facilitate higher unloading rates than their predecessors, an important consideration given the high cost of deep water well operations.

The relative merits of gas lift completion design with low pressure lift gas and unloading valves vs high pressure lift gas and no unloading valves will also be discussed.

Introduction

• Subsea gas lift – the key differences

– What are they

– How to address them

• New gas lift valves for subsea gas lift

– Design objectives

– Solution delivered

– Performance

– Track record

• Conclusions

Image used with the permission of Xodus Group

Subsea Gas Lift: The key differences

• Cost of well intervention if things go wrong

– Land gas lift valve change out cost $ 0.08 million

– Platform gas lift valve change out cost $ 0.2 million

– Subsea gas lift valve change out cost $ 4 million

• Availability of intervention vessels can also be challenging

Subsea Gas Lift: The key differences

• Completion reliability and lifetime critical

– Keep designs simple and robust

• Use as high lift gas pressure as possible to get lift gas deep

– Recognising impact on subsea pipeline spec / costs etc

• Avoid using unloading valves if possible

– Or at least use unloaders that fail in the closed position

– Specify high integrity / high reliability gas lift valves

• Various major OPCO’s now doing so

– New standards for gas lift valve testing

– Far more stringent than existing API specs

New gas lift valve design objectives

• New gas lift valves to:

– Form part of the primary well barrier

• Same leak rate as permitted by packers / bridge plugs

– 0.1 scf/day

– i.e. satisfying “V1 criteria“ : 20 cc/ 10 mins

• Operating check valve to close at a dp of 0 psi

• Unloading valve to close in event of bellows failure

– Address the most commonly observed failure modes

• Seal face erosion during unloading.

– Because API RP 11V is not always adhered to

• Spring fatigue

• Multiphase injection or wet gas erosion

• Seat damage due to valve vibration and chattering

Image used with the permission of J Bellarby

Solution to gas lift valve challenges

• Required a complete valve design rethink

– Fresh sheet of paper

– First principles physics

– Common sense practicality

New Gas Lift Valve Unique Features Designed for retrofit in standard 1” – 1.75” SPM’s

• Unique in almost all other respects– Patented orifice dart linkage

– No internal elastomers

– Spring location, size & utilisation range

– Flow Path Geometry

– Materials and Coatings

– Bellows working dp 10k psi

– Bellows tested to 3500 cycles

– Shear system which does not impact on orifice size after shear

• Many unique advantages – No valve chatter and vibration

– A true metal / metal seal

• Vo option available

– Fatigue is minimised

– Valves would fail in closed position

• Unloading valve held by spring

• Orifice valve closed w 0 psi dp

– Valves suitable for wet lift gas or lift gas with entrained chemical injection

– Higher gas flow rates vs competitor valves at maximum orifice size

– Deeper more reliable unloading valves

• Increased production

– Completion operational efficiency

Stavanger Aberdeen Houston

Particle Velocity Modelling

New Gas Lift valve erosion performance Test Water erosion test API GLV

requirement

1” SafeLift 1.5” SafeLift 1.75” SafeLift

1 Pump rate bbl/min 1.00 1.25 1.5 1.5 std 3 max

Volume pumped bbl 400 600 600 600

Test media N2 N2 N2 N2

Leak rate scf/D < 35 0 0 0

2 Gas flow Test

Rate steps --- 20 20 20

Max gas rate mmscf/D --- 3,53 6,7 17

Flowing time, hrs --- 148 145 145

Leak rate scf/D --- 0 0 0

Fatigue test, cycles --- 100 100 100

3 Final function test

Max temp, dec C --- 185 165 165

No of cycles --- 6 6 6

Leak rate, scf/D --- 0 0 0

4 Extensive erosion test

Test fluid --- Tap water Brine w/Barite Water with barite

Particle content, lbs/bbl --- 0 0,70 1,40

Pump rate bbl/min --- 1,00 A)1,0 B)1,2 C)1,5 A)1,5 B)3,0

Volume pumped, bbl --- 4000 600 in each step A)1200 B)600

Leak rate, scf/D --- ZERO ZERO ZERO

New Gas Lift valve performance

• Operational efficiency

– Shear out option can save 1 -2 days installation time

– Faster unloading times can save 1 -2 days commissioning

– Very low dp for critical flow

• Higher throughput for same lift gas pressure

• Important at largest orifice sizes

New Gas Lift valve track record

• 180 valves installed for up to 2 years now

– To date , no requirement to pull valves due to premature failures

• Even in multiphase injection applications where gas lift valves previously required changing out every 3 – 4 months

• Only family of valves to fully comply with new gas lift valve test criteria

Conclusions

• A new family of high integrity / high reliability gas lift valves developed

• The valves have been thoroughly tested well beyond API specs

– By a number of leading OPCO’s

– Now approved for use in demanding applications

• The valves have been in use for over 2 years

– With no premature failures

• Their high integrity / reliability makes them ideally suited for subsea apps

– Where well intervention costs are extremely high

Image used with the permission of Xodus Group

Feb. 1 - 5, 2010 2010 Gas-Lift Workshop 13

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Feb. 1 - 5, 2010 2010 Gas-Lift Workshop 14

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