1OMAE2008-57047

OMAE 2008-57047 Offshore Drilling Riser VIV Suppression Devices

What’s Available to Operators?Samuel Taggart & Mike Tognarelli –

BP America June 2008

2OMAE2008-57047

Deepwater Drilling in Loop Currents

Operational Issues :

•

Types of drill rig – DP and Moored – manoeuvrability

•

In combination with hurricane season – retrieval ability

•

Production drilling over subsea architecture – consequential damage

•

Unproductive drilling time – 2005 many tens of millions of dollars

3OMAE2008-57047

Improving Drilling Operations in High Currents

A company equipment review produced two main areas of interest :

1. Riser devices that decrease drag and suppress VIV

2. Development of improved mechanical drilling riser centraliser - Increases the operational window for retrieval of riser- Particularly important during hurricane season- To be deployed for operation in 2008

This paper will address the work done in the area of available devices for drag reduction and suppression of VIV

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FLOW DEVICES –

Summary History

Types of flow improving devices:

Passive Devices

• fairings, shrouds, etc.

Active Devices

• Air, water jetting,etc

Drilling Riser hard up against

diverter housing in a 2 knot current

The BENEFITS

• Reduce drag - Riser top and bottom angle

• Suppress VIV – Riser vibrations

5OMAE2008-57047

Some Passive Devices

Passive Devices

• Fairings (rigid)• Deformable Shrouds• Buoyancy Modules

• Distribution• Helical Grooved

• Axial Rod Shrouds• Perforated Shrouds• Windings / helical wraps• Hoops / Spaced Spoilers• Fins / Bumper Bars• Splitter plates• Bumps / Waves AIMS Splitter

Full fairing

6OMAE2008-57047

Passive Devices, cont’d

Inverted Helically Grooved buoyancy

Wavy Buoyancy profileAxial Rod Shrouds

Perforated Cylindrical Shroud

Lankhorst Fins on Drilling Riser

Helical Rope Wrap

Hoops / Spaced Spoilers

7OMAE2008-57047

Operational Device Review -

Findings

Nearer Term most favourable options for operation

1. Fairings (rigid) – various designs and associated performance claims2. Fairings (flexible) – prototype construction underway3. Fins / Bumper bars – designs in use4. Helical Wraps – previously used as temporary mitigation

All but one in use today on GoM Drill Rigs

Benefit Decision for Deployment

a. Performance – dynamic behaviour benefit ?b. Robustness – survivabilityc. Marine logistics – container transfer , storage and available work areasd. Deployment/Recovery efficiency – time management GoM Hurricane impact e. Mechanical Handling – Crew resources, cross lifting, rig modificationsf. Health/Safety/Environment – dropped objects, failure risks and consequence

Need to perform an Operational Benefit Analysis – Numeric (Time / Cost)

8OMAE2008-57047

Fairings –

Need for Performance Acceptance

To help understand and clarify Fairing Performance against Claims

1. Establish a performance acceptance criteria for fairing products(i.e. see paper for specifics)

•

Drag Reduction level set•

VIV Suppression , Stability and Motion Amplitude

2. Invite suppliers to put forward products for large scale BP proving tests

Two fairing suppliers came forward with products

•

AIMS Inc. – Dual Fin Splitter Fairing•

Trelleborg Offshore – RiserFin Fairing

3. A 3rd company Allbrown also requested proof of concept tests on their flexible fairing -

9OMAE2008-57047

Fairings –

Acceptance Model Tests

• Performed at Institute for Ocean Technology in St. John’s – Free Vibration on Springs

• Specific deepwater drilling riser (OD=1.33m) scaled to 0.24 for tests

• Model test matrix targeted for full scale ranges of Re and VrnModel Cylinder

0.00

5.00

10.00

15.00

20.00

25.00

1.00E+04 1.00E+05 1.00E+06 1.00E+07

Reynolds Number

Red

uced

vel

ocity

0.25 Hz0.50 Hz0.75Hz1.00Hz1.50Hz2.00Hz3.00Hz

`

• Comprehensive fixed and freely vibrating tests performed • Bare pipe benchmarking tests• 2 Off fairing type acceptance test sets

10OMAE2008-57047

AIMS Dual Fin Splitter -

ADFS

AIMS Splitters Installed and Prepped for Testing

(88% Coverage Including Dummy Section)

Fairing SectionThrust collar

Endplate

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Trelleborg RiserFin Fairing

Fairing Section

Thrust collar

Endplate

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Fairing Results + Conclusions

•

Both Fairing Products tested satisfied the ‘Acceptance Criteria’ for Drag Reduction and VIV suppression

• Typical drag coefficient (Cd) were around 0.6 with good VIV suppressionDrag Cofficient vs. Reynolds Number

AIMS Fairing

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 200000 400000 600000 800000 1000000 1200000 1400000 1600000 1800000Reynolds Number (Re)

Dra

g C

oeffi

cien

t (C

D)

Fixed (rough)Free (rough)Fixed (polished)

Drag Coefficient vs. Reynolds NumberCRP Fairing - Free Vibration

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 200000 400000 600000 800000 1000000 1200000 1400000 1600000Reynolds Number (Re)

Dra

g C

oeffi

cien

t (C

d)

Free Test Poly. (Free Test )

Amplitude ration vs. Nominal Reduced VelocityAIMS Fairing

0.00

0.02

0.04

0.06

0.08

0.10

0 5 10 15 20 25 30Nominal Reduced Velocity (U*)

Am

plitu

de R

atio

(A*)

13OMAE2008-57047

VT Fairing –

Concept Proving

•

Operational target is to get over some of the downside impact of working with rigid fairing – lighter , flexible , easy storage , less work area demand

•

Concept proving model tests completed at University of Southampton – limited Re range tested

•

Results showed that VT highly effective at suppressing VIV with reduced dynamic drag loading

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Full Scale Operational Experience

•

Model tests indicate benefit but how do fairings perform for real ?

•

BP measuring and monitoring behaviour of deepwater drilling risers for a number of years

•

Two drilling campaigns have been under taken with different types of fairings (SGSI designs)

•

Indications are that the fairings did suppress VIV behaviour in higher current situations

15OMAE2008-57047

GSF Explorer Drilling Riser

Fairings Data:

•

7 buoyant joints equipped with fairings

•

Shell Global Solutions, Inc. (SGSI) -

full wrap fairings

•

Chord/Diameter (C/D) Ratio: 1.5

•

Length: 6 ft

Monitoring Data:

•

9 months of monitoring

•

VIV occurs 1.6% of time

•

Max current below 0.5 knots except for period of 21st

July to 27th

July 07 when a max current speed of 2.1

knots observed

11 Slick Joints WT =0.875"

BOP

LMRP

Lower FJ

21 joints 3000ft rating Buoyancy

13.0 ft ––––––

Seabed

39.0 ft ––––––

62.8 ft ––––––

1187.8 ft ––––––

MSL 4595 ft

Well head

4 Slick Joints WT =0.750"

887.8 ft ––––––

1637.8 ft ––––––

Drill Floor

Intermediate FJ

Termination Joint & Pup

Tensioner Ring

Outer Barrel

Inner Barrel & Pup Joint

Diverter & Upper FJ

4542.8 ft ––––––

4669 ft

4620 ft ––––––

4647.8 ft ––––––

4412.8 ft ––––––

6 joints 5000ft rating Buoyancy

3887.8 ft ––––––

7 joints 3000ft rating Buoyancy with Fairings

Staggered section 4 jts 3000ft rating Buoyancy 5 jts Slick

3212.8 ft ––––––

36” & 28” Conductor (157.5 ft)

16OMAE2008-57047

Ocean Confidence

Drilling

Riser

Fairings Data:

•

14 buoyant joints equipped with fairings

•

SGSI -

tailfin fairings

•

Chord/Diameter (C/D) Ratio: 1.45

•

Length: 6 ft

Monitoring Data:

•

2 months of monitoring

•

VIV occurs 4.1% of time

•

Max current speed: 0.95 knots

35 ft Termination Joint

BOP

LMRP

Lower FJ

10 ft ––––––

Seabed

63 ft ––––––

473 ft ––––––

MSL 4065 ft

5 Slick Joints

2273 ft ––––––

Drill Floor

Intermediate FJTermination Joint & Pup Joints

Tensioner Ring

Outer Barrel

Inner Barrel

Diverter & Upper FJ

4033 ft ––––––

4153 ft

4112 ft ––––––

4135 ft ––––––

3998 ft ––––––

24 joints 5000ft rating Buoyancy

3173 ft ––––––

Well head

98 ft ––––––

12 joints 3000ft rating Buoyancy (3 Top joints with Fairings)

11 joints 2000ft rating Buoyancy (with Fairings)

1125 ft of Fairings

17OMAE2008-57047

Conclusions

•

Fairing performance has been demonstrated to various levels of rigor

•

The final choice for fairing use on a drilling riser for a particular well location tends to be a pure

Cost / Benefit Decision

•

Recommendations:

−

Operability analyses using fairing performance data

−

Cost-benefit analysis: “saved”

downtime vs. “lost”

trip time and handling / storage issues

−

Attention to minimizing “lost”

time in fairing designs