OMAE 2008-57047 Offshore Drilling Riser VIV Suppression Devices What’s Available to Operators? Samuel Taggart & Mike Tognarelli – BP America June 2008 OMAE2008-57047 1
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 OMAE2008-57047 2
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 OMAE2008-57047 3
FLOW DEVICES – Summary History The BENEFITS • Reduce drag - Riser top and bottom angle • Suppress VIV – Riser vibrations Types of flow improving devices: Passive Devices • fairings, shrouds, etc. Drilling Riser hard Active Devices up against diverter housing in a 2 knot current • Air, water jetting,etc OMAE2008-57047 4
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 AIMS Splitter • Bumps / Waves Full fairing OMAE2008-57047 5
Passive Devices, cont’d Perforated Cylindrical Shroud Hoops / Spaced Spoilers Axial Rod Wavy Buoyancy profile Shrouds Lankhorst Fins on Drilling Riser Inverted Helically Grooved buoyancy Helical Rope Wrap OMAE2008-57047 6
Operational Device Review - Findings Nearer Term most favourable options for operation 1. Fairings (rigid) – various designs and associated performance claims 2. Fairings (flexible) – prototype construction underway 3. Fins / Bumper bars – designs in use 4. 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 – survivability c. Marine logistics – container transfer , storage and available work areas d. Deployment/Recovery efficiency – time management GoM Hurricane impact e. Mechanical Handling – Crew resources, cross lifting, rig modifications f. Health/Safety/Environment – dropped objects, failure risks and consequence Need to perform an Operational Benefit Analysis – Numeric (Time / Cost) OMAE2008-57047 7
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 A 3 rd company Allbrown also requested proof of concept tests on their 3. flexible fairing - OMAE2008-57047 8
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 Vrn Model Cylinder 25.00 20.00 0.25 Hz Reduced velocity 0.50 Hz 15.00 0.75Hz 1.00Hz ` 1.50Hz 10.00 2.00Hz 3.00Hz 5.00 0.00 1.00E+04 1.00E+05 1.00E+06 1.00E+07 Reynolds Number • Comprehensive fixed and freely vibrating tests performed • Bare pipe benchmarking tests • 2 Off fairing type acceptance test sets OMAE2008-57047 9
AIMS Dual Fin Splitter - ADFS AIMS Splitters Installed and Prepped for Testing (88% Coverage Including Dummy Section) Endplate Thrust collar Fairing Section OMAE2008-57047 10
Trelleborg RiserFin Fairing Thrust collar Fairing Section Endplate OMAE2008-57047 11
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 suppression Drag Cofficient vs. Reynolds Number AIMS Fairing 1 Amplitude ration vs. Nominal Reduced Velocity Fixed (rough) 0.9 AIMS Fairing Free (rough) 0.10 0.8 Fixed (polished) 0.7 Drag Coefficient (C D ) 0.08 0.6 Drag Coefficient vs. Reynolds Number CRP Fairing - Free Vibration 0.5 Am plitude Ratio (A*) 1 0.06 0.4 0.9 0.3 0.8 0.04 0.2 0.7 Drag Coefficient (Cd) 0.1 0.6 0.02 0 0.5 0 200000 400000 600000 800000 1000000 1200000 1400000 1600000 1800000 0.4 Reynolds Number (Re) 0.00 0.3 0 5 10 15 20 25 30 0.2 Nominal Reduced Velocity (U*) Free Test 0.1 Poly. (Free Test ) 0 0 200000 400000 600000 800000 1000000 1200000 1400000 1600000 Reynolds Number (Re) OMAE2008-57047 12
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 OMAE2008-57047 13
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 OMAE2008-57047 14
GSF Explorer Drilling Riser 4669 ft Drill Floor Diverter & Upper FJ 4647.8 ft –––––– Inner Barrel & Pup Joint Fairings Data: 4620 ft –––––– Tensioner Ring MSL 4595 ft Outer Barrel • 7 buoyant joints equipped with fairings 4542.8 ft –––––– Intermediate FJ • Shell Global Solutions, Inc. (SGSI) - full wrap fairings Termination Joint & Pup 4412.8 ft –––––– • Chord/Diameter (C/D) Ratio: 1.5 7 joints 3000ft rating Buoyancy with F airings 3887.8 ft –––––– • Length: 6 ft Staggered section 4 jts 3000ft rating Buoyancy 5 jts Slick 3212.8 ft –––––– 21 joints 3000ft rating Buoyancy Monitoring Data: 1637.8 ft –––––– 6 joints 5000ft rating • 9 months of monitoring Buoyancy 1187.8 ft –––––– • VIV occurs 1.6% of time 4 Slick Joints WT =0.750" 887.8 ft –––––– • Max current below 0.5 knots except for period of 21 st 11 Slick Joints WT =0.875" July to 27 th July 07 when a max current speed of 2.1 knots observed Lower FJ 62.8 ft –––––– LMRP 39.0 ft –––––– BOP 13.0 ft –––––– Well head Seabed OMAE2008-57047 15 36” & 28” Conductor (157.5 ft)
Ocean Confidence Drilling Riser Drill Floor 4153 ft Fairings Data: Diverter & Upper FJ 4135 ft –––––– Inner Barrel 4112 ft –––––– Tensioner Ring • 14 buoyant joints equipped with fairings MSL 4065 ft Outer Barrel 4033 ft –––––– • SGSI - tailfin fairings Intermediate FJ Termination Joint & Pup Joints 3998 ft –––––– • Chord/Diameter (C/D) Ratio: 1.45 11 joints 2000ft rating Buoyancy (with Fairings) • Length: 6 ft 1125 ft of Fairings 3173 ft –––––– 12 joints 3000ft rating Buoyancy (3 Top joints with Fairings) 2273 ft –––––– 24 joints 5000ft rating Buoyancy Monitoring Data: 473 ft –––––– 5 Slick Joints • 2 months of monitoring 98 ft –––––– 35 ft Termination Joint Lower FJ • VIV occurs 4.1% of time 63 ft –––––– LMRP BOP • Max current speed: 0.95 knots 10 ft –––––– Well head Seabed OMAE2008-57047 16
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 − OMAE2008-57047 17
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