mitigating drilling riser and conductor fatigue...mitigating drilling riser and conductor fatigue dr...
Post on 27-Mar-2020
11 Views
Preview:
TRANSCRIPT
Mitigating Drilling Riser and Conductor Fatigue
Dr Hugh Howells2H Offshore Engineering Limited
30th October 2013IBC Energy, 2nd Annual Drillships, Seoul, Korea
Learn more at www.2hoffshore.com
Agenda
Sources of fatigueRiser, wellhead and conductor fatigue hotspotsFatigue analysisWhat factors contribute to high fatigueWhy drilling riser fatigue is an increasing concernSteps to minimise riser and wellhead system fatigue damageDrilling riser maintenance and fatigue management
Learn more at www.2hoffshore.com
Riser Loading
Learn more at www.2hoffshore.com
Wellhead System Loading
BOP
LMRP
Flex-joint
Riser
36” x 1.5” seam welded conductor pipe
36” x 1” seam welded conductor pipe
3.5m 1.5m
6.2m
13m
19m
-10.5m Weld-on connector
Housing extension weld
Tree
HP and LP housing
Riser tension Cyclic loading
Snag Load
Learn more at www.2hoffshore.com
Vortex Induced Vibration
Learn more at www.2hoffshore.com
Wellhead System VIV Fatigue
Learn more at www.2hoffshore.com
Wave Induced Motion – Flowbase
Learn more at www.2hoffshore.com
Wave Induced Motion - BOP
Learn more at www.2hoffshore.com
Riser Fatigue Hotspots
Pipe to pipe weldsOne or two per joint
Pipe to coupling welds
Riser couplingsTransitions in sectionLoad shouldersBolts
Along entire riser length
10
Learn more at www.2hoffshore.com
WellheadSystemFatigue Hotspots
Conductor to Wellhead Girth WeldE-Class, SCF=1.3
Conductor to Compression Ring Girth Welds
E-Class, SCF=1.3
Extension Girth WeldE-Class, SCF=1.5
Conductor CouplingB-Class, SCF=5.0
Conductor to Coupling WeldE-Class, SCF=1.3
ConductorSeam Weld
C-Class, SCF=1.0
LMRP / BOPNo fatigue check
performed
Riser pipeE-Class, SCF=1.3
(Not Typical)
Learn more at www.2hoffshore.com
Conductor Fatigue
0.01
0.1
1
10
100
1000
10000
100000
-16 -14 -12 -10 -8 -6 -4 -2 0 2 4
Fati
gue
Life
(Y
ears
)
Elevation Above Sea Bed (m)
UNFACTORED FIRST ORDER FATIGUE LIVES ALONG CONDUCTORRigid Lockdown WH
Lower Bound Upper BoundLearn more at www.2hoffshore.com
Wellhead Fatigue Hotspots
Woodside Xeres and Laverda BOP Oscillation AssessmentUNFACTORED FATIGUE LIFE
Xeres Well, BH1 Soil Data, Hs=5.1m, Tp=7s
-15
-10
-5
0
5
1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04
Fatigue Life (Years)
Elev
atio
n A
bove
Mu
dlin
e (m
)
Conductor Casing
LPWH
36x1.5"XO Jt
36x2"UpperHAC
36x1.5"LowerHAC
HPWH
20"Jt
13-3/8"Pup Jt
13-3/8" Jt
Unavoidable hotspot atLP housing weld
Connectors < 10m belowmudline impair OVERALL
fatigue resistance
Peak bending loads at3-5m below mudline
Learn more at www.2hoffshore.com
VIV and First Order FatigueFATIGUE LIFE ALONG LENGTH OF DRILLING RISER
485.6ft Water Depth, Water Filled, Dual Annular BOP Model, E-Class Curve
0.001
0.01
0.1
1
10
100
1000
10000
100000
1000000
-120 -60 0 60 120 180 240 300 360 420 480 540
Elevation (ft)
Fatig
ue L
ife (Y
ears
)
Slick Joint
Mandrel
Buoyant Joint
UFJDual Annular BOP
ConductorWellhead
RKB
Outer and Inner Barrel
TreeLower
LMRP Connector
LFJ
Learn more at www.2hoffshore.com
VIV Fatigue Damage Build-Up
Learn more at www.2hoffshore.com
Wellhead VIV Variation with Location
WELLHEAD VIV FATIGUE LIVES WORLDWIDE ( Low Pressure Housing Weld)
1.0
10.0
100.0
1000.0
10000.0
0 200 400 600 800 1000 1200 1400Water Depth (m)
Fatig
ue L
ife (D
ays)
WoS - 2 WoS - 3 Asia Pacific North of Shetland West of HebridesAtlantic Margin Norwegian Sea Malaysia Egypt West of Shetland**
** Calibrated software and safety factors - x3 improvement
Envi
ronm
enta
l Har
shne
ss
Scatter due to different BOP heights and
weights
Learn more at www.2hoffshore.com
BOP Stack VIV
• BOP stack natural frequency excitation hasbeen observed in loop currents and underwave loading
• This can result in high accumulated fatiguedamage in the wellhead and conductorsystem below the mudline
17
Seabed
BOP
LMRP
Wellhead
36” / 20" pipe
38” / 36"pipe
Conductor_____Connector
Drilling Riser BOP Stack Excitation
Learn more at www.2hoffshore.com
BOP ResonanceBOP RESONANCE
Effect Of BOP Stack on Curvature at LP Housing Weld
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Mode Number
Cu
rvat
ure
(1/
m)
Increasing BOP Height and Weight (addition of tree)
Load Case 3
Load Case 12
Load Case 13
Load Case 15
Load Case 16
Curvature Factor 2.6
Curvature Factor = 2.6
Damage Factor (2.6)3 = 19
New vessels with large BOP’s give more severe fatigue damageLearn more at www.2hoffshore.com
19
Just how bad can it be?
Summary Acceleration Spectra for 10 min Window
GoM BOP stack VIV at 0.16Hz (6.25 sec stack natural period), Total fatigue consumption at the first connector is 40% in 12 days
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Frequency (Hz)
Acc
eler
atio
nA
mpl
itude
(m/s
2 )
BP Ocean Confidence Event 112 - Magnitude of Peak Response vs. Frequency
Z Axis SpectraMaxima Spectra
1st Harmonic
2nd Harmonic
3rd Harmonic
BP Ocean Confidence Riser VIV Monitoring CUMULATIVE FATIGUE DAMAGE AT CONDUCTOR CONNECTOR
DnV B-Class Curve, SCF = 8.0
0
5
10
15
20
25
30
35
40
45
50
8/3/05 8/8/05 8/13/05 8/18/05 8/23/05
Date
Cum
ulat
ive
Fati
gue
Dam
age
(%)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Cur
ren
t Sp
eed
(kn
ots)
Cumulative Fatigue Damage, SCF=8.0 Max Current Speed
Event 1338th Aug,05 00:00
Event 975th Aug,05 00:00
Event 1126th Aug,05 06:00
Learn more at www.2hoffshore.com
What We Don’t Want to Happen
West of Shetland RegionDiscoverer534 DP drillship440 meter water depth42in air cans on riserPeriodic cycle 5-12 sec2 degree angular motion at riser baseFailed in 29 daysReference DOT paper 1983, C. Hopper, Britoil
One (the only) well documented fatigue failureLearn more at www.2hoffshore.com
Fatigue Drivers
Deep waterHigh VIV fatigue damageCurrents greater than 1m/s (2 kts)Generally low FOF damage
Shallower waterWave generally drives fatigueRiser vibration frequencies may not correspond with current excitation (VIV) frequencies
Large BOP and LMRP’s enable wellhead excitation at higher periods (lower frequencies)
Results in greater wave and VIV induced fatigue
Learn more at www.2hoffshore.com
Fatigue Damage Mitigation –Things to Consider/Avoid
Extension joint length/connector locationCasing swedges (20 to 13-3/8in)“Add-ons” that do not consider fatigueNon-rigid-lockdown wellheadsFatigue details/weld qualityVIV suppression
Learn more at www.2hoffshore.com
Cement Top-Up System
Learn more at www.2hoffshore.com
Guidance System Below Wellhead
Learn more at www.2hoffshore.com
Anti-RotationFins
Learn more at www.2hoffshore.com
BullseyeMountings
Learn more at www.2hoffshore.com
Non-Rigid Lockdown Wellhead
Resting on Landing Shoulder
Lateral Gap Closed
Vertical Gap
Lateral Gap
Learn more at www.2hoffshore.com
Non-Rigid Lockdown Wellhead -Conductor and Casing Stresses
Maximum Stress in Casing, Conductor & Wellhead0.0m Cement Height
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
-12 -9 -6 -3 0 3 6 9 12Vessel Offset (% Water Depth)
Ben
ding
Str
ess
/ Yie
ld S
tres
s
Casing Stress - Light Casing Stress - Heavy Conductor Stress - LightConductor Stress - Heavy Wellhead Stress - Light Wellhead Stress - Heavy
Learn more at www.2hoffshore.com
Fatigue Improvement –VIV Suppression Devices
Learn more at www.2hoffshore.com
Strakes – Below Choke and Kill Lines
OMAE2008-57046
Learn more at www.2hoffshore.com
Fins –(Langhorst)
Learn more at www.2hoffshore.com
Riser Fabrication Considerations
Need to achieve high quality
Welding to get good quality fatigue details with high grade steels is not simple
How does C-class quality need to be proved?
Effort spent on qualifying and obtaining good quality fabrication is generally good value
Pipe dimensional control, welding, coating
Casing
Slick andBuoyant Joints
BOP
LMRP
Lower Flex-Joint
Telescopic
Joint
Tension Ring
Upper Flex-Joint
Drill Floor
Conductor
Learn more at www.2hoffshore.com
Fatigue Integrity Management
Record riser joint usage and times on wellSchedule and implement regular joint inspection
Typical - every 5 years in service Brazil - every 2 years offshore
InspectionLimited ability to inspect fitted riser jointsStrip down of auxiliary lines and buoyancy neededInspection of fatigue hotspots needs good access requiring strip down of joints
Use extended monitoring where needed to measure riser and wellhead system fatigue
Calibrate analysis software and assumptions – reduce conservatismVerify design data – soils
Learn more at www.2hoffshore.com
Example Wellhead Monitoring
3 axis accelerometerDual axis angular rateLoggers located on
BOPWellheadConductorTemplate
Magnetic holdersROV Installed
Learn more at www.2hoffshore.com
Stress and Motion Monitoring - Steps
Monitoring system designOffshore installationSignal processing of measured data
1 LOGGER ON STACK BELOW LOWER FLEX JOINT
5LOGGERS SPACED APPROX .1 EVERY 2 JOINTS
1 LOGGER ON VESSEL
5 LOGGERS SPACED APPROX. 1 EVERY 2 JOINTS
Learn more at www.2hoffshore.com
Current / Wave / Tension / Mud weight monitoring
Ways to Manage Fatigue - MonitoringSoftware and Model Calibration
36
On Rig:
Indicates VIV
Learn more at www.2hoffshore.com
VIV Fatigue Analysis Calibration
Learn more at www.2hoffshore.com
Future Current Concerns
Increased recovery targetsLonger times on the well
Higher pressure (deeper) wellsLonger drilling durations
Post-Macondo design requirementsLarger BOP’s, capping stacks
Use of newer vessels on older wells
Learn more at www.2hoffshore.com
What Works Where?
Wellhead and Conductor Configuration
Low Fatigue Resistance High Fatigue Resistance
3rd and 4th Generation Vessels
5th and 6th Generation Vessels
Wat
er D
epth
Shal
low
Dee
p
Influence of Soil Strength
Learn more at www.2hoffshore.com
Developments
Greater emphasis on fatigue specification of wellhead systems
Longer wellhead extension joints (18m)
Braced wellheads
Wellhead caissons
Larger diameter (42in) conductors
Learn more at www.2hoffshore.com
Summary
Fatigue wasn’t a major design challenge
Vessels, risers and BOP’s are changing to provide greater capability and operating conditions are more diverse
The wellheads are lagging behind
Greater care is required when developing new wells or working on old wells (with new equipment) to ensure fatigue fitness-for-purpose
Learn more at www.2hoffshore.com
Thank you for your time.
Questions……
Further information:
2H Offshore Engineeringwww.2hoffshore.com+44 1483 774900
Learn more at www.2hoffshore.com
Learn more at www.2hoffshore.com
top related