Post on 02-Feb-2021
Session 3: Drilling and Completions
SPE Workshop
20th October 2011
Shreenaath Natarajan
Drilling Riser Design Challenges and Improving Integrity
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Shreenaath Natarajan
Should we be concerned?
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Shreenaath Natarajan
Objectives
• Loading
• Design Issues and Field Problems
• Strength and Fatigue Assessment
• Past Failures
• Integrity Monitoring and Effective Operations Management
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Shreenaath Natarajan
Design Challenges
• Uncertainty in soils and currents
• Limited or no data for new regions
• Uncertainty in rig selection
• Want to assess fitness-for-purpose before selection
• Data may not be available
• Lack of guidance on wellhead selection
• Why choose one over another
• Variability in casing programme
• No two programmes are the same
• Variability in soil properties
• Even when data is defined we have to work between bounds
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Shreenaath Natarajan
Loading
• Well Construction Loads (Exploration and Development)
• Weight of casing
• Pressure from mud, cement and formation fluids
• Temperature
• Drilling Mode (Exploration and Development)
• Weight of BOP and LMRP
• Loads due to vessel offset
• Wave action and first order vessel motions
• VIV response of riser (currents)
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Shreenaath Natarajan
Loading
• Intervention/Workover Mode (Development)
• Loading from drilling riser with horizontal tree in place
• Loading from WO/completion riser (like drilling riser) – applicable on the wellhead and conductor system
• Production Mode (Development)
• Snag loading from fishing gear
• Thermal and pressure loading from well fluids
• Seismic (Development)
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
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Shreenaath Natarajan
Unknowns
• How many slick/buoyant joints to use?
• Optimum top tension to pull?
• Limiting seastate/current loading for drilling operations
• Limiting seastate/current for staying connected to the wellhead with the BOP
• Response time to disconnect riser during mooring line/DP failure
• Strength and fatigue capacity
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Shreenaath Natarajan
Operating Envelope
• Minimise rig down time with prior knowledge of field specific operating limits
Shell - Drilling Riser and Conductor AnalysisOPERATING ENVELOPE WITH CURRENT ONLY
300kips Base Tension - 350m WD - 13.6ppg Mud Weight - Operating Pressure
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
-20 -15 -10 -5 0 5 10 15 20
Vessel Offset (% of Water Depth)
Surf
ace
Cu
rren
t V
eloc
ity
(m/s
)
SurvivalFJ Rotation < 90% maxVM / Yield Stress < 1.0Connector Bending MomentLimit < 1.0
Connected (Not Drilling)FJ Rotation < 90% maxVM / Yield Stress < 0.8Connector Bending MomentLimit < 0.8
DrillingFJ Rotation < 2deg (mean)FJ Rotation < 4deg (max)VM / Yield Stress < 0.67
Motion Upstream Motion Downstream
1 Year Current0.1% Ex. CurrentStroke Limit
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Shreenaath Natarajan
Operating Envelope
• Minimise rig down time with prior knowledge of field specific operating limits
DYNAMIC DRILLING ENVELOPE 181 Te Base Tension - Mud Filled 1.35SG - Soft Soil Profile
0.0
0.2
0.4
0.6
0.8
1.0
1.2
-8 -6 -4 -2 0 2 4 6 8
Vessel Offset (% of water depth)
Surf
ace
Cu
rren
t V
eloc
ity
(m/s
)
Hs < 3m
Hs < 4m
Hs < 5m
Hs < 6m
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Shreenaath Natarajan
Wellhead and Conductor System
• Wellhead and conductor components are integral part of the whole system
• Know the component limits and maximise rig operabilityWhat-Breaks-First Analysis For 350m Water Depth
30in Conductor, Moderate Loading, 300kips Base Tension, 13.6ppg Mud
1.43.3
10.213.9
18.016.6
22.5
9.910.7
5.88.2
8.99.39.3
10.414.0
19.3
9.912.6
20.421.9
18.7
>26.0
>26.0
>26.0
>26.0>26.0>26.0
>26.0
>26.0>26.0>26.0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
upper flex-joint (mean 2deg)lower flex-joint (mean 2deg)
18 3/4" API 10M BOP flange, 5000psi shut-in (bolt makeup=50% σy, 1920 kip-ft)18 3/4" API 10M BOP flange, 3000psi shut-in (bolt makeup=50% σy, 2470 kip-ft)
18 3/4" API 10M BOP flange, mud head (bolt makeup=50% σy, 3063 kip-ft)18 3/4" API 10M BOP flange, 5000psi shut-in (bolt makeup=75% σy, 2870 kip-ft)18 3/4" API 10M BOP flange, 3000psi shut-in (bolt makeup=75% σy, 3700 kip-ft)
18 3/4" API 10M BOP flange, mud head (bolt makeup=75% σy, 4595 kip-ft)
18 3/4" API 5M LMRP flange (1632 kip-ft)
conductor pipe (52ksi)conductor pipe (56ksi)
DrilQuip D60 conductor connector (2440 kip-ft)XLC-S conductor connector (3369 kip-ft)
DrilQuip D90 conductor connector (3660 kip-ft)Vetco RL-4 conductor connector (3800 kip-ft)
Vetco RL-4RB conductor connector (3800 kip-ft)Vetco ALT-2HT conductor connector (4200 kip-ft)
DrilQuip HC-100 conductor connector (5560 kip-ft)Viper conductor connector (7456 kip-ft)
Vetco H4 E wellhead connector (2050 kip-ft @ 5000psi)Vetco ExF H4 wellhead connector (2500 kip-ft @ 5000psi)Cameron HC wellhead connector (3770 kip-ft @ 5000psi)Vetco HD H4 wellhead connector (4000 kip-ft @ 5000psi)DrilQuip DX wellhead connector (6450 kip-ft @ 5000psi)
slip joint/tensioner stroke out (19ft)
lower flex-joint max. rating, upper bound soil (9deg)lower flex-joint max. rating, lower bound soil (9deg)
upper flex-joint max. rating (13.5deg)
LMRP max. release angle, 300kips at LFJ base (10°)
moonpool clearance fore-aft (20.3ft)moonpool clearance port-stdboard (beam in - 12.5ft)
moonpool clearance port-stdboard (beam away - 30ft)
Vessel Offset (% Water Depth)
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Shreenaath Natarajan
Fatigue Capacity
• How long can I stay connected to the wellhead
• Do I expect to re-enter the well for intervention/workover?
• Is it possible to extend the drilling duration due to side-tracking of the well?
Shell - Drilling Riser and Conductor Analysis
CONDUCTOR VIV FATIGUE LIFE (UNFACTORED)Fatigue Life At Connector and Welded Connection - 1370m WD
1E-02
1E-01
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
1E+07
1E+08
1E+09
-20 -15 -10 -5 0 5
Elevation above Mudline (m)
Fati
gue
Life
(Y
ears
)
LB Soil
Conductor Coupling Weld
DnV E/SCF=1.3
30" Wellhead
18 3/4" WellheadConductor Pipe
DnV B/SCF=1.0
Conductor Coupling
DnV B/SCF=5.0
Wellhead Housing Weld
DnV E/SCF=1.3
Seabed
30" Conductor LPH HPH BOP
Shell - Drilling Riser and Conductor AnalysisRISER VIV FATIGUE LIFE (UNFACTORED)DnV E Class (SCF 1.3) - 150kips Base Tension
1E+00
1E+02
1E+04
1E+06
1E+08
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
Elevation above Mudline (m)
Fati
gue
Life
(Y
ears
)
LB Soil UB Soil
Seabed
UFJLFJ
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Shreenaath Natarajan
Can Failure Happen?
• High pressure housing to surface casing weld fatigue failure
• Facts
• West of Shetland Region
• 440m water depth
• Run from a drill ship
• Fatigue life – 29 days?Censored intentionally
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Shreenaath Natarajan
Can Failure Happen?
• Soft soil coupled with large motions
Censored intentionally
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Shreenaath Natarajan
Field Problems
• Design Issues
• Inadequate fatigue life, usually VIV driven
• Changes in vessel and riser arrangement
• Field Problems
• External cement shortfall
• Conductor-casing cement shortfall
• Wellhead stick-up
• LP to HP housing lock malfunction
• Extended drilling /workover operations
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Shreenaath Natarajan
Conductor and Casing Installation Issues
• Elevation Tolerance
• +2m not uncommon (drilling or jetting)
• Adds to lever arm of loading on wellhead
• Can make VIV response severe
• Inclination Tolerance
• Typical target +/- 1.5degrees
• Expectation less than 0.5degrees due to weight of conductor
• Quality dependent on care during initial penetration
• Vessel position
• Current conditions
• Soil uniformity
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Shreenaath Natarajan
Improving System Integrity
• BP Schiehallion – severe currents and high VIV in 350-500m West of Shetland
• BP GoM – severe currents
• BP West Nile Delta VIV (4 well campaign)
• Statoil – old wells, new vessels with big BOP’s and large motions observed
• Total – severe currents and high VIV in 350-500m West of Shetland
• Woodside, Petronas, Repsol, and many others ..
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
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Shreenaath Natarajan
Improving System Integrity
• Norwegian North Sea
• Motions and Fatigue
• West Nile Delta
• Fatigue
• 3 Axis Accelerometer
• Dual axis angular rate
• Loggers located on
• BOP
• Wellhead
• Conductor
• Template
• Magnetic Holders
• ROV Installed
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Shreenaath Natarajan
Conclusions
• Design issues due to complex response and lack of prior field specific data can be overcome by the following:
• Develop operating envelopes and incorporate in to a manual
• Observe requirements of the manuals
• Record operating conditions and confirm limits are not exceeded
• Record times on well
• Monitoring riser/wellhead to confirm acceptable fatigue response
• Calibrate analysis software
• Verify design data – soils, currents etc
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