LGS technology for Drilling Risers - Reducing Costs by increasing Operability whilst improving safety. Courtesy of AMOG, presented at the RINA Conference - AOG 2017 by Adrian Eassom.
5. VIV Suppression Solutions
> Although there are existing solutions for VIV suppression in
drilling risers, there is still a demand for a VIV suppression
technology that combines the following:
• A solution that effectively suppresses VIV without an increase in static drag.
• A solution that is reliable, increases operability and improves safety during
drilling operations.
7. LGS Development
> Concept
• Inspired by the Saguaro cactus.
> Small Scale Testing
• Geometry Optimisation.
> Large Scale Testing
• High Reynolds Number testing of the optimal LGS design.
> Full Scale Deployment
• Deployed in July 2016 in the Gulf of Mexico.
8. Small Scale Testing
> Testing performed at Monash University
Water Channel
> 35 Geometries
> +100 Tests
9. > VIV and drag behavior for a cylindrical object is dependent on
the Reynolds Number.
What about High Reynolds Number?
DragCoefficient
Reynolds Number
High Re Testing
Low Re Testing
11. > NRCC Towing Tank Test Facility (St John’s Canada)
> The optimal LGS design was tested
> Grooves run longitudinally alternating down the buoyancy
module
> Scale= 1:3.5
Large Scale Testing
13. Key Results: Amplitude of Vibration
Bare Cylinder
LGS Low Re results
LGS Testing Results
LGS High Re results
Diameter, D, based on the Outer Diameter
14. Key Results: Fixed Drag Coefficient
LGS High Re results
Fairings Results
15. > LGS® Technology has clear hydrodynamic advantages and
desirable characteristics for use in drilling risers.
> These advantages and characteristics translate into the following
benefits:
• Increased drilling operations uptime
• Increased fatigue life of drilling risers
> The following concept evaluations are based on results from
High Reynolds testing, and analysis performed with industry
leading VIV prediction software SHEAR7.
Integrating LGS® technology into Drilling Riser Buoyancy Modules
Drilling Riser Application
17. Concept Evaluation Results –
Extreme Current Offset Performance
> Extreme current
• Surface speed =
2.3 m/s
> LGS out-performs
both Conventional and
Conv. Buoyancy with
Fairings:
• LGS has lower top angle
• LGS has lower offset
0
200
400
600
800
1000
1200
1400
0 1 2 3
Depth
[m]
Current Speed
[m/s]
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30
ArcLengthDownTheRiser
[m]
Offset
[m]
LGS
Buoyancy
Top 675ft
w/Fairings
Conventional
Buoyancy
18. > For a particular example site,
all loop current profiles that
persist over a year were
simulated
> Took account of:
• Magnitude variations
• Annualised Probability and
persistence
Concept Evaluation Results –
Annualised Operability
19. > Relative increase in operability = 33%
> Increase in operational hours = 366 hours (~15 days)
> Overall, approximately a 25% increase in absolute operability during annual
Eddy currents is expected at the example site. This is based current conditions
on an annualised basis.
LGS® was shown to increase operability uptime in GoM during
Eddy Current Episodes
Concept Evaluation Results –
Annualised Operability
Operability Uptime
Measure
Conventional Circular
DRBMs
Conventional DRBMs with
Fairings
LGS
DRBMs
% of Eddy Current Period
Operable
67% 86% 89%
Annual Hours Increase
(Relative to Conventional DRBMs)
0
322
(13.4 days)
366
(15.3 days)
20. > Damage Rate relative difference:
• Conv. : R8 Ratio
• 50 : 1
> Over a 1 Yr period, conventional
buoyancy riser has been damaged at a
rate 50 times faster than the LGS®riser.
LGS® Technology demonstrates improved fatigue performance over
conventional buoyancy modules
Concept Evaluation Results –
Annualised Fatigue Performance
Fatigue Performance
Measure
Conventional
Round DRBMs
Conventional
DRBMs with
Fairings
LGS
DRBMs
Annual Damage Rate [1/Yr] 8.8E-02 1.3E-03 1.8E-03
Design Life (unfactored years
of continuous service) [Yr] 11.4 769 556
Design Life (with Safety Factor
of 10) [Yr] 1.14 76.9 55.6