Improving Operability and Reducing Costs of Drilling Riser - - PowerPoint PPT Presentation

Andrés Tovar Rodríguez – AMOG Consulting Latino América

Improving Operability and Reducing Costs of Drilling Riser Operations Through the Use of LGS VIV And Drag Suppression Technology

September 27, 2017

A significant challenge for offshore oil and gas globally

Vortex-Induced Vibration - VIV

Vortices shed by cylindrical body Shedding frequency similar to a natural frequency of the structure Vortex Induced Vibrations

Effects include:

• Fatigue Damage
• Amplified Drag
• Impacts on operability

Deeper water increases the risk

Effect on offshore infrastructure

VIV affects many types of offshore infrastructure

Drill string can only operate with a low curvature in the riser In strong currents, VIV amplifies the drag on the riser, and deflections become unacceptable Fatigue damage can accumulate quickly Significant cost implications – projects have been postponed for years as a result

Impact on drilling risers

Deepwater drilling risers are covered with DRBMs to lower the top tension DRBMs must:

• Maximize cross sectional area

(maximum buoyancy)

• Fit through the limited space available

in the drill floor

Drilling Riser Buoyancy Modules

Image: Trelleborg 2017

Helical Strakes:

• Used throughout the offshore industry

to suppress VIV

• Almost completely eliminate VIV
• Increase drag
• Not suitable for DRBMs due to loss of

buoyancy

Traditional VIV Suppression

Image: Trelleborg 2017

DRBMs requiring VIV suppression typically use fairings Fairings must rotate to align with the current direction Fairings can:

• Lock, or fail to rotate (performance is

unknown)

• Fall off (up to 20% of fairings)

Traditional VIV Suppression

Image: Matrix Composites & Engineering

Fairings require significant additional time to install Impacts:

• Additional risk to installation

personnel

• Additional time paying spread rates
• Reduced ability to quickly retrieve and

run from a storm

Traditional VIV Suppression

Image: Matrix Composites & Engineering

A new VIV suppression technology that can be integrated into DRBMs Balances competing requirements:

• VIV suppression
• Low drag
• Maximum buoyancy
• Ease of use

Longitudinally Grooved Suppression

Image: Matrix Composites & Engineering

Inspired by the Saguaro cactus, which has evolved a low drag shape to withstand strong winds

LGS Development

Image: Matrix Composites & Engineering Image: Hillhaus

LGS Development Small Scale

• Rapid prototyping
• Measured performance
• Selection of best

geometries

Large Scale

• Performance under

realistic conditions Images: AMOG

LGS Performance

0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Bare Cylinder LGS

Drag

0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Bare Cylinder LGS

VIV Amplitude

South American offshore currents can include significant counter currents at depth VIV suppression may be required at both the top and the bottom of the riser The effect of LGS had not previously been studied in counter currents

South American Currents

Current Speed Water Depth

Current profiles used in the analysis:

• Both extreme and long term

currents

• With and without counter

currents

Current Profiles

250 500 750 1000 1250 1500

• 1
• 0,5

0,5 1 1,5 2

Water Depth (m) Current Speed (m/s)

Long Term Current Long Term Current with Countercurrent Extreme Current Extreme Current with Countercurrent

Riser Arrangements

LGS does not behave like a bare cylinder:

• Drag amplification,
• Vibration behavior and
• Vibration frequency
• Are all different

A customized version of SHEAR7 was used for the analysis

Analysis Method

Without counter current

Results – Long Term Current

With counter current

200 400 600 800 1000 1200 1400 1600 2 4 6 8 10 Water Depth (m) Riser Offset (m) LGS Conventional Fairings 200 400 600 800 1000 1200 1400 1600

• 8
• 6
• 4
• 2

2 Water Depth (m) Riser Offset (m) LGS Conventional Fairings

Without counter current

Results – Extreme Currents

With counter current

200 400 600 800 1000 1200 1400 1600 5 10 15 20 25 30 Water Depth (m) Riser Offset (m) LGS Conventional Fairings 200 400 600 800 1000 1200 1400 1600

• 2

2 6 10 14 18 Water Depth (m) Riser Offset (m) LGS Conventional Fairings

Results – Top Angles

Top angle in Degrees Conventional Fairings LGS Long Term Current 1.6 1.3 1.0 Long Term Current with Countercurrent 0.6 0.5 0.4 Extreme Current 6.6 4.1 4.3 Extreme Current with Countercurrent 5.3 3.4 3.5

Results – Fatigue Life

Fatigue Life in Years Conventional Fairings LGS Long Term Current 65.5 267 2461 Long Term Current with Countercurrent 30.9 80.4 1812 Extreme Current 2.35 93.6 33.9 Extreme Current with Countercurrent 3.59 24.8 19.2

When strong currents exist at depth, VIV suppression over the entire length of the riser is advantageous This cannot be practically achieved with fairings LGS provides VIV suppression which will be effective in all current conditions This performance is achieved without any additional handling time LGS not subject to mechanical failure as with fairings

Conclusions

Model testing and computational simulations have shown the predicted benefits of LGS Validation via instrumented riser is underway Preliminary results indicate performance as expected

Conclusions

Image: Matrix Composites & Engineering

AMOG would like to thank Matrix Composites & Engineering Pty Ltd for their support of the high Reynolds number testing and field trials

• f LGS.

LGS is a registered trademark

• f AMOG Technologies Pty Ltd

and has patents pending.

Acknowledgements

Image: Matrix Composites & Engineering

LGS is manufactured under license by Matrix Composites & Engineering