On the Oceanography of Brazil’s Equatorial Margin: Hazardous Offshore Currents and Strategies for Mitigation

Dave Fratantoni, Andre Gellers, and Neha Sharma

Horizon Marine, Inc.Massachusetts, USA

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• Brazil’s Equatorial Margin has both extraordinary development opportunities and significant operational challenges.

• Strong and variable ocean currents are a primary concern.

• Exchange between blue-water and coastal regimes is poorly understood.

• A regional ocean observing and prediction system can provide improved situational awareness to mitigate the impact of strong currents on offshore operations, enhance safety, and protect the environment.

Conclusions

Outline

• Geographic Context and Operational Challenges

• Oceanographic Environment

• Strategies for Mitigation

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Geographic Context

BEM potential may be similar to West Africa

Zaedyus find in French Guiana is encouraging

Coastline is extensive, sensitive

5 basins

TotalQuieroz GalvaoBPBHP Billiton

Quieroz Galvao

BGBPOGPBHP Billiton

ExxonMobilChevronBPOGPBHP Billiton

OGPEcopetrolExxonMobilPetrobras

5 basins

5 basins3 regions

5 basins3 regions2 regimes

• Tides and tidal currents• River outflow

Intense, persistent, and vertically-complex boundary current

Sensitive habitats

• Tides and tidal currents• River outflow

Intense, persistent, and vertically-complex boundary current

Sensitive habitats

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Operational ChallengesENSCO 8503TullowFrench Guiana

• Remote location

• Extensive coastline with sensitive ecosystems

• Strong and variable ocean currents

• Poorly understood connections between offshore and coastal regimes

Holding station with 90% thrust

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Oceanographic Environment

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SeaWiFS Ocean Color

Satellite observations are descriptive – but not always quantitative.

12 years of surface drifter trajectories (n=450)

Color = Current Speed

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• Direct measure of surface velocity, exchange processes

• Analog for anything drifting at the ocean surface

• Excellent for model validation

• Easy to deploy from a variety of platforms

• Inexpensive robust statistics

Why surface drifters?

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Histogram of all drifter-derived current measurements in each BEM region

Average measured current speed as a function of WATER DEPTH

Gray dots are all measurements

Average measured current speed as a function of WATER DEPTH

Gray dots are all measurements1000 m

1/3-deg Gridded log(NDATA)

Number of hourly velocity estimates from drifter position record

1/3-deg Gridded Current Velocity

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Numerical Ocean Model

VELOCITY (kts)

Models are ALWAYS wrong

Models are ALWAYS wrong

Models are ALWAYS wrong

Models can be useful if constrained and validated by observations

We must know HOW the model is wrong, and WHEN it can be trusted

Strategies for Mitigation

To mitigate the impact of strong ocean currents and operate successfully in the equatorial margin we require enhanced situational awareness, specifically:

• Accurate measurement of currents TODAY

• Accurate forecast of currents TOMORROW

Observations ForecastModel

A regional observation and prediction system

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• In-situ measurements of ocean currents• Inexpensive• Sustainable• Spatially diverse

• Family of appropriate numerical models• Global and regional blue-water ocean models• Coastal models with accurate tidal and river forcing• Local oil spill models for incident response

A regional observation and prediction system

• Seismic Survey• Engineering Design• Installation• Diving• ROV Operations• Pipelaying• Incident Response

A regional observation and prediction system

Observation System Status: 18 Sep 2014

Observation System Status: 18 Sep 2014

• Surface drifters have been deployed in the BEM about every two weeks since July 2014

• Surveys utilizing expendables (CTD, SV, CP) expected to begin in early 2015

• Regional 1/32o model run daily – working on drifter data assimilation

• Interpretive reports generated weekly

Observing System Summary

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• Brazil’s Equatorial Margin has both extraordinary development opportunities and significant operational challenges.

• Strong and variable ocean currents are a primary concern.

• Exchange between blue-water and coastal regimes is poorly understood.

• A regional ocean observing and prediction system can provide improved situational awareness to mitigate the impact of strong currents on offshore operations, enhance safety, and protect the environment.

• A prototype observing and prediction system is operational TODAY

Conclusions

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Thank you

Dr. David M. FratantoniHorizon Marine, Inc.Massachusetts, USAdave@horizonmarine.com

Mr. Andre GellersHorizon Marine do BrasilRio de Janeiro, Brasilandre@horizonmarine.com