Paul D. Panetta1,4, Leslie G. Bland1,2, Domi Paxton3, Grace Cartwright4, and Carl Friedrichs4

1Applied Research Associates, Inc.2University of Virginia

3Department of Geology, College of William & Mary4Virginia Institute of Marine Science, College of William & Mary

Oceans ’12October 18, 2012

Ultrasonic Scattering to Measure Dispersed Oil Droplet Size and Sediment Particle Size

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Outline Motivation and background Lab tests Field tests at Ohmsett wave

tank with Canadian Hebron crude

Sediment measurements SINTEF Tower Tank tests Conclusions and Future Work

U.S. Air Force chemical dispersing aircraft drops an oil dispersing chemical into the Gulf of Mexico as part of the Deepwater Horizon Response effort, May 5, 2010. U.S. Air Force Photo by Tech. Sgt. Adrian Cadiz; RestoreTheGulf.govDeepwater Horizon oil spill

Subsea blow out from the Deepwater Horizon leakDeepwater Horizon fire

Deepwater Horizon fire

Subsea blow out from the Deepwater Horizon leakAerial application of dispersant

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MotivationDeepwater Horizon Incident• 4.9 million barrels of oil released• 1.1 million gallons of dispersants

used subsea for the first time• No subsea methods to assess

dispersants effectiveness exist

Motivation: Develop acoustic methods to measure dispersant effectiveness subsea and transfer technology to sonar and marine acoustic instruments.

Images courtesy of Alun Lewis

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Dispersant effects on oil

0

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0.0

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Conc

entr

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(PPM

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Conc

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Average Droplet Size (microns)

Crude oilCrude oil with Corexit 9500

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Stokes law

Dh/t = D2(rw - ro)g18hw

• Dh/t is the oil droplets rising velocity (m/s),

• D is the oil droplet diameter (m)

• ρw is the density of the water (kg/m3), and

• ρo is the density of the oil (kg/m3)

• g is the gravitational acceleration (m/s2),

• hw is the viscosity of the water

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Lab measurements 15 mL Canadian Hebron crude 15 mL Canadian Hebron Crude DOR 1:10 Corexit 9500

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Ohmsett Facility, NJ

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Various views from the Tow Bridge

Towards wave maker Canadian Hebron crude slick

Dispersant application After breaking waves

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Laser In-situ Scattering Transmissometer (LISST) with acoustic sensor attached

Installation from Tow Bridge

Acoustic sensor

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Acoustic results from Ohmsett testing as bridge is moved

Background DOR 1:20 No breakers0.

51.

0D

epth

(met

ers)

Ping number

(a) Background - prior to addition of oil (b) After Adding Corexit 9500, DOR 1:20 – no breakers

% Screen Height

012

Ultrasonic transducer

Ping number

Dep

th (m

eter

s)0.

51.

0

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Acoustic signals at Ohmsett of partial dispersion and full dispersion

Partial Dispersion Full Dispersion0.

51.

0D

epth

(met

ers)

(a) Just Breaking Waves

0.5

1.0

Dep

th (m

eter

s)

(b) Heavy Breaking Waves

% Screen Height

012

Ultrasonic transducer

Ping number Ping number

0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100

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Acoustic test chamber

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Acoustic signals in the lab of dispersed crude oil

Hebron Crude Oil

Hebron Crude Oiland Corexit 9500 dispersant

Time (seconds)0 20 40 60 80 100 120

0 20 40 60 80 100 120

Time (seconds)

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th (

cm)

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cm)

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Attenuation of isolated droplets

se = extinction cross section• sum of the scattering cross

section and the absorption cross section

a = droplet radius f = frequency fr = resonance frequency d = damping constant at fr c0 = speed of sound

𝑘𝑟=2𝜋 𝑎 𝑓 𝑟𝑐0

𝑎𝑡𝑡𝑒𝑛𝑢𝑎𝑡𝑖𝑜𝑛 ( 𝑓 ,𝑎) 𝜎𝑒=

4𝜋 𝑎2𝛿𝑘𝑟 𝑎

( 𝑓 𝑟2

𝑓 2−1)

2

+𝛿2

𝑓𝑟 = 12𝜋𝑎ඨ3𝛾𝑃𝜌

g = ratio of specific heat at constant pressure and volumeP = hydrostatic pressurer = density of water

At 5 MHz, Attenuation ~ a

For 100 micron oil droplet , fr = 55 kHz

Robert J. Urick, “Principles of underwater sound”, 3e, Mc Graw Hill 1983

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Acoustic determination of oil droplet size

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Lase

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Acoustic Average Droplet Size (microns)

Laboratory testing

Ohmsett DOR 1:20

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(PPM

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Conc

entr

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(PPM

)

Average Droplet Size (microns)

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Motivation for high frequency acoustic sediment characterization

• In the water column there is a need to determine grain size and sediment type.

• In the seafloor the properties of the top ~5cm control erodibility and sediment transport.

• Typically measurements are performed on cores in the lab.• There is a need to determine these properties in the water

without disturbing the sediment by coring and transporting to the lab.• Ideally we want to measure sediment properties in-situ over time

• Knowledge of the sediment properties will also help wave propagation models that include seafloor reflections

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Sand and mud

Sand

Mud

Acoustic Transducer

Acoustic Transducer

Sand ~63 mm

Acoustic Imaging of Sediment Dynamics (5 MHz)

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Seabed Sediment Characterization

Acoustic scan of sediment core Placement of

X-ray subcore Subsampling for grain size and %moisture

measurements (every 1 cm)

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Sediment characterization of York River Ferry Point (5035)X-ray 2.25 MHz Acoustic Backscattering

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Sonar, marine acoustic, and portable ultrasonic tools

Marine Sonic 900 kHz Side Scan Sonar

Imagenex 881 rotary sonar Edgetech SB-216S Chirp

Acoustic Doppler Current Profiler

Acoustic Doppler Velocimeter and Laser In-Situ Scattering Transmissometer (LISST)

Portable acoustics 50 kHz to 25 MHz

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Conclusions Acoustic images can be used to qualitatively characterize oil slick

dispersion and plume size. We developed acoustic measurements to size oil droplets for surface

dispersant applications at Ohmsett and in the lab. Additional measurements of subsurface releases of oil and

dispersant are needed. Initial measurements on suspended and consolidated sediment

show promise for in-situ characterization.

Acknowledgements This work is supported by the Department of Interior, Bureau of Safety and

Environmental Enforcement (BSEE) under project number E12PC00011. Student funding was provided by National Science Foundation grant OCE-1061781.

Special Thanks to Randy Belore from SL Ross and Tim Nedwed from ExxonMobil during the work at Ohmsett and Per Johan Brandvik during the work at SINTEF and Kyle Winfield for his help with laboratory measurements.