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

1. Ultrasonic Scattering to Measure Dispersed Oil Droplet Size and Sediment Particle Size Paul D. Panetta1,4, Leslie G. Bland1,2, DomiPaxton3, Grace Cartwright4, and Carl Friedrichs4 1Applied Research Associates, Inc. 2University of Virginia 3Department of Geology, College of William & Mary 4Virginia Institute of Marine Science, College of William & Mary Oceans ’12 October 18, 2012

2. 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 Deepwater Horizon fire Subsea blow out from the Deepwater Horizon leak Aerial application of dispersant

3. Motivation Deepwater 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 AlunLewis

4. Dispersant effects on oil Crude oil with Corexit 9500 Crude oil

5. Stokes law Dh/t =D2(rw - ro)g 18hw • 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

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

7. Ohmsett Facility, NJ

8. Various views from the Tow Bridge Canadian Hebron crude slick Towards wave maker After breaking waves Dispersant application

9. Laser In-situ Scattering Transmissometer (LISST) with acoustic sensor attached Installation from Tow Bridge Acoustic sensor

10. Acoustic results from Ohmsett testing as bridge is moved Background DOR 1:20 No breakers

11. Acoustic signals at Ohmsett of partial dispersion and full dispersion Partial Dispersion Full Dispersion

12. Acoustic test chamber

13. Acoustic signals in the lab of dispersed crude oil 0.0 4.5 Hebron Crude Oil Depth (cm) 9.0 12.0 0 20 40 60 80 100 120 Time (seconds) 0.0 4.5 Hebron Crude Oil and Corexit 9500 dispersant Depth (cm) 9.0 12.0 0 20 40 60 80 100 120 Time (seconds)

14. 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 • g = ratio of specific heat at constant pressure and volume • P = hydrostatic pressure • = density of water • At 5 MHz, Attenuation ~ a • For 100 micron oil droplet , fr = 55 kHz Robert J. Urick, “Principles of underwater sound”, 3e, McGraw Hill 1983

15. Acoustic determination of oil droplet size Laboratory testing Ohmsett DOR 1:20

16. 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

17. Acoustic Imaging of Sediment Dynamics (5 MHz) Acoustic Transducer Sand ~63 mm Sand Mud Acoustic Transducer Sand and mud

18. Seabed Sediment Characterization Acoustic scan of sediment core Placement of X-ray subcore Subsampling for grain size and %moisture measurements (every 1 cm)

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

20. Sonar, marine acoustic, and portable ultrasonic tools Imagenex 881 rotary sonar Edgetech SB-216S Chirp Portable acoustics 50 kHz to 25 MHz Acoustic Doppler Velocimeter and Laser In-Situ Scattering Transmissometer (LISST) Acoustic Doppler Current Profiler Marine Sonic 900 kHz Side Scan Sonar

21. 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.