MMS ENVIRONMENTAL STUDIES PROGRAM: ONGOING STUDIES
MMS OCS Region: Pacific
Title: Oil Slicks in the Ocean: Predicting Their Release Points Using the Natural Laboratory of the Santa Barbara Channel (PC-00-02-15)
Total Cost: $172,000 Period of Performance: FY 2001-2003
Conducting Organization: Coastal Marine Institute, University of California, Santa Barbara-Santa Barbara, CA (Contact: Ira Leifer)
MMS Contact: Dr. Fred Piltz
Description:
Background
Sea floor sources of petroleum include natural seepage, blowouts, and leaky submerged pipelines. For example, natural marine hydrocarbon seepage in the Santa Barbara Channel and elsewhere along the California coast degrades both the local and regional quality of the atmosphere, coastal ocean, and shoreline. These emit both oil gaseous hydrocarbons, often creating kilometer-long slicks that form tar balls. Researchers estimated that virtually all of the tar balls found on Santa Barbara County beaches and more than half found on beaches in Santa Monica Bay originated from one group of seeps found off shore of Coal Oil Point. Recent observations in the Santa Barbara Channel and elsewhere suggest that oil often rises in hydrocarbon gas bubble plumes which significantly modify the local marine environment, decreasing oil rise time and altering its trajectory. Predicting the exact location of the sea floor vents from the location of surface slicks is challenging due to the variety of processes influencing oil-bubble plumes in the ocean.
Objectives
To build and validate a field-based, transferable model of oil-bubble transport through the water-column. Specifically, to model the physical and chemical processes governing the dynamics of oil-bubble plumes emanating from natural marine seeps. The project creates an improved numerical model of hydrocarbon gas and oil plumes rising from the sea floor.
Methods
The approach combines laboratory experiments and detailed field observations of the hydrocarbon plumes (bubble size distribution, oiliness, and gas composition, dissolved gas concentrations, upwelling flows at some of these seeps) with a theoretical description of mass transport.
  1. Update the model of bubble behavior by establishing parameters that are currently poorly characterized. Create a transport module to incorporate the mixing and advection of gas between the ocean and bubble plume. After field observations and laboratory experiments, develop a plume flow module to calculate the upwelling flow and turbulence diffusion rates from the bubble stream density and flux.
  2. Construct a laboratory bubble tank for studies to determine bubble parameters, since without them, bubble model validation cannot be confidently undertaken.
  3. Study three additional seeps to establish parameters for the upwelling flow in terms of total bubble flux and the bubble flux distribution. Divers collect high resolution (1 m) horizontal sampling of dissolved and bubble and dissolved gas composition, bubble size distribution, and fluid motions at various depths (usually four) spanning the sea floor to the sea surface. Collect and analyze bubble gas and water samples using gas chromatography and spectrofluorometry. Determine bubble size distributions from video images and fluid motions from dye tracer releases. Sample dissolved methane outside of the seep bubble plume to quantify the exchange rate between the plume and bulk ocean.
  4. Survey additional seeps using an Acoustic Doppler Current Profiler (ADCP) to test the applicability of the derived parameters. For these seeps, bubbles will be measured only at the surface.
Importance to MMS
By upgrading and validating an existing bubble plume model it will be possible to simulate natural hydrocarbon seepage, an underwater oil/gas spill or a seafloor pipeline leak. The proposed model will greatly improve the ability to predict where oil released at the sea floor surfaces, how much is deposited subsurface, and the hydrocarbon flux into the ocean (dissolution) and to the atmosphere. A validated numerical model of rising hydrocarbon plumes can be applied to a variety of problems including oil spill preparedness, disaster response, managing the impact of natural seeps on fragile marine ecosystems, and linking ocean surface expressions of seep oil to sea floor vents for petroleum exploration.
Current Status:
Awaiting final report.
Final Report Due: 3/30/2006
Publications: None at this time.
Affiliated WWW Sites: http://coastalresearchcenter.ucsb.edu.cmi/
Revised date:  November 17, 2005
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