Fate of Dispersed Oil under Ice

Scope of Work

The overall goal of this research project is to provide critical information in support of dispersants use in ice-covered marine environments and develop a tool to support contingency planning decisions with respect to dispersant use. The aim is to provide additional evidence to support dispersant use and decision making in ice-covered waters and to determine optimal operational dispersion criteria.  The primary research objective is to develop a detailed numerical model that predicts the potential for a dispersed oil plume to resurface and reform a new slick under the ice and then run the model with varying ice concentrations, release types, environmental conditions, oil types, and levels of turbulence.  The model is being designed to evaluate whether or not dispersed oil droplets formed under continuous or concentrated ice could resurface under the ice to form a significant accumulation within two days.

SINTEF, Trondheim, Norway is the contractor for this project, subcontractors are Plymouth University, Plymouth, UK and Ben Gurion University, Be’er Sheva, Israel. Project objectives were

  • To choose an appropriate existing plume model to describe the resurfacing potential of surface slicks
  • Determine what metocean input parameters will be needed to run the model
  • Conduct a technology assessment to determine what under ice turbulence/current data sets exist that are suitable for our modelling purposes

The primary need identified by this effort was to collect the appropriate under ice turbulence data required to run a numerical model that predicts the fate of a plume of dispersed oil droplets

Phase 1:

The initial phase of this project is complete and the final report entitled:” Fate of Dispersed Oil Under Ice – Literature Review” is available on the JIP website. The report provides a summary of background information on the state of knowledge concerning under-ice turbulence and methods for obtaining additional data as necessary to allow the development of a reliable model to predict whether oil droplets could surface within a two day period based upon an initial oil droplet size distribution.

Phase 2:

Research currently underway includes flume tank turbulence experiments, under ice turbulence and dye study field experiments at Svea, Svalbard, Norway, modelling studies, development of oil droplet rise tables and two manuscripts for peer-reviewed publication.

Under ice turbulence data was collected in van Mijen Fjord at Svea, Norway in March 16-20, 2015. The aim of the field work was to quantify the properties of under-ice turbulence in low-energy conditions. Low turbulence conditions are key to set the base case, because if the model predicts successful dispersion at the lowest turbulence levels, then measurements from the field of higher turbulence would indicate success of the dispersant operations. The field measurements included base measurements of factors controlling turbulence and measurements of the turbulence profiles:

  • Under-ice roughness using a high-resolution acoustic scanner and mini-ROV to conduct a wide-area survey, so that field observations can be compared against planned flume studies
  • Water current profiles using an acoustic doppler current profiler (ADCP)
  • Water column temperature and salinity profiles were made with CTD sensors.
  • Turbulence measurements from both a free-rising micro-structure profiler (MSS90) carrying turbulence shear probes and micro-structure current, temperature, and depth CTD sensors, and a Turbulence Instrument Cluster (TIC) developed by Miles McPhee.

Flume work at the Coastal, Ocean and Sediment Transport Laboratory, Plymouth University was successfully conducted January 11-22, 2016. The images and movies clearly show the droplet spreading vertically and horizontal drag form the under ice boundary layer. Dr. Ephim Golbraikh of Ben Gurion University, Israel is currently working to adapt a portion of his model of the vortical circulation in ship wakes to the dynamics of moving droplets in propeller driven turbulence during mixing of chemical dispersant with surface oil during a spill.

A second set of field experiments were safely and successfully conducted in the van Mijen Fjord at Svea, Norway April 7-16, 2016. Field measurements included:

  • One full, uninterrupted tidal cycle of turbulence measurements (both from repeated MSS profiles and TIC measurements)
  • Release and mapping of dye spreading to measure currents at slack water and at peak flow (at least three tests).
  • Two ADCPs in the water continuously logging background currents during the entire experimental period.
  • Two surveys of the under-ice roughness at both ends of the study site, using the 3D acoustic scanner.

Data analysis is in progress. This project will deliver a modelling tool that predicts the potential for a dispersed oil plume to resurface and reform a new slick under the ice.  This project will produce two peer-reviewed publications showing how well dispersed oil remains dispersed in the low turbulence conditions often found under ice.