Oil Droplet Surfacing Probabilities Under Realistic Low Turbulence in Arctic Ice

Responders need to choose among oil spill response options to combat spills in ice covered waters as effectively as possible. A decision to apply dispersants in remote ice covered waters requires an estimation of whether or not the oil will initially disperse and then remain dispersed. A concern is that an effectively dispersed plume of oil will not remain dispersed under ice because the mixing energy required is insufficient. We are advancing the predictive capability to determine whether small oil droplets will rise in the calmer, more stable conditions that can occur in ice covered waters. The results will be presented as lookup tables that can be used to assess whether or not oil has been successfully dispersed in ice covered waters. Ice covered waters can have very low vertical turbulence (mixing) energy, so smaller droplets may rise to the surface in ice covered waters than in open water at lower latitudes. Laboratory studies with oil droplets and field experiments to measure the turbulence directly under ice are being used to provide input and validation data to numerically simulate an oil spill in ice. We assumed that oil slicks were effectively dispersed to form plumes in the water column. Dispersion was assumed to be from natural mixing energy or forced by applying the propeller wash from vessels. The numerical simulations will be performed to determine if these dispersed plumes could significantly resurface. The International Oil and Gas Producers (IOGP) funded the Joint Industry Project (JIP) “Fate of Dispersed Oil Under Ice”. Sintef led two field campaigns (2015 and 2016) with fast ice (ice attached to land) in Van Miljenfjorden in Svalbard. These data for realistic water currents and mixing energy (turbulence) were used in model development. In the second field experiment, dye was released and followed under the ice in order to measure dilution of the dye, as a check on our model. Neap tide periods were targeted in order to look at low mixing energy conditions. At the Plymouth University mesoscale laboratory, studies in a 30 m flume allowed oil droplets of known size to be released in water flowing under synthetic ice under controlled water velocity and under ice roughness conditions. In addition, an analytical model is being developed to estimate the magnitude and dissipation rate of prop wash turbulence. This was necessary to give the time zero basis for estimating how quickly droplets produced by prop wash would rise to the surface. Size classes of oil droplets that do not rise in low vertical turbulence will certainly not rise in higher turbulence. This will allow future research to target larger oil droplet size classes in the Marginal Ice Zone (MIZ). This project was led by SINTEF (Norway) with participation by McPhee Research (USA), University of Plymouth (UK), and Ben Gurion University (Israel).