Effects of sea ice seasonal evolution and oil properties on crude oil upward migration through sea ice

Abstract

Sea ice plays an essential role in polar ecosystems as a habitat for organisms at the base of the food web. Receding Arctic perennial sea ice, potential oil and gas reserves, and increasing industrial activities in the Arctic are likely to increase oil extraction and transport in the maritime Arctic. Despite a decrease in summer sea ice extent, Arctic waters remain covered with sea ice for much of the year, increasing the risk of an oil spill in and under Arctic sea ice. This dissertation addresses the need for a quantitative understanding of the timing of and constraints on oil mobilization through the full seasonal cycle as well as the resulting oil distribution within the ice cover. All of these factors have major implications for spill clean-up efforts and habitat damage assessments. In Chapter 1, I assemble sea ice physical properties derived from long-term observations to characterize sea ice seasonal development stages. In Chapter 2, guided by results from three sets of oil-in-ice tank experiments, I present a semi-empirical multistage oil migration model linked to sea ice seasonal stages. I also find that ice stratigraphy plays a major role in oil movement, with granular ice hindering oil movement. In Chapter 3, I quantify the microstructural differences between granular and columnar ice texture. While both pore spaces have similar pore and throat size distribution, the higher tortuosity of granular ice increases the distance oil and brine have to travel by up to 30% to cover the same vertical distance as in columnar ice. With a less connected pore space, granular ice permeability is estimated as one order of magnitude smaller than that of columnar ice during winter and at the onset of spring warming. Chapter 4 introduces a simple 1D vertical model with a small set of initial conditions to describe oil movement along a connected pore pathway, I constrain the oil flow by accounting for the lateral displacement of brine into the surrounding ice volume to improve prediction of the timing and distribution of oil-in-ice flow. Future coupling of this model to a model of ice growth and melt may help inform oil spill response and clean-up operations, and improve the understanding of oil migration in the context of natural resource damage assessments.