Heavy Oil Spills: Out of Sight, Out of Mind

Abstract

Heavy oils include those low API gravity (LAPIO) petroleum hydrocarbons that will sink below the water surface, either to the bottom or to some level in the water column. While there is a tendency to ignore spilled oil that is no longer visible at the surface, submerged oil may resurface or be transported onto shorelines where it can present unexpected and reoccurring cleanup problems. Factors influencing sinking and movement of sunken oil must be considered to guide heavy-oil spill contingency planning and response. Procedures that have been used successfully or show potential application for the location, mapping, and recovery of submerged oil should be included in planning. Decision diagrams are useful in the identification of appropriate procedures and technologies for varying oil characteristics and environmental situations. These decision diagrams include consideration of sunken oil assessment procedures, possible containment technology, and candidate recovery technologies.

Post-incident monitoring to evaluate environmental damage from shipping incidents: Chemical and biological assessments

“…This occurs when the density of oil is higher than the density of seawater, which is clearly the case for heavy residual fuels; or, in the case of lighter fuels, when oil density increases due to the evaporation, emulsification, suspended particle incorporation in the emulsion or decreased temperature (e.g. cold seas) (Castle et al, 2005). Furthermore, oil droplets can interact with suspended mineral particles and form high density agglomerates that sink and sediment to the bottom or suspend in the water column.…”

“…Furthermore, oil droplets can interact with suspended mineral particles and form high density agglomerates that sink and sediment to the bottom or suspend in the water column. Once sedimented, oil pollution is degraded more slowly and presents a long-term contamination source (Castle et al, 2005;Fingas, 2001). Therefore, sampling of sediments and suspended-sinking particles is an indispensable step for comprehensive oil spill assessment.…”

Compositional properties characterizing commonly transported oils and controlling their fate in the marine environment

“…12 The model was populated using the database constructed for a total of 20 oils (Diesel C was not included since distillation data were not available). Three spill scenarios for a continuous release of 120 tons (109 tonnes, representing a medium scale spill) of oil during a 24 hour period were modelled for three contrasting geographical areas: the Northwest Mediterranean Sea (Tarragona buoy, 40 . Averaged annual data were used for wind/current speed and direction, and summer water temperature.…”

“…Normally, oils float on water, but due to changes in the water temperature and/or weathering (evaporation, dispersion, interaction with sediment particles) oil density can increase up to a point where it sinks, either to the bottom, or to a point in the water column that has higher density. 40 In some cases, e.g. a high particulate load with a large proportion of the oil in the dispersed phase, this is even possible for light oils such as diesels.…”