Modelling the Transport of Oil–Mineral-Aggregates (OMAs) in the Marine Environment and Assessment of Their Potential Risks

Abstract

Spilled oil can interact with suspended particles in marine environments and form oil-mineral aggregates (OMAs). Some OMAs with densities higher than seawater density can settle to the seedbed to pose potential risks to benthic organisms. To understand the transport and fate of oil associated with OMAs and evaluate their potential risks, an integrated hydrodynamic and fate/transport model has been used in a hypothetical case study of 1,000 tonnes of South Louisiana oil spilled in the Bristol Channel. Several scenarios have been simulated under different wave and current conditions. By using OMA properties derived from laboratory measurements reported in literature, it has been found that the risk to the benthos is unlikely for the two hypothetical cases with strong currents, but it is likely for the wave only (weak current) case. The effects of other factors such as OMA properties and sediment concentration were also examined in terms of their effects on the transport process and risks.

Formation of rapidly-sinking, oil-associated marine snow

“…The processes which caused the redistribution of oil to the seafloor are currently not well understood; however, the rapid transport of particles from the sea surface to the deep ocean is a common global process that is frequently mediated by marine snow, which are rapidly sinking composite particles 40.5 mm (Alldredge and Silver, 1988;Armstrong et al, 2009;Asper et al, 1992;Diercks and Asper, 1997;Pilskaln et al, 1998). Additionally, it is known that oil may be transported to depths via oil-mineral aggregates (called OMAs or SPM-oil aggregates; Khelifa et al, 2005;Niu et al, 2011). Tar-like residues from weathered oil may also sink directly.…”

“…Oil-mineral aggregates are usually o50 mm (Omotoso et al, 2002;Stoffyn-Egli and Lee, 2002), much smaller than marine snow, but may, depending on clay content and wave action, contribute appreciably towards moving oil residues to the sea floor (Khelifa et al, 2005;Niu et al, 2011), because of the high excess density of minerals. The wide continental shelf of the Northern GoM receives inorganic particles from continental rivers, run-off and coastal erosion and the mid-depth intermediate nephloid layers may extend far past the shelf edge (Dickson and McCave, 1986).…”

Environmental Impacts of the Deep-Water Oil and Gas Industry: A Review to Guide Management Strategies

“…The spatial footprint of discharge varies with the volume of discharge, depth of discharge, local hydrography, particle size distribution, rates of settlement and floc formation, and time since discharge (Neff, 2005;Niu et al, 2009). Although volumes are likely to vary greatly depending on the local conditions during the active stage of drilling, discharges from one deep-water well at 900 m depth off the coast of Brazil were ∼270 m 3 of cuttings, 320 m 3 of water-based fluids, and 70 m 3 of non-aqueous fluids (Pivel et al, 2009).…”

A Method for Assessing Environmental Risks of Oil-Mineral-Aggregate to Benthic Organisms

“…Recently, Niu et al (2009) have studied the dispersion and settling of OMAs in the marine environment using a random-walk-based particle tracking model. An attempt to evaluate the risks of eight hydrocarbon groups to benthic organisms was also made in their study by comparison of the predicted environment concentration (PEC) of the eight hydrocarbon groups with a benchmark concentration (BC).…”

“…An attempt to evaluate the risks of eight hydrocarbon groups to benthic organisms was also made in their study by comparison of the predicted environment concentration (PEC) of the eight hydrocarbon groups with a benchmark concentration (BC). A limitation of the Niu et al (2009) study is that a deterministic approach was used and the uncertainties associated with the BC were not considered. As a result, the precision of the calculated risks can not be evaluated.…”