Fate of Surface Spills of Cold Lake Blend Diluted Bitumen Treated with Dispersant and Mineral Fines in a Wave Tank

Abstract

Cold Lake Blend (CLB) diluted bitumen (dilbit) was used to evaluate the fate and transport of preweathered (6.2% w/w) dilbit under environmental conditions both in spring (seawater temperature 8.5°C -1.3°C and salinity 27.7 -1.6 practical salinity units [psu]) and in summer (seawater temperature 17.0°C -2.6°C and salinity 26.8 -2.4 psu). The following oil spill treatments were considered: no treatment, dispersant alone, mineral fines (MF) alone, and dispersant + MF. The aim was to determine their influences on the fate of spilled CLB at sea. When dispersant alone was used, the highest dispersion effectiveness (DE) was noted, and DE ranged from 45% to 59% under the selected environmental conditions. With no treatment and treatment of MF alone, CLB DE was insufficient under tested conditions. Total petroleum hydrocarbon (TPH) concentration in the water column was highest for the dispersant alone, followed by that of dispersant + MF. TPH concentration for the dispersant alone increased abruptly with time. Droplet size distribution (DSD) resulting from dispersant alone had a unimodal shape, which was different than previously observed when conventional oils were treated with the dispersant. Cases of dispersant + MF were thus characterized by a broader DSD compared with dispersant only and a gradual increase in TPH concentration. This suggests that MF could be used with dispersant as a means to control the release of toxic compounds into the water column and for better engineering the response.

Estimating the Usefulness of Chemical Dispersant to Treat Surface Spills of Oil Sands Products

“…The tank dimensions are 30 m long, 0.6 m wide and 2.0 m high, with a typical water level of 1.5 m ( Figure 1). The tank is equipped with a series of manifolds to generate a more or less uniform current along the wave propagation direction; hence, the label flow-through system has been used to evaluate dispersant effectiveness of fresh and weathered crude oils [4,5,8,[14][15][16]. The hydrodynamics of the various wave types generated in the wave tank facility has been characterized in prior works [17,18].…”

“…Two particle size counters (Laser In-situ Scattering Transmissometry (LISST)-100X, Sequoia Scientific, Inc., Bellevue, WA, USA) were employed during the experiments, one at 1.2 m and another at 12 m downstream of the oil release point and both at a depth of 0.45 m ( Figure 1). Particle size (2 to 500 µm) distributions were recorded at 2.0 s intervals for 1 h per experiment as in previous studies [4,8,10,[14][15][16].…”

“…The use of a spill treating agent in offshore areas, by the responding parties, is to reduce damage to shoreline areas that are highly productive and sensitive, and also costly to clean. The application of conventional techniques, such as spill treating agents, are limited to studies showing significant, but incomplete effectiveness of COREXIT ® EC9500A on a Cold Lake bitumen blend (e.g., Cold Lake crude bitumen blend with 30% condensate, dilbit) spilled under different environmental conditions [4,5]. However, there is no information in the literature to support the use of chemical dispersant to treat surface spills of various other oil sands products (e.g., Access Western Blend (AWB) or dilbit, Western Canadian Select (WCS) of dilsynbit and synthetic bitumen or synbit) that have weathered at sea, post spill.…”

Oil sands and the marine environment: current knowledge and future challenges

“…In fact, whether bitumen products will float or sink, their response to evaporation, solar exposure, and mixing with water and sediment are determined by their chemical composition (eg King et al . ), which is largely unknown (Crosby et al . ) but is the most fundamental requirement for understanding the consequences of bitumen spills (Chang et al .…”

“…Due to the paucity of publicly available research on the effects of diluted bitumen on marine biota, we assigned the highest research priority to this source (Table 1 and Figure 3). In fact, whether bitumen products will float or sink, their response to evaporation, solar exposure, and mixing with water and sediment are determined by their chemical composition (eg King et al 2015), which is largely unknown (Crosby et al 2013) but is the most fundamental requirement for understanding the consequences of bitumen spills (Chang et al 2014). For example, one laboratory study on the behavior of diluted bitumen products in saltwater found that dilbit floated in a similar fashion to conventional oil in water free of sediment, but sank and dispersed as "tarballs" when mixed by wave action with fine seawater sediments (Environment Canada 2013).…”