Spill behaviours of pipeline-transportable processed bitumen products in fresh water

Abstract

Bitumen extracted from Canada’s oil sands resources is an abundant, unconventional crude oil used to produce liquid fuels. To permit its transportation by transmission pipelines from production sites to upgraders and refineries, the highly-viscous bitumen must first be blended with up to 50 vol% of light oil (“diluent”) to produce a diluted bitumen (DB) with sufficiently low viscosity and density. Diluents occupy substantial pipeline capacity, and are relatively expensive, so Canada is developing “partial upgrading” processes to reduce the diluent content of pipeline-transportable bitumen products. Such processes lower bitumen’s density and viscosity by removing some portion of its heaviest, asphaltene-rich fraction by, for instance, solvent-induced separation and/or thermochemical conversion. Thus, processed bitumen products (PBPs) require less diluent to meet specifications for transmission pipeline transportation. We compare the minimum diluent content requirements of several PBPs meeting such specifications for density (≤ 940 kg/m3 at 15.0 °C) and viscosity (≤ 350 cSt at a pipeline temperature of 10.6 °C, selected on the basis of DB viscosity measurements). In this work, PBPs meeting pipeline transportation specifications are prepared by visbreaking and/or solvent-deasphalting of bitumen followed by dilution with 32–47 wt% less diluent than the corresponding unprocessed DB. Public concern about environmental risks associated with spillage of emerging PBPs during transportation has spurred investigations of these products’ interactions with water. With little currently known about their aquatic behaviours, we evaluate the emulsification and dispersion tendencies of pipeline-transportable PBPs after mixing these with fresh water following a reported protocol, and compare these results with those for DB, bitumen-derived synthetic crude (SC) oil, and conventional crude (CC) oil. The characteristics of floating water-in-oil emulsions are shown to depend upon the oil’s asphaltene content and thermochemical process history. At high mixing energy, dispersed oil content within the water column is seen to increase with oil resin-to-asphaltene ratio. In the aquatic system employed, oil content of the water column is greatest for SC, followed by solvent-deasphalted products and DB, followed by only-vis-broken product and CC. These results may aid in the development of oil spill behaviour models and response plans needed for transporting PBPs.