Dilbit Crude Oil Weathering on Brackish Water: Meso-scale Tests of Behavior and Spill Countermeasures

Elliott Taylor, Greg Challenger, Jose Rios, Jim Morris, MAC McCARTHY, and Colin Brown

Abstract:
Oil weathering and countermeasures testing was conducted with Cold Lake Blend and Access Western Blend dilbits from May 13 through May 26, 2013 at the Kinder Morgan/Trans Mountain Pipeline pump station in Gainford, Alberta. Based mostly on visual observations, both dilbits exhibited properties that one would expect of a heavy “conventional” crude oil. In no instance was any oil observed to have sunk. Densities increased as oil weathered, approaching—and in some cases exceeding—values of 1000 kg/m3. Viscosities increased rapidly with weathering exceeding 10,000cP within 24 hours for both dilbits exposed to moderate agitation. Visual observations of the oil’s surface in the various tanks showed that a crust formed as the oil weathered. Chemical analyses of the weathered oils and water column showed that concentrations of BTEX diminished rapidly, although TPH values in the water column were variable and dependent on the degree of surface agitation. Countermeasures tested included dispersant application, burning, shoreline cleaners, and skimmers. Visual observations of the dispersant test revealed that Corexit 9500 was marginally effective on 6-hour weathered oil and not particularly effective for more weathered dilbit. The test burn on 6-hour weathered oil was effective with a sustained burn and an estimated 70% oil combusted. Estimates show that approximately 50% of 24-hour weathered oil was burned, but only after sustained effort to ignite. The 72-hour weathered oil was not successfully ignited. Tests with Corexit 9580 found the cleaning agent to be effective on oils weathered up to 5 days and applied to granite tile. Observers noted that the time oil weathers on water before being placed on the tile was less important than the time the weathered oil was exposed to air. The three brush skimmers tested all effectively recovered dilbit throughout the oil weathering tests.