Sinking the myth – The science of bitumen in seawater

On April 20, 2010, the Deepwater Horizon platform exploded and sank in the Gulf of Mexico, spilling almost 5-million barrels of oil into the ocean.  In spite of a massive cleanup effort, oil continues to foul the seafloor and emerge during storms to foul gulf beaches.  The damage to marine food chains and the people who depend on them is ongoing.
Rescued Blue penguin, Rena Oil Spill, New Zealand, 2011
Oil dmaged Blue Penguin, Rena Oil Spill, New Zealand, 2011

WWF staff rescue oil-soaked blue penguins in Rena oil spill in New Zealand, 2011. (C) WWF-Canon / Bob Zuur

The anniversary of the BP spill serves as a grim reminder that very little can be done to recover oil when it’s spilled in the marine environment.  Recent amendments to federal shipping legislation to improve oil spill prevention don’t alter the stubborn fact that more than 90 per cent of oil spilled by tankers at sea is never recovered. And oils such as bitumen, proposed for transport by the Northern Gateway pipeline, can submerge, making them impossible to find, much less recover.
The federal government is floating myth, not science, when it assures the public that diluted bitumen will float.  Recalling the 2007 Kinder Morgan oil spill in Burnaby, Natural Resources Minister Joe Oliver told the Business Council of B.C. in November that crews “put out an oil boom and laid down absorbent cloth under the spill site attached to lobster traps [sic].  Following the cleanup, they recovered the cloth and no oil had sunk. So we know, in that instance, dilbit floated.”
It’s a shame to wreck a good story with facts.  But given the risk to B.C.’s marine environment, it’s important to consider the real science behind diluted bitumen (dilbit). The oil spilled that day wasn’t dilbit.  It was Albian Heavy Crude Oil, a blend of synthetic crude and heavier oil (aka synbit).  Trying to understand what dilbit might do in the sea by reviewing the Burnaby spill is akin to studying the black box data from the wrong plane crash.
Enbridge, for its part, is providing the public with an incomplete picture of the actual risk associated with diluted bitumen. Its website states “…crude oils, including diluted bitumen, are less dense than water and therefore float.”  There is some truth to this – just not enough to withstand the scrutiny of a reasonable person armed with the facts.
So what’s the real story behind dilbit? The American Petroleum Institute defines bitumen as semi-solid petroleum dense enough to sink in fresh water.   To allow it to flow through a pipeline, industry mixes bitumen with natural gas condensate, the lightest liquid hydrocarbons. The resulting mixture, dilbit, is light enough to float on water — initially.
When dilbit spills, the condensate evaporates, leaving the bitumen residue.   Does this residue sink?  In a beaker of full-strength seawater, no, and that’s where Enbridge’s website is correct.  But what would happen to dilbit in the actual conditions of a spill on B.C.’s coast?
Enbridge claims dilbit won’t sink unless it becomes denser than seawater.  But conditions on the coast are unlike those in the lab. First, not all seawater has the same density. The water in coastal inlets like Douglas Channel, where dilbit would be transported, isn’t nearly as dense as the water out at sea. Dilbit residue only has to share a similar density to these waters to submerge.

Jo whales

Humpback whale breaching in the Great Bear Sea. Their habitat would be directly impacted by a marine oil spill and oil tanker traffic. (C) 

Second, experiments conducted in Canada show that oil doesn’t have to be denser than water to submerge.   Waves can wash over heavy oils, creating ‘tar balls’ that drift great distances with ocean currents. In 1988, when heavy oil spilled from the Nestucca fuel barge off Washington’s west coast, it disappeared beneath the waves, washing ashore two weeks later, 175 km away, killing more than 9,000 seabirds on Vancouver Island’s west coast.  Dilbit residue can become as dense as these heavy oils so we can expect it to behave in a similar way. In fact, B.C’s brackish, coastal waters share a density similar to Alberta bitumen. In the event of a spill here, dilbit residue would submerge, making it near impossible to find all the submerged oil, much less clean it up before it fouls a distant shore.
It’s a shame to wreck a good story, one that Northern Gateway proponents like to tell.  But our coast’s future should be decided on the facts.  The people, whose lives and livelihoods will be put at risk by spilled bitumen, deserve nothing less.

This op-ed was originally posted in the Georgia Straight and can be found here