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A Dilbit Primer: How It's Different from Conventional Oil

Bitumen extracted from tar sands has the consistency of peanut butter and must be diluted to flow through pipelines. And that's just the beginning.

Jun 26, 2012
(Page 2 of 3 )
A handful of Canadian oil sands

How do you know whether a particular type of crude oil will sink or float?

The industry classifies different crude oils as light, medium or heavy, based on their densities. There is debate over the cutoffs for these categories, but bitumen falls into the "extra heavy" category because it is more dense than water. The diluted bitumen that spilled from 6B was lighter than water and considered heavy crude oil.

But density alone doesn't determine whether a particular type of crude oil will sink or float, said Nancy Kinner, a professor of civil and environmental engineering at the University of New Hampshire who studies submerged oil. Weather and other conditions can change the buoyancy of crude oils: for example, crudes that are lighter than water can sink if they mix with sediment.

That's exactly what happened with the bitumen from 6B. In general, the density of bitumen ranges from slightly heavier than water to barely lighter than water. The bitumen that spilled in Marshall was at the lighter end of the scale. Marc Huot, a technical and policy analyst at the Pembina Institute's Oilsands Program, said the bitumen's density was so close to that of water that it was in "a gray area. It may or may not float depending on [conditions]…think of a log—it floats, but not very well."

But as the bitumen mixed with grains of sand and other particles in the river, the weight of the sediment pulled the bitumen underwater.

Why has it been so hard to clean up submerged oil in the Kalamazoo?

Existing cleanup procedures and equipment are designed to capture floating oil. Because the Marshall accident was the first major spill of dilbit in U.S. waters, cleanup experts at the scene were unprepared for the challenge of submerged oil.

The EPA has supervised the cleanup of nearly 8,400 spills since 1970, but in multiple interviews with InsideClimate News, agency officials said the Marshall spill cleanup was unlike anything they'd ever faced.

"[It's] not something a lot of people have dealt with," said Kinner. "When you can't see [the oil], you don't know where it is, so it's very hard to clean it up."

Once cleanup crews locate submerged oil, it's hard to remove it without destroying the riverbed. Cleanup workers in Marshall were forced to improvise less invasive procedures that balanced oil cleanup with protecting the ecosystem.

On July 16, 2010, just nine days before the Marshall accident, the EPA warned that the proprietary nature of the diluents found in dilbit could complicate cleanup efforts. The agency was commenting on the State Department's Draft Environmental Impact Statement (EIS) of the Keystone XL, a proposed pipeline that would carry Canadian dilbit across six U.S. states and the critically-important Ogallala aquifer.

"First, we note that in order for the bitumen to be transported by the pipeline, it will be either 'diluted with cutter stock (the specific composition of which is proprietary information to each shipper) or an upgrading technology is applied to convert the bitumen to synthetic crude oil,'" the EPA wrote. "…Without more information on the chemical characteristics of the diluent or the synthetic crude, it is difficult to determine the fate and transport of any spilled oil in the aquatic environment.

"For example, the chemical nature of dilutent may have significant implications for response as it may negatively impact the efficacy of traditional floating oil spill response equipment or response strategies. In addition, the Draft EIS addresses oil in general and as explained earlier, it may not be appropriate to assume this bitumen crude/synthetic crude shares the same characteristics as other oils."

How does dilbit affect pipeline safety?

Some watchdog groups contend that dilbit is more corrosive than conventional oil and causes more pipeline leaks. The industry disputes that theory, and there are no independent studies to support either side. In late 2011, Congress passed a bill that ordered the Pipeline and Hazardous Materials Safety Administration (PHMSA) to study if dilbit increases the risk of spills. Results are expected in 2013.

The industry says that Canadian tar sands oil is very similar to conventional heavy crudes from places such as Venezuela, Mexico and Bakersfield, California. Those crude oils, however, aren't transported through the nation's pipelines. The Bakersfield oil is processed at on-site refineries, while the Venezuelan and Mexican imports are shipped via tankers to refineries on the U.S. Gulf Coast.

The same watchdogs that criticize dilbit say that synthetic crude—which is also made from bitumen—poses no additional threats to pipeline safety. The U.S. currently imports more than 1.2 million barrels of Canadian dilbit and synthetic crude per day, and that figure is expected to grow dramatically in next decade. Most of the increased production will come from dilbit—because Canada's synthetic crude upgraders have reached capacity, and because it's more financially lucrative for U.S. refineries to process dilbit.

Does the government regulate dilbit differently from conventional crude oil?

For the most part, no.

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