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View Diary: Uncappable underground blowout spills thousands of barrels of tar sands oil in Cold Lake, Alberta (183 comments)

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  •  Two factors may be at play (0+ / 0-)

    Both the specific gravity and the viscosity of bitumen are temperature dependent. Both decrease with increased temperature.

    Bitumen in the U.S. is defined as having a specific gravity greater than 1, whereas Canadian bitumen is defined as having a specific gravity greater than 0.9.  

    Consequently, the material classified as bitumen in the U.S., at ambient temperatures, will be heavier than water and would tend to sink in either an aquifer or surface water body. Canadian bitumen may do the same thing or, if it is at the very light end of its range, may be slightly lighter than water.

    So what could be happening with steam injection could be two fold:

    1. The reduced viscosity of bitumen at elevated temperatures (associated with steam injection) would allow it to migrate more easily in the subsurface, because (getting technical here) the resistance to entry into a pore where it must displace water to do so would be reduced due to lower viscosity.

    2. If the bitumen had slightly higher specific gravity than water in-situ (say, 1.04 to 1.08), heating it with steam may cause the specific gravity to drop below 1, causing the bitumen to start to float due to its specific gravity being less than water.

    This could be part of the reason why the observed conditions are occurring.

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