Oil Spill Challenge “Solution Revealed” #7: The Freeze

Posted by JohnDila on Aug 31, 2010 3:37:51 PM

With a static kill procedure solution in place on the MC252 well in the Gulf, pressure tests are being performed and results are being reviewed.

Today we’re featuring a solution we received from InnoCentive Solver, Joseph Pegna, which focused on freezing MC252 while it was still blasting oil into the cold waters at the bottom of the Gulf.

The purpose of Pegna’s solution was not to contain the leak from the ocean floor indefinitely, but rather to contain it efficiently until such time as a more permanent plug could be found.

Joseph PegnaThe solution takes advantage of the relatively stable and low temperature of the sea floor to provide a temporary obstruction to the leak by freezing locally available materials: oil and water.

A back-of-the-envelope estimate of leak flow-rates indicates that a few ten’s of cubic meters of liquid Nitrogen would be sufficient to stop the oil in its track. Subsequent freezing of the surrounding water, either by additional liquid N2 or by lowering an industrial refrigeration unit to the ocean floor, would keep an ice plug over the leak.

Summary

This proposal takes advantage of the following conditions that exist at the depth of the leak:

  1. Local temperature is about four degrees Celsius.
  2. High salinity and pressure means that the surrounding water will freeze at around -25C below the surface freezing point.
  3. At -25C, oil becomes so viscous that it will behave like tarmac.

The prevailing conditions of the water at the ocean bottom, along with the flow rate of the oil spill indicates  that the amount of “cooling” necessary to bring water to its freezing point in the well’s vicinity is relatively modest. While I have not performed an extensive analysis of the heat exchange, it appears that between 10 and 100 cubic meters of liquid nitrogen would be sufficient  to block the flow of oil long enough to maintain a local frozen cap with an industrial refrigeration unit. The refrigeration unit can be powered from the surface but will be operating on the sea floor. This refrigeration can be used to contain the leak for a long enough time that alternative, permanent plugs can be inserted, or an alternative relief well can be drilled.

An initial injection of liquid N2 is envisioned by inserting a delivery nozzle as far down into the well as possible. This initial burst of liquid N2 can turn the surrounding oil into an increasingly hardened material, resembling a tar-like foam,  that will hold off the flow. As this foam comes into contact with water, it is expected that it will create a surrounding shell of ice.

The addition of an industrial refrigeration unit  would then be sufficient to maintain the temperature locally low enough to preserve the temporary blockage.

The main risk of this proposal resides in the fact that the composite ice and solidified oil foam will have a density much lower than the surrounding liquid water. Hence, to prevent the foam’s buoyancy force from tearing off the ice cap, sand or any other high density material would have to be added as the ice forms to increase the composite density.

Alternatively, this ice cap could be easily captured at the surface to prevent oil from spreading after the cap is released.

Topics: Solvers, Challenges, Seekers

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