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June 18th, 2010

Iowa State Portland cement expert provide some insights on Deepwater Horizon oil well failure

Published on June 18th, 2010 | By: pwray@ceramics.org

A Portland cement concrete research engineer at Iowa State University says poor decision making, not poor technology, doomed the Deepwater Horizon.

Bob Steffes, ISU’s Institute for Transportation, bases his conclusions on 17 years of overseas oil rig experience, including a blowout on an offshore well in the Middle East.

In a release from the university, Steffes asserts that a number of factors played a role in the disaster. He says that many of them relate to “loss circulation”—a common problem in this sort of drilling, in which drilling material (such as water and clay with dense additives such as barite or hematite) intended to be circulated back up the drill pipe instead filters out into the surrounding porous rock

“When I heard that loss circulation was a problem, I knew right away” what might have contributed to the blowout, Steffes says in the release.

Here are some of the factors Steffes believes played a role:

• The chemical wash operators decided to use to clear away the “filter cake” – the drilling mud that accumulates on the face of the drill hole through loss circulation – was not completely effective.
• Operators decided to use too few casing centralizers to keep the final casing in line. That may have resulted in the final cement seal being off-center, which can allow gases to escape.
• Operators used nitrified (or foamed) cement instead of a heavier, stronger version to seal the bottom of the well. Steffes says that the cement may have been lost in the same way as the drilling mud.
• Operators failed to perform a bond log, a process that uses sensors to determine if there is a uniform sheath of cement between the outside of the casing and the drilled hole. Gaps, if detected, are routinely filled – a “squeeze” operation, according to Steffes.
• Drilling mud was replaced by seawater. The net effect of this time-saving step reduced approximately 180,000 pounds of overhead load.
• The full-length casing that was used provided only a bottom hole cement seal. Using a liner would have provided a bottom hole cement seal plus a liner hanger seal.

Steffes notes that none of this would have mattered if the blowout preventer had not failed.


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