Just a week before the Deepwater Horizon exploded, BP PLC asked regulators to approve three successive changes to its oil well over 24 hours, according to federal records reviewed by the Wall Street Journal.
The unusual rapid-fire requests to modify permits reveal that BP was tweaking a crucial aspect of the well's design up until its final days.
One of the design decisions outlined in the revised permits, drilling experts say, may have left the well more vulnerable to the blowout that occurred April 20, killing 11 workers and leaving crude oil gushing into the Gulf of Mexico.
The Minerals Management Service approved all the changes quickly, in one instance within five minutes of submission.
BP's flurry of revisions and re-revisions stands out as uncommon. Of the more than 2,200 wells that have been drilled in the Gulf since 2004, only 5% have had multiple permit revisions submitted to MMS within one calendar day, according to a Wall Street Journal analysis of MMS records.
In only one other case, a 2005 well drilled in just 48 feet of water, has a company submitted three revisions within 24 hours, as happened on BP's well. BP's well was in nearly 5,000 feet of water, which has made dealing with the well far more complicated.
MMS declined to comment, citing the ongoing investigation into the causes of the Deepwater Horizon disaster.