Did a risky decision on the part of BP – one made to save the oil giant a few million dollars – lead to or contribute to the blowout aboard the Deepwater Horizon oil rig explosion?

A report on the May 24 “Rachel Maddow Show” explained the series of events that may have led to the explosion aboard the Deepwater Horizon rig. In an offshore well like Deepwater Horizon, there are supposed to be 3 separate cement plugs in the pipeline to seal off the pipe after the exploratory drilling is done. In between the plugs is usually thick drilling mud to keep added pressure on the seals. Later these seals and the mud are removed when production drilling takes over.

When possible, sea water is used in the top portion above the middle cement plug instead of mud. This saves the company millions of dollars when the plugs are removed later to start production drilling. However, the pressure seal integrity of the lower two plugs must be tested first before the top portion of mud is removed to be replaced by sea water.

At the top of the pipeline is a larger rubber seal or gasket (called an annular) which is used to close the pipe when the pressure is being tested. Unfortunately, this annular apparently was starting to break apart, as evidenced by pieces of rubber coming up the pipe. This would have caused readings of the pressure below the annular to appear artificially low or normal. BP took the normal (but erroneous) pressure measurements as evidence that it was safe to remove the mud and replace it with water. The cement plug at the top was to be placed after the sea water was pumped into the pipeline.

As soon as the top portion of the mud seal was removed, that’s when pressurized methane below blew up thru the pipe and exploded. The top cement plug was not yet in place.

A May 13 article in the Wall Street Journal backs up what was reported on the “Rachel Maddow Show.” According to the article, during a hearing conducted by his committee, House Energy and Commerce Committee Chairman Henry Waxman said that congressional investigators learned that the well failed a critical pressure test hours before the explosion. The test indicated that gas from the oil reservoir was leaking into the drill pipe in a way it shouldn’t have.

James Dupree, the BP senior vice president for the Gulf of Mexico, told congressional investigators that since test results were not satisfactory and inconclusive, significant pressure discrepancies were recorded. As a result, another negative pressure test was conducted just hours before the blast. This also produced unsatisfactory results, Waxman said. All of the tests suggested that highly combustible gas had seeped into the well.

According to Waxman, information reviewed by his committee “describes an internal debate between TransOcean and BP personnel about how to proceed.” One course would have been to try to shore up the cement, the Journal said. But this would have taken a week to 10 days, and cost BP between $5 million and $10 million.

In the end, despite the worrisome tests, BP officials decided to begin withdrawing the heavy drilling fluid that prevents gas from escaping the well before a final cement plug could be placed in the well. According the Journal’s report, the cement plug would have been one more safeguard against natural gas surging from the well. Once mud came out, the last safeguard, the blowout preventer, didn’t do its job. This failure could have been the result of a defect such as leaking hydraulics or because it was jammed by debris from the well, documents produced by congressional investigators show.