Monday, September 13, 2010

BP’s Report: No Smoking Gun, But a Lot of Smoke

The long oily summer of the BP oil spill is over, and now the investigation season has begun. BP itself has completed and issued a summary of its own internal investigation, posted for public access on its website. I have had time to read only the executive summary, but even that brief six-page document has technical details I don’t completely understand. However, the basic picture is clear: what happened last April 20 to cause the explosion, fire, deaths, and consequent oil spill that blackened miles of coastline and disrupted entire industries was not a simple one-failure event. Instead, it was a cascade of failures, both mechanical and human, that all went the wrong way to produce the tragedy.

At the time of the accident, the well drilling itself had been completed, and BP together with the actual operator of the rig, Transocean, were under pressure to cap off the well temporarily until a production structure could be put in place. Every modern oil well consists of a hole drilled in the rock, into which a long pipe called the casing is inserted. To keep the highly pressurized oil and gas where it belongs, most of the space (the “annulus” or ring-shaped area) between the outside of the casing and the raw hole is filled with a special cement, so the only place the “hydrocarbons” (BP’s term for oil and gas) can go is into the casing at a controlled location near the bottom of the well. At the very bottom of the casing between it and the bottom of the hole itself is something called a “shoe track.” I’m not sure what it is, but it looks in their drawing like a long can with holes at the bottom. The intention was to seal off this shoe track with the same cement that was being used to fill the space between the casing and the drill-hole wall.

Well, something went wrong: too much nitrogen in the cement, or something. But when the rig operators went to check the integrity of the cement seal by removing the heavy drill mud and replacing it with seawater to check for leaks, the pressure in the well rose beyond allowable limits.

The first place the accident could have been prevented had arrived. If the operators had put back the drill mud and figured out what was wrong instead of proceeding as if things were normal, they would have at least had a chance to avoid problems. But being in a hurry, they accepted the data as showing the cement seal was okay, even though it wasn’t, and eventually left lighter seawater in the well. This allowed high-pressure natural gas to enter the well.

Once the operators realized they had a problem, they sent signals down the well to operate the infamous blowout preventer (BOP), and connected the top of the well to a mud-gas separator on the rig itself. (As most readers probably know by now, the blowout preventer is a big piece of machinery on the ocean floor with two or three redundant systems designed to shut off the well in just such an eventuality as having high-pressure gas flow through it out of control.) Neither of these actions had the intended effect. For a couple of reasons (a bad solenoid valve and a low battery) the BOP failed to operate, and the gas flow coming from the well soon overwhelmed the mud-gas separator’s ability to deal with it. There was a separate overboard diverter line they could have used which might have kept the gas away from places it could ignite a little longer, but it wasn’t used.

Eyewitnesses who were in nearby vessels noted a high-pitched noise of escaping gas just before the explosion. By the time the gas got to areas that were not “electrically classified” (meaning certified as free of ignition sources), it was just a matter of time before an engine sucked in enough natural gas to set it afire. And the tragedy had begun.

The executive summary was written in dry, technical language in which people appear only in the passive voice (e. g. “The first well actions were to close. . .”). But as the immediate party responsible for day-to-day rig operations, Transocean is at fault for a number of things: poor training and management, careless maintenance of critical equipment such as blowout preventers, and allowing schedule pressures to take precedence over safety. But in the eyes of most laws, it is the owner of a rig, not just the operator, whose ultimate responsibility it is to see that the thing doesn’t befoul a good bit of the Gulf of Mexico, as the Deepwater Horizon failure did.

To their credit, BP did establish a fund to pay legitimate claims of damage resulting from the spill, and has paid out a lot of money already. But obviously, it would have been better to operate the rig like the 99+% of other deep-water rigs that successfully drill for and produce oil without major spills or fatal accidents. Besides fouling miles of shoreline, the carelessness exemplified by this tragedy of errors has blackened the reputation of the entire offshore drilling industry, and provoked a harsh government response in the form of the controversial moratorium on drilling operations. Some of the most vocal opponents of this ban were people along the coast that stand to be most affected by any accidents. But the reason for that is simple: offshore oil drilling is a big part of the gulf states’ economy. History may show that this decision was yet another bad judgment call in a cascade of bad judgment calls that began on April 20 on the rig.

At any rate, we will be finding out even more as the Presidential commission and other investigative bodies complete their findings. But already, the technical outlines of the accident are pretty clear. And pretty depressing.

Sources: I referred only to BP’s executive summary of their internal report, available at

1 comment:

  1. relevant to this blog, the BP report makes no mention of existence or relevance of engineering ethics, rules of professional conduct, PE licensure, etc. I predict the future reports will also be silent to this essential factor and that the engineering profession will take no exception to it.