The BP Deepwater Horizon oil spill is already an appalling environmental disaster. It may turn out to be America's Aral Sea. But what if it's about to get a lot worse?
The rig Deepwater Horizon started drilling the Macondo well in February 2010. They drilled a 5.5 kilometre shaft from the sea floor (which was itself 1.5 kilometres below surface) and encased the shaft in cement. BP had advised the US government that the risk of a spill was unlikely, but internally, its engineers warned of serious problems with pressurized natural gas in the well.
On April 24, a high-pressure gas release ignited on the rig, causing an explosion and fire. The rig burned for 36 hours and then sank. Eleven of the rig workers were not rescued or found and are presumed dead.
BP had fitted the wellhead with a blowout preventer that was supposed to seal the well automatically if it lost contact with the rig, but on April 22, the Coast Guard noticed oil leaking from the rig site. BP dispatched remote vehicles to the wellhead, but they were not able to plug the leak either.
Since then, the wellhead has been gushing between 30,000 and 60,000 barrels a day (one barrel is 117 litres) into the Gulf. After nearly two months of flow, the oil spill covers an area of 6,500 square kilometres. BP is catching a fraction of the oil as it leaks into the ocean, and they are flaring some of the methane gas
BP has attempted to seal the wellhead using a top kill, which is a temporary injection of drilling mud into the blowout preventer to plug it until they can install a more permanent cap.
However, their attempts have failed so far, and observers have noted that while top kills are a standard way to plug wells on the surface of the earth, the method has never been attempted at 1.5 kilometres below sea level.
The longer-term strategy is to drill two relief wells to divert the flow of oil away from the main wellhead and capture the oil before it is released into the Gulf. Once the pressure comes off the main wellhead, it should be easier to plug.
However, a recent comment on The Oil Drum that is generating a lot of interest on the internet right now presents a coherent, well-sourced claim for a worst-case scenario. The comment is long, detailed and worth reading in full, but here's a quick summary:
The failure of the top kill procedure tells us that the well system is more leaky and unstable than BP is letting on.
I took some time to go into a bit of detail concerning the failure of Top Kill because this was a significant event. To those of us outside the real inside loop, yet still fairly knowledgeable, it was a major confirmation of what many feared. That the system below the sea floor has serious failures of varying magnitude in the complicated chain, and it is breaking down and it will continue to.
Even if BP actually manages to cap the main break, the pressurized oil will just burst out through other leaks below the sea floor and be even harder to catch than it is now. Yet as long as the oil continues to flow through the main break, that flow will continue to erode the damaged well casing.
The breakdown of the seabed under the 450-tonne blowout preventer could result in the entire structure collapsing into an oil-spewing sinkhole, at which point the current rate of flow will look like a mere trickle by comparison.
[BP] have shifted from stopping or restricting the gusher to opening it up and catching it. This only makes sense if they want to relieve pressure at the leak hidden down below the seabed ... and that sort of leak is one of the most dangerous and potentially damaging kind of leak there could be.
This scenario puts BP in a race against time. They need to drill the relief wells to catch the oil coming out and relieve pressure on the main line, which they can then safely cap. The question is: will BP complete the relief wells in time to prevent a collapse?
Of course, I Am Not An Oil Geologist (IANAOG), but as Sharon Astyk writes on Scienceblogs:
This one passes my smell test, which is usually pretty good. That doesn't mean I claim commenter Doug R is right; it means I think his information is interesting enough to be worth exposing to a wider audience for clarification or correction.
In support of this, TOD is frequented by oil geologists and engineers, and if DougR's comment were way off-base, someone would have called him out on it by now.
It doesn't help that the Government officials are helping BP to block journalists from investigating and covering the disaster even as they remain tight-lipped about what is actually happening. In the vacuum created by this information blackout, all that remains is plausible scenario-building by shrewd observers piecing together the snippets that are available.
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