BP's Oil Disaster: The Dangers and Difficulties of 'Bottom Kill'

By Philip Bethge

BP has only one arrow left in its quiver, a method known as 'bottom kill.' The idea is for relief wells to stop the gushing oil from below, but the technical challenges are formidable. Past experiences show that the oil may continue flowing into late autumn.

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For the engineers, it was a blessing in disguise. They had drilled to a depth of up to 3,500 meters (11,500 feet) below the sea floor when gas and oil suddenly began shooting upward. But there was no explosion. The 69 workers at the site were evacuated and no one was killed.

It was the morning of Aug. 21, 2009, when engineers lost control of the well beneath the West Atlas oil rig in the Timor Sea off Australia's northern coast. It took 10 weeks to stop the flow of oil. By that time, about 4,300 tons of oil had flowed into the sea. It was only by drilling a so-called relief well that the Thai company overseeing the operation managed to pump enough mud into the well to cap the flow of oil.

For the BP engineers attempting to stop the out-of-control well still gushing oil into the Gulf of Mexico following the explosion of the Deepwater Horizon oil rig on April 20, the relief well method -- so-called "bottom kill" -- is also seen as the last solution available. The company began drilling the two relief wells in May, and BP CEO Tony Hayward says that he is confident that "the relief wells ultimately will be successful." He expects that the spill in the Macondo oil field will finally be capped by early August.

Hayward's forecasts, however, have not always proven to be reliable and independent experts warn that relief wells, like any well, are not without risk. "More oil could leak than before, because the field is being drilled into again," says Fred Aminzadeh, a geophysicist at the University of Southern California. Ira Leifer, a geochemist at the University of California in Santa Barbara, voices similar concerns: "In the worst case, we would suddenly be dealing with two spills, and we'd have twice the problem."

Making the Situation Worse

Leifer is a member of a team of experts deployed by US President Barack Obama to estimate the volume of oil currently flowing in the Gulf of Mexico. Just last week, the scientists almost doubled their estimate and now say that between 25,000 and 30,000 barrels of oil a day is gushing out of the well into the Gulf of Mexico. On Tuesday, they once again upped their estimate -- to between 35,000 and 60,000 barrels per day.

BP's most recent efforts to stop the flow of oil have only made the situation worse, says Leifer. The engineers' attempt to seal off the well from above, using a method known as "top kill," failed and only enlarged the borehole, according to Leifer. Now, he adds, there is almost nothing stopping the oil from flowing out of the well.

Most experts now believe that the relief wells, despite the risks, are the only option left. The principle of the method sounds simple enough. The engineers start by drilling vertically, and then diagonally toward the out-of-control well. Once they've reached the well, they drill into it from the side and pump large amounts of mud into it. The material fills up the well from below and eventually acts as a plug. In the end the well, like a decayed tooth, is capped with cement.

As straightforward as it sounds, this approach has not always been easy to implement in the past. The disaster in the Timor Sea, for example, ended in a debacle. It took engineer five tries to even find the borehole under the sea floor. Shortly before the end, the West Atlas oilrig went up in flames, after all.

Repeat of History?

Another case is also a warning sign for BP. In June 1979, engineers with the Mexican oil company Pemex lost control of the Ixtox I, an exploratory well in the Gulf of Mexico. Just as BP is now attempting to do, engineers at the time drilled two relief wells.

The first relief well was finished by the end of November, but it took until March 1980, more than nine months after the accident, to cap the well. By then, 480,000 tons of crude had flowed into the Gulf, the second-biggest oil spill the world has seen to date.

Is history repeating itself? The spill in the Macondo oil field could also continue to gush uncontrollably well beyond BP's August deadline. Pemex Director Carlos Morales, currently providing BP with technical advice, expects the spill to continue for another "four to five months." Leifer also believes that the disaster on the sea floor could drag on "until late fall."

Although the BP engineers have already completed two-thirds of the first relief well, it is extremely difficult to find the out-of-control well in the middle of the bedrock, says David Rensink, incoming president of the American Association of Petroleum Geologists.

"You're trying to intersect the well bore, which is about a foot wide, with another well bore, which is about a foot wide," Rensink said recently. Hitting it with the first attempt, he adds, "would truly be like winning the lottery."

Instead, the engineers will presumably have to repeatedly pull back the drill head to adjust the direction, Rensink predicts. "If they get it on the first three or four shots, they'd be very lucky."

More Caution

Rensink is particularly concerned that BP, in drilling the relief wells, will penetrate into precisely those rock formations in which extreme pressure and temperature conditions facilitated the April blowout in the first place. Gas bubbles and gushing oil from the depths are real possibilities. "Any relief well has to be drilled more cautiously than the original well," warns Donal Van Nieuwenhuise, a geologist at the University of Houston. "You don't want to experience the same disaster a second time."

Still, most geologists are confident that the bottom kill method will ultimately be successful. Van Nieuwenhuise says he has never seen the method fail entirely and points out that BP has ultra-modern drill bits bristling with sensors scanning the bedrock. Furthermore, the bits can quickly change direction. Once the stricken well is found, the drilling mud that will be pumped in is heavy enough to stop even the most high-pressure oil flows. Rensink too believes that the relief well method will eventually plug the leak. "The question is only when exactly that will happen," he says.

Indeed, the engineers aren't only facing a formidable technical challenge. Weather will also play a significant role. Forecasters have already predicted that this hurricane season, which began this month, could be one of the most active on record. Drilling would have to be ceased for the duration of each strong storm.

Translated from the German by Christopher Sultan

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1. Coming hurricane season in Gulf of Mexico
crudeoilpeak 06/18/2010
Let's compare oil production in 2010 and 2005, we are now 5 years into peak oil. 2005 was the Katrina year. The oil spill in this year is another Black Swan event. In the 1st quarter of 2010, oil production was basically on the same level as 2005, but oil prices $25 a barrel higher. Have a look at the graph: 18/6/2010 Crude oil 2010 vs. 2005 (1st quarter) http://www.crudeoilpeak.com/?p=1615 And why are we drilling in deep water anyway? Read this: 11/6/2010 BP Statistical Review June 2010: Oil reserves and production don't match http://www.crudeoilpeak.com/?p=1591
2.
BTraven 06/22/2010
---Quote (Originally by crudeoilpeak)--- Let's compare oil production in 2010 and 2005, we are now 5 years into peak oil. 2005 was the Katrina year. The oil spill in this year is another Black Swan event. In the 1st quarter of 2010, oil production was basically on the same level as 2005, but oil prices $25 a barrel higher. Have a look at the graph: 18/6/2010 Crude oil 2010 vs. 2005 (1st quarter) http://www.crudeoilpeak.com/?p=1615 And why are we drilling in deep water anyway? Read this: 11/6/2010 BP Statistical Review June 2010: Oil reserves and production don't match http://www.crudeoilpeak.com/?p=1591 ---End Quote--- Since there is no sufficient willingness to restrict the consumption of oil companies are forced to develop even deeper off-shore wells. Unfortunately the (German) saying that experience makes bright seems to be true. It would have been much better had BP prepared for closing leaks before the accident happened. Perhaps it is in the nature of people not being capable of handling of all imaginable scenarios of whom many have never happened at all.
3. bottom kill, also impressive name, but won't work eather ... why?
rudymartin 07/07/2010
---Quote (Originally by sysop)--- BP has only one arrow left in its quiver, a method known as 'bottom kill.' The idea is for relief wells to stop the gushing oil from below, but the technical challenges are formidable. Past experiences show that the oil may continue flowing into late autumn. http://www.spiegel.de/international/world/0,1518,700759,00.html ---End Quote--- The bottom kill won't work either. Why? Pressure and flow have to be very much higher than what comes out. Because part of the higher pressure and flow will vanish upwards and will add upwards to the pressure and flow already existing in the old well. Sealing an old well is different, there the pressure and flow are low and can even be stopped while pumping mud against it and letting it settle. Whereas here it works like quick sand, it cannot settle and will be spit out.
4.
BTraven 07/12/2010
---Quote (Originally by rudymartin)--- The bottom kill won't work either. Why? Pressure and flow have to be very much higher than what comes out. Because part of the higher pressure and flow will vanish upwards and will add upwards to the pressure and flow already existing in the old well. Sealing an old well is different, there the pressure and flow are low and can even be stopped while pumping mud against it and letting it settle. Whereas here it works like quick sand, it cannot settle and will be spit out. ---End Quote--- BP failed, and the question is whether the company wasted too much resources and energy on a technologies of which experts had believed that the chances of success would be quite small. Fortunately, they managed to construct an absorber which should have the capacity to get all oil coming up trough the leak. I hope they can stop the spill. BP must have generated a lot of knowledge concerning the way of dealing with such calamities therefore it would be a pity if big companies like Exxon is allowed to take over the concern.
5. I like the way it edges onto the coast
plotinus 07/14/2010
---Quote (Originally by esperonto)--- This is my sketch of BP sucking blood like a British insect: http://pooresperanto.files.wordpress.com/2010/07/misquito.jpg ---End Quote--- Very nice image. It should be in the New Yorker! .
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