DRILLING for oil is a balancing act. If the pressure of the working fluids in the well, or the strength of concrete holding the piping in place, cannot balance the immense pressure of the oil down below, then things get very bad, very quickly. On April 20th, for some reason as yet unknown, the pressure in a well that had been drilled by the Deepwater Horizon, a rig that BP, one of the world’s largest oil companies, was using to explore a new field in the Gulf of Mexico, got out of balance. The well blew its top, causing an explosion and subsequent fire which claimed the lives of 11 of the rig’s crew of 126 and eventually sent the rig itself to the bottom of the ocean, a mile below the surface and some 40 miles (64km) off the Louisiana coast.
In the aftermath, oil started to seep to the surface. Since then the slick has grown inexorably, despite attempts to contain and disperse it. On the distant shore they watch with concern and a certain fatalism. “This is just like waiting for a hurricane,” says LeRoy Meaux, a Louisiana welder, as he works on fixing a winch to a barge. “Been there, done that.” What no one yet knows is whether the Gulf spill will, like some hurricanes, soon fade in the memories of all but those most directly affected, or whether, like Katrina, it will cause havoc that has repercussions much farther afield. Such an outcome is certainly possible. BP has its bottom line and reputation at risk. The technology of deepwater drilling, rightly celebrated for its ingenuity, faces the prospect of more critical assessment than it has received to date. And human livelihoods and natural habitats on the coasts of four states are in jeopardy at a time when offshore drilling is playing an important role in America’s national debate about the nature and security of the country’s energy supply.
At the end of the tether 已是智穷才尽
On the sea floor beneath the Deepwater Horizon sat a device called a blowout preventer, capable of sealing off the well with a number of hydraulic systems, including one designed to slice right through the whole stack. Had it been activated beforehand it should have been able to contain the pressure in the well, saving the rig. Activated after the blowout, it would have done nothing to save the rig, but should still have been able to isolate the oil in the well from the sea above it. But neither of the two systems that should have activated the preventer after the blowout seems to have done so—or if they did, the preventer did not do its job. Oil continued to flow into the spindled and mutilated remains of the piping that had originally risen from the sea floor to the drilling platform, coming out of that wreckage at three different points and spreading over thousands of square kilometres.
The United States Coast Guard has estimated that 5,000 barrels of oil are being added to the slick every day. Ian MacDonald, a marine biologist at Florida State University who studies oil that comes out of natural seeps on the sea floor, estimates on the basis of pictures and maps from the coastguard that the rate may be as much as five times that. The largest accidental oil spill in history, which was also in the Gulf, was due to a 1979 blowout on a Mexican rig called Ixtoc-1 (see chart). Between June 1979 and March 1980 it released around 3.3m barrels. For comparison, the Exxon Valdez fiasco in Alaska in 1989, America’s most infamous oil spill, released just 260,000 barrels. At the coastguard rate the Deepwater Horizon leak would take years to match Ixtoc-1; at Mr MacDonald’s rate, months.
BP has developed a number of plans for stemming the flow before then. The one（ most assured of success ）requires the drilling of a new well that would intersect the existing one. Remarkably, there seems little doubt that threading such a well into the old one is possible, despite its being only seven inches across（宽） and 18,000 feet (5,500 metres) down. But more than one attempt may be needed, which is why BP has two rigs earmarked for relief wells. One has already started drilling; the other is expected to get under way shortly. Their work, though, will take months.
Even if the leakage is only at the lower end of the estimates, months could add up to a great deal of oil on coastlines important for fishing, tourism and the environment. So the race is on for approaches that could work quicker. On May 5th remotely operated submersibles managed to seal off the smallest of the three leaks, which did not reduce the overall flow, but has simplified matters. BP is also building a pair of cofferdams that could sit over the leaks like inverted funnels（倒转的漏斗）, with（借助） piping allowing the oil up to a drilling ship at the surface.
The first of these cofferdams is already built and due to be sunk by May 7th. No such system has been put together at this sort of depth before, so getting it to work is unlikely to be easy. There are, though, other options. While attempts to get the blowout preventer to shut off the flow entirely have so far failed, BP is investigating a technique called “top kill” that entails putting new pipe into the preventer through which to apply downward pressure（向下的压力）.
Many local fishing boats have signed on as vessels of opportunity to help the coastguard; the rest are tied up at their docks, as fishing in the area is no longer permitted. The seafood industry is worth $2.4 billion to the state of Louisiana when fishing, processing, selling and cooking in restaurants are all taken into account, and a fishing ban will eat into that. Tuan Nguyen, a seafood wholesaler in the small community of Venice, Louisiana, says his business was shut down for eight months after Katrina, in 2005, and his savings were obliterated: “I don’t know what we’re going to do, because the bills are coming in every day.”
The first known animal victim of the spill was a northern gannet, currently recovering. Dead jellyfish and turtles are now washing up on the beaches, and fish are suffocating（奄奄一息）. When the oil starts to wash up in quantity, the greatest environmental threat will be to the Louisiana wetlands. Oil on the fine white sand of the Mississippi, Alabama and Florida coastlines would depress tourism, but workers could scrape it up and haul it away. The muddy lattice of marshes, bayous, and barrier islands that makes up southern Louisiana is different.
The erosion of these delicate environments was a pressing issue even before the spill, made worse by the damage Katrina did to barrier islands. If the oil penetrates the wetlands it could worsen the problem further by killing the vegetation that does its best to hold the marshes together. It（浮油） will also affect the wildlife therein. Mike Carloss, a biologist with the Louisiana Department of Wildlife and Fisheries, says the brown pelicans and terns in the area are already stressed by the seasonal demands of nest building and fighting for territory, and are thus particularly vulnerable.
One of the things that the fishing boats helping the coastguard can do to help is spread dispersants. Oil is dangerous to seabirds because it（浮油） dissolves the grease that insulates their feathers; they get cold and die. Dispersants cut the oil as washing-up liquid cuts the grease on dishes, allowing oil on the surface to spread down into the water. This lessens its effects on surfaces and shorelines, though it might make things worse for fish. Once dispersed ，the oil can then be broken down more easily by bacteria that have evolved to live off natural sources of hydrocarbons.
To avoid contaminating the sea floor, most dispersants are used only in deep water. Today’s dispersants are not as toxic as those used on the big spills of the 1970s, but they still require care, and must be kept away from some sensitive places, such as reefs and spawning grounds.
Boom and bust 盛衰
There is only a short window—from a few hours to up to two days—in which dispersants are useful, says Simon Rickaby, a marine-pollution expert at Britain’s Institute of Marine Engineering Science and Technology. This is because the light fractions of an oil spill—as much as 40% of the total—will evaporate quite quickly (air-quality monitoring stations have been set up along the coast to make sure that this, in itself, does not become a health hazard). The oil left behind becomes thicker and forms a sort of mousse that is less susceptible to dispersants.
The need for early action, and the fact that the Deepwater Horizon spill is in much deeper water than most, has given rise to a new way of using dispersants. A remotely operated underwater vehicle with a “wand” rather like those used for weedkiller has been dispensing nine gallons a minute of dispersant thousands of feet below the surface, close to the leaks. The idea is to see if the slick can be broken up before it even reaches the surface.
As well as dispersants, some of the 200 or so boats and ships fighting the slick are deploying booms to prevent the oil getting into sensitive coastal locations and to corral it in places where it is concentrated enough to skim or, if the conditions are right, burn. A typical skimmer备 uses rotating drums or discs of plastic onto which the oil clings and is then scraped off by something like a windscreen wiper. Like dispersants, both burning and skimming need fresh oil—once things get mousseux there is much less that can be done.
By May 4th, 487,000 feet of booms had been deployed, and over 650,000 feet more were available for use. Success, though, will depend on the conditions. Currents draw water under the booms, while waves splash the oil over; strong winds capsize or sink them. Although bad weather, like that of the May Day weekend, keeps boats and booms at bay, it also acts as a dispersant itself, mixing the oil into the water. Over the coming weeks and months the prevailing weather will determine whether the oil stays reasonably contained or spreads farther afield.
The various efforts to deal with the crude were, as of May 5th, costing BP about $6m a day. The costs fall to BP because, as the majority shareholder in the consortium leasing the Deepwater Horizon (the junior partners are America’s Anadarko and Japan’s Mitsui) and the project’s operator, it is liable under American law for the costs of cleaning up. BP is also, at the moment, taking most of the blame from angry Louisianans and from stockmarkets. By May 5th its capitalisation had fallen by $30 billion, or about 16%.
But a number of other companies played a role. Transocean, the world’s largest offshore-drilling firm, owned and ran the Deepwater Horizon. The blowout preventer was made by Cameron International, a specialist engineer. Then there is the cementing of the wellhead, a process which is necessarily tricky. When the cement is wet, its pressure serves to balance the forces inside the well; when it is dry its strength does. But as it sets from wet to dry things can go wrong. This process, which has been implicated in a number of blowouts, was carried out by Halliburton, an engineering-services firm. How blame is eventually allocated among these companies remains to be seen.
Meanwhile the costs of dealing with the spill are going up.The relief wells will cost $150m apiece, and the cofferdam experiment will cost millions, too. Cleaning up after a lot of oil hits the shore will raise the stakes considerably higher. Financial analysts forecast that in the worst case BP could spend as much as $12 billion fixing the mess, though it would later recoup some of that from its partners. That would be “utterly” within BP’s financial capabilities, a company spokesman says.
Being nasty to oil companies is never hard, and BP’s record over the past years has not endeared it to American public opinion. A fire at the company’s Texas City refinery in 2005 killed 15 workers and revealed what at the time was clearly a poor safety culture. The subsequent corporate soul-searching and reform was not particularly obvious to the public; the Alaskan North Slope’s largest-ever oil spill, in which at least 4,800 barrels of crude seeped out of a BP pipeline just a year later, was more noticeable. In 2007 the company paid more than $300m to settle an investigation into allegations that it had fixed the propane market in 2004. This all gives Washington the whip hand. BP’s chief executive, Tony Hayward, and Andy Inglis, the head of its upstream division, can look forward to a hard time on Capitol Hill in the weeks to come.