National Geographic : 2004 Jun
(Continuedfrom page 89) the green shallows of the Gulf in the past 30 to 40 years. Like the fields on the U.S. mainland, they are in their twi light, their oil production slipping year by year. The platforms thin out and vanish by the time the ocean turns the blue of deep water, an hour from shore. Soon, another platform emerges from the haze. Called Marlin, it rides the waves on stout orange pontoons, its bright gas flare streaming in the breeze. Marlin is where BP engi neers first learned to tap the Gulf's deepwater riches. Discovered in 1993, the Marlin field is now in full-scale production. Tethered to the bottom half a mile down by thick steel tendons, Marlin taps 48,000 bar rels of oil a day from reservoirs two miles below the seafloor. Silvery ducts carry the crude to a complex of separator tanks. There natural gas, water, and sand are stripped out of the oil before it is pumped off the platform into a sub merged pipeline, which carries it to shore. Geologists once doubted oil could be found this far from shore. Twenty years ago, as drilling marched seaward across the shallow continen tal shelf, the oil-bearing sandstone layer seemed to be petering out. Scientists concluded that the sand deposited tens of millions of years ago by great rivers had not spread all the way out on the shelf. But they were mistaken. The sand and oil-was there all right. The sand had spilled off the edge of the shelf and down the steep continental slope to the deep-ocean floor. There it had pooled in apron like deposits that turned into porous rock - perfect for capturing oil oozing from still deeper rock layers. In the 1990s, as hints of these deposits began showing up in seismic data, the vanguard of oil production stepped off the con tinental shelf, into waters thousands of feet deep. Now giant new fields, the biggest of them Thunder Horse, beckon at 6,000 feet and more. At still greater depths approaching 10,000 feet, says geophysicist Roger Anderson of Columbia University, "there have been a whole series of finds," although they have yet to be exploited. All in all, oil experts estimate that the deep waters of the Gulf of Mexico will yield more than 25 billion barrels of oil. That's twice as much as in Alaska's giant Prudhoe Bay field, and far more than in any untapped U.S. prospect, including the controversial Arctic National Wildlife Refuge. "There's a major consensus that there's more oil 96 NATIONAL GEOGRAPHIC * JUNE 2004 "PEOPLE SHOULD BE DOING SOMETHING NOW TO REDUCE OIL DEPENDENCE," SAYS PHYSICIST ALFRED CAVALLO, "AND NOT WAITING FOR MOTHER NATURE TO SLAP THEM INTHE FACE." there than you'd ever find in ANWR" says Ander son. With the boost from deepwater wells, offshore oil should increase from a third of U.S. oil production now to more than 40 percent by 2008, before tapering off. But it will still barely ease the American thirst for oil. On the other side of the Atlantic, just off the coast of Cameroon, in West Africa, a giant pipeline terminal is helping quench that thirst. Every few days a tanker departs from the terminal with a belly full of oil piped 665 miles through savanna and rain forest from the billion-barrel Doba fields in Chad. The oil began flowing in July 2003, much of it bound for the United States. At 3.7 billion dollars, the project is the biggest private-sector investment in sub Saharan Africa-a measure of U.S. interest in the 30 billion to 50 billion barrels of oil trapped in and near the Gulf of Guinea. A swelling river of crude from Chad, Nigeria, Angola, and other African countries now makes up 15 percent of U.S. imports and is expected to rise. The Chad-Cameroon pipeline is more than another assurance that U.S. gas stations won't run short. It's also an effort by the World Bank and an industry consortium led by Exxon Mobil to reverse the mounting human costs of oil development in Africa. So far, says Terry Lynn Karl, a Stanford Universitypoliticalscientist,the track record is "about as bleak as you can get."