National Geographic : 2010 Oct
• Shallow water Deep Ultradeep Billions of barrels, by depth U.S. Gulf oil from federal leases, 1985-2009 Onshore Alaska and California offshore Gulf offshore U.S. domestic oil production, 1985-2009 Billions of barrels 0 0.1 0.2 0.3 1990 1985 1995 2000 2005 2009 0 1 2 3 1990 1985 1995 2000 2005 2009 -1,000 Feet below sea level -3,000 -5,000 -7,000 -9,000 Pilottown Venice Port Eads In the Gulf since 1977 In the Gulf since 1938 Up to 999 ft deep DEEPWATER WELLS SHALLOW- WATER WELLS N Mississippi River Delta its cement job. It failed to circulate heavy drill- ing mud outside the casing before cementing, a practice that helps the cement cure properly. It didn't put in enough centralizers---devices that ensure that the cement forms a complete seal around the casing. And it failed to run a test to see if the cement had bonded properly. Finally, just before the accident, BP replaced the heavy drilling mud in the well with much lighter sea- water, as it prepared to nish and disconnect the rig from the well. BP declined to comment on these matters, citing the ongoing investigation. All these decisions may have been perfectly legal, and they surely saved BP time and mon- ey---yet each increased the risk of a blowout. On the night of April 20, investigators suspect, a large gas bubble somehow infiltrated the casing, perhaps through gaps in the cement, and shot straight up. e blowout preventer should have stopped that powerful kick at the sea oor; its heavy hydraulic rams were supposed to shear the drill pipe like a soda straw, blocking the up- ward surge and protecting the rig above. But that fail-safe device had itself been beset by leaks and maintenance problems. When a geyser of drilling mud erupted onto the rig, all attempts to activate the blowout preventer failed. e way BP drilled the Macondo well sur- prised Magne Ognedal, director general of the Petroleum Safety Authority Norway (PSA). e Nor wegians have drilled high-temperature, high-pressure wells on their shallow continental shelf for decades, he said in a telephone inter- view, and haven't had a catastrophic blowout ORIGINS OF GULF OIL Organic material that settled in the Gulf over the past 120 million years was transformed into vast pools of oil and natural gas by time, pressure, and heat. The petroleum rises through faults until it is trapped by salt structures, some more than a mile below the seafloor. JUAN VELASCO, NGM STAFF. ART BY BRYAN CHRISTIE SOURCES: RENAUD BOUROULLEC, COLORADO SCHOOL OF MINES, AND PAUL WEIMER, UNIVERSITY OF COLORADO GEOLOGY AND BATHYMETRY ; LOUISIANA DEPARTMENT OF NATURAL RESOURCES SHALLOW WATER WELLS ; MMS DEEP AND ULTRADEEP WELLS, OIL FROM FEDERAL LEASES ; ENERGY INFORMATION ADMINISTRATION, OR EIA U.S. PRODUCTION DRILLING DEEPER As oil and gas reserves close to shore have been pumped dry, prospectors are plumbing a new frontier: the depths of the Gulf of Mexico. In 2009 Gulf oil production jumped 34 percent---largely from waters deeper than 5,000 feet. New technologies have made it possible to drill more than 35,000 feet down through water and rock.