WASHINGTON—If someone had suggested a decade ago that oil could be pumped from beneath 29,000 feet of water in the Gulf of Mexico, the notion would've been dismissed as a tale rivaling Jules Verne's "Twenty Thousand Leagues Under the Sea."
So when Chevron Corp. and its partners announced last week that they'd pumped oil from 5.3 miles below the gulf's surface, it spoke volumes about the pace of technological advance.
Giant new drill ships and sophisticated computer technology made Tuesday's announcement possible.
Drill ships more than seven football fields long have drilling platforms and derricks in their centers. They rely on electric motors beneath their hulls to maintain their positions over the drill sites or wells. That's no easy task given that the ships work as far as 200 miles offshore in heavy seas.
Their electric motors work in tandem with onboard computer systems that keep the vessels above the drill sites or wells by using satellite positioning technology and sensors on drilling templates.
The drilling itself is done with heavy, massive diamond bits, not unlike the knobby diamond bits that weekend handymen use to drill through stone or concrete. Giant pumps circulate the drilling mud as layers of drill pipe are forced down via top drives that rotate the drill pipes as heavy additional pipe is added.
Visualize the process as giant drinking straws being connected one to another in a long chain. Those that stretch down almost 6 miles apply more than a million pounds of pressure.
The next generation of gargantuan ultra-deep-water drill ships—Chevron ordered two this year for deployment in 2010—will be able to drill below 12,000 feet of water to a depth of about 7.6 miles from the ocean's surface to the bottom of the well.
Complementing the new ships and rigs are advances in computer modeling and seismic imaging that allow geologists to estimate accurately what lies miles below the ocean floor.
In the 1950s, deep-water drilling was defined as about 100 feet of water. Today, ultra-deep water is defined as 5,000 feet or more.
When oil companies began to explore the deep waters of the Gulf of Mexico, they dragged a single long cable measuring almost 3,300 feet to shoot sound waves along the ocean floor. The acoustic data received were crunched in computers to create a two-dimensional seismic image, sort of a vertical slice of what lay beneath.
Today, tow vessels can drag up to nine cables, each stretching as much as 33,000 feet. Computers with better processing capabilities generate three-dimensional—or cubed—images for geologists and engineers to examine in "visualization" laboratories.
What had long stymied ultra-deep exploration were thick layers of salt below the ocean floor that distorted the sound waves geologists use to gauge density. That made it difficult to assess the rock formations below the salt layers to determine whether they held trapped hydrocarbons.
Generally, oil flows up from porous rock such as sandstone and pools into reservoirs that are trapped under nonporous rock. Visually, it's like water trapped under an upside-down cereal bowl. These reservoirs are what energy companies are looking for with seismic imaging and what they target when drilling.
More powerful computers and software advances helped overcome salt layer-imaging problems, allowing for remarkably accurate computer modeling. Oil companies are high-tech gamblers. Exploratory drilling in ultra-deep water can cost as much as $120 million per well.
Thanks to the imaging advances, Devon Energy, which holds many exploration leases in the Gulf of Mexico, boasts four strikes in six drills, a success rate of 66 percent. Company officials said that was remarkable given that the usual success ratio averaged closer to 10 percent.
"As you look to the future, those advances will continue, so we'll be able to look deeper—both in the water and under the earth—and we'll be able to get better images and use that information to place our wells," said Steve Hadden, the senior vice president of exploration and production for Devon Energy.
To date, oil companies have drilled at a water-depth record of 10,011 feet and a total depth record of 34,189 feet. Making this possible are larger and larger drill ships, able to withstand greater weight, or deck load. Fifth-generation vessels being built in South Korea for Houston-based Transocean Inc., the world's largest offshore driller, will have a deck-load capacity of 22,000 short tons, allowing more weight to push drill bits deeper below the ocean floor.
"The process is simple, but the equipment you use is pretty complex," said Guy Cantwell, a spokesman for Transocean.
———
(c) 2006, McClatchy-Tribune Information Services.
Need to map
Comments