"NaCl of the Earth," Feature Article, March 2006

NaCl of the earth

Salt deposits complicate the picture in the search for undersea oil; high-power computer imaging helps sort things out.

by Harry Hutchinson, Executive Editor

the value of oil in terms of personal freedom and comfort is almost incalculable. People will certainly pay plenty to get it. As demand and prices continue to rise, it has become necessary, and profitable, to look for deposits in increasingly severe environments—in ever colder seas, for example, and at greater depths.

Sometimes, though, it is not the depth of water or the thickness of ice that poses a challenge for the petroleum seeker. Sometimes it's the sea floor itself.

Chevron, for instance, finds that it needs a lot more computer power these days for investigating undersea oil fields. The company is investing in hundreds of IBM computers with dual-core processors because too much salt is getting in its way to the oil.

Peter Breunig, general manager for technical computing in Chevron's Energy Technology Co., and a colleague, Chap Wong, explained the problem and the solution.

Depth imaging converts seismic data recorded over potential oil fields into three-dimensional images of what lies beneath the sea floor. The information helps the company decide where to drill.

The process starts when boats trailing cables of hydrophones take soundings with an air gun. (Unlike the explosions of the old days, the air gun kills no fish.)

Computers can turn seismic recordings into 3-D images of potential undersea oilfields, like the one projected on the wall in this photo.

A sound wave penetrating the sea floor returns an echo each time it passes the boundary between different formations— say, between a layer of dense rock and another bearing oil. The hydrophones pick up the echoes. To those like Breunig and Wong, who know how to interpret them, the properties of the acoustic reflections tell a story of what lies below.

Frequently, analysts can combine the data from several soundings over the same spot and that way minimize the effects of system noise. The picture gets clearer then, and a computer's workload is reduced.

Breunig said that Chevron has been exploring parts of the Gulf of Mexico where layers of salt have formed. Dense salt layers, like those the company is encountering under the Gulf, scatter the acoustic reflections. The result is more noise in the data.

Chevron has worked out algorithms to account for the disruption caused by highly reflective salt, but assumptions that permit the consolidation of readings are no longer practical. As a result, the volume of data going into the computer to analyze soundings through salt or complex structures can be an order of magnitude greater than it is for other areas of the sea floor, Breunig said.

So far, Chevron has bought 700 eServer 326 computers from IBM to help handle the increasing computational load. The computers use the AMD Opteron processor in a dual-core configuration. That is, the central chip contains two central processors. Because they are built on the same chip, they generate less heat than two separate chips would, IBM says. The servers run on the Linux platform and handle 32- and 64-bit processing.

Multiplied by 700, that's a lot of thinking power, but then these aren't easy puzzles to solve. Sometimes in the search for oil or gas somebody has to unravel the tricks played by a layer of salt.