Faster Mapping Speeds Up the Search for Oil

New algorithms are helping Shell to map possible oil reservoirs deep below the Gulf of Mexico.

With demand and prices so high for crude oil, petroleum companies are searching for new reservoirs deep below the ocean floor, in areas of more geological complexity. But drilling under the ocean is very expensive, so oil companies need to have as complete an understanding of the geology where they're drilling as possible.

A map of salt deposits located kilometers under the ocean floor in the Gulf of Mexico, where Shell hopes to find new oil reservoirs. The map was generated using algorithms developed at MIT to analyze seismic data. (Courtesy of Jason K. Johnson, MIT department of electrical engineering and computer science)

Even armed with reams of seismic data about the Earth's subterranean features, though, making accurate maps of the geology underlying the ocean is a challenge. Now Shell is working with computer scientists at MIT to design algorithms that will allow them to more quickly and more accurately create maps of these underground areas.

Generating maps of the deep and complex areas now under exploration by oil companies can take several people many months, says Richard Sears, a visiting scientist from Shell at MIT. Regions under study may be hundreds of kilometers in area and several kilometers deep. Those working to create 3-D maps of these areas must process huge amounts of data.

Shell turned to Alan Willsky, professor of electrical engineering at MIT, for a way to make sense of the vast amount of seismic data that the company gathers for map-making. Willsky's group specializes in computational methods for extracting the shapes of objects from complex data.

For its first project with Shell, his group is tailoring algorithms to help the company's geologists study salt deposits under the Gulf of Mexico. Shell hopes that these formations, which are difficult to map, have trapped large deposits of oil under the sea floor. Willsky and colleagues are helping Shell map the surfaces, shapes, and boundaries of these deposits.

Willsky says that determining the shape and size of salt deposits under the earth is a similar to another undertaking of his group: collaborating with radiologists to develop image analysis algorithms for mapping the prostate to determine where to insert a cancer-killing radioactive pellets. Their algorithms "could impact many fields," he says, including biomedicine and oceanography.

The oil surveying process starts with ships sweeping over a large area around the clock for several weeks, while sending high-intensity vibrations into the Earth and measuring their echoes. About every 10 seconds, compressed air is shot into the water from many cylinders simultaneously. Vibrations from these blasts travel through the water and into the earth until they bump into something. Then they echo back to the water's surface, where they're registered by kilometers-long streamers of pressure-sensitive microphones trailing the ship. Although each echo is weak, multiple signals reinforce each other.