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Here is a comparison of interferograms from four different years mapping the rapid ground subsidence over the Lost HIlls oil field in California. Lost Hills is about 40 miles northwest of Bakersfield in the San Joaquin Valley. The oil field is about 1 mile wide and 3-5 miles long.

1 January 2002

Radar may help sinking oil fields

Pasadena, Calif.—Radar images of the surface of an oil field are helping scientists understand how rocks deep within the field behave, which may help oil companies reduce costs and increase production.

In this pilot study, researchers are monitoring where and how much the ground surface sinks as oil pumps out from a large oil field.

Subsidence means rocks are collapsing deep underground. This can damage oil wells and reduce the amount of oil you can pump from a field. In their study, geophysicist Dr. Eric Fielding of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and Dr. Tadeusz Patzek, associate professor of petroleum engineering at the University of California at Berkeley, looked at Chevron's Lost Hills oil field. Lost Hills is about 40 miles northwest of Bakersfield in California's San Joaquin Valley. About a mile wide and more than three miles long, parts of the oil field have subsided 10 feet since 1989.

The researchers compared radar images of the oil field taken during 1995, 1996, 1998, and 1999 using a technique called radar interferometry. This involves precisely aligning two radar images taken at different times. It produces accurate measurements of topography and surfaces that may have changed in the time between collection of the data.

Using this radar data, scientists found that parts of the oil field were subsiding unusually rapidly—more than 1.2 inches a month—in 1995 and 1996. They also discovered that while the ground subsidence rate decreased in the center part of the oil field, it increased in the northern part in every year observed between 1995 and 1999.

"This is an exciting new application for synthetic aperture radar, monitoring subsidence over an oil field from space," said Fielding. "We're now working with Chevron to combine these subsidence maps with the records of oil and water extraction and injection to understand how oil-containing rock is behaving beneath the surface."

The project is a collaboration supported by NASA, the University of California at Berkeley, the U.S. Department of Energy, and Chevron U.S.A.