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, the researchers are monitoring where and how much the ground surface sinks as oil is pumped from a large oil field.

This figure shows a comparison of interferograms from four different years mapping the rapid ground subsidence over the Lost Hills oil field in California. Lost Hills is located about 60 kilometers (40 miles) northwest of Bakersfield in the San Joaquin Valley. The oil field is about 1.5 kilometer (1 mile) wide and 6 kilometers (3.5 miles) long. Each interferogram was created using pairs of images taken by synthetic aperture radar that have been combined to measure surface deformation or changes that may have occurred in the time between when data for the two images were taken. The images were collected by the European Space Agency's first and second remote sensing satellites during two months of each year shown (1995, 1996, 1998 and 1999). They were combined to produce these image maps of the apparent surface changes. Photo: NASA/JPL

Subsidence means that rocks are collapsing deep underground. It can damage oil wells and reduce the amount of oil that can be pumped from a field. In their study, geophysicist Dr. Eric Fielding, of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Dr. Tadeusz Patzek, associate professor of petroleum engineering at the University of California, Berkeley, looked at Chevron's Lost Hills oil field. Lost Hills is located 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 3 meters (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 of surfaces that may have changed in the time between collection of the data.

Using these radar data, scientists found that parts of the oil field were subsiding unusually rapidly, more than 3 centimeters (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 oilfield, 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, Berkeley, the Department of Energy and Chevron U.S.A. The results were presented in October 2001 at the Society of Petroleum Engineers Annual Technical Conference and Exhibition. JPL is a division of the California Institute of Technology in Pasadena.