Use of Satellite Radar Images in Surveillance and Control of Two Giant Oilfields in California

A global analysis of the evolution of an entire giant oilfield is now feasible. The oilfield can be viewed as a single complex system consisting of reservoir rock and fluids, and coupled injectors and producers. The vertically averaged areal signatures of primary and waterflood projects in the field can be tracked in time as the displacement of ground surface above these projects. The Synthetic Aperture Radar interferograms (InSAR) from satellites are the enabling technology. In this paper, we add a new element to our multilevel, integrated surveillance and control system: time-lapse satellite InSAR images of the oilfield surface. In particular, we analyze ten differential InSAR images of the South/North Belridge and Lost Hills diatomite fields, CA, between 04/95 and 12/99. The images have been reprocessed and normalized to obtain the ground surface displacement rate. In return, we have been able to calculate section-by-section the net subsidence of ground surface over the entire field areas. The calculated subsidence volumes are thought to be close to the subsidence at the tops of the reservoirs. The images show that the rate of subsidence has decreased in some parts of Lost Hills and Belridge, while it increased in others. Using the production and injection data from the California Conservation Commission and Chevron, we have been able to demonstrate the remarkable behavior of both fields: (1) There is recirculation of injected water through the "tubes" of damaged soft rock that link injectors with producers, resulting in diminished pressure support from the waterfloods. (2) Consequently, despite more water injection, there is more subsidence in Sections 29, 34, and 33 in Belridge and in Sections 29, 4, 5, and 32 in Lost Hills. (3) As much of the injected water is recirculated, the rate of subsidence is proportional to water production rate. (4) Compaction remains an important mechanism of hydrocarbon production. (5) In addition to accelerated compaction in the densest and most advanced waterfloods, there is a sizable oil production response to water injection. Means of controlling and improving the existing waterfloods are discussed.