SPATIAL AND TEMPORAL RELATIONSHIP BETWEEN INSAR-DERIVED SUBSIDENCE, FLUID BALANCE, AND FORMATION PRESSURES IN THE KERN FRONT AND KERN RIVER OIL FIELDS

Land subsidence has long been recognized in areas of oil and gas production. This subsidence is driven by extraction of fluids (hydrocarbons and water) without complete replacement by natural or injected fluids (water and steam). Previous geodetic studies have focused on the spatial distribution and rate of subsidence. However, the relationship of subsidence to the temporal and spatial evolution of fluid balance (net difference of produced and injected fluid volumes) and formation pressures has not been fully explored. This relationship is key to understanding fluid pressure gradients that drive migration of injected fluids within or potentially outside oil-production reservoirs.

In order to explore the relationship of subsidence to fluid balance and formation pressure, we apply interferometric synthetic aperture radar (InSAR) methods to the Kern River and Kern Front Oil Fields near Bakersfield, California. Synthetic aperture radar (SAR) images obtained from the Sentinel-1 A/B mission from 2015-2020 are used to produce interferograms using GMTSAR, an open-source InSAR processing codebase. These are then stacked using the small baseline subset (SBAS) method to create a time series of line-of-sight (LOS) deformation. The observed deformation is compared to the spatial distribution of fluid balance calculated from monthly well-by-well production and injection volumes and idle well fluid levels reported to the California Geologic Energy Management Division.

Preliminary results show that recent subsidence is concentrated in the eastern part of the Kern Front field and the southwest part of the Kern River field. In the Kern River field, the locus of subsidence, net fluid withdrawal, and minimum idle well elevations are co-located. Conversely, in Kern Front, the locus of subsidence and net fluid withdrawal are offset from the minimum idle well fluid elevation. We continue to explore the implications of these observations.