Geodetic imaging: reservoir monitoring using satellite interferometry

Fluid fluxes within subsurface reservoirs give rise to surface displacements, particularly over periods of a year or more. Observations of such deformation provide a powerful tool for mapping fluid migration within the Earth, providing new insights into reservoir dynamics. In this paper we use Interferometric Synthetic Aperture Radar (InSAR) range changes to infer subsurface fluid volume strain at the Coso geothermal field. Furthermore, we conduct a complete model assessment, using an iterative approach to compute model parameter resolution and covariance matrices. The method is a generalization of a Lanczos-based technique which allows us to include fairly general regularization, such as roughness penalties. We find that we can resolve quite detailed lateral variations in volume strain both within the reservoir depth range (0.4–2.5 km) and below the geothermal production zone (2.5–5.0 km). The fractional volume change in all three layers of the model exceeds the estimated model parameter uncertainty by a factor of two or more. In the reservoir depth interval (0.4–2.5 km), the predominant volume change is associated with northerly and westerly oriented faults and their intersections. However, below the geothermal production zone proper [the depth range 2.5–5.0 km], there is the suggestion that both north- and northeast-trending faults may act as conduits for fluid flow.