Surface Deformation at the Heber Geothermal Field in Southern California

Abstract

The Heber Geothermal Field is one of four operating geothermal fields in the Imperial Valley of southern California. The field represents a blind geothermal system located north of the border with Mexico, and south-southeast of the town of El Centro. The HGF has one double flash and three binary plants, with a total generating capacity of 120 MWe, and current production of ~90 MWe. As part of projects with the California Energy Commission (CEC), we have studied surface deformation at Heber using SqueeSAR, an interferometric synthetic aperture radar (InSAR) technique applied to Envisat (August 2005 – August 2010) and Sentinel (April 2015 – April 2018) satellite data. SqueeSAR is based on permanent and distributed scatterers, often aligned along roads and canals. This makes it possible to detect surface movements in vegetated areas where conventional InSAR techniques do not work. The spatial patterns and changes in time of surface deformation are related to changes in production and injection, and are confirmed by ground-based leveling data. Prominent subsidence is observed in both study periods, of up to −45 mm/year. In addition, after an increase in injection in 2005, uplift appears in some previously subsiding areas in the northeastern part of the field. This uplift is detected in the Envisat period, but gets reduced or resumes subsidence in the Sentinel period. In addition, horizontal movements are observed, following a pattern of westward displacements on the eastern flanks of subsidence areas and eastward displacements on the western flanks. Since surface deformation is dynamically connected to production and injection, and InSAR provides cost-effective and dense spatial and temporal coverage, such satellite measurements can greatly benefit field management and operations.