Integrated InSAR-GPS Monitoring of an Underground Gas Storage (UGS) Field: The Minerbio Pilot Test

In 2014 the Italian Oil & Gas Safety Authority published technical guidelines (Italian Guidelines for monitoring the seismicity, ground deformation and pore pressure) to regulate the monitoring of all existing and future underground activities on the Italian territory. The guidelines suggested that ground deformation monitoring of underground activities was carried out by integrating InSAR and continuous GPS techniques to detect possible surface deformation phenomena linked to the monitored activities during the considered time interval, and to provide information of their space-time variations with respect to the background conditions. The guidelines application on underground gas storage (UGS) was tested on the Minerbio gas field under the supervision of the National Institute of Geophysics and Volcanology (INGV). At the time of the pilot test, Minerbio had a high-quality record of about 15 years of InSAR data and 10 years of CGPS data (from the MINE station). The presented case study shows how the Minerbio ground deformation monitoring system was implemented during the testing phase. The time series of MINE, sited in 2008 in a peripheral area of the field, show that it measures seasonal oscillations in the North-planar component and a certain seasonality in the East-planar component: considering such results, the InSAR data were used to identify a proper site for a second CGPS station with the aim to integrate the results of MINE. The new station MIN2 was placed in 2019 in the center of the field, near the vertical and East-planar InSAR amplitude peaks. The correlation analysis between the CGPS signals and the cumulative curve of UGS volumes of the Minerbio field indicates a strong correlation in the North-planar component for the MINE station and a strong correlation in the East-planar and vertical components for the MIN2 station. According with ILG target, such results indicate that: (i) MIN2 effectively integrates the MINE results by detecting the peak of UGS-related, vertical and East-planar oscillations, (ii) the current geometric configuration of the two-station CGPS system effectively integrates the InSAR information by giving information on the spatial distribution of the North-planar component of ground deformation, and (iii) the integrated InSAR-CGPS monitoring system provides a complete picture of the distribution of UGS-related ground deformations on the Minerbio field.