Ground Deformations Observed for Three Decades (1992-2022) above Old and Deep Coal Mines Reused for Deep Gas Storage Sites (Wallonia, Belgium) using PS-InSAR Time-series.

The coal mining exploitations in Wallonia was gradually phased out till the end of the last century. Groundwater pumping was ceased, implying a groundwater rebound at varying rates that can still be observed by radar interferometry. The sustainability of architectural and technical facilities within those zones must be monitored to reduce environmental concerns during the post-mining phase and their reuse as gas storage reservoir locations. PS-InSAR approach has shown land surface deformations during three decades in a large area (96 km²) covering the cities from Binche to Anderlues (Wallonia, Belgium). Two coal mines are concerned: (i) to the West, the Ressaix-Mariemont-La Louvière concession where a small part was used as the Peronnes Gas Storage (PGS) reservoir; (ii) to the East, the Bois de la Haye concession where about half of the area has been used as the Anderlues Gas Storage (AGS) reservoir. To maintain the PGS reservoir dry, a private company has maintained groundwater pumping activities till 1998 with a dewatering rate of 40 m³/h. After 1998, the water levels raised from 8 m/yr at the beginning to 2.5 m/yr around 2010. The gas storage reservoir of Anderlues is known to be relatively dry. Using a multi-sensor radar dataset including radar images acquired by the European Space Agency’s satellites of ERS1/2, ENVISAT ASAR, and Sentinel-1A, 236 interferograms were constructed. Ground displacements are mapped and subdivided into three successive time intervals showing: (1) during ERS1/2 (1991-2000), a gradient from positive annual average velocities (West) to negative ones (East) across the PGS site and mostly negative values (-0.5 to -3.0 mm/yr) above the AGS site; (2) during ENVISAT ASAR (2003-2010), the positive LOS velocities (0.5 to 2.89 mm/yr) are present along an NW-SE ellipsoid across PGS leaving only negative LOS values in the NW corner while negative LOS velocities were also recorded along the Binche city (-0.5 to -2 mm/yr). During the same period, the AGS is facing negative LOS velocity values and extending to the south as well; (3) during Sentinel-1A (2015-2022), almost all the PGS is affected by positive annual LOS velocities (0.5 to about 4-5 mm/yr) even extending towards the north outside the limits of PGS. AGS is still affected by negative LOS values in the middle and SE parts. Ground displacements measured at the surface of old coal mine concessions and recent gas storage sites allow following the impact of the use of the subsurface through time.

Abstract of an Oral Presentation or a Poster

Belgium, InSAR, (15) géologie