GPR tomography in a water saturated context using a 13 boreholes configuration

Abstract

This study takes part in an integrated project whose goal is to characterize the permeability heterogeneity controlling the water flow in a saturated environment. Our approach, as part as this project, is based on the use of ground penetrating radar (GPR) in order to determine the water content by means of an EM velocity model. We investigate a porous, permeable and water saturated formation (bioclastic limestones dating from the Burdigalian). The studied area is located in the South of France, near the city of Montpellier. Thirteen vertical 35 meters deep boreholes, including 3 continuous cores, were drilled in 2016. A total of 32 tomographies have been acquired between the 13 wells with 100 MHz antennas. In addition to the tomographies, GPR log has been carried out in each well with 250 MHz antennas. The 32 dataset have been separately inverted in order to obtain 32 2D velocity models. These inversions were based on the SIRT (Simultaneous Iterative Reconstruction Technique) algorithm. The analysis of these 2D models shows velocity variations interpreted as water content heterogeneities. Correlations between tomographies, logs and core measurements show strong similarities in terms of global trend. However, absolute velocity differences between each panel justify 3D perspectives.