In the Mediterranean region, the most productive carbonate aquifers with significant underground reserves are mainly located in massive limestones or dolomites of the Jurassic or Cretaceous age. During their geological evolution, these carbonate formations have undergone various tectonic phases that structure such reservoirs, by folds, faults or fractures. While the scientific community of hydrogeologists agrees that the presence of fractures contributes to the occurrence of karstification and that the development of karst networks depends on the existence of these fracture networks in interaction with the various planes of stratification, many issues are still to be resolved regarding the impact of major faults on groundwater flows in such environments: (i) do these act as a impervious boundary, especially when these structures are put into contact the main reservoir with a impervious layer ? - (ii) or is it a preferential pathway for groundwater flows, particularly with the development of karstic drains within these major fault zones? - (iii) or finally, do they allow flows only through the fractures located in the damaged zones of these faults, in lack of karstification.
This project is part of the study of the dynamic analogues, and concerns in particular the characterization of fluid transfers within a fault zone in a carbonate environment. In such environments, a key issue remains, which concerns the occurrence of karst or not, with or without an impact on groundwater flows within and/or through a fault zone.
In the North of Montpellier, about 20 sites located in Jurassic and/or Cretaceous aquifers were investigated in order to characterize the flow patterns within major faults that affect these reservoirs. Through the example of the Kimmeridgian-Berriasian reservoir drained by the source of the Lez which supplies Montpellier, and which is affected by many major faults (Matelles-Corconne, Saint-Clément faults...), we have characterized the hydrogeological behaviour of the latter. The aim of this study is therefore to present how, in the case of massive carbonate media, -(i) the faults are karstified or not, and - (ii) how flows occur through and within them.
The authors thank TOTAL for funding this R&D project and giving permission to publish this paper.