Présentations Colloques

Oral Presentation
8.05
Session 8.05: Karst aquifers
Leonardi Veronique
Karst genesis modelling of a regional Mediterranean aquifer (Lez, France)
The exploitation of karst aquifers is a risky activity as far as the drilling of the main conduits of the karstic network is not systematically successful. However, a better knowledge of the karst development along time could help to predict the preferential areas in which the karstic drains occur. Several attempts have tried to understand how the drains are growing along time. These studies concern either –(i) geological studies on the field+ or –(ii) numerical modelling. Combining both the field observations and the numerical modelling appears as a promising solution for a better forecast of the preferential zones of karst development. However, such a combination is still a challenging objective.**For the last few millions years, the aquifer of Lez (Montpellier, France) has been developed in a Mediterranean setting. However, several evidences show that other previous karstification stages affected this aquifer. The problem is to weight the impact of each of these stages on the present-day karst network. For example, the Messinian crisis is considered as mainly driving the architecture of the karst conduits, but how to quantify its impact compared to the ones of the previous and following stages? In order to provide quantitative arguments and elements of responses to these questions, a numerical modelling of diagenetic overprints (using an in-house TOTAL S.A. modelling toolbox) has been applied. **This study shows that the main conduits of the present-day karstic network were created during the early karstification stages, and then used again during the Messinian. A preferential karstic area, located at the top of the Jurassic layer (jurassic epikarst), developed during the earliest period of karstification (late Jurassic). The karstification during the Messinian crisis emphasized and increased the dissolution in this superficial zone, but also created a new and deeper karstic network. **For the first time, such a study has been carried out at the regional scale. Results are so exciting that the same methodology shall be applied in other locations and other reservoirs.
France