Geological discontinuities, main flow path and chemical alteration in a marly hill prone to slope instability: Assessment from petrophysical measurements and borehole image analysis

摘要

Clay shale landscapes are sensitive to landslide, erosion, and re-sedimentation processes. In this context, tectonized clay shalesnhave peculiar hydrological and mechanical behaviours. In order to improve our understanding of the processes involved innsuch systems, an experimental site has been settled in the Draix Observatory (ORE DRAIX) on a black marl hill slope of thenSouthern Alps (France) in the framework of the ECOU-PREF project. The site is a natural laboratory to study the evolutionnof clay shale landscapes at several scales (regional to μm). In this study, we aim to characterize the internal structure andnfissure patterns of a stable interfluve, in order to locate preferential water flows within the system, and anticipate its evolution.nThis work is based on a series of mutli-disciplinary approaches including petrophysical analyses, well pulse injection testsnand downhole geophysical measurements. Borehole geophysical results were combined with laboratory measurements on corenplugs (permeability, density, porosity, and acoustic velocity). Optical and acoustical images have been used as an original toolnfor internal discontinuities characterisation and potential active flow path detection. They allowed the identification of threenmain lithological units interpreted as several stages of shale alteration. In addition, several main structural plane discontinuitiesn(open fractures, schistosity planes, and fractures infilled with calcite or clays) were identified from the images and their potentialntransmissivity discussed with regard to piezometric and tracer measurements. In all, the integration of measurements leads tonpropose a simple scenario of fluid circulation and chemical alteration of the interfluve