Quantitative characterization to construct hard rock lithological model using dual resistivity borehole logging
Résumé
Borehole logging is a very robust tool to accurately locate transitions between weathered layers and fractures in hard rock settings; therefore, it can help substantially in the construction of regional and local hydrogeological models. A simple and low-cost resistivity probe, named dual resistivity logger (DRL), was experimented to map the formation resistivity at two investigation distances by means of three active electrodes. Forward response of DRL was analysed on the synthetic data generated for a conceptual hard rock hydrogeological model as well as tested at two field sites in hard rock aquifers of southern India. The DRL was proven efficient in demarcating the aquifer into successive hydrogeological zones, i.e. the laminated-fissured (L-F), the fissured-semi-fissured (F-SF), and semi-fissured-basement (SF-B) layers. The results were verified by comparison with well lithologs based on rock cuttings and temperature logging. The DRL has proven its ability to locate the hydraulically active fractures as well as contacts between weathered layers. It offers a simple but efficient way to acquire underground data for building hydrogeological models.