PhD defense of Abdoul Nasser YACOUBA

Abstract

In a context of global changes and ecological and energy transitions, climate change induces recurrent drought and water resource crisis in several regions and continents. It is crucial to study groundwater in order to support these transitions and ensure effective management and use of this vital resource. In particular, the vadose zone which plays an important role in the recharge of these groundwater and the transfer of possible pollutants and inputs. Most of time this unsaturated zone, is characterized by multi-scale heterogeneities (e.g., pore structure, fractures, mineralogical variation) particularly in a limestone environment. These heterogeneities are complexified by diagenetic processes linked mainly to physicochemical and mineralogical alteration which leads to uncertainty in reservoir property (e.g., porosity, permeability, water saturation) estimation from geophysical methods. Among these methods, acoustic and electrical methods are well suited because of the strong relation between heterogeneities and the measured properties. This thesis relies on a multi-geophysical approach in order to better characterize a complex carbonate reservoir using petrophysical measurements combined with microstructural descriptions. Based on this approach, we demonstrated the influence of rock structure on the prediction and modeling of petroacoustic properties. This work leads to a good discrimination of some facies, which can be used to improve simulation and flow models. In addition, we demonstrate the relevance of complex conductivity measurements in limestone characterization and permeability prediction. However, additional developments are needed to understand the upscaling problematic for heterogeneous and complex reservoirs.