Fluids transfer in porous media, the case of carbonates and clay/limestone interfaces. Integrated study of petrophysical, sedimentology and microstructures.The case of two carbonates: the case of two carbonates the Oolithe Blanche from the Paris Basin and the Globigerina Limestone of maltese islands

Geological storage is now considered as a technical solution for CO₂ storage and nuclear waste management (for high-level and intermediate-level long-lived radioactive waste). A geological storage is a long term project which implies a particular protocol in order to better determine and to better understand the host rock, especially in terms of transport mechanisms. The geological formations studied are chosen in function of their storage capacity because gas storage or nuclear waste storage do not need the same requirements. In case of CO₂ storage, the host formation must provide good reservoir properties in order to facilitate the injection. Here, the safety of the storage is guaranteed by traps (structural, residual, mineral) and by the presence of a cap rock. Concerning nuclear waste storage, the host must retain at best the potential radioactive fluids and gas leaks, and this is the reason why storage sites are studied within low porous and low permeable formation, like argillite organelles. The work presented in the PhD thesis is related to two storage projects. The first one is focused on the petrophysical study of a potential host for CO₂ storage in the Paris Basin, the 'Oolithe Blanche' carbonate formation. The second project is an analogue study of the sedimentary structure explored in the Meuse/Haute-Marne laboratory. This laboratory is studied by ANDRA to be the first nuclear waste storage in a deep geological formation in France. The analogue was found in maltese archipelagos, which presents almost the same tabular structure as the one observed in the Meuse/Haute-Marne laboratory: limestone/clay/limestone affected by a weak tectonic deformation. In the first part, the Oolithe Blanche Formation study allowed to determine the reservoir properties of the three principals facies of the formation. This study was realized on plugs sampled on quarries in Burgundy (France). Those facies are characterized by different environmental processes and deposit energy; nonetheless, they are all located within ashore face depositional environment. They are composed of ooids, pellets and bio-clasts invarying proportions. The reservoir properties studied showed the Oolithe Blanche Formation is a microporous one. Microstructural parameters which influence reservoir properties are: the cement type (sparite or micrite), amount of compaction characterized by the cement quantity and the contact between elements and, at last, the pore size distribution within porous elements (micro, meso, macro-pores).The second part of this project is focused on a more petrophysical study which aimed at characterizing the pore network influence (volume, shape in space) on acoustic velocities, electrical conductivity and on permeability. The study is completed by the use of permeability predictive models based on mercury porosimetry spectra.The maltese archipelagos study is based on observations made by Missenard et al. (in prep.).), Rocher et al., (2008) and Missenard et al. (2009, 2011) on the Blue Clay Formation, thick clay formation (100 m) and on the underlying Globigerina Limestone. The clay formation presents an important fracture network characterized by gypsum filling and by an oxidizing zone near the fractures. A similar oxidation, in the shape of lobes and mushrooms, is observed within the Globigerina Limestone. This study is also divided in two parts. In the first one, the focus is on the study of gypsum filling fractures. Studying this filling is directly linked with the storage topic, because, in the case of a nuclear waste storage, the absence of fractures and fluid motion is an important condition to insure the storage security. In the case of gypsums filling, the study is based on geochemical measurements on oxygen (d¹⁸O), sulphur (d³⁴S) and strontium isotopes (⁸⁷Sr/⁸⁶Sr) coupled with a fluid inclusion study, all measurements performed on gypsum crystal. Those analyses allow us to propose a downward fluids circulation model through the clays. Fluids source which is at the origin of gypsum's precipitation seems to be younger than the hosted formation. Because of the position of the maltese islands, in Mediterranean sea, one potential source is the Messinian evaporites, which Sr isotopic ratio corresponds well to our data set. The second part of the maltese study concerns the oxidation shape observed within the Globigerina Limestone. The aim is to determine the processes which allowed this oxidation. The main question is: are those structures the results of an internal heterogeneity in the rock or the sign of a stop in a fluid motion (stop of the fluid or stop of the oxidizing mechanism)? In order to answer those questions we based our interpretation on the skeleton of the rock (mineralogy, magnetic mineralogy, microstructural study, geochemistry), on pore and porosity (porosity measurements, mercury porosimetry), on permeability and on the rock anisotropy (susceptibility of magnetic anisotropy (SMA) and acoustic velocities anisotropy). Some conflicting differences on the dataset exist, especially on anisotropy data, which can suppose some complex processes