3D Characterization of Aquifers in the Cenozoic Sedimentary Formations of the Paris Basin

The objective of this study is to synthesize the geological and hydrogeological characteristics of the main aquifers in the Paris Basin within the Cenozoic sedimentary formations. This work is part of the multi-annual scientific program RGF (Référentiel Géologique de la France, https://rgf.brgm.fr/page/bassin-parisien), which aims to update the representation and mapping of French geology on a national scale. The program also funds several PhD projects in collaboration with the academic community, focusing on the geometry, distribution of petrophysical properties, modeling, and mapping of key Cenozoic geological formations in the basin. Particular emphasis is placed on the major aquifers as part of this modeling effort.

The geology of the Paris Basin has been extensively documented by various authors (Pomerol, 1967; Mégnien, 1980; Gély and Lorenz, 1991; Briais, 2015). Data from well logs and core descriptions collected from over 2,000 petroleum wells have been used to reconstruct the stratigraphic surfaces of the main formations, while also identifying the large-scale geometries of associated aquifers and aquitards. Recent studies have enhanced the dating of specific stratigraphic markers (Marlot, 2023; Moreau, 2023), described the geometries of alluvial formations in the Seine River (Chourio-Camacho, 2024), advanced knowledge in structural geology (Brown, 2024), and provided petrophysical characterizations of reservoir rocks (Moreau, 2023; Marie, 2024).

The hydrogeology of the Paris Basin has been studied and modeled for decades (Mégnien, 1980; Goncalves, 2003; Lamé, 2013). The lateral extent of aquifers varies significantly across regions. For instance, in Île-de-France, the hydrosystem comprises six primary aquifers: the Alluvial, Brie, Champigny, Lutetian, Ypresian, and Chalk aquifers. However, lateral facies variations can significantly alter hydrogeological properties, influencing groundwater resource potential. In the Oligocene formations, the main aquifers are primarily located in Île-de-France and the northern part of the Centre-Val de Loire region: i) on the Beauce plateau, commonly referred to as the "Beauce aquifer," ii) in the Yvelines area, primarily associated with the Fontainebleau Sands, and iii) on the Brie and Bière plateaus, where they are predominantly contained within the Brie Limestone.

These lateral facies variations, coupled with the presence of fractures or karstification, result in substantial differences in the petrophysical properties of the identified aquifers and aquitards. Pumping test data have been compiled and converted into permeability and transmissivity coefficients, which were subsequently mapped along lateral transects in the Brie region of the basin (Marie, 2024).

This study will also contribute to the harmonization of the lithostratigraphic framework across the 187 geological maps covering the territory. Furthermore, the 3D model will facilitate vertical and lateral interpolation of hydrological reference data from the BDLISA database (https://bdlisa.eaufrance.fr/), which currently provides detailed mapping of water bodies at the scale of metropolitan France.