The chalk of the Paris Basin is characterised by high porosity and great thickness. To understand this reservoir, we need to characterise the variations in its hydraulic properties. However, these variations, although observed (double to triple porosity), are not spatialised and quantified, while sedimentary, fracturing and karstification heterogeneities are recognised at different scales. The lack of knowledge linking geological heterogeneities and petrophysical variability is a real scientific barrier to understanding the hydrodynamic properties of the chalk. To solve this problem, we propose a multi-scale approach to quantify porosity organisation at different scales, from the sample to the aquifer, using P-wave propagation at different frequencies. In the laboratory, petrophysical and ultrasonic measurements will characterise the microporous space. In the field, we will quantify the distribution of geological heterogeneities (sedimentology, diagenesis, fractures and karsts) in conjunction with measurements of the speed of propagation of sonic and seismic waves, thus providing access to the scale of the aquifer. The evolution of wave propagation properties with the change in scale will make it possible to quantify these different scales of porosity. This multidisciplinary approach should make it possible to better define, spatialise and quantify hydraulic properties in the chalk.
Project leader : Cédric Bailly
Funding : Brgm – RGF https://rgf.brgm.fr/
Staff involved at GEOPS : Andrès Mejia (PhD candidate), Cédric Bailly, Yves Missenard
Collaboration with : Cergy Paris Université and BRGM