Résumé
Processes affecting geological media often show complex and unpredictable behavior due to the presence of heterogeneities. This remains problematic when facing contaminant transport problems, in the CO2 storage industryor dealing with the mechanisms underneath natural processes where chemical reactions can be observed during thepercolation of rock non-equilibrated fluid (e.g. karst formation, seawater intrusion). To understand the mechanismstaking place in a porous medium as a result of this water-rock interaction, we need to know the flow parametersthat control them, and how they evolve with time as a result of that concurrence. This is fundamental to ensurerealistic predictions of the behavior of natural systems in response of reactive transport processes. We investigatethe coupled influence of structural and hydrodynamic heterogeneities in limestone rock samples tracking its variations during chemical reactions. To do so we use laboratory petrophysical techniques such as helium porosimetry,gas permeability, centrifugue, electrical resistivity and sonic waves measurements to obtain the parameters thatcharacterize flow within rock matrix (porosity, permeability, retention curve and pore size distribution, electricalconductivity, formation factor, cementation index and tortuosity) before and after percolation experiments. Webuilt an experimental setup that allows injection of acid brine into core samples under well controlled conditions,monitor changes in hydrodynamic properties and obtain the chemical composition of the injected solution at different stages. 3D rock images were also acquired before and after the experiments using a micro-CT to locate thealteration processes and perform an acurate analysis of the structural changes. Two limestones with distinct textural classification and thus contrasting transport properties have been used in the laboratory experiments: a crinoidlimestone and an oolithic limestone. Core samples dimensions were 1 inch in diameter and varied from 0.5 to 2inches in length. Experiments were performed at room temperature, 8 bar of total pressure and 3 bar of PCO2. Theacidic fluid has been injected at constant flow rate ranging from 0.4 mL/min to 6.7 mL/min depending of the rocktypology and sample length. As expected, limestone dissolution occurred during the different percolation experiments, porosity and permeability augmented and sonic waves speed propagation decreased, showing an increasein the degree of heterogeneity of the rocks. The integration of all these parameters measured at different stagesof dissolution provides contrasted and realistic geochemical, hydrodynamic and structural parameters to improvenumerical simulations.