CO2 effects on an unsaturated and saturated carbonate reservoir from geoelectric-geochemical coupling

The objective of this work is to understand and characterize how dissolved CO2 concentrations can influence physicochemical parameters, in particular the electrical conductivity and pH. In previous work, a CO2 injection experiment was carried out directly in a freshwater aquifer within an Oligocene carbonate underground quarry located in Saint-Emilion (Gironde, France). Different parameters emerged as excellent indicators for monitoring a gas plume during CO2 geological storage, especially the electrical conductivity and pH. We tried to reproduce field observations on a laboratory scale by batch experiments and measurements on Hassler cell, and to make the link between the geochemical results (electrical conductivity, pH, CO2 concentrations) and the electrical properties (electrical resistivity index) depending on the saturation state of the carbonate rock. A calibration line has been highlighted, making it possible to link the relation between electrical conductivityCO2-pH. This line is only valid for Saint-Emilion limestones at the injection well because it is dependent on the petrophysical properties of the environment. As field observations are reproducible in the laboratory, this calibration line allows to pass from one scale to another by combining different results, and estimate the CO2 concentrations obtained for such values of electrical conductivity and pH.

Automated summary

The study aims to understand the impact of dissolved CO2 concentrations on physicochemical parameters, particularly electrical conductivity and pH. Through laboratory experiments and measurements, a calibration line has been established to link the relation between electrical conductivity, CO2 concentrations, and pH values, providing a way to estimate CO2 concentrations based on electrical properties.