Abstract: A device for monitoring an formation below the ground G containing a fluid such as CO2 or methane comprising a measuring cell arranged in a cavity, can an F analyzer disposed on the surface and a sealed connection connecting measuring cell to the analyzer. The measuring cell comprises two chambers that can sealingly communicate with one another. The first chamber comprises a plurality of orifices allowing passage of the fluid into first chamber, at least two inner electrodes and fluid circulator. The second chamber is impervious to the fluid. Applications include monitoring of geological storages sites for gas such as CO2.

Abstract: A device for monitoring an underground formation containing a fluid such as CO2 or methane comprising a measuring cell (CM) arranged in a cavity, analysis means (MA) arranged on the surface and sealed connection means (ML) connecting measuring cell (CM) to analysis means (MA). The measuring cell comprises two chambers (CH1, CH2) that can sealingly communicate with one another. The First chamber (CH1) comprises a plurality of orifices (OR) allowing passage of the fluid into first chamber (CH1), at least two inner electrodes (EI) and fluid circulation means (MC). Second chamber (CH2) is impervious to the fluid.