The gas membrane sensor (GMS): A new method for gas measurements in deep boreholes applied at the CO2SINK site

A newly developed geochemical monitoring tool for the real time and in situ determination of CO2 and other gases in the underground and in boreholes was successfully applied for the first time at the CO2SINK test site in Ketzin, Germany.The method uses a phase separating membrane to separate gases dissolved in borehole fluids, water and brines. Ar is used as a carrier gas to conduct the collected gases through capillaries to the surface, where the gas phase is analyzed in real-time with a portable mass spectrometer for all permanent gases.In the observation wells of the CO2SINK storage site, the dissolved CO2 concentrations in the borehole fluid were quantified using permeation rates determined in the laboratory for the applied membrane type. Increasing reservoir gas concentrations of He, H2, CH4 and N2 as well as the arrival of the injected Kr tracer gas and of N2, used for technical operations, at the monitoring wells were observed. The breakthrough of the CO2 front into both observation wells, at a distance of 50 m and 112 m was recorded after the injection of about 500 and 11.000 tons CO2, respectively.