Spatial and temporal changes of pressure and CO2 concentration in isolated borehole sections in the marginal area of a cavernous structure - an underground in-situ study in rock salts

We present a dataset of in-situ measurements in the marginal area of a CO2- and brine-rich cavernous structure in an underground salt mine. The data were collected within the framework of the BMBF-project ProSalz. One aim was to reveal the sources and dynamics of fluid movement as well as temporal and spatial distribution of fluids in a potentially weakened cavern rim. Over a period of three years pressure and gas monitoring was carried out along a transect from a cavernous structure to undisturbed rock salt. In addition, temperature and relative humidity data from the underground gallery were recorded. The gas inflow into isolated borehole sections provided an insight into short- and long-term changes of gas migration patterns in rock salt. Pressure increases of up to 4kPa/day and CO2 concentrations of up to 1.2%, especially at the start of the campaign were measured. The gas migration is coupled to discrete fractures and was limited spatially and temporary. Overall, gas occurrences were not correlated to their distance to the cavern, suggesting no wide-ranging fluid-rock interaction within the rim of the investigated natural cavernous structure in rock salt.

The gas pressures in C1, B3, B6, B10A and B10B were measured with pressure sensors (Greisinger) connected to the packer system. The data were recorded with a data logger (ADL-MX Advanced Datalogger, Meier-NT). The humidity and temperature data were recorded using a humidity sensor (Galltec + Mela). The gases were collected underground in sampling bags (calibrated instruments), and analysed in the lab using an OmniStar mass spectrometer (Pfeiffer).