The dataset is on analyses on formation confinement based on available results of laboratory geochemical measurements of brine samples for several field sites (shale wells, acidic gas storage within a depleted gas field and a saline aquifer structure – a possible CO2 storage site). The goal of these analyses was to assess the presence of relic brine within reservoirs/aquifers in question or brine exchange between reservoirs/aquifers within these sites. Results of these analyses can be used to evaluate caprock integrity for they could be indirect evidence of possible migration paths (faults, fractures) and hence possible leaks within the site currently, in the not-too-distant geological past, or no migration or fluid exchange at all (relic brine). The dataset was created within SECURe project (Subsurface Evaluation of CCS and Unconventional Risks) - https://www.securegeoenergy.eu/. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 764531