In order to investigate the effects of impurities on subsurface storage of CO 2 , experiments were carried out on Permian Rotliegend reservoir and Zechstein caprock core samples at subsurface conditions of 300 bar and 100 C. The experiments were performed in the presence of brine and the following gas compositions: CO 2 , CO 2 +5000 ppm H 2 S, CO 2 +100 ppm H 2 S and CO 2 +100 ppm So 2 for a 30 day duration. Following CO 2 injection, permeability of the reservoir and caprock samples increased by 10-30% and by a factor of 3-10 respectively. After co-injection of 5000 ppm H 2 S permeability of both reservoir and caprock samples reduced significantly. When the concentration of H 2 S was reduced to 100 ppm, minimal variation of permeability took place because the dissolution of minerals was balanced with the precipitation of secondary phases. In the case of co-injection of 100 ppm So 2 permeability of reservoir samples increased by a factor of 1.18 to 2.2. In the caprock samples permeability changed by a factor of 0.8 to 23. In addition, in order to determine long term (>100 years) interaction between CO 2 and the reservoir mineralogy we need to rely on modelling programs. This requires accurate and fit for purpose input parameters, associated with the lithological composition of reservoirs and seals at the storage site. For this purpose, we specifically focused on the reactive surface area of minerals, which we measured by scanning electron microscopy. Using the range of measured reactive surface area of minerals as an input in the modelling software, we could obtain the distribution of the sequestered CO 2 as a mineral (3-9 kg of CO 2 / m3).