Massive emissions of CO2 into the atmosphere are the most direct reason causing global warming and climate change, so more and more countries are starting to focus on carbon abatement technologies. In recent years, the method GCS (Geological Carbon Storage), injecting the CO2 in a supercritical state underground for storage, is considered the most effective way to reduce greenhouse gas emissions. Saline aquifers are given special attention because of its huge amount of storage and, therefore, a deep saline aquifer is the best choice for the storage of CO2. Exemplified by the well-explored Konary structure in the Polish Lowlands, results of assessments of CO2 storage capacity are compared for three cases: (1) a simplified formula based on averaged geological and reservoir parameters and (2) a model of the structure based on averaged geological and reservoir parameters (homogeneous model) and (3) a model of the structure with more detailed geological data (including those on clay interbeds in the sandstone series of the reservoir horizon – heterogeneous model). This allows the estimation of how providing of details of geological and reservoir data, introduced into the model, can affect the ability of CO2 migration within a reservoir horizon intended for CO2 storage, and, consequently, also obtain a more accurate assessment of the capacity that the structure is capable of attaining.