Upper Miocene sandstones in the Sava Depression (Northern Croatia) are already reviewed as the potential target for CO₂ based EOR process or carbonation in the reservoir brine. In general such lithology, even rich with aluminosilicate minerals, is not the most favourable rock medium for efficient CO₂ sequestration in minerals. In fact, those are ultramafic rocks and accompanied minerals. But, such process naturally happens in sandstones reservoirs where CO₂ is injected and subdued to carbonation. The unfavourable is time scale of such sequestration which is expressed into 10⁴-10⁵ years period. However, Upper Miocene sandstones in the Sava Depression could incorporate up to 25% of aluminosilicate minerals and often are laterally changed with transitional lithofacies between dominantly pelitic and psammitic ones, rich in clay minerals. Both facts are favourable for CO₂ storage into such lithofacies during carbonation and forming secondary minerals. The numerical rate or percentage of total injected carbon-dioxide that could be expected immobilised on such way into analysed sandstones could be given after laboratory testing and yearly based monitoring of injection wells.