Search

When CO2 is injected into a subsurface reservoir, it undergoes structural-stratigraphic, residual, dissolution and mineral trapping mechanisms. Among these, the most permanent and preferable is the mineral trapping, in which carbonate minerals build the CO2 into their structures. In this study the amount of CO2 trapped in minerals was estimated from both analytical data of and thermodynamic geochemical models for a natural CO2 occurrence. Models underestimate the amount of trapped CO2 to be 0.004 tons/m3 reservoir in comparison with measured amount of dawsonite and other carbonates in rock samples indicating that 0.02-0.18 tons CO2 is trapped in one m3 reservoir.

Stable isotope systems provide exceptional insight into fluid-solid interactions occurring in the sub-surface. We provide detailed insight into the stable isotope distribution of carbonate minerals in a natural CO 2 reservoir system from Mihalyi-Repcelak area, NW-Hungary. Several types of measurements and calculations have been applied for the estimation of CO 2 and H 2 O isotopic composition in equilibrium with dawsonite. The estimated δ 13 C of CO 2 exhibit values around -4.5 to -2.6 ‰ overlapping with assumed magmatic values and the presently measured gas data confirming magmatic origin, whereas we may assume that the water present during carbonate formation likely had meteoric origin.

The caprock is the only physical barrier in the migration path of CO2 during CO2 geological storage. For this reason, caprock integrity is one of the most important factors regarding the long-term safe underground storage of CO2. As a result of geochemical reactions, among the caprock minerals and CO2 saturated pore water, the physical properties of caprocks such as porosity and permeability may change, which could affect their sealing capacity. Natural CO2 occurrences can help to understand these long-term reactions under storage conditions on geological timescale.