Laboratory experiments and geochemical modeling of gas–water–rock interactions for a CO2 storage pilot project in a carbonate reservoir in the Czech Republic

Abstract

The aim of this study was to characterize the influence of CO2 in geological structures on mineralogical changes in rocks and assess the sequestration capacity in mineral form and solution of a potential pilot storage site in the Czech Republic. Rock samples from a dolomite reservoir and the overburden level, as well as the corresponding pore water, were used. The most important chemical process occurring in the reservoir rock is the dissolution of carbonate minerals and feldspars during the injection of CO2 into the structure, which increases the porosity of the structure by approximately 0.25 percentage points and affects the sequestration capacity of the reservoir rock. According to the results of geochemical modeling, the secondary carbonate minerals (dolomite, siderite, and ephemeral dawsonite) were present only during the first 50 years of storage, and the porosity at this stage decreased by 1.20 pp. In the caprocks, the decomposition of K-feldspar and calcite resulted in an increase in porosity by 0.15 percentage points at the injection stage only, while no changes in porosity were noted during storage. This suggests that their insulation efficiency can be maintained during the injection and post-injection periods. However, further experimental research is needed to support this observation. The results of this study indicate that the analyzed formation has a low potential for CO2 sequestration in mineral form and solution over 10,000 years of storage, amounting to 5.50 kg CO2/m(3) for reservoir rocks (4.37 kg CO2/m(3) in mineral form and 1.13 kg CO2/m(3) in dissolved form) and 3.22 kg CO2/m(3) for caprock rocks (3.01 kg CO2/m(3) in mineral form and 0.21 kg CO2/m(3) in dissolved form). These values are lower than in the case of the depleted Brodsk & eacute; oil field, which is a porous reservoir located in the Moravian part of the Vienna Basin.