Experimental study on rock-CO2 interaction processes at HP/HT conditions

The interaction of CO2-rich fluids with reservoir rocks from two different geothermal settings was studied in a series of batch reaction experiments to improve predictions on mineral alteration reactions under HP/HT reservoir conditions.
Experiments were carried out with a basaltic sample from the Nesjavellir geothermal field in Iceland and a metamorphic schist from the Kızıldere geothermal field in Turkey. The samples were analyzed before and after the batch reactor experiments using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Observed mineralogical changes were correlated with changes in fluid chemistry.
The Icelandic basaltic rock produced an extensive secondary mineral assemblage consisting of clay, chlorite, anhydrite and zeolites. In contrast, the experiment with the metamorphic schist from Turkey produced only small quantities of smectite.
It was concluded that the mineralogy of the Turkish sample is not suited to provide the necessary divalent cations for CO2 mineralization. Data from the basalt from Iceland indicate a strong control of the initial fluid composition on the resulting secondary mineral assemblage, which, together with the thermodynamically unfavorable high temperature, constrains the CO2 sequestration.