Experimental Study of CO2 – Saline Aquifer-Carbonate Rock Interaction during CO2 Sequestration

Combustion of fossil fuels, as well as exploration and production operations in petroleum industry is a source of greenhouse gases, mainly CO2, which has been accounted for increasing concern over global warming. Deep saline aquifers are proposed as a promising sink for disposal of greenhouse gases in order to mitigate the air pollution. In this work, carbonate cores saturated with saline aquifer samples were exposed to CO2 to investigate the role of geochemical reactions during CO2 sequestration. Experiments were conducted for 91 days at temperature of 40 ̊C and pressure of 62 bar with brine samples containing Na+, Ca2+, Mg2+, Fe2+, and K+ ions present in the system, and in the presence of dolomite rock and CO2. Comparison of CO2-treated and untreated cores and analysis of brine samples taken during experiments revealed that dolomite was dissolved during experiments and concentration of Mg2+ and Ca2+ ions in the brine increased. In addition, the permeability and porosity of all cores increased after experiment. Meanwhile, analysis of SEM and XRD images showed there is no secondary mineralization, thus solubility trapping is the dominant mechanism of CO2 trapping in carbonate reservoir. The results of this study will provide an insight into future development of full-field sequestration of CO2 into saline aquifers.