## Abstract

Injection of free-phase supercritical ${\displaystyle CO_{2}}$ into deep geological reservoirs is associated with risk of considerable return flows towards the land surface due to the buoyancy of ${\displaystyle CO_{2}}$, which is lighter than the resident brine in the reservoir. Such upward movements can be avoided if ${\displaystyle CO_{2}}$ is injected in the dissolved phase (${\displaystyle CO_{2aq}}$). In this work, injection of ${\displaystyle CO_{2}}$-saturated brine in a subsurface carbonate reservoir was modelled. Physical and geochemical interactions of injected low-pH ${\displaystyle CO_{2}}$-saturated brine with the carbonate minerals (calcite, dolomite and siderite) were investigated in the reactive transport modelling. ${\displaystyle CO_{2}}$-saturated brine, being low in pH, showed high reactivity with the reservoir minerals, resulting in a significant mineral dissolution and ${\displaystyle CO_{2}}$ conversion in reactions. Over the injection period of 10 yr, up to 16% of the injected ${\displaystyle CO_{2}}$ was found consumed in geochemical reactions. Sorption included in the transport analysis resulted in additional quantities of ${\displaystyle CO_{2}}$ mass stored. However, for the considered carbonate minerals, the consumption of injected ${\displaystyle CO_{2aq}}$ was found mainly in the form of ionic trapping.

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Published on 01/01/2016

DOI: 10.1016/j.ijggc.2016.08.028