Injection of CO2-saturated brine in geological reservoir: a way to enhanced storage safety

Abstract

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

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