Seawater acts as an EOR-fluid, “Smart Water”, in chalk by improving the water wetness at high temperatures, T>90 °C. It has been verified that Ca2+, Mg2+, and SO42- are the active ions in the chemical mechanism for wettability alteration. In this paper, we have identified the chemical reactions involved and compared the reactivity of outcrop chalk and reservoir limestone cores. In general, and as expected, the active ions showed the same chemical reactions towards the chalk and limestone surface, but the reactivity of the limestone surface was significantly lower than that of the pure biogenic chalk surface. It is, however, expected that seawater can act as a “Smart Water” also for limestone at the right conditions.


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