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Calcite dissolution and Ca–Mg ion exchange on carbonate rock surfaces have been proposed as potential mechanisms occurring during smart waterflooding in carbonate reservoirs. However, there is still a lack of fundamental understanding of these reactions to quantitatively evaluate their effects in the reservoir flooding process. Especially, the data on precipitation and dissolution kinetics are insufficient. In this work, the equilibration kinetics of calcite dissolution and Ca–Mg exchange was experimentally studied. The behavior of three powders was compared: pure calcium carbonate, Stevns Klint outcrop chalk, and North Sea reservoir chalk. It was found that the equilibration time for calcite dissolution was of the order of seconds for a given surface-area-to-liquid-volume ratio. The existing theory of calcite dissolution could well reproduce our observations. The Ca–Mg exchange showed two-step kinetics: the first step was fast, and it dominated the process within the first hour of reaction; the second step was slow, and it continued longer than the time of observation (2 weeks). Characteristic times for the two steps were extracted by fitting the experimental curves. A two-layer adsorption model was proposed to characterize the kinetic process and successfully matched with experimental data. The findings were further extended to flow-through scenarios. By comparing with literature data and surface complexation models, it was concluded that calcite dissolution alone was unlikely to be able to explain the additional recovery reported in the literature. The Ca–Mg exchange process could dominate the fluid–rock interactions at a high temperature in pure calcium carbonate rocks, while competitive adsorption of cations appeared to control the process at a lower temperature. Different carbonate rocks possess different properties with regard to the ion-exchange process.

Compaction of the reservoir chalk (e.g. surface subsidence) may facilitate oil production. However, only few works have linked smart water flooding with chalk compaction and additional oil recovery. In this work, core flooding experiments with sequential injection of low salinity brines were performed to examine the effect of chalk compaction on oil recovery under smart water flooding. X-ray computer tomography scanning was applied to select outcrop and reservoir cores with different level of heterogeneity, which was demonstrated to be an important factor that determines the recovery even on core scale. A linear variable differential transformer (LVDT) device made it possible to detect changes of the core length during the experiments, which served as an indication of the compaction. Overburden pressure was increased stepwise at the final stages of the flooding to achieve higher compaction of the cores. During secondary flooding, slight gradual compaction of the cores was observed. Subsequent low salinity flooding did not lead to further compaction for all the samples, nor additional oil recovery. Under final compaction, significantly more oil was produced from the heterogeneous cores, especially, from the reservoir core. Some fines production was observed during the core cleaning after the experiments. Fluid diversion due to closing micro-fractures under compaction and/or relocation of the fines is speculated to be a driving mechanism behind additional recovery from heterogeneous cores. Rock compaction appears to be a potential mechanism for enhanced oil recovery, however with a limited efficiency.