In marine Carboniferous limestone, precipitation of calcium carbonate (CaCO \(_3\)) from saline water results in minerals, filling the interparticle pore spaces. Among a wide spectrum of diagenetic processes that have resulted in the formation of the Devonian fore-reef limestone of Germany or the Silurian limestone of Gotland, Sweden, for instance, cementation has been identified as the major phenomenon that governs the microstructure in carbonate rocks (Krebs 1969 Munnecke et al. Therefore, the reduction of such high porosities to its present low value (<5 \(\%\)) is believed to be almost entirely due to introduction of cements (Bathurst 1970). Most limestones exhibit very little signs of compaction (Pray 1960). During the early periods after deposition, porosities of carbonate muds and sands normally lie in the range of 40–70 \(\%\) (Pray and Choquette 1966). Lithification of carbonate sediments in saline environments is a result of complex physical, chemical, and biological processes. Finally, the capability of present modeling approach in simulating dynamics of calcite cementation in 3D is demonstrated based on post-processing analyses and advanced visualization techniques. Moreover, the grain size distributions obtained from the numerically cemented microstructural data tend to get statistically dispersed and horizontally shifted with increasing mean grain size. The increase in cement overgrowths is found to be inversely dependent (non-linear) on the initial grain size. A significant deviation in the 3D overgrowth kinetics is observed as compared to 2D. Next, we perform calcite growth simulations with multiple grains in 2D as well as 3D in order to computationally mimic the anisotropic cement overgrowths as observed in saline limestone aquifers. In order to define rhombohedral calcite geometry, we consider a faceted-type surface energy anisotropy and validate the crystal shape using volume preservation technique in three dimensions.
The present article investigates the effect of initial grain size on the overall growth kinetics during calcite cementation from supersaturated geothermal fluid whilst tracking the grain boundary behavior of the evolving microstructure using a multiphase-field model.
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