Experimental investigation of carbonate wettability as a function of mineralogical and thermo-physical conditions

Precise characterization of carbonate wettability is challenging and is broadly debated in recent past. While carbonates are known to be oil-wet, the influence of complex mineralogy, surface chemistry, and surface topographic features (e.g. surface roughness) on carbonate wettability did not receive much attention. Furthermore, despite scores of publications analyzing the influence of operating pressure and temperature on carbonate wettability, there are several contradictory trends. Therefore, to address these uncertainties associated with carbonate rock wettability, we report experimental observations of contact angles (theta) for carbonate/crude-oil/brine systems on five different carbonate samples (four real carbonate rocks and a pure calcite mineral) as a function of pressure, temperature, as well as variable mineralogy. In addition, the RMS (root mean square) surface roughness and the pertinent 2D and 3D surface topographic profiles of these rock samples were analyzed and correlated with the observed wetting behaviors. We find that increase in pressure results in an increase in theta in the low-pressure range, while relatively stable theta in high-pressure range. However, the observed theta values, follow both increasing and distinct trends with respect to temperature. Further, surface chemistry of samples suggest that calcite-based samples are relatively more hydrophilic compared to dolomitic carbonates. In addition, the RMS roughness and the corresponding 3D topographic profiles suggest that the samples with abundance of peaks demonstrated much higher theta values. These results may lead to a better understanding of the wider variability associated with the wettability behavior of carbonate rocks.