Wettability Characterization of Carbonate Rocks Using a Micro-Scale Approach

Wettability is an important factor that influences relative permeabilities and capillary pressure, which in turn impacts the hydrocarbon recovery. Wettability of carbonate surfaces is typically challenging due to their diverse wetting behavior. Wettability has been conventionally quantified using the macro-scale contact angle observations. However, macro contact angle suffers in terms of precise identification of the three-phase contact line. In this study, a new micro-scale approach is presented to determine rock surface wettability. Here we used five different Middle Eastern carbonate samples with different mineralogy. The micro-scale contact angles are evaluated via Environmental Scanning Electron Microscopy (ESEM) using condensation-evaporation approach while the classical sessile drop method is used to determine the macro-contact angles. The results show a notable difference between macro and micro contact angles which suggests wettability variation at different scale of measurement. Depending on micro contact angles, mixed-wet state for all samples is observed, as some samples experienced water-wet behaviour at most of the measured locations, while they showed intermediate-wet behaviour at a few locations. However, based on macro contact angles, only one wetting behaviour is recognized. Therefore, a thorough wettability characterization would require insights at the micro-scale to capture variations in wetting behavior.