Underlying Mechanism of Time Dependent Surface Properties of Calcite (CaCO₃): A Baseline for Investigations of Reservoirs Wettability

The increasing number of reports on the influence of wettability on oil recovery and waterflood performance recognizes wettability of porous surfaces within reservoir rocks as the key factor that affects the success of water flooding processes. Unfortunately, a conclusive and satisfactory understanding of all the factors affecting the wettability of the reservoir rocks is still elusive. This is mainly due to the complexity of the intrinsic properties affecting the rock surface and due to the lack of techniques with sufficient spatial resolution necessary to assess the wettability at the pore scale. Using both macro- and microscopic analytical techniques, an idealized flat surface of mineral composition representative for carbonate type formation, i.e., calcite (CaCO₃), is studied to provide a baseline for future investigation of the underlining mechanisms influencing reservoir wettability. The development of heterogeneities on different calcite planes when exposure to the atmosphere is responsible for the transition in the observed wettability behavior. This work fills the absence of a baseline for the wettability of calcite and provides a reference for future investigation in oil reservoirs.