Surface alteration of calcite: Interpreting macroscopic observations by means of AFM

Wettability has been recognized to play a fundamental role in the efficacy of water flooding processes of carbonate oil and gas reservoirs. However, the theoretical mechanism governing this process is still not entirely understood. This can be partly attributed to the absence of ad hoc tools and standardized sample-preparation methodologies for comprehensive transient characterization of the mineral surface. Here, we use atomic force microscopy (AFM) to investigate the effect of different calcite sample-preparation methodologies in estimating the macroscopic water static contact angle (SCA). Single crystal calcite surfaces are aged in deionized (DI) water baths, for different exposure times, and dried by different techniques, to reveal SCA discrepancies. Trends and observations are explained with the use of time-dependent adhesion maps of the surface obtained by bimodal AFM. In this context, the AFM interpretation of macroscopic observations provides a means to single out the different factors influencing wettability, thus allowing for a more standardized description of the processes responsible for the modification of the affinity between the mineral rock and injected water.