The competition between H2O and CO2 adhesion at reservoir conditions: A DFT study of simple mineral models and the entropy, ZPE, dispersion and T,P variations

Density functional theory was applied (B3LYP) to answer whether conditions exist where CO2 adhesion to three different lithologies becomes stronger than H2O adhesion. The answer is that it does not seem to be the case. This is taken to indicate that the reservoirs that we have represented by simple models are prone to CO2 storage. Moreover, we have obtained an overview of the effect of including entropy contributions and zero point vibrational energies in the calculation of the adhesion energies. The consequence of applying simple dispersion and solvent models are also addressed. The study is based around very simplified model systems of calcite, quartz and clays in order address the basic effects. Rather than attempting to obtain quantitative agreement we are observing the qualitative trends. When entropy, ZPE and a continuum model is included the result is smaller binding energies. However, the inclusion of dispersion effects leads to the prediction of a much stronger binding. There is a tendency for the clay model to bind water the strongest, this indicate a potential impact of having clay present in media for capillary trapping of carbon dioxide. (C) 2015 Elsevier B.V. All rights reserved.