Modeling of Contact Angle versus pH and Derivation of Contact Angle versus Pressure in Deep Saline Aquifers under Geological Carbon Storage

Geological storage of anthropogenic carbon dioxide is regarded as a technically and economically viable strategy for mitigating carbon dioxide induced climate warming. Central to geological storage of anthropogenic carbon dioxide is the water rock interaction, which has a direct bearing on pH induced wettability evolution in saline aquifers. Consequently, understanding contact angle trend versus injected gas pressure is useful, considering its relationship to pH evolution in formation brine due to dissolved gas at prevailing temperatures and salinities. Several research works have published experimental data on contact angle versus pressure pertaining to geological conditions of anthropogenic carbon storage. In the present study, we have used thermodynamic theories relating to a surface charge model, contact angle and the classical Nernst equation to derive a logarithmic pH dependent contact angle equation. Considering the relationship between carbon dioxide solubility and pressure for a given temperature and salinity as well as the link between pH and the extent of solubility, we have plotted calculated contact angles versus corresponding pressures. Results of the plots obtained compare well with literature values. Therefore, given the lack of theoretical approach regarding contact angle versus pressure, our research work fills the knowledge gap considering the novelty in the derivation of the pH dependent contact angle equation.