Abstract
To reduce current high concentrations of anthropogenic greenhouse gases in the atmosphere to levels stipulated by the Intergovernmental Panel on Climate Change, geological sequestration has been universally proposed. On the basis of cost analysis and global availability, deep saline aquifers are the prime targets for most proposed commercial and pilot scale projects.While the geological storage of anthropogenic carbon dioxide is expected to mitigate global warming, the technical aspects of the injection deserve to be considered for efficient injection projects. The water rock interaction phenomenon occurs due to carbonic acid generation which causes surface protonation reactions and has the potential to decrease water wettability of the system leading to enhanced water mobility and efficient gas injection. Therefore, for a saline aquifer rock with minerals capable of ion exchange reactions that consume solution protons, the wettability of such a system is likely to be preserved leading to reduced water mobility and poor gas injection. Generally, the extents to which surface protonation and ion exchange reactions occur depend on the free energy change of the reaction.In this paper, we have carried out thermodynamic computations for the free energies of surface protonation and ion exchange reactions. Based on the values of computed free energies, which show that ion exchange reactions have lower free energies, we have discussed the wettability implications for geological storage in silica rich saline aquifer systems.
Highlights
As global warming, due to anthropogenic emission of carbon dioxide assumes alarming dimensions, the capture and geological isolation of this gas is considered necessary though there exist some limitations (Meer, Investigations regarding the storage of carbon dioxide in aquifers in the Netherlands, 1992)
Monomineralic rocks such as those consisting of nearly 99% quartz and quartz cement will lack ion exchange reactions, which will enhance surface protonation reactions and increase solid-water interfacial tension leading to wettability reduction (Jung & Wan, 2012)
The extent to which ion exchange reactions and surface protonation reactions occur and compete for hydrogen ions produced from the dissociation of carbonic acid (McGrail, et al, 2006) will depend on the thermodynamic free energy of the reactions (Miller, Calcaterra, & Closs, 1984)
Summary
Due to anthropogenic emission of carbon dioxide assumes alarming dimensions, the capture and geological isolation of this gas is considered necessary though there exist some limitations (Meer, Investigations regarding the storage of carbon dioxide in aquifers in the Netherlands, 1992). Siliciclastic (quartz rich) (Mcbride, A Classification of Common Sandstones, 1963) saline aquifer rocks with digenetic minerals such as glauconite and muscovite will have the potential for ion exchange reactions In these reactions, hydrogen ions produced from the dissociation of carbonic acid, which are supposed to reduce formation water pH and reduce wettability (Jung & Wan, 2012) will be exchanged for frame work potassium ions (Sainz-Diaz & Coudros, 2001). The extent to which ion exchange reactions and surface protonation reactions occur and compete for hydrogen ions produced from the dissociation of carbonic acid (McGrail, et al, 2006) will depend on the thermodynamic free energy of the reactions (Miller, Calcaterra, & Closs, 1984) This is because, the thermodynamic free energy of a reaction measures the extent of feasibility. The thermodynamic implications in light of contact angle evolution will be further discussed for saline aquifers under geological carbon storage
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