CARBON GEOLOGICAL SEQUESTRATION IN SALINE AQUIFERS: EFFECT OF ROCK MINEROLOGY ON WETTABILITY CHANGE TREND AND IMPLICATION FOR EFFICIENT STORAGE IN DIFFERENT AQUIFERS
In view of the accelerated increase in anthropogenic carbon dioxide in the atmosphere and the resulting climate warming, the capture and storage of this greenhouse gas in geologic media is considered a technically viable option. Consequently, the injection of carbon dioxide into a saline aquifer initially containing formation brine will lead to two-phase flow. In this regard, the wettability of the system that controls the relative mobility of fluid phases is a fundamental petrophysical parameter that deserves attention. Generally, the wettability is controlled by water-rock interaction phenomena which consists of cation exchange and surface adsorption of ions. So far, the wettability of the system carbon dioxide-solid-brine has been studied in a manner where substrates do not reflect those of actual geologic systems that are hosts for carbon storage. Consequently, contact angles measured so far give conclusive evidence that wettability will decrease with gas injection but they do not give any clue as to the manner in which this will decrease. This is because contact angles are measured on individual minerals of rocks rather than on rock samples. In this study, I have used two mineralogically distinct rock samples to show how contact angles will evolve given the water-rock interaction phenomena that control wettability. The two rocks are Wallace sandstone from Nova Scotia and Fontainebleau sandstone from France. The experimental methodology is based on spontaneous imbibition rise of brine of varying pH in core samples. Contact angle computations are carried out using early spontaneous imbibition dynamics theory. In addition, cation exchange reactions pertinent to the geologic system which are principal causes of formation water pH buffering, have been investigated using pulverized rock samples. Furthermore, X-Ray diffraction analysis of rock samples to support experimental results have been carried out. Results of these experiments give further conclusive evidence that cation exchange reactions can buffer formation water pH to impact expected trends in wettability evolution. In view of the point of zero charge pH of the solid surface being fundamental to the water-rock interaction, a mathematical model has been presented that links wettability to the pH of aqueous solution.