Monovalent Cation-Induced Rock-Fluid Interactions in Saline Aquifers

Abstract

Deep saline aquifers are suitable reservoirs for long-term storage and mitigation of CO2 emissions into the atmosphere. Injection and dissolution of CO2 in the formation brine lead to pH reduction of the reservoir fluid. The low pH environment accompanied with high pressure and high temperature (HPHT) conditions typical of deep saline aquifers trigger rock dissolution. Ion type can affect the amount of rock dissolution which in turn will impact the micro-scale pore structure of formation rock. Although formation brines consist of ions with different types, only a few studies have focused on the impact of this parameter on mineral dissolution. Therefore, this research aims to improve our understanding of ion-induced rock dissolution after CO2 injection. In this work, two batch experiments were conducted to compare the effect of Na+ and K+ on the extent of CO2-saturated brine reactivity in contact with a rock sample. Regarding the effect of monovalent ions, the existence of Na+ ion resulted in greater chemical rock-fluid interactions in comparison with K+ ion which can be related to the smaller radii of Na+ ion. Results of this study can aid in selecting more suitable saline aquifers for CO2 storage and more accurate long-term predictions from geochemical modelling.