Impact of SO₂ on Alteration of Reservoir Rock with Ca-Deficient Conditions and Poor Buffering Capacity under a CO₂ Geologic Storage Condition

Abstract

The objective of this study is to evaluate the impact of SO 2 -CO 2 -water-rock interaction on the alteration of a reservoir rock having Ca-deficient conditions and little buffering capacity and its implication for porosity change near the injection well from a CO 2 storage pilot site, Republic of Korea. For our study, three cases of experimental and geochemical modeling were carried out (pure CO 2 , 0.1% SO 2 in CO 2 , and 1% SO 2 in CO 2 , resp.) under realistic geologic storage conditions. Our results show that SO 2 accelerated waterrock interactions by lowering the pH. In the 1% SO 2 case, pH remained less than 2 during the experiments because of insufficient buffering capacity. Sulfate minerals were not precipitated because of an insufficient supply of Ca. Because the total volume of precipitated secondary minerals was less than that of the dissolved primary minerals, the porosity of rock increased in all cases. Chlorite largely contributed to the decrease in total rock volume although it formed only 4.8 wt.% of the rock. Our study shows that the coinjection of a certain amount of SO 2 at CO 2 storage reservoirs without carbonate and Ca-rich minerals can significantly increase the porosity by enhancing water-rock interactions. This procedure can be beneficial to CO 2 injection under some conditions.