Carbon dioxide sequestration: Effect of the presence of sulfur dioxide on the mineralogical reactions and on the injectivity of CO2+SO2 mixtures

This report presents experimental and modeling data on certain aspects of carbon dioxide (CO2) sequestration. As different processes are developed and implemented to facilitate the capture of CO2, other contaminant gases (sulfur dioxide, hydrogen sulfide and ammonia) may be present in the sequestration stream. One of the important questions is how SO2 changes the overall chemistry of the system. It is also important to understand how this change impacts practical aspects of sequestration, such as gas injectivity. In this study, a detailed experimental investigation of the reactivity of CO2+SO2 mixtures with brines and rocks of specific mineralogy (typical of sequestration environments) was conducted. CO2 with 10% SO2 was reacted with brine and arkose at 1000C and 600 psia, and the mineralogical and brine chemistry changes were compared with base-case experiments with no SO2 in the mixture and with results of experiments carried out at low pH. The base case CO2 experiments carried out over different time periods showed initial calcium carbonate dissolution followed by re-precipitation of calcite. A few other mineral precipitations (notably ankerite) were observed. The brine chemistry changes were consistent with the mineralogical changes observed. When SO2 was present in the mixture, continued dissolution of calcite and precipitation of anhydrite (calcium carbonate) was observed. Numerical simulations of the injection of CO2 and CO2 and SO2 mixtures into rocks of different mineralogy did not show significant differences in injectivity between the two cases. A simulation study about vertical migration and mixing was also carried out. It was shown that absolute permeabilities of the seal play an important role in free-gas and dissolved gas distribution, but relative permeability effects are also important in determining how CO2 distributes in the saline formation into which it is injected.