PNNL

Abstract

Laboratory experiments showed that low viscosity scCO2 displacement of the brine into Mt Simon Sandstone and Eau Clair formation cores (FutureGen 2.0 Geologic Sequestration site, Jacksonville, Illinois, USA) was slow by advection, as scCO2 travels predominantly in larger pores, leaving significant brine in smaller pores. As the scCO2 displaces the brine in larger pores and carbonate partitions into the brine, the resulting acidification (pH 3 to 4) causes short-term mineral dissolution, ion desorption, and iron oxide particulate movement. Major aqueous biogeochemical changes observed over 1.2 years from core/brine/scCO2 interactions includes: a) significant increase in Mg2+, K+, and SO42- concentrations (10s to 100s of mmol/L), b) dissolution of the hematite coating on the quartz grains, c) significant precipitation of NaCl and KCl, and d) some anaerobic microbial growth. Electron microprobe analysis showed the formation of some NaCl and KCl, but precipitates were too small a volume to significantly change permeability. Anaerobic microbial growth correlated with scCO2 (23.5x in 1300h), was also too small to influence permeability. Iron oxide particulate movement was observed as a result of scCO2 injection (acidification), but results could not conclusively correlate with formation permeability change. The electrical resistivity change of the rock core from 100% brine to 100% scCO2 was in the expected range (3x to 5x), with most of the change observed between 70% to 100% scCO2. Field scale conditions simulated using these laboratory-measured electrical resistivity changes indicated insufficient resolution was likely at the field site using surface electrodes due to the depth of injection (1200 m). Overall, injection of scCO2 into the Mt Simon sandstone brine aquifer resulted in small geochemical changes over the short-term (