Laboratory study of the influence of scCO2 injection on metals migration, precipitation, and microbial growth

Laboratory experiments were conducted to evaluate the impact of supercritical carbon dioxide (scCO2) injection on aqueous and solid phase geochemistry, and subsequent changes in permeability. These experiments showed that brine displacement from the Mount Simon Sandstone cores (∼1200 m depth) by scCO2 was inefficient by advection, because the low viscosity scCO2 flows predominantly in larger pores, leaving a significant amount of brine in smaller pores. Acidification caused by scCO2 injection resulted in significant increases in Mg2+, K+, Na+, SO42− Al3+, and silica concentrations are likely from differing rates of carbonate, clay, albite, and K-feldspar dissolution. The mass of precipitates that formed over 1.2 years (NaCl, KCl, lead oxide, and forsterite) was small, as observed by electron microprobe analysis and did not influence permeability. Trace metals that increased during scCO2 injection included Ba, Mn, Sr, Ni, Sn, Bi, Cu, Li, P, and Zn, and trace metals that decreased included Hg, Pb, and Co. The scCO2 injection experiments also showed a moderate amount of particulate (iron oxide) movement correlated with the fraction of scCO2, but the sandstone permeability did not change, even after substantial (i.e., 115 pore volumes) scCO2 injection. Anaerobic and aerobic microbial growth was observed (23 and 14 times, respectively) correlated with higher scCO2 concentration, but the calculated change in pore space occupied by the increase in biomass is insignificant. The small observed geochemical and microbial changes are not expected to reduce the ability to inject scCO2 into the reservoir, but significant increases in trace metal concentrations could magnify the water quality impact of a potential leak of reservoir fluids into an overlying aquifer.