Limiting the risk inherent to geological CO₂ storage: The importance of predicting inorganic and organic chemical species behavior under supercritical CO₂ fluid conditions

Abstract

Field tests have clearly demonstrated that injecting CO2 in geological storage sites results in the release of heavy metals and organic species to groundwater, implying that CO2 injection may have potentially dramatic consequences for the environment. Numerous laboratory experiments using rock and cement samples from different geological formations typical of injection sites show that rocks reacting with synthetic or natural fluids and supercritical CO2 at their respective temperature and pressure conditions generate fluids with As, Cr, Cu, Cd, Pb, Fe, and Mn concentrations above Environmental Protection Agency drinking water standards. The solubility of a compound in supercritical‐CO2 (sc‐CO2), expressed in terms of the compound's activity or fugacity, also depends on the composition of the phases present at the pressure and temperature of the storage site. In a brine sc‐CO2 system, estimating the activity of an inorganic compound or the fugacity of an organic compound is a prerequisite to predicting the solubility of a compound in sc‐CO2 phases. Available models (e.g. Pitzer equations) require the use of binary salt concentrations and are best applicable to polar ionic compounds; but the effect of brines on larger hydrocarbons has not yet been explored. New experimental data will be needed to determine the magnitude of pH effects on the partitioning behavior of organic acids and trace metal complexes from brine to sc‐CO2.

Thermodynamic Modeling of Aqueous Electrolyte Systems: Current Status

“…Topical issues associated with CO 2 (g) dissolved in aqueous solutions have also attracted considerable attention, especially regarding solubility. ,− There has been special interest in the general importance of electrolyte interactions, scrubbing technologies, , potential scale-formation, ,, modeling chemical processes in rock pore waters, , the exploitation of saline aquifers for carbon capture and storage, − and ocean acidification. ,, Such investigations typify the need for generalized thermodynamic modeling capabilities in aqueous chemistry for simulating the variety and complexity of the many prospective practical applications.…”

Geochemical reactivity in CO2 geological storage sites

“…This special issue contains seven manuscripts from research institutes in France, Germany, Norway, and Spain. Two Review papers focus on the role of mineral dawsonite as a possible mineralogical trap for geologically stored CO 2 and the importance of limiting the risk associated to CO 2 storage using organic and inorganic chemical species within CO 2 storage sites . One In the Field paper proposes a new tool for identifying CO 2 leakage at the surface using Diffusive Gradient in Thin films (DGT) methodology .…”