WHY SHOULD WE CARE ABOUT FLUID CHEMISTRIES DURING SUPERCRITICAL CO2-RELATED SUBSURFACE OPERATIONS?

A deeper understanding of the impacts of brine chemistries on brine−mineral interactions is the foundation of safer and more efficient scCO₂-related engineered subsurface operations. Here, using biotite as a model phyllosilicate, we investigated the effects of various subsurface-abundant inorganic (potassium, sodium, sulfate, and phosphate) and organic ligands (acetate, oxalate, and phosphonate) on dissolution and precipitation of minerals and assessed their impacts on mineral surface wettability. We conducted these experiments under conditions relevant to geologic CO₂ sequestration and supercritical CO₂-enhanced energy recovery/storage processes (e.g., 95 °C and 102 atm of CO₂). The different ligands influenced biotite dissolution distinctively through surface complexation and/or aqueous complexation: For example, while sulfate, acetate, and oxalate did not promote secondary mineral formation, phosphate and phosphonates significantly promoted secondary precipitation of Fe- and Al-bearing minerals. These dissolution of phyllosilicate minerals and precipitation of secondary mineral phases can affect the pore geometry, surface chemical affinity, and permeability. In addition, we found that the surface wettability of minerals can also affected by the types and concentrations of ligands in the subsurface systems. This study provides new insights into the effects of brine chemistries on brine−mineral interactions, pertinent to more efficient and safer geologic CO₂ sequestration and supercritical CO₂-enabld energy recovery/storage processes.