Porosity and Mineralogical Changes in Iron-Bearing Sandstone with CO2 Injection

One of the four trapping mechanisms for long term CO₂ geological storage is mineral trapping. Increased acidity from CO₂ solubility in brine results in carbonate and silicate mineral dissolution and potential secondary precipitation of more stable clay and oxide minerals. This study is focused on better understating the geochemical reactions, and porosity and mineralogy changes in Berea sandstone with CO₂ injection. A core flooding system was used in which supercritical CO₂ at 60 °C and 2000 psi and 2% NaCl brine was flown through the 7-inch cores. The changes in the core structure and porosity were observed using Micro-CT, QEMSCAN, and He porosimeter and the data was supplemented with mineralogical measurements and effluent solution chemistry obtained by XRD and ICP-MS, respectively. Significant iron concentration in the effluent solution was observed and three iron-bearing minerals were detected in sandstone. Numerical modeling using TOUGHREACT with the EOS module of ECO2N dedicated to CO₂-water-NaCl system was employed to assist data interpretation in order to identify the primary source(s) of Fe, the extent of the reactions, and the resulting porosity and permeability changes that would affect the storage capabilities for CO₂. Modifications to published kinetic and thermodynamic constants and the inclusion of incongruent reaction terms were investigated to capture the changes in solution composition, and predictions were made for a new set of data under different flow conditions.