Geochemical effects of CO2 sequestration in sandstones under simulated in situ conditions of deep saline aquifers

The geochemical effects of brine and supercritical CO2 (SCCO2) on reservoir rocks from deep (1500–2000 m) saline aquifers were examined via experimental simulation at in situ conditions. Dry sandstone samples were mounted in a triaxial cell and autoclave system, evacuated, and saturated with 1 M NaCl solution. The brine-rock system was allowed to react at 30 MPa confining pressure, 15 MPa pore fluid pressure, and 60 °C while SCCO2 was injected at a pressure gradient of 1–2 MPa. The experiment was conducted for a period of 1496 h, during which fluids were periodically sampled and analyzed. The pH measured in partially degassed fluid samples at 25 °C decreased from a starting value of 7.0–4.3 (9 days) and finally 5.1 after saturation with SCCO2.