Mineral trapping of CO2: Hydrothermal experimental system and thermodynamic simulation on interaction between CO2–H2O–dawsonite bearing sandstone with the pH of 4–9, temperature of 80–140 °C, and increasing pCO2

Abstract

Abstract Dawsonite commonly occurs in CO2-enriched strata and gas reservoirs, which is the product of CO2 trapping or “mineral fixation”. In this study, we focused on dawsonite and conducted series of experiments with three groups of variables: temperature (80/100/120/140 °C), pH (4/6/7/9), pCO2 (0/4.3 Mpa) for comparison, aiming at understanding potential natural processes within CO2–H2O–dawsonite bearing sandstones systems. We conducted a series of studies on the alteration characteristics of dawsonite-bearing sandstones, evolutionary mode of fluid properties, alteration of dawsonite by fluid, and the mechanism of mineral precipitation and dissolution in closed systems. Based on Scanning Electron Microprobe (SEM) observation, energy spectrum analysis, X-ray diffraction analysis, and thermodynamic numerical simulation, we evaluated the influences of temperature, pH and pCO2 on the stability of dawsonite preserved in sandstone, and further identified the favorable conditions for mineral trapping of CO2. The hydrothermal experiments suggested that: for the temperature in the range of 80 °C–140 °C, the stability of dawsonite decreased with increasing temperature, and the fluid alteration influence on dawsonite mainly followed transformation path. When the pH is in range of 4–9, the stability of dawsonite decreased with the decreasing pH, and the alteration of dawsonite by fluid mainly followed decomposition path. pCO2 decided the thermal stability of dawsonite, and when pCO2 increased from 0 MPa to 4.3 MPa, the degree of dawsonite corrosion decreased and its stability increased. The results of hydrothermal experiment agree well with the thermodynamic numerical simulation, and indicate that the alkaline closed system with low temperature and high pCO2 is ideal for “Carbon Capture and Storage”, which can promote the formation and conservation of CO2 “entrapment minerals”, and benefit the long-term and stable geological CO2 sequestration.