CO2–Brine–rock interaction and sequestration capacity in carbonate reservoirs of the Tahe Oilfield, Xinjiang, China

The characteristics of each carbonate reservoir are greatly different, and current databases are insufficient to support engineering scheme design and optimization of carbon dioxide (CO2) sequestration and enhanced oil recovery. In this paper, the behavior of CO2‐brine‐rock interactions was investigated under supercritical CO2 (50°C and 8.5 MPa) conditions. Five experiments were carried out, including CO2 solubility in brine, mass loss analysis by static reaction of CO2–brine–rock, mineralogical composition analysis by X‐ray diffraction (XRD), core surface morphology analysis by scanning electron microscopy (SEM), and wettability alteration by contact angle analysis. The experimental results showed that: (a) the CO2 solubility in brine increases with increasing pressure, but it increases slowly and gradually reaches equilibrium; (b) the mass loss of carbonate increases with reaction time, but its increments decrease with reaction time; (c) the calcite content gradually decreases and the quartz content slightly increases with reaction time, as evidenced by XRD analysis; (d) based on SEM image analysis, calcite was dissolved into brine by carbonic acid to make the pores larger, and then subsequent precipitation made the pores smaller; and (e) the carbonate rock surface became more water‐wet after CO2–brine–rock interaction experiments due to surface corrosion and increased quartz content. Using the experimental results, a mathematical model was developed to predict CO2 sequestration capacity under reservoir conditions. The results suggest that CO2 solubility in brine was the main aspect compared with mineral trapping in carbonate reservoirs, and CO2 sequestration capacity increased with increasing temperature and pressure. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.