Geochemical effects of cement mineral variations on water–rock–CO2 interactions in a sandstone reservoir as an experiment and modeling study

The complexity of water–rock–CO2 interactions associated with CO2 geological storage requires more comprehensive understanding with regard to the geochemical characteristics of reservoirs. In this paper, five groups of batch reactions and coupled simulations were conducted, in which rocks of different cementation types were reacted with purified water and CO2 at 180°C and 18 Mpa for 15 days, to reveal the possible geochemical effects of cement mineral variations on water–rock–CO2 interactions. With water chemistry and mineral alteration being monitored, the thermodynamics and kinetic characteristics of each CO2–water–rock system were fully analyzed in PHREEQC by the method of mineral saturation index, mineral phases diagram, and kinetics modeling to reveal the possible reaction paths and to compare their geochemical differences, which are caused by cement mineral variations. The experiment identified quite different dissolution characteristics and rates for cement minerals, and as a result, favored a diverse water chemistry and precipitation of different secondary minerals. Generally, the sensitive orders of cement mineral variations due to water–rock–CO2 interactions are carbonates, argillaceous, and siliceous minerals. The modeling showed good consistency with experiment results especially in cation evolution but underestimated the dissolution rate of alkali feldspar and carbonate mineral solubility. In addition, the modeling also predicted the carbonate reprecipitation of dolomite and calcite as cement minerals themselves, as well as dolomite precipitation at the expense of chlorite and calcite dissolution, which we failed to observe in the experiment. Thus, special attention should be paid to cement mineral variations when conducting CO2 injection in sandstone reservoirs. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.