Аннотация:In the context of the current global transition toward low-carbon energy, the issue ofCO2 utilization has become increasingly important. One of the most promising naturaltargets for CO2 sequestration is the terrigenous sedimentary formations found in oil, gas,and coal basins. It is generally assumed that CO2 injected into such formations can bestored indefinitely in a stable form. However, the dissolution of CO2 into subsurface waterleads to a reduction in pH, which may cause partial dissolution of the host formation,altering the structure of the subsurface in the injection zone. This process is relativelyslow, potentially unfolding over decades or even centuries, and its long-term consequencesrequire careful investigation through mathematical modeling. The geological formationis treated as a partially soluble porous medium, where the dissolution rate is governedby surface chemical reactions occurring at the pore boundaries. In this study, we presentan applied mathematical model that captures the coupled processes of mass transport,surface chemical reactions, and the resulting microscopic changes in the pore structure ofthe formation. To ensure the model remains grounded in realistic geological conditions,we based it on exploration data characterizing the composition and microstructure ofthe pore space typical of the Cenomanian suite in northern Western Siberia. The modelincorporates the dominant geochemical reactions involving calcium carbonate (calcite,CaCO3), characteristic of Cenomanian reservoir rocks. It describes the dissolution of CO2in the pore fluid and the associated evolution of ion concentrations, specifically H+, Ca2+,and HCO−3 . The input parameters are derived from experimental data. While the modelfocuses on calcite-based formations, the algorithm can be adapted to other mineralogieswith appropriate modifications to the reaction terms. The simulation domain is definedas a cubic region with a side length of 1 μm, representing a fragment of the geologicalformation with a porosity of 0.33. The pore space is initially filled with a mixture of liquidCO2 and water at known saturation levels. The mathematical framework consists of asystem of diffusion–reaction equations describing the dissolution of CO2 in water and thesubsequent mineral dissolution, coupled with a model for surface evolution of the solidphase. This model enables calculation of surface reaction rates within the porous mediumand estimates the timescales over which significant changes in pore structure may occur,depending on the relative saturations of water and liquid CO2.
