Study on the influence mechanism of primary mineral components on CO₂geological trapping forms

The increasingly intensifying global climatic change necessitates carbon capture and storage (also referred to as CCS). Based on China's first whole-process CCS demonstration project in saline aquifers and using the TOUGHREACT ECO2N software, this study constructed a water-CO₂-thermal-chemical reaction coupling model for long-term CCS in reservoirs at the Shenhua CCS demonstration site. Using this model, this study investigated the influence of primary mineral components in reservoirs on the transformation of different CO₂ capture mechanisms. The results indicate that the deep saline aquifers in the Ordos Basin are favorable for CO₂ storage capacity through the mineralization mechanismmineral trapping, with a storage capacity reaching up to 64.02% of the total injectivity at 1000 a. The calcite, orthoclase, albite, chlorite, and kaolinite in the reservoir undergo varying degrees of dissolution, resulting in the precipitation of montmorillonite, iron-bearing dolomite, and analcime. Iron dolomite is the main carbon fixing mineral, with the highest storage capacity in the water gas two-phase zone, reaching up to 15 kg/m³. The changes in the content of plagioclase, albite, and calcite have little impact on gas and dissolution trapping, and have no effect on mineralization trapping. The variation in the content of chlorite has a significant impact on the three types of trapping forms. When the initial volume fraction of chlorite increases from 1.9% to 8.4%, the mineralization trapping amount increases from 7×10⁸ kg to 1.6×10⁹ kg at 1000 a, with a change of 9×10⁸ kg. The results of this study can serve as a reference for the design optimization of existing CO₂ storage projects and the proper assessment of the siting of future CO₂ storage, assisting in the achievement of China's carbon neutrality target.