Background Geologic CO₂ sequestration in basalts has attracted wide attention in recent years owing to its safe, stable, and efficient CO₂ trapping mechanisms.

Methods Focusing on basalts in the Longtan Formation within western Guizhou Province, China, this study simulated the CO₂-water-basalt geochemical reactions under varying temperatures, pressures, and times. Through tests and comparison of mineralogy, geochemistry, and reservoir physical properties before and after the reactions, this study investigated the factors influencing the reactions and elucidated the post-reaction co-evolution mechanism between minerals and pores. Furthermore, the mechanisms behind CO₂ trapping in basalts were summarized, and the prospects of geologic CO₂ sequestration in basalts in southwestern China were explored.

Results The temperature, pressure, and reaction time exhibited different influence mechanisms on mineral dissolution and precipitation during CO₂-water-basalt reactions. Nevertheless, a high temperature (200 °C), high pressure (＞ 12 MPa), and long reaction time (20 days) could promote the precipitation of carbonate minerals. The reactions during CO₂ trapping in basalts were essentially the dissolution and corrosion of original minerals, coupled with the generation of new minerals. In their early stage, the reactions were dominated by the corrosion of plagioclases, augite, and minor altered minerals. With increases in Ca²⁺ and Mg²⁺ concentrations in the solution, the precipitation of calcites, dolomites, and clay minerals intensified gradually. During CO₂-water-basalt reactions, the reservoir pores and fractures showed a three-stage evolution pattern, which was coupled with dissolution-precipitation reactions. During the reaction process, the reservoir porosity and permeability jointly increased in the early stage; continuously increased but decreased, respectively, in the middle stage, and jointly decreased in the late stage. The CO₂ mineral trapping in basalts was characterized by complex reaction types, which corresponded to intricate reservoir response processes. The carbonate precipitation was identified as the core mechanism behind the reactions.

Conclusions Southwestern China enjoys favorable geological conditions for engineering tests on geologic CO₂ sequestration in basalts, such as extensively distributed basalt reservoirs and abundant groundwater rich in Ca²⁺ and Mg²⁺. Nevertheless, due consideration should be given to the substitution of groundwater with seawater in coastal areas, along with techniques for removing reservoir plugging after reactions in CO₂ mineral trapping. The results of this study will provide an important theoretical basis for understanding the mechanism and feasibility of geologic CO₂ sequestration in basalts in southwestern China.