CO2 storage performance influenced by CO2-brine-carbonate reactions: A case from China's first CCUS project in carbonate gas reservoir

Geological storage of CO2 represents an effective strategy for reducing atmospheric carbon emissions and mitigating global warming. Carbonate gas reservoirs—characterized by their substantial reserves and high productivity—offer promising conditions for large-scale CO2 storage. However, CO2 injection induces complex geochemical interactions with reactive minerals, altering petrophysical properties and posing challenges to long-term security. In this study, taking China's first CCUS project in carbonate gas reservoir as an example (Wolonghe gas reservoir), the evolution of mineralogy, fluid composition, and the surface morphology of pore structures was systematically investigated. The impact of CO2-brine-carbonate reactions on petrophysical properties, CO2 migration, well injectivity, and storage capacity are revealed through in-situ experiment and multi-scale numerical simulations. The results show that the dissolutions of dolomite and calcite enhance pore connectivity. The porosity and permeability increase by 2.52 × 10−6 and 0.015 mD over a 30-year injection period. During a 500-year storage period, mineral precipitation reduces porosity and permeability by 5.07 × 10−6 and 0.23 mD. Overall, CO2-brine-carbonate reactions reduced CO2 migration range and rate by 6.05% and 14.30%, respectively. Moreover, these reactions improved well injectivity, as evidenced by a 3.96 × 104 t increase in structural CO2 at the end of injection, alongside reductions of 0.28 × 104 t and 0.30 × 104 t in dissolved and hysteresis CO2. After 500 years of storage, the proportions of mobile CO2 decline, while mineralized CO2 increases, enhancing storage security. These findings provide a crucial basis for the advancement of CO2 storage in carbonate gas reservoirs and offer valuable insights for the development of long-term, large-scale energy storage.