Molecular simulation on CO2 adsorption in partially water-saturated kaolinite nanopores in relation to carbon geological sequestration

CO2 geological sequestration in depleted gas/oil reservoirs is regarded as a promising strategy to mitigate CO2 emission thanks to the well-developed nanoscale pore structures providing substantial adsorption spaces. Therefore, the fundamental understanding of CO2 adsorption in shale nanopores can provide important insights into geological CO2 sequestration. In this work, we use molecular dynamics (MD) and Grand canonical Monte Carlo (GCMC) simulations to investigate CO2 adsorption in kaolinite nanopores with two different basal surfaces and study moisture effect. In the absence of water, CO2 presents stronger adsorption in gibbsite nanopores than siloxane nanopores. In gibbsite pores, water tends to spread over the surfaces forming thin water films. While CO2 is driven to the middle of the pore, an enrichment of CO2 is observed at the water-CO2 interface. On the other hand, water bridges form in siloxane pores. In siloxane mesopores, the shape of water clusters gradually turns to be spherical ones as pressure increases suggesting a more CO2 -wet surface, while the deformation of water clusters in micropores is not obvious due to stronger confinement effects. The CO2 distributions in siloxane mesopores can be divided into six zones. The highest CO2 density appears in the three-phase contact areas, while CO2 has a high tendency to accumulate in two-phase contact areas. In general, the presence of water results in the reduction of CO2 adsorption in both gibbsite and siloxane pores. Overall, water has a more detrimental influence on CO2 adsorption in gibbsite pores than siloxane pores. Our work should provide important insights into CO2 adsorption in kaolinite nanopores and reveal CO2 adsorption mechanisms in the presence of water.