Molecular Simulation Study of Water-Rock Interfaces During Supercritical CO₂ Sequestration

Area of Science:

• Geochemistry
• Materials Science
• Environmental Science

Background:

• Understanding supercritical CO2-water-mineral interactions is crucial for geological carbon storage safety and efficiency.
• The influence of mineral surface chemistry and pore geometry on interfacial behavior at the molecular scale is not fully understood.

Purpose of the Study:

• To quantify how different mineral surfaces (methylated SiO2, hydroxylated SiO2, kaolinite) affect CO2-water interfacial behavior.
• To investigate the roles of wettability and electrostatic interactions in regulating these interfaces.

Main Methods:

• Molecular dynamics simulations were used to model CO2-water interactions with three distinct mineral surfaces.
• Contact angles and electrostatic binding energies were calculated to assess water affinity and interfacial properties.

Main Results:

• A clear hierarchy of water affinity was observed: methylated SiO2 (contact angle ~140°), hydroxylated SiO2 (~61.3°), and kaolinite (~24.5°).
• Stronger mineral-water electrostatic attractions correlated with increased hydrophilicity and altered interfacial morphology.
• Carbon dioxide-water attractions were moderate but influenced CO2 distribution within confined spaces.

Conclusions:

• Mineral surface functionalization and type significantly control interfacial morphology, fluid confinement, and electrostatic stabilization.
• Mineral wettability is a key factor in CO2 trapping, fluid segregation, and pore-scale sealing in carbon storage.
• This study provides molecular-level insights into the mechanisms governing CO2 storage performance.