Dewetting of Silica Surfaces upon Reactions with Supercritical CO₂ and Brine: Pore-Scale Studies in Micromodels

TLDR

Wettability of reservoir minerals governs CO₂ mobility, residual trapping, and safe storage, yet little is known about wettability in supercritical CO₂–mineral–brine systems, creating major uncertainty in capillary predictions. Using transparent micromodels at 8.5 MPa and 45 °C with NaCl up to 5 M, the study observed pore‑scale dewetting of silica surfaces in scCO₂–brine, evidenced by water film thinning, droplet formation, and increasing contact angles. Contact angles rose from near 0° to 80°—larger at higher ionic strength—suggesting CO₂‑induced dewetting could lower capillary entry pressure and alter residual trapping, relative permeability, and caprock integrity.

Abstract

Wettability of reservoir minerals and rocks is a critical factor controlling CO2 mobility, residual trapping, and safe-storage in geologic carbon sequestration, and currently is the factor imparting the greatest uncertainty in predicting capillary behavior in porous media. Very little information on wettability in supercritical CO2 (scCO2)–mineral-brine systems is available. We studied pore-scale wettability and wettability alteration in scCO2–silica-brine systems using engineered micromodels (transparent pore networks), at 8.5 MPa and 45 °C, over a wide range of NaCl concentrations up to 5.0 M. Dewetting of silica surfaces upon reactions with scCO2 was observed through water film thinning, water droplet formation, and contact angle increases within single pores. The brine contact angles increased from initial values near 0° up to 80° with larger increases under higher ionic strength conditions. Given the abundance of silica surfaces in reservoirs and caprocks, these results indicate that CO2 induced dewetting may have important consequences on CO2 sequestration including reducing capillary entry pressure, and altering quantities of CO2 residual trapping, relative permeability, and caprock integrity.