Pore-Scale Investigation of Calcium Carbonate Precipitation at Dynamic Oil–Brine Interfaces during CO2 Geological Sequestration in Depleted Oil Reservoirs

Geological carbon sequestration in depleted oil reservoirs represents a promising climate mitigation strategy, although its efficiency is complicated by CaCO3 precipitation and the presence of residual oil. This study combines microfluidic experiments, numerical simulations, and theoretical analysis to investigate how dynamic oil–brine interfaces regulate precipitation under varying Pe/Da/SI conditions in confined pores. With 50 mPa·s residual oil, it was observed that (1) enhanced local shear at the interface reduces supersaturation, with interfacial tension less influential than velocity and supersaturation for ACC nucleation; (2) local shear and supersaturation control precipitation rates, while frictional resistance governs nuclei attachment and growth; (3) reduced mass-transfer resistance, enhanced ion flux, and lowered water diffusivity (supported by residence time analysis) promote crystal growth; and (4) local shear and advection induce growth anisotropy, while oil viscosity and dielectric properties stabilize metastable phases (e.g., vein-like ACC and cauliflower-like aragonite). Results across different pore sizes revealed formation-specific impacts: in sandstone pores, light oil accelerated precipitation and clogging risk, while in carbonate vugs, it promoted polymorph dispersion, alleviating localized clogging. These pore-scale insights into oil–brine interfacial dynamics extend beyond carbon storage, providing critical guidance for predicting CaCO3 behavior in geothermal exploitation and NAPL-contaminated site remediation, where similar multiphase interfaces govern precipitation outcomes.