Interfacial interactions between oil and porous calcium carbonate in brine: Insights for enhanced oil recovery and spill remediation

Potential determining ions (Mg 2+ , Ca 2+ , and SO 4 2− ) control oil-brine‑carbonate interfacial interactions, influencing oil adhesion, coalescence, and transport in porous media. However, discrepancies in ion effects persist, likely due to undefined oil properties and single-scale experimental limitations. We hypothesize that for acidic oils, divalent cations dominate interfacial interactions via ion-bridging and electrostatic screening, thereby promoting adhesion and retention. Conversely, sulfate ions are hypothesized to induce electrostatic repulsion, thus facilitating desorption and transport. Validating this mechanism necessitates bridging nanoscale interaction forces with mesoscopic interfacial dynamics and macroscopic multiphase flows. A multiscale framework was established to decouple ion effects in acidic oil-brine‑calcium carbonate systems. Macroscopic displacement efficiency and fluid redistribution were monitored via nuclear magnetic resonance (NMR)-core flooding. These observations were bridged to mesoscopic interfacial dynamics through thin-film drainage (TFD) analysis of droplet adhesion and coalescence, alongside contact angle and interfacial tension measurements. The molecular origins of these phenomena were investigated at the nanoscale using drop-probe atomic force microscopy (AFM) to measure disjoining pressures, while zeta potential analysis tracked surface charge modification across distinct brine chemistries (35 mM NaCl, CaCl₂, MgCl₂; 17.5 mM Na₂SO₄) versus deionized water. NMR-flow experiments showed that cations (sequence: Mg 2+ > Ca 2+ > Na + ) facilitated oil ingress into pores even the smaller ones but reduced subsequent oil recovery, whereas SO₄ 2− restricted oil to larger pores and enhanced mobilization. TFD and drop-probe AFM measurements revealed: cations increased attractive forces, promoting acidic oil adhesion to carbonate surfaces and droplet coalescence. These observations align with the enhanced oil-wettability and reduced interfacial tension recorded in bulk measurements. Mechanistically, zeta potential analysis confirms that cations suppress electrostatic repulsion via screening and ion bridging, thereby anchoring oil within the pore structure. Conversely, SO₄ 2− intensified the negative charge on both oil and carbonate surfaces, generating electrostatic repulsion that suppressed adhesion and coalescence, shifting the system toward a water-wet state and increasing interfacial tension. This cross-validated framework resolves prior inconsistencies by demonstrating that for acidic oils, cations drive retention through bridging interactions, while sulfates facilitate transport via electrostatic repulsion. • Surface interactions among oil, brine, and calcium carbonate were quantified. • Oil-brine‑carbonate interactions influence multiphase flow in porous media. • Cations enhance attractive forces at oil‑carbonate and reduce oil-oil repulsive forces. • Sulfate strengthens repulsive forces at oil-rock and oil-oil interfaces.