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

NMR-flow experiments showed that cations (sequence: Mg²⁺ > Ca²⁺ > 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.