Synergy of surface modified nanoparticles and surfactant in wettability alteration of calcite at high salinity and temperature

• The surface modified nanoparticles are stable under high salinity and temperature. • The new nanoparticles are efficient in wettability alteration under harsh conditions. • Synergy is observed between the cationic nanoparticles and cationic surfactants. • The hydrophilic nanoparticles noticeably decrease the interfacial viscoelasticity. The surface of silica nanoparticles (NPs) was modified by chemical grafting of ligands to: (1) achieve colloidal stability in concentrated brine at salinities up to 25.7 % total dissolved solids (TDS) and temperatures up to 90 °C and (2) change the wettability of carbonate reservoirs from oil-wet to water-wet. The ligand precursors included low molecular weight cationic N -trimethoxysilylpropyl-N, N, N -trimethylammonium chloride or nonionic 3-glycidyloxypropyl trimethoxysilane. The water-phase contact angle θ w of a crude oil droplet on calcite was measured for binary mixtures of the modified NPs combined with different types of surfactants, for a heavy and a light crude oil. For two types of reservoir conditions (16.7 % TDS at 55 °C and 25.7 % TDS at 90 °C), positively charged NPs with quaternary nitrogens (QNP) at 1 wt% altered the wettability of the calcite surface from strongly oil-wet (θ w = 125° to 159°) to intermediate wet with a θ w = 69° to 85° for light crude oil and θ w = 71° to 107° for heavy crude oil. Meanwhile, cationic surfactants tetradecyltrimethylammonium bromide (TTAB) at 1 wt% altered the wettability to water-wet with a θ w = 41° to 59° for light crude oil and θ w = 70° to 90° for heavy crude oil. Synergy between the QNP and TTAB was observed in lowering the θ w by another 10°. The reduced θ w is beneficial for secondary oil recovery from carbonates, along with a significant decrease in the viscoelasticity of the crude oil-brine interface that helps destabilize undesirable water-in-crude oil emulsions.