Novel polyhydroxy anionic surfactants with excellent water-solid interfacial wettability control capability for enhanced oil recovery

Abstract Surfactant flooding has received considerable attention as a proven chemically enhanced oil recovery method. Traditional surfactants are mainly focused on water-oil interfacial tension reduction. However, a large amount of oil film remains on rock surfaces after surfactant flooding. Therefore, developing novel surfactants with excellent water-solid interfacial wettability control capability would significantly enhance oil recovery. In this study, novel polyhydroxy anionic surfactants, 9,10-dihydroxyl sodium stearate (SDHS) and 9,10,12,13-tetrahydroxyl sodium stearate, were synthesized by oxidation and hydrolysis of oleic acid and linoleic acid, respectively, followed by a neutralisation reaction. The polyhydroxy structure on the long hydrophobic carbon chains facilitated the adsorption of surfactants on the rock surface. Atomic force microscopy results showed that the SDHS layer had a uniform sheet structure. The exposed anions led to the accumulation of negative charges, significantly improving the hydrophilicity of the rock surface, with the underwater oil contact angle of the rock surface changing substantially from 18.1° to 152°. The surface (super)hydrophilicity and electrostatic repulsive force between the rock surface and the oil film synergistically contributed to the superior oil-film-peeling performance of SDHS. After SDHS treatment, the area reduction of the oil film surpassed 92.5%, which was significantly higher than that with other traditional surfactants. Furthermore, an increase of 10.15% in oil recovery was achieved by SDHS flooding. The novel surfactants with excellent water-solid interfacial wettability control capability exhibited superior performance in recovering residual oil adhered to oil-wet rocks. This is significant for efficient oilfield development.