The structure effect on the physicochemical properties of Gemini surfactants used as viscosity reducer for heavy oil

Abstract

The structure of surfactants is a key factor affecting their physicochemical properties. Our earlier work synthesized Gemini surfactants CEA-n with different structures. In this paper, the effects of polyether chain length, spacer groups number and the hydrophobic alkyl chain length of surfactants CEA-n on the interfacial properties, wettability, rheological properties and emulsion stability were fully studied in detail, and the effects of surfactant structure on their temperature tolerance and salt resistance properties were explored. The results showed that the variation of polyether chain length of surfactant molecules had the greatest impact on the interfacial tension (IFT), and the surfactants with longer alkyl chains had better interfacial film strength. The wettability of various surfactant systems was investigated by the sessile drop method, and the contact angle decreased remarkably from 92.6° to 17.9° in a short time (300 s) after adding surfactant CEA-6. Judging from the fluid type, each heavy oil emulsion system exhibited pseudoplastic fluid characteristics, and dilute shear phenomenon was observed in the range of 0–50 s−1 with an increasing shear ratio. The particle size, dispersibility and coalescence of the heavy oil O/W emulsion droplets of each system were observed through the microscopic images of the emulsions, and the factors affecting the stability of the emulsions were systematically studied by bottle test. It was found that the increase of oil-water ratio, surfactant concentration and mixing speed would improve the stability of O/W emulsions, while high temperature would accelerate the demulsification process. All these results established the structure-property relationship of surfactant molecules.