Rheological Properties of a New Microbial Exopolysaccharide Produced by Sphingomonas sp. HS and Its Potential in Enhanced Oil Recovery

The alkali-free surfactant-polymer flooding system with ultralow interfacial tensions is still a challenge to enhance oil recovery at present. In this study, a new thermally stable and salt tolerant biopolymer (HS-EPS) was obtained from thje broth of Sphingomonas sp. HS, a newly isolated strain (CGMCC No. 22954). Compared to HPAM, the elasticity of HS-EPS was dominant which is conducive to enhancing oil recovery. The HS-EPS showed good viscosity stability at salinities up to 360 g/L of NaCl, 60 g/L of Ca2+, and 60 g/L of Mg2+, temperatures up to 90 degrees C, and pH 4-10. Meanwhile, a new alkali-free surfactant-polymer binary system was developed using HS-EPS and a biobased surfactant newly synthesized in our laboratory. The interfacial tension between this binary flooding system and Daqing crude oil was below 10(-2) mN/m with 100 g/L of NaCl, 400 mg/L of Ca2+, or at a temperature of 80 degrees C. In addition, this binary system possesses a good oil sand adsorption resistance, dilution resistance, and aging stability. These results demonstrate that the new biopolymer HS-EPS secreted by Sphingomonas sp. HS is promising in oil recovery in the alkali-free flooding system.