Wormlike micelles properties and oil displacement efficiency of a salt-tolerant C22-tailed amidosulfobetaine surfactant

Wormlike micelles formed by amidosulfobetaine surfactants present advantage in increasing viscosity, salt-tolerance, thermal-stability and shear-resistance. In the past few years, much attention has been paid on rheology behaviours of amidosulfobetaine surfactants that normally bear C18 or shorter tails. Properties and oil displacement performances of the wormlike micelles formed by counterparts bearing the long carbon chain have not been well documented. In this paper, the various properties of C22-tailed amidosulfobetaine surfactant EHSB under high salinity (TDS = 40g/L) are investigated systematically, including solubility, rheology and interfacial activity. Moreover, its oil displacement performance is studied for the first time. These properties are first compared with those of C16-tailed counterpart HDPS. Results show that the Krafft temperature(T-K) of EHSB decreases from above 100 degrees C to 53 degrees C with the increase of TDS to 40 g/L. Increasing concentration of EHSB in the semidilute region induces micelle growth from rod-like micelles to wormlike micelles, and then the worms become entangled or branched to form viscoelastic micelle solution, which will increase the viscosity by several orders of magnitude. The interfacial tension with oil can be reduced to ultra-low level by EHSB solution with concentration below 4.5 mM. Possessing dual functions of mobility control and reducing interfacial tension, wormlike micelles formed by EHSB present a good displacement effect as a flooding system, which is more than 10% higher than HPAM with the same viscosity. Compared with the shorter tailed surfactant, the ultra-long tailed surfactant is more efficient in enhancing viscosity and reducing interfacial tension, so as to enhance more oil recovery. Our work provides a helpful insight for comprehending surfactant-based viscoelastic fluid and provides a new viscoelastic surfactant flooding agent which is quite efficient in chemical flooding of offshore oilfield.