Synthesis and evaluation of magnetic surfactants for high temperature oilfield application

Magnetic surfactants are a unique class of amphiphiles that can manage self-assembly in a controlled manner in the presence of the applied magnetic field. However, any surfactant for oilfield application must be soluble in water and exhibit high heat stability as it needs to stay in harsh reservoir conditions. Herein, we report a synthesis of two new magnetic surfactants that contain different hydrophobic moieties (ethoxylated alky tail and oleic tail). The chemical structures of the magnetic surfactants and their nonmagnetic parent surfactants were elucidated by ESI-MS, NMR (1H, 13C), and FTIR analysis. Both surfactants display good aqueous solubility due to the insertion of ethoxy units and unsaturation in the hydrophobic tail. The effect of hydrophobic tails on heat and surface/interface properties was investigated. Rendering to thermal gravimetric curves, the degradation temperature of magnetic surfactants was near 270 °C. This clearly showed that the magnetic surfactants contain high thermal stability for elevated temperature reservoirs. However, the effect of change of hydrophobic tail appears to be insignificant in thermal stability tests. An analysis of the surface tension showed that magnetic surfactants were more effective than corresponding nonmagnetic surfactants exhibiting higher surface tension (γ) reduction of water even with no magnetic field. Moreover, the magnetic surfactant containing an ethoxylated alkyl tail showed more surface tension (γ) reduction of water than a magnetic surfactant with an oleic tail. The research outcome on the synthesized magnetic surfactants makes them an attractive choice in a harsh oilfield environment. To the best of our knowledge, this is the first report on the magnetic surfactants that can toleratate high temperature reservoir conditions.