Properties and Aggregation Behavior of Gemini Surfactants for Heavy Oil Recovery in High Temperature and Salinity Conditions

In this paper, the thermal stability of the surfactant CEA-n molecules with different structures was determined by thermal gravimetric analysis. The aggregation behavior in aqueous solution was studied by dynamic light scattering and transmission electron microscopy (TEM). The interfacial behavior, emulsification performance, and heavy oil universality of the surfactants under high temperature and high salinity conditions were evaluated by interfacial tension (IFT), viscosity reduction rate (VRR), and multiple light scattering. Also, microscopic oil displacement experiments were performed to investigate the oil displacement mechanism of the surfactant. Results indicated that the surfactant molecules had good thermal stability. The initial decomposition temperature (T-i) of surfactants CEA-n was greater than 280 C-degrees. The average hydrodynamic radius (R-h) of the surfactant CEA-2 system after aging was larger than that of the unaged system, and the aggregation of CEA-2 molecules was promoted by the addition of NaCl. Moreover, the IFT of surfactant CEA-2 had a small change with the increase of aging temperature (100-300 C-degrees), which could be maintained on the order of 10(-1) mN/m. And the VRR of the surfactants was higher than 95.0%, showing good emulsifying and viscosity reduction effects. Although the turbiscan stability index (TSI) value of the oil LD2-1 emulsion system was the lowest and had the best emulsion stability, the VRR between the surfactant and oil NB35-2 could reach more than 99.0%, indicating that CEA-2 had good heavy oil universality. Furthermore, the sand-pack flooding experiments were also carried out to confirm the great potential of the Gemini surfactant systems for heavy oil recovery.