Interfacial tension between crude oil and decylmethylnaphthalene sulfonate surfactant alkali-free flooding systems

The surface tensions of decylmethylnaphthalene sulfonate (DMNS) surfactant aqueous solution and the dynamic interfacial tensions between crude oil, from Shandong Shengli Oil Field of China, and solution of the surfactants had been measured. The effects of surfactant concentration and salinity on the interfacial behavior of crud oil–water were investigated in detail. Results indicate that DMNS surfactant possessed great capability and efficiency of lowering the solution surface tension and the critical micelle concentration (cmc) is 0.02 mass% and the surface tension at this concentration is 31.61 mN m−1. It is found that the DMNS surfactant is also greatly effective in reducing the interfacial tensions and can lower the tension of crude oil–water interface to ultra-low at very low concentration, 0.002 mass%, without alkali and the other additives. Both chromatogram separation of flooding and breakage of stratum are avoided effectively. The addition of salt, sodium chloride results in more effectiveness of surfactant in reducing interfacial tension and shows the surfactant has a good synergism with salt. It is also found that the surfactant can reduce the interfacial tension to ultra-low only at a certain sodium chloride concentration range.