Synergistic effects of surfactant and polymer on the viscosity and oil displacement efficiency

For chemical flooding, choosing suitable surfactant and polymer mixture to optimize the viscosity and interfacial tension is an important procedure for preparing the combination flooding system. In this work, a systematic study was conducted on the properties of the surfactant/polymer mixed solution, involving viscoelasticity, oil/water interfacial tension and oil displacement efficiency. Zwitterionic-anionic surfactant mixture (HDPS-SDS) was chosen to show the effect of concentration and micelles type. Partially hydrolyzed polyacrylamide (HPAM) and hydrophobically associating polymer (HPOC) were selected to show the effect of polymer concentration and type. It has been found that for polymer solutions, adding HDPS-SDS reduces the oil/water interfacial tensions to the magnitude of 10−2 mN·m−1, but negative synergistic effect for spherical micelles and positive synergistic effect for wormlike micelles on viscosity are observed. For wormlike micelles solutions, adding HPAM or HPOC increases the viscosity. Moreover, the positive synergistic effect on viscosity by HPOC is far stronger than that of HPAM, and the viscosity of wormlike micelle solution can be reinforced by adding a small amount of HPOC. The synergistic effect on viscosity will also affect the oil displacement efficiency of the surfactant/polymer mixed system. For example, the enhanced oil displacement efficiency E of surfactant/polymer flooding unexpectedly reduces with adding spherical micelles formed by low concentration HDPS-SDS to 1500 mg L−1 HPOC solutions. Whereas the enhanced oil displacement efficiency E of wormlike micelles/polymer flooding reaches 28.8% with adding 800 mg L−1 HPOC to 5500 mg L−1 HDPS-SDS wormlike micelles solutions.