Theoretical And Experimental Study Of Anionic Surfactant Adsorbed Behavior At Water/Oil Interface

Surfactant can greatly raise the displacement efficiency and the oil recovery factor through reducing the interfacial tension of crude/water interface and changing the emulsify properties of formation crude. The reservoir environment is complex, so the active mechanism of surfactant with water and crude is affected by many factors. This is severely restricted the basic research of surfactant flooding mechanism, and it is detrimental to promote the application in complex reservoirs. In this paper, the surfactants which were usually used in oilfield, sodium dodecyl sulphonate (SAS), Sodium dodecyl benzene sulfonate (SDBS), Sodium lauryl sulfate (SDS) and Sodium lauryl polyoxyethylene ether sulfate (AES) were chosen to investigate the absorbed behavior and microscopic mechanism at oil/water interface by combination of experimental and theoretical method.Experimental results show that the order of reducing interfacial tension at dodecane/water interface is AES >SDBS>SDS>SAS; and it is different to reduce the interfacial tension at different alkane/water interface for different surfactant, but the interfacial tension is reduced to minimum at decane/water interface for all surfactants. It is also shows that the effect of temperature for the surfactants interfacial activity is very complex; but generally speaking, SDBS and AES have a high temperature resistance, and both still keep in reducing the interfacial tension on higher temperature. Simultaneously, the experimental results show that surfactant has a greater difference in salt tolerance;SDBS and AES molecules can reduce the interfacial tension to 10-1 mN/m in a certain concentration of NaCl solution, and AES molecules can maintain e lower interfacial tension under a more width concentration region of NaCl; in the divalent salt (Ca2+, Mg2+) solution, SDBS molecules solution would appear some precipitation and the interfacial activity was reduced, but AES showed a good ability of anti-salt in higher divalent salt concentration.The theoretical simulation result shows that surfactant could form a stable monolayer at oil/water interface; thorough calculating the interface information energy, thickness of interface, radial distribution function,coordination number, order parameter, diffusion coefficient and rotational time correction function, the ability of reducing the interfacial tension of surfactant was evaluated, the order of four surfactant adsorbed at dodecane/water interface was AES>SDBS>SDS>SAS, and the order of SDS monolayer adsorbed at different alkanes was decane>octane>dodecane> hexadecane, also the order of AES monolayer adsorbed at different temperature is 343K>313 K>353K>328K, all the theoretical evaluation was consisted with experimental result s.