Effect of Rheology Properties of Oil/Water Interface on Demulsification of Crude Oil Emulsions

Chemical demulsification is widely used in the petroleum industry to remove water from crude oil all over the world. In this work, the relationship between the rheological properties of oil/water interfacial film and demulsification of crude oil emulsions was investigated. The results showed that the elastic modulus was the critical factor for the dehydration ratio, the emulsions showed high dehydration ratio when demulsifiers reduced the elastic modulus of oil–water film to a certain extent (below 5 mN/m). Correlations between dehydration ratio and equilibrium interfacial tension, dynamic interfacial tension, and loss modulus were also investigated. The results showed no correlation between the interfacial tension (IFT), the loss modulus, and the dehydration ratio. However, correlations were observed between dynamic IFT, loss modulus, and demulsification speed when the demulsifier could reduce the elastic modulus of the oil–water film to <5 mN/m. The loss modulus was directly proportional to the surface viscosity and could influence the demulsification speed, but it was not the critical factor. The dynamic interfacial tension was decisive factor to influence the demulsification speed. Dynamic Interfacial tension could be used to characterize the adsorption time (τ 1 ) and the reorganization time (τ 2 ) of demulsifier molecules at the interface, with the decrease of the τ (τ = τ 1 + τ 2 ), the demulsification speed increased. The rupture rate constant ( k ) of interfacial film increased with the decrease of τ, which accelerated the thinning and rupture of the film, thus increasing the demulsification speed.