Contribution of the Sedimentation and Coalescence Mechanisms to the Separation of Concentrated Water-in-Oil Emulsions

Crude oil is, in the vast majority of cases, produced together with formation water in the form of water/oil emulsions. Until recently oil/water separators were simply designed using Stokes' law. In order to improve the design of these separators the two main contributing mechanisms, sedimentation and coalescence, have to be better understood. This article presents a method that distinguishes the respective contributions of the sedimentation and coalescence mechanisms. Two series of experiments have been carried out, the first with a system heavily charged in surfactant that only allows sedimentation of the emulsions droplets. The second with a much lower surfactant concentration allows both sedimentation and coalescence to take place. By comparing the separation velocities of the oil/emulsion interfaces of the two series of experiments, it seems possible to determine the contribution of the two mechanisms towards the separation.