An issue encountered by oil and gas companies is the formation of emulsions of oil and brine in pipelines. The presence of a dense emulsion in the flow causes an increased pressure drop which impacts the production, and optimization of separation between oily and aqueous phases is needed before further processing. Being able to predict and control coalescence time in crude oil/brine emulsions is crucial to model the dense emulsion evolution.

Field observations show a clear influence of tension-active additives and lab experiments [1] suggest delayed coalescence when oil/water interfaces have a tangential relative motion. One mechanism, derived from hydrodynamics only, can explain part of this delay [2, 3], but the role played by the surfactant is not clear.

Our study aims at clarifying the causes of delayed coalescence and at modelling its mechanism. A simplified situation is considered which consists of one drop of water pressed on a moving flat oil/water interface. I have developed an original, automatized experimental setup to measure the statistics of the drop rest time before coalescence, as a function of several parameters, including the velocity of the interface and the surfactant concentration.

We expect the lift force created by the relative motion to be enhanced by Marangoni effects, but we also want to reveal why different surfactants can have different influences on the coalescence delay.

1. Weheliye W.H., Dong T., Wang F., Angeli P. Delayed coalescence of drops at moving liquid/liquid interfaces. Bull. Am. Phys. Soc., 2019.
2. Sreenivas K. R., De P. K., Araker. J.H. Levitation of a drop over a film flow. J. Fluid Mech. 380:297‑307, 1999.
3. Lhuissier H., Tagawa Y., Tran T., Sun C. Levitation of a drop over a moving surface. J. Fluid Mech. 733:R4, 2013.