A Microfluidic Method to Assess Emulsion Stability in Crude-Oil/Water Separators

The control of emulsion stability and droplet size is of crucial importance for oil production, especially for the processes of crude/oil water separation and cleanup of produced water. To recover pure oil and water, coalescence between droplets needs to take place, the extent of which will depend on the flow parameters as well as on the presence of emulsifying agents. For a successful separation, the demulsification time of the mixture must be smaller than its residence time in the separator. A direct measurement of the coalescence rate in dense flowing emulsions has not been achieved until now. In this work we present a microfluidic method that permits to assess the kinetic parameters governing coalescence in flowing emulsions. Monodisperse droplets of oil in water formed at a microfluidic T-junction were injected into a wide channel where droplets are accumulated to form a twodimensional emulsion layer (see figure). The droplets undergo collisions and coalesce. The coalescence process was followed with a microscope and a highspeed camera. Counting the number of coalescence events permits to calculate the coalescence rate and evolution of the droplet size distribution, which were mapped as a function of initial droplet size, flow rate and dispersed phase volume fraction. The results obtained provide information about the timescale of separation of the liquid mixture and may thus help in the design of the separation process for a given produced fluid