Exploring the mechanisms of emulsion separation via millimetric droplet coalescence
Résumé
During petroleum production, emulsification phenomena occur and the metastable phase of W/O emulsion (a dense-packed zone) forms due to the presence of the surfactant species in the oil. Recent studies [1] have described the separation kinetics of such an emulsion with the micrometric droplet size distribution (below 50 μm) at the bottle-test conditions. However, the real separator unit is a dynamic system with inlet and outlet flows where the droplet size distribution varies from micrometres (at the separator inlet) to millimetres (at the water-DPZ interface).
In this research, we use a simple millifluidics setup to generate monodisperse droplets from 0.2 mm to 2 mm one-by-one and stock them in the recipient. The experiment has two stages: the emulsion accumulation while the droplet generation and coalescence are concurrent,
the emulsion separation with no more droplets arriving into the DPZ. Emulsion interfaces are traced in time with spatiotemporal images to obtain the data on the separation speed. The first significant difference with [1] is the linear separation rate instead of the formation of the metastable phase for the same system (“water in dodecane + 800 ppm Span 80”). This can be explained with a complete droplet deformation depending on the emulsion height and the droplet size. Another major difference is the coalescence only at the water-emulsion interface (contrary to the model [1]). Visually the droplets from below have a polyhedral “foam-like” shape, while ones on top are spherical with a thick oil layer around them. The presented results and perspective of millifluidics application in the emulsion generation will be useful in the study of the different factors of coalescence.