Study of Turbulent Break-up of Oil Droplets in Choke Valves

This paper was presented as part of the student paper contest associated with the European Petroleum Conference. Abstract Production of a well at high water cut is associated with problems in separation efficiency of the oil-in-water emulsion. In this, the smallest sizes of the oil droplets are the decisive factor, negatively and greatly influenced by the choke valve. This valve breaks the produced distribution down to too many and too small droplets for the separation equipment to economically clean the water and isolate the oil. Laboratory experiments allowed us to investigate the break-up effects of choke valves and to validate existing predictive theories. By using different choke types, significant reduction of break-up was accomplished. The effect of choke geometry on break-up is explained by an interplay of the time that droplets remain in a choke on the one hand, and the time needed for complete break-up under the current turbulence regime on the other. Hereby, the spatial distribution of energy dissipation, linked to the geometry of the choke, plays an important role. Introduction Often water is produced along with oil. When the age of a well matures, the water cut tends to increase. In the after-life of a well, the percentage of water can by far exceed that of oil. Wells with water cuts of 95% are no exception, which implies that these wells produce an oil-in-water emulsion. Chokes are installed on every well to control the pressure and flow rate. They work on the basis of energy dissipation by increased turbulence. Downstream of the valve the pressure is brought down to safer values to work with, and the emulsified liquids must be separated. This should be done carefully in order not to loose valuable oil and to clean the water before disposal. The efficiency of a separator is confined by the droplet-size distribution offered to it.