Overall surface activity of produced water and impact on oil droplet coalescence using microfluidics

Production of oil is associated with big volumes of produced water that is co-produced as a byproduct. In most cases it is either used for re-injection or discharged to sea in offshore production. Operation of the oil production site and the quality of oil demand certain production chemicals to be added in different doses. These chemicals might be found in the discharged produced water that can pose a hazardous risk to the marine environment if it is not adequately treated. The surface activity of produced water from five different oil fields sampled at the discharge point are characterized using microfluidic droplet technology. Toluene is used as the dispersed phase and produced water as the continuous phase. The tendency of toluene droplets to coalesce is quantified by the coalescence frequency using high-speed camera video acquisition. We find large variations in the ability of the produced water samples to stabilize oil droplets e.g. water sample B exhibits the highest droplet stability resisting coalescence mostly. Compared to Milli-Q water as the continuous phase, the coalescence frequency reduces from 84 to 1 mean coalescence events per time unit. The visual data is assisted by analytical data from capillary electrophoresis where the ionic composition of the produced water samples is quantified. No quantitative correlation was found between the measured properties of the water and the microfluidic results, although the data provided potential explanations of e.g. differences in oil-in-water content. A commercial corrosion inhibitor is measured to be present in the produced water samples and it ranged between 166 ppm in produced water sample B to 405 ppm in produced water sample A.