Produced Water Quality and Microfluidic Methods for Studying Drop-Drop and Drop-Bubble Interactions in Produced Water

Abstract

Produced water originates from crude oil production, during which it is extracted to the surface together with hydrocarbons. It consists of various dissolved and dispersed components, such as dissolved organic and inorganic compounds, suspended solids, production chemicals, and oil dispersed in the form of droplets. The latter is typically targeted by several treatment processes before the water can be discharged to sea or re-injected to an underground formation. Typical treatment processes, such as gravity or enhanced-gravity separation, strongly rely on the rising velocity of the dispersed droplets, whereas gas flotation aims at enhancing the density difference between the continuous and the dispersed phases through attachment of gas bubbles. This means that the fundamental phenomena occurring on a microscale, like droplet growth through coalescence or bubble-droplet interactions, will play a key role during these processes. That is why the development of new, microfluidic research tools and their application for studying these interactions in various conditions was one of the main goals of this thesis.

First, the produced water quality and its connection to both crude oil and water compositions was investigated. The water was mixed with crude oil and later analysed with respect to the total oil concentration, droplet size, total organic carbon and pH change. Next, a microfluidic method was developed to study the coalescence of model oils in the presence and absence of dissolved atmospheric gases, also at elevated pressures. This was followed by a report on the application of microfluidics for probing coalescence between crude oil droplets in produced water. Various aspects, like the oil and water composition, the presence of dissolved components or pressure levels were studied. Finally, a novel microfluidic methodology for investigating the removal of dispersed hydrocarbons through spreading on gas bubbles was presented. It also involved changing relevant parameters and testing their effect on the spreading process.