Interfacial properties of dissolved crude oil components in produced water

Abstract

Produced water is a mixture of water trapped in underground formations and injection water that is brought to the surface along with oil or gas. In general, produced water is a mixture of dispersed oil in water (o/w), dissolved organic compounds (including hydrocarbons), residual concentration of chemical additives from the production line, heavy metals, dissolved minerals and suspended solids.

In the year 2011, 131 million m3 of produced water were discharged on the Norwegian Continental Shelf (NCS). Discharges will increase in the years ahead, primarily because of increased water production from the major fields on the NCS. The majority of the produced water treatment technologies currently applied by the industry focus on removing dispersed oil and some technologies have also demonstrated their ability to reduce the dissolved compounds from the produced water. However, the efficiency of these techniques strongly depends on the variations in water quality and quantity over the lifetime of the production. Therefore, flexibility and robustness of technical solutions have proved to be a very important factor and can not be achieved without proper understanding of fundamentals of different separation techniques and produced water fluids.

This thesis presents studies of interfacial properties of dissolved crude oil components in produced water. The findings which have been summarized in this thesis include dynamic adsorption of dissolved crude oil hydrocarbons in synthetic produced water at air bubbles. The water soluble components of the crude oils were partitioned into aqueous phases by mixing 50% crude oil and 50% simulated brine solutions. Brines with different ionic compositions have been used for produced water preparation to determine how the ionic composition of water influenced the partitioning of crude oil components into the aqueous phases, and subsequently the affinity of these components for air-water interfaces. In order to obtain better understanding of the type of crude oil components that partition into the water phase, interfacially active acidic and basic compounds from crude oils have been selectively extracted and synthetic produced water was prepared from these fractions and analyzed.

Furthermore, the correlations between crude oils properties and concentration and surface affinity of the dissolved hydrocarbons present in produced water have been investigated using multivariate data analysis. Finally, the interactions between crude oil droplets and air bubbles have been studied by looking at the stability of the thin aqueous film between droplet and bubble and subsequent spreading of the crude oil droplet over air bubble.