Characterization of solid particle suspensions with organic coatings in oilfield produced water
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Produced water is water trapped in underground formations 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 (included hydrocarbons), residual concentration of chemical additives from the production line, heavy metals, dissolved minerals and suspended solids. In the year 2006, 173 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, and because the use of chemicals is greater in fields with seabed completions. Although removal of pollutants from produced water is possible with existing technology, the applicability, effectiveness and costs of these technologies are not acceptable for the industry. It is necessary to develop more suitable and cost effective solutions tailored for both the treatment process on offshore installations and site specific conditions with respect to produced water quality. The technologies for enhanced removal of dispersed oil and selected dissolved/soluble compounds were studied within the TOP Water project. This thesis presents studies of dispersed solid particles in the waste water systems prior to treatment. In order to achieve the desired treatment efficiency it is necessary to have a basic understanding of the stabilisation/destabilisation mechanisms of dispersed constituents present in waste water. The findings which have been summarized in this thesis include adsorption of surface active crude oil components – asphaltenes on the planar model solid surfaces as well as model inorganic particles, and particle suspension studies of pure and asphaltene coated particles. The adsorption study was done on asphaltenes of different origin and solids with different surface properties in order to mimic the history of particles from the reservoir to the sea. This gave better understanding of interactions upon asphaltenes adsorption in the broader context. The adsorption of asphaltenes altered the particle surface properties and therefore the particles were characterized (e.g. wettability) before and after adsorption. Later, stabilities of the pure and asphaltene coated particle suspensions were determined, and the effect of different variables (coating, concentration, temperature) on the suspension stability was investigated. It was also found, for example, that coating can have different effect on the suspension stability. The study continued with investigations of binary and ternary model particle mixtures since the produced water usually contains a blend of particles. The relationship between suspension consisting of a single particle type and suspension with binary and ternary particle mixtures was provided. Finally, the real produced water samples were obtained and the results were compared to the model systems.