De-Oiling is the process of separating oil, solids, and water to a desired effluent quality. Depending on the particular process there are different options available and some of these would be based on the differences in density of the oil and water values, temperatures, ppm ranges of the various components, and emulsified levels of the constituents involved.
While oil and water do not mix and so will naturally separate, it can be difficult to actually remove the oil from the water. First of all, the water and oil do not mix because they are very different chemically. The water is polar, which means each molecule has parts with small positive and negative electric charges. Oil is very nonpolar, which is why it doesn't mix well with polar liquids. As well, the density of oil is lower than water, so it naturally rises up, just like a helium balloon rises in air. Differing here are heavy oil applications like SAGD processes where the density of the oil and water are closer together and can be harder to separate than conventional oil production operations with lighter crudes.
Chemical treatment, filtration Medias, and mechanical separation equipment may be used individually or combined to meet a desired target. Besides different chemical treatment, some typical options could be as simple as settling skim tanks, various Media style filters (Normally polypropylene as most absorbent materials, work to separate oil and water because polypropylene is nonpolar like the oil and so prefers to absorb the oil layer), hydro-cyclones, centrifuges, IGF (Induced Gas Flotation) and backwashing ORF (Oil Removal Filters) to name a few. Having an up to date water analysis can be helpful to narrow down options for the most effective solution for the particular process.
Large volumes of reservoir and process water are produced as a by-product of various oil and gas production operations. In order to protect the environment, production operation, and the formation, this water has to be processed. If it is not treated, it cannot be re-cycled (SAGD Facilities), returned directly into the sea (Offshore Production), nor can it be used for re-injection purposes to boost the pressure in the reservoir (Water-Flood Operations). De-oiling water treatment is important to effectively meet effluent requirements for re-use and disposal of by-product water from oil & gas processes. Consult with an experienced filtration specialist to ensure you will achieve your desired outcome.