Produced water

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Produced water is a term used in the oil industry to describe water that is produced along with the oil and gas. Oil and gas reservoirs have a natural water layer (formation water) that lies under the hydrocarbons. Oil reservoirs frequently contain large volumes of water, while gas reservoirs tend to have smaller quantities. To achieve maximum oil recovery additional water is often injected into the reservoirs to help force the oil to the surface. Both the formation water and the injected water are eventually produced along with the oil and therefore as the field becomes depleted the produced water content of the oil increases.

Most offshore oil platforms produce large quantities of produced water and this can have significant environmental effects if not handled properly. The produced water is separated from the main oil stream using separators and coalescers. The separated produced water will contain significant amounts of oil and solids and secondary treatment is usually applied using de-oiling/de-sanding hydrocyclones. Occasionally tertiary treatment is also applied using filters and/or gas flotation to further reduce the oil and sand content. The treated produced water is either discharged into the sea or injected back into the wells. [1]

Discharges into the sea are controlled by legislation. Under the terms of an international convention the target for discharges from offshore oil installations is 40ppm oil-in-water. The commission stated that it was important that all new platforms be equipped with the best practicable means for separating oil from discharged water and reducing the average oil content of a discharge to within the range of 30 to 50ppm. The 40ppm figure is therefore a mean to be aimed at, not a maximum to be complied with.

In the UK oil platform operators must analyse the oil-in-water concentration twice a day and report the results to the regulatory authorities. Up to 3% of the measurements can be above the 40ppm, but all must be below 100ppm. Anything above 100ppm must be reported as an oil spill.[2]

[edit] References

  1. ^ http://www.alderleygroup.com/products%20and%20services/Produced%20Water%20Treatment.asp | Separation Equipment Vendor
  2. ^ http://www.offshore-environment.com/producedwaters.html Offshore Environment