The presence of water in crude oils is caused by:
- Natural mixing with oils during their migration
- Washing of tubing for scale dissolving
- Injection in secondary recovery operations to maintain pressure
- Leaking from formation above the producing one
- Seawater contamination during marine transportation.
Water causes problems downstream of the production. It increases cost of transportation and corrosion problems in pipelines and vessels. Since water is almost always salted, it may lead to fouling of heat exchanger and corrosion of distillation equipment in refining. Both water and salt content are regulated. Thus, it is economically important to separate brine from crude oil directly at the production site.
Water mixed in the crude oil can be “free” or as an “emulsion”. Free water is separated by simple settling. Emulsions form and stabilize at many areas where there is turbulence such as tubing, pump and valves and require adequate treatment.