Mature crude oil fields often contain higher water cuts and higher content of fines. The combination of a large population of water droplets and fines produces very stable crude oil emulsions that are difficult to break. 

The higher water cuts provide higher crude oil emulsion viscosity because of the larger population of small water droplets, often leading to a need for higher operating temperatures and high demulsifier dosage, and resulting in frequent production upsets. 

Another challenge is arcing between electrodes as a result of the higher water cuts. Typically older crude oil dehydration and desalting treaters use AC type electrostatic technology, which is less effective in treating crude oils with higher water cuts. 

The use of combined AC-DC electrostatic technology provides a two-prong approach, where bulk water is removed in a weaker AC field and the remaining smaller water droplets are removed in a stronger DC field. Further improvements to the AC-DC treaters include use of composite electrode plates, modulated electrostatic fields, and improved fluid distribution inside the treaters. 

AC-DC treaters provide an attractive opportunity for retrofitting existing AC treaters in mature fields and make the treaters more suitable for dehydrating the crude oil emulsions from these fields. 

This paper describes new, enhanced electrostatic dehydration technologies suitable for treating higher-water-cut crudes from mature fields and efficient test methods for optimized usage of production chemicals and selection of electrostatic technologies; case studies are included.