Highly Efficient Dehydration and Desalting of Crude Oil from Mature Fields in the Middle East

Abstract

Mature crude oil fields are often prone to high water cuts and high content of fines. The large population of small water droplets and fines forms very stable crude oil emulsions that are difficult to break using conventional treaters. The high water cut creates a high-viscosity crude oil emulsion, often leading to a need for higher operating temperatures, high demulsifier dosage, and frequent production upsets. The high water cut also causes arcing between electrodes. Typically, older crude oil dehydration and desalting treaters use AC-type electrostatic technology, which is less effective in treating crude oils with high water cuts. The use of AC/DC-type electrostatic technology provides a two-pronged approach—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 electrodes, 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. Recent upgrading of a large number of older electrostatic treaters and desalters in the Middle East provided the operators with several benefits in the form of higher production, ability to operate the facility at a lower temperature, lower wash water consumption, and improved overall performance. This paper describes a new enhanced electrostatic dehydration technology that provides improved efficiency in treating high-water-cut crude oil emulsions in mature fields and efficient test methods to optimize use of production chemicals and selection of electrostatic technologies. Several case studies from the Middle East are included.