Abstract: The properties of Tahe crude oil produced in 2008-2014 were analyzed to investigate the reasons for difficult demulsification. The analysis reveals a inferior trend in crude quality year by year due to increased asphaltene content and the mechanical impurities while decreased mass ratio of resin/asphaltene, which may be the reasons accounting for difficult demulsification of Tahe crude oil. The oil soluble demulsifier RP-04 was developed by mixing polyacrylate polyether, a main agent with alkyl phenolic polyether A, an aid agent. The water soluble demulsifier RP-05 was obtained by compositing the main agent 05-M with aid agent R30 which has the effect that makes the iron particles wetting. The RP-04 and RP-05 were used jointly in a 3.5 Mt/a desalting unit of a refinery. The results show that in the steady operation conditions of high water injection rate and high mixing intensity, the salt content of treated oil decreases from 10.5 mgNaCl/L to 5-6 mgNaCl/L without desalting current jump.

Key words: Tahe heavy crude oil, demulsification, desalting, mechanic impurities, commercial test