Abstract: Viscous water-in-oi1 crude of Xintan in Shengli Oilfield has high viscosity , poor flowability , high consumption of energy when gathering and transportation at normal temperature. Some measures have to be taken to reduce its viscosity; otherwise its gathering and transportation are difficult. Therefore a kind of
phase inversion and viscosity reduction agent VRKD18 for the crude has been developed on the basis of viscosity reduction effect and stability after some chemicals are added. VRKD18 is composed of two kinds of nonionic surfactant and can reduce apparent viscosity from 7 000-11 000 mPa·s to below 100
mPa·s at 50`C and51s^-1.The phase inversion process, mi-crostructure and granule diameter distribution of dispersed liquid droplets for the crude with VRKD18 agent have been analyzed by means of an image analysis method, and then their viscosity reduction mechanism has been discussed. Results show that the viscous oil can reverse its phase spontaneously. The reason of
viscosity reduction is that VRKD18 has changed its outer and in-ner phase structures，the size and mode of the droplet interac-lion, which provides a basis for the renovation of their gathering and transportation technics.

Key words: viscous oil, water-in-oil crude, phase inver-sion, viscosity reduction microanalysis