Abstract: On the basis of analyzing the components and structure of the viscous crude from zone 109-1 in Dagang oilfield, a high effective viscosity reducer was developed for high temperature and high mineral salt reservoir. The mixture of water and viscous crude could form a stable O/W emulsion when using the developed viscosity reducer having water content of more than 30% and with an added dosage of 1000 mg/L (based on the total amount of water and viscous crude). The viscosity reduction rate was more than 97% and no negative effect was observed on the demulsification of produced liquid having viscosity reducer. The results of core flood experiments showed that the oil recovery rate of displacement system containing viscosity reducer increased by 22% as compared with that of water flooding system, which indicated that with the decrease of crude viscosity, the oil-water mobility ratio was improved, the sweep efficiency was increased and the oil recovery was enhanced significantly.

Key words: viscous crude, waterflooding, recovery percent of reserves, viscosity reducer, oil recovery