Abstract: Viscosity reduction and cold production of heavy oil is the main method for offshore oilfield development. In order to deeply understand the viscosity reduction mechanism and application effect of heavy oil activator in heavy oil reservoirs with crude oil viscosity ranging from 150 mPa·s to 1 000 mPa·s, by means of indoor physical simulation experiment and dissipative particle dynamics simulation technology, the viscosity reduction mechanism and displacement effect of the activator on heavy oil was studied. The results show that the heavy oil activator can increase the viscosity of the water phase, reduce the oil-water interfacial tension, and can effectively reduce the viscosity of the conventional flowable heavy oil. The research results on the molecular scale show that the molecule of heavy oil activator has a significant inhibitory-dispersing effect on asphaltene aggregates. The active groups in the activator molecule can increase the interlayer spacing and chain spacing of the aromatic hydrocarbon in asphaltene, reduce the asphaltene aggregation height and layers, weaken the interaction among asphaltenes, destroy the aggregation structure of the heavy components in heavy oil, and disperse the heavy oil, thereby enhancing the fluidity of crude oil. Whether in indoor core displacement experiments or in field applications, the synergistic effects of multiple mechanisms of heavy oil activators can achieve good water decrease and oil enhancement effects. From the molecular level, the study clarified the viscosity reduction mechanism of heavy oil activator, which can provide a theoretical guidance for the field application of heavy oil activator.

Key words: heavy oil activator, viscosity reduction mechanism, disassembled viscosity reduction, asphaltene aggregate, molecular simulation, oil recovery enhancement