**1. Introduction**

By the end of December 2017, China's offshore oil production accounted for 22.3% of the national oil production [1–4]. The average offshore field water cut of oil fields was 86.6%, with relatively low oil recovery rate, only 21.1%. Bohai oil field is the largest offshore oil field in China. In 2010, its oil and gas output reached 30 million square meters, accounting for about 15% of the national total, which played an important role in stabilizing the energy supply in eastern China. Heavy oil accounts for 85% of the oil reserves in Bohai oil field, and the main development bottlenecks of these heavy oil fields are high crude oil viscosity, strong reservoir heterogeneity, and poor water drive efficiency. In particular, the viscosity of underground crude oil in some heavy oil reservoirs reaches 200–700 mPa s, and their recovery factor from traditional water flooding could only reach about 12% [5–9]. It could be seen that the research and application of enhanced oil recovery technology in offshore heavy oil reservoirs are of great significance for the stable production and economic efficient development of Bohai oil field.
