Abstract: The operating characteristic of down dual-stage tandem oil-water separator is essential for the condition diagnosis and adjustment of downhole oil-water separation system. Based on algebraic slip mixture model(ASMM) and large eddy simulation(LES), related parameters and boundary conditions are set according to T228 well status to research the split and separation characteristics of down dual-stage tandem oil-water separator. And the numerical simulation results compared with the ground text results. The results show that：When the inlet flow rate is between 80 m3•d–1 and 200 m3•d–1, the range of total split ratio become larger and larger, and the variation relationship between the ratio of the first and second hydrocyclones’ overflow and the total split ratio is deterministic function, and the oil mass fraction of underflow decreases firstly and then increases with the increasing total split ratio; under the rated condition, the first hydrocyclone separates most of the oil and the second one plays a key role in further reducing the oil mass fraction of underflow; when the combinations of inlet flow rate and total split ratio are (120-140 m3•d–1/0.36-0.74), (140-160 m3•d–1/0.31-0.77) or (160-180 m3•d–1/0.33-0.76), the oil mass fraction of underflow is not more than 0.02%; the split characteristic predicted by numerical simulation is consistent with ground text result, while the relationship between the total split ratio and the oil mass fraction of underflow predicted by it is qualitatively consistent with ground text result. The reasonable ranges of inlet flow rate and total split ratio for the adjustment of downhole operating conditions are given through the comprehensive analysis of split and separation characteristics. It will provide guidance for field text.

Key words: oil-water hydrocyclone;numerical simulation;split characteristic;separation characteristic;multiphase flow