Ansys Employee
Run standard SST as turbulence model , use Eulerian Multiphase with oil being the secondary phase. With Eulerian you can choose MultiVOF, leave default diameter for the secondary phase: Use that enable Sharp/dispersed use Compressive for VOF Fraction Discretization. I think first of all as beginner you might need to read documentation and some text book and carry out some tutorials.

If you have less volume loading for oil or water one can think about using other models. But for now a "generalized" approach is best.