Downhole oil/water separation methods are based on hydrocyclone technique. Most of the related investigations have a focus on the flow structure inside the cyclone. There is a lack of studies and simulations on the wellbore flow pre-And post-separation. The current computational simulation of the oil/water flowing inside wellbore before and after separation by counter current hydrocyclone. The emulsion of oil/water in the well production and dumping zones in the downhole, was simulated using ANSYS-Fluent 14 software and it was attempted to visualize the volume fraction profiles, density distribution profiles and the flow patterns in a real downhole environment. The well geometries and the oil/water production candidates at the downhole have been adopted from a real well in an offshore field in Malaysia. The results illustrated the great complexity of oil/water flows, reflecting the many competing processes; e.g.Turbulence, gravitational separation, droplets interaction and the shear between the two liquids and with the solid surfaces. The simulation results in the production zone indicate that distribution of the oil volume fraction depends highly on the mean oil volume fraction. The contour results showed that the phases mix and achieve uniform distribution as the flow proceeds down the annulus. The achieved simulation results will contribute to better forecasting of the behaviour of oil/water mixture inside the wellbores with the presence of a hydrocyclone with one or multi inlets. © 2017 WIT Press.