||Water coning causes a reduction of oil production and an increase of production costs. Dual completion (downhole water sink) is one of the methods adopted to attenuate water coning. This work describes numerical results associated with this completion technique. The water cone shape and water breakthrough time are investigated to define the mechanism and performance of this technical procedure. The numerical results show that dual completion deforms the shape of the cone. For instance, the top of the wateroil interface is shifted away from the well yielding (under high water production rates) oil breakthrough into water perforations. The water breakthrough is proportional to dimensionless density difference and horizontal permeability and inversely proportional to oil production rate, mobility, and anisotropy ratios. High oil production rates yield elevation of water coning height that intercepts oil flow. Paradoxically, high production rate at water sink is not recommended, the improvement of water breakthrough begins when dimensionless density difference is greater than 0.05. The dual completion technique delays water breakthrough time (BT*). In general, the BT* is delayed by two times that of single completion and critical oil rate is augmented compared to single completion.