Well plugging consists in injecting a fluid, called plug, over another, less dense, fluid. The most common scenario in the oil and gas industry is that with a cement plug injected over drilling fluid with the purpose of sealing off the well permanently or temporarily. The objective of this study is to relate the velocity of the fluids during the inversion process and their differences of density and viscosity by means of numeric simulations done with Ansys Inc. Fluent software and to create a model thats can be easily used in the Industry.