Displacement flow and mixing of fluids occur in many operations present in the construction and completion of oil & gas wells e.g. primary cementing, drilling, gravel-packing, hydraulic fracturing. Over the past many years oil prices have increased significantly as a result of a diminishing supply of oil and gas from easily accessible reservoirs coupled with an increased demand due to population and consumption growth. Inevitably, there is a tendency towards deeper wells offshore and towards more challenging wells onshore. Many oil and gas wells required are long and are inclined anywhere...