Displacement processes are part of several drilling fluid operations. These operations include non-trivial items like changing from water based drilling fluid to oil based or opposite, casing cleaning operations, change to completion fluids or displacement operations during cementing. Among these operations, cementing is the most important and difficult because the scope is to create a permanent barrier and permanent zonal isolation in operations involving only limited volumes of fluids and slurries.
Empirical guidelines have been implemented to improve displacement processes in wells. Analytical and numerical models are frequently used. The models seem to be efficient in predicting pressure losses. However, they seem to be incapable of accurately predict the displacement efficiency. Laboratory experimental results have been evaluated and have been scaled up to for field application with variable success rate. These difficulties are caused by the presence of too many length scales or other dimensional scales.