It is widely known that the drilling fluid´s primary function is to keep well control and prevent an influx of formation fluid to the well causing a blowout. The mud also prevents loss to the formation by keeping the hydrostatical pressure. Not a big issue in the top sections of the well. As we approach the reservoir, however, the consequences of a loss to the formation is critical. The permeability is reduced, and the danger of emulsion is lurking in the dark.
We may call them the three defenders of the wellbore: The mud, the casing and the BOP. They all play a vital part in every project. Each one covering up for the other and helping you keeping well control and prevent blow-out.