There is no advantage with foam in drilling fluid. When drilling fluid is foaming, it's not cooling or lubricating.

sometimes when we are drilling we need to use drilling fluid which are mixture of two phase like oil and gas or water and oil. In such case the fluid which is running outside is known as continuous phase of drilling fluid.

Yes, it is. Drilling fluids, the circulating fluid for drilling operations, is a mixture of the fluid, the solid and chemical agents. It is usually known as the "mud" or the "blood of drilling" deriving from its distinctive significance.

lubricant

It's used to prevent anything coming back up the hole.

Drilling fluids, the circulating fluid for drilling operations, is a mixture of the fluid, the solid and chemical agents. It is usually known as the "mud" or the "blood of drilling" deriving from its distinctive significance.

The main functions of drilling fluids include providing hydrostatic pressure to prevent formation fluids from entering into the well bore, keeping the drill bit cool and clean during drilling, carrying out drill cuttings, and suspending the drill cuttings while drilling is paused and when the drilling assembly is brought in and out of the hole. The drilling fluid used for a particular job is selected to avoid formation damage and to limit corrosion.