Bentonite mud is a mixture of bentonite with water.[1]​.

Bentonite is a type of montmorillonite clay with a very high liquid limit. This means that even though a lot of water is added, the mixture does not lose stability or consistency.

Bentonite sludge has a very important property that makes it very useful in construction: when a bentonite sludge is mixed without water variation, it loses resistance (cohesion between solid particles) and behaves like a fluid. However, in a short time, it regains this cohesive resistance once it comes to rest. This property is called thixotropy.

Drilling mud is an aqueous suspension of a special clay: bentonite, this mud is placed on the walls of the ground during excavation and serves to prevent or reduce land collapses. It is necessary to control some characteristics of the mud during its use. Such as: density, viscosity and sand content, since the mud is loaded with sand particles from the ground.

In geotechnical engineering, drilling fluid, also called drilling mud, is used to help drill wells into the ground. Often used during drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler drilling such as water wells. One of the functions of drilling mud is to remove the pieces of soil that the drill bit has cut out of the well.

The three main categories of drilling fluids are: water-based muds (WB), which can be dispersed and non-dispersed; non-aqueous sludge, generally called oil-based sludge (OB); and gaseous drilling fluid, in which a wide range of gases can be used. Along with their formatives, these are used along with appropriate polymer and clay additives to drill various oil and gas formations.[2]​.

The primary functions of drilling fluids include providing hydrostatic pressure to prevent formation fluids from entering the wellbore, keeping the bit cool and clean while drilling, making drilling cuts, and suspending drilling cuts while drilling is paused and when the drilling assembly is entered and exited the hole. The drilling fluid used for a particular job is selected to prevent formation damage and limit corrosion.