Mud is the life fluid of drilling. It is one the main factor to reach the success. Selection of the drill fluid's specifications is a science unto itself. The main components are bentonite and water. Polymers and also some rehabilitative chemicals are used very often.

Drilling mud has 6 main functions:

1 - Transporting drill cuttings to the surface by suspending and carrying them in a slurry that flows in the annulus between the bore wall and the drill/product pipe. Contaminated mud is pumped to recycling system and sieved. Clean mud is re-pumped to the bore hole. The cuttings that stayed on the sieve shows soil conditions drilled through. Drilling fluid is reseted according to cutting samples.

2 - Stabilizing the bore path, especially in loose or soft soils, by building a low-permeability filter cake and exerting a positive hydrostatic pressure against the bore path wall. The filter cake and positive hydrostatic pressure reduce obstruction of the bore path and prevent formation fluids (i.e. groundwater) from flowing into the bore, or drilling fluids from exiting the bore path into the formation (loss of circulation).

3 - Cleaning build-up on drill bits or reamer cutters by directing fluid streams at the cutters.

4 - Cooling the downhole tools and electronic equipment.

5 - Lubricating to reduce the friction between the drill pipe/ product and the bore wall.

 

6 - Providing hydraulic power to downhole mud motors.

7 - Surrounds all sides of the process pipe and behaves as a protective layer. Reduces the stress on the pipe by spreadind the vertical pressure to all surface. It is so important where iterative loadings is subjected like highways or railways.