2. What was mud used for in the oil drilling rig?

Drilling mud. Drilling mud, also called drilling fluid, in petroleum engineering, a heavy, viscous fluid mixture that is used in oil and gas drilling operations to carry rock cuttings to the surface and also to lubricate and cool the drill bit.

In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth.

Explanation:

Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells.