1. vb. [Drilling Fluids]

To add commercial materials to convert water or a water-clay slurry into a mud. Mudding up is usually done after drilling a well to a certain depth with relatively inexpensive spud mud or other native-clay mud, or with water or air. By delaying the use of drilling fluid, operators can save money in the initial stages of drilling a well.

See: mud,  mud additive,  mudding up,  native-solids mud,  spud mud