1. . 
A mud in which the suspended solids are dispersed clays, sand, chert and other rock that originated from formations being drilled. A spud mud is commonly a type of native-solids mud. Native muds can be economically diluted with water and passed through banks of desilters and desanders to keep solids down. No expensive weighting materials are being discarded and replaced in such a process. At the depth that higher density is required, native mud is usually totally or partially discarded and new mud is made using commercially prepared mud additives and barite.
Alternate Form: unweighted mud