1. n. [Drilling Fluids]

A test to determine the amount of clay-like materials in a water-base drilling fluid based on the amount of methylene blue dye absorbed by the sample. Results are reported as "MBT" and also as "lbm/bbl, bentonite equivalent" when performed to API specifications.

Synonyms: bentonite equivalent,  MBT test

See related terms: cation exchange capacity,  endpoint,  ion exchange,  kaolinite,  low-yield clay,  titration,  water-based mud