1. n. [Drilling Fluids]

A term used to express the results of the methylene blue test, which determines the amount of clay-like materials in a water-based 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.

See: cation exchange capacity,  endpoint,  ion exchange,  kaolinite,  low-yield clay,  methylene blue test,  titration,  water-based mud