1. n. [Drilling Fluids]

Quantity of positively charged ions (cations) that a clay mineral (or similar material) can accommodate on its negative charged surface, expressed as milliequivalents per 100 grams. CEC of solids in drilling muds is measured on a whole mud sample by a methylene blue capacity (MBC) test, which is typically performed to specifications established by API. CEC for a mud sample is reported as MBC, methylene blue test (MBT), or bentonite equivalent, lbm/bbl or kg/m3.

Synonyms: base exchange

Alternate Form: cation exchange capacity