MBT

The methylene blue capacity of a drilling fluid is an indication of the amount of reactive clays (bentonite or drilled solids) present as determined by the methylene blue test (MBT). The methylene blue capacity gives an estimate of the total cation exchange capacity (CEC) of the solids in the drilling fluid. The methylene blue capacity and the cation exchange capacity are not necessarily equivalent, with the methylene blue capacity normally being somewhat less than the actual cation exchange capacity. ethylene blue solution is added to a sample of drilling fluid which has been treated with hydrogen peroxide and acidified until saturation is noted by the formation of a “dye halo” around a drop of solids placed on filter paper. Drilling fluids frequently contain substances in addition to reactive clays that also absorb methylene blue dye. Pretreatment with hydrogen peroxide removes these effects from organic materials such as lignosulfonates, lignites, cellulosic polymers and polyacrylates, etc. HADI: you want to know if you are drilling the active shales or not. you normally do this test 2-3 times during the day.