What Does Cation Exchange Capacity (CEC) Mean?
Cation exchange capacity (CEC) is a clay mineral's ability to absorb positively charged ions (cations) on its negatively charged surface so that they are easily exchangeable for other cations in an aqueous solution. It's expressed in million equivalent (meq) per 100 gm. Methylene blue capacity (MBC) test is done to determine CEC of solids in a water based drilling mud and only the reactive portions of the clay are used for the test.
MBC gives an indication of the concentration of reactive clays present in a drilling fluid.
Trenchlesspedia Explains Cation Exchange Capacity (CEC)
The MBC test to determine the CEC of drilling fluids is carried out by adding methylene blue dye to the mud sample till all reactive portions have adsorbed the dye. For mud systems based on bentonite, MBC gives an indication of the amount of reactive clay present in the drilling mud solids.
For water based mud systems, MBT indicates the reactivity of the drilled solids. Drilling muds may contain other materials that also adsorb the dye and the mud can be treated with hydrogen peroxide to neutralize the effect of organic materials present in the clay.
The presence of barites and carbonates do not affect the test results because they do not adsorb the methylene blue.