The MBT is a rather crude chromatographic measure of the active clay content in water based muds. The MBT value must be controlled below the maximum value specified in the drilling fluids programme.
When the MBT approaches the pre-defined maximum, mud must be treated.
Mud condition, in terms of rheology and fluid loss, can deteriorate above this value.
Reporting
MBT shall be reported as ppb Bentonite to an accuracy of +/- 10.
Sources of Error
The test is very subjective since, in practice, it can be very difficult to see the blue ring forming around the sample spot.
Methylene Blue and Hydrogen Peroxide solutions must be renewed every 4 - 6 weeks.