Total Hardness and Chloride Content in Water Based Mud

“Total Hardness” or “Water Hardness” is a measurement of calcium (Ca2+) and magnesium (Mg 2+) ions in water base mud. The total of both soluble ions of calcium (Ca2+) and magnesium (Mg 2+) is given by titration with standard Vesenate solution.


What will be happening if you have a lot of total hardness in your drilling mud?

  • Bad mud cake (thick and mushy)
  • High fluid loss
  • Flocculation of clay content
  • Less polymer effectiveness
  • Ineffective chemical treatment

For most of the water base mud, the acceptable value of total hardness must be below 300 mg/L. If the lime drilling mud is used, it is acceptable to have a higher valu,e but is should be kept below 400 mg/L.

Chloride Content in the water based mud

Thechloridecomesfromsaltintheformation,andchloride concentrationcan be determinedbytitrationwithasilvernitratesolution.Theamountofchloridemustbecheckedfrequently.Ifthere are any abnormal changesinthechloridecontent,itcanbe an indicationofdrillingintoasaltformationortakingwaterinfluxfromthereservoirs.

Why is it so important to maintain the amount of chloride in the drilling fluids?


How can the chloride content be maintained?

The chloride content in the drilling fluid can be maintained by adding salts such as potassium chloride (KCl) and sodium chloride (NaCl). If  potassium chloride (KCl) is used, it is imperative to have sufficient potassium ions to react with the clay content from the formation. Generally, 3 – 4% KCL is recommended for normal drilling. However, it may require increasing the concentration of KCl if you are drilling into formations which have a lot of reactive clay content.

Methylene Blue Test (MBT)

Methylene Blue Test (MBT) or Cation Exchange Capacity is used to determine the amount of reactive clay (clay-like materials) in a water base mud. A methylene blue dye (a cation dye) is utilized for this test because it powerfully magnetizes the negative ions in the clay. Typically, the test is reported in terms of the reactive clay concentration in pounds per barrel, bentonite equivalent.

Same as other mud properties, tracking the MBT and observed for trend changes are required in order to maintain good mud conditions. If an increase in MBT is observed, it indicates that the drill solid concentration in the drilling mud increases. For a good drilling operation, the MBT should be kept at 15 lb/barrel or less.


Andy Philips, 2012. So You Want to be a Mud Engineer: An Introduction to Drilling Fluids Technology. Edition. CreateSpace Independent Publishing Platform.

Ryen Caenn, 2011. Composition and Properties of Drilling and Completion Fluids, Sixth Edition. 6 Edition. Gulf Professional Publishing.

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