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. Continue reading

Pm, Pf and Mf of Drilling Mud (Water based mud)

Pm, Pf and Mf are values indicating the alkalinity of drilling mud and the following is meaning of each value.


Pm stands for “phenolphthalein end point of the mud” and it indicates quantities of Potassium Hydroxide (KOH), caustic soda, cement, etc., in the water base mud.  The Pm refers to the amount of acid required to reduce the pH of mud to 8.3. The Pm test includes the effect of both dissolved and non-dissolved bases and salts in drilling fluid.  Especially in lime mud, Pm is used to determine the ratio of insoluble lime to soluble lime in the filtrate.


Pf stands for the phenolphthalein alkalinity of the mud filtrate. Pf is different from the Pm because it tests the affect of only dissolved bases and salts.  However, Pm includes the effect of both dissolved and non-dissolved bases and salts in drilling mud. Continue reading

pH in Drilling Mud (Water Based Mud)

pH is a value representing the hydrogen ion concentration in liquid and it is used to indicate acidity or alkalinity of drilling mud. The pH is presented in a numerical value (0-14), which means an inverse measurement of hydrogen concentration in the fluid.

The pH formula is listed below;

pH = -log10[H]

Where: H is the hydrogen ion concentration in mol.

According to the pH formula, the more hydrogen atoms present, the more acidity of substance is but the pH valve decreases. Generally speaking, a pH of 7 means neutral. Fluids with a pH above 7 are considered as being alkaline. On the other hand, the fluids with pH below 7 are defined as being acidic.

In the drilling mud, there are three main chemical components involved in Alkalinity of drilling fluid, which are bicarbonate ions (HCO3), hydroxyl ions (OH), and carbonate ions (CO3-2). The Alkalinity means ions that will reduce the acidity. Continue reading

Maximum Surface Pressure from Gas Influx in Water Based Mud

When a well is shut in due to well control operation, the casing pressure will increase due to gas migration and gas expansion. In water based mud, you are able to estimate the maximum surface pressure with this following formula.


Max surface pressure in psi.

P is expected formation pressure in psi.

V is pit volume gain in bbl.

KWM is kill weight mud in ppg.

An is an annular capacity in bbl/ft.

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