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.
Mf stands for the methyl orange alkalinity end point of mud filtrate and the definition of the methyl orange alkalinity is the amount acid used to reduce the pH to 4.3. According to the API test, Pm, Pf and Mf are shown in a daily mud report and all the figures are reported in cubic centimeters of 0.02N sulfuric acid per cubic centimeter of drilling fluid sample.
Pf and Mf are based on the mud filtrate tests that will help people know about ions in the drilling mud.
There are three cases regarding Pf and Mf.
First case: Pf and Mf are similar in value to each other. It indicates that the ions (hydroxyl ions) are the main contributor to the mud alkalinity.
Second case: If Pf is low but the Mf is high, it indicates that bicarbonate ions are in the mud.
Third case: if both figures (Pf and Mf) are high, it means that carbonate ions are in the mud system.