Hydrated Lime or calcium hydroxide is a source of Ca and OH and is used to raise the pH. In clear water drilling, Hydrated Lime is added to the sump water to increase the pH and to provide calcium ions. In a Gyp-based mud system, Hydrated Lime is added at a concentration of 1.0 kg/m³, and then used as needed to maintain a pH of 10.0-11.0 in the drilling fluid.
Hydrated Lime is used as a means of adjusting the alkalinity when bicarbonate/carbonate contamination exists. It is used to maintain the alkalinity of oil-based drilling fluids where it enhances the performance of emulsifiers and offers a degree of corrosion protection.