Lime

Lime is used as a source of calcium and alkalinity in both water- and oil-based drilling fluids. Lime, a widely available commercial chemical, is an economical source of calcium (Ca2+) and hydroxyl ions (OH–).

Drilling fluid applications for lime include increasing pH, providing excess lime as an alkalinity buffer, flocculating bentonite muds, removing soluble carbonate (CO32–) ions, controlling corrosion, and activating fatty-acid, oil-based mud additives.

Lime is used as an economical source of calcium for flocculating bentonite slurries (spud mud) for improved hole cleaning. 

Since it is only slightly soluble in water, it is used to maintain an excess of insoluble Lime in a wide range of both water- and oil-base systems. 

Excess Lime buffers pH; provides a reserve quantity of calcium to precipitate soluble carbonates; and activates fatty-acid, oil-base additives. 

Lime is used for both calcium and pH control in gyp and Lime systems. An alkaline pH which is buffered by excess Lime will prevent acidic conditions from occurring which can lead to accelerated corrosion from acid gases.