Caustic soda | SLB

Caustic soda

Used in water-based muds as a source of hydroxyl ions to control pH

Schlumberger Oilfield Services

Caustic soda, caustic, alkali, and lye are all common names for sodium hydroxide (NaOH). It is a strong base that is extremely soluble in water and dissociates into sodium and hydroxyl ions in solution.

Caustic soda is used to maintain or increase pH. Increasing pH with caustic soda precipitates magnesium (Mg2+) and suppresses calcium (Ca2+) in high-hardness waters such as seawater, reduces corrosion, and neutralizes acid gases such as carbon dioxide (CO2) and hydrogen sulfide (H2S).

Typical concentrations range from 0.25 to 4 lbm/bbl [0.7 to 11.4 kg/m3] with treatments depending on water chemistry and type of drilling fluid. In seawater and waters containing buffering salts, a higher concentration of caustic soda is required. Gulf of Mexico seawater requires 1.5 to 2 lbm/bbl [4.3 to 5.7 kg/m3] to precipitate all magnesium then convert the calcium to lime.

When treating muds with lignosulfonate or lignite, which have low pH (±4), typical usage is one sack of caustic soda for every four sacks of lignosulfonate or lignite product.


  • Widely available and an economic source of hydroxyl ions to control pH
  • Concentrated chemical and very effective at small treatment levels
  • Increases pH which reduces corrosion of steel exposed to drilling fluids
  • Can be used in most drilling fluids
Typical Physical Properties
Physical appearance White beads, pellets, flakes or crystals
Specific gravity 2.13
pH (1% solution) 13
Solubility at 86 degF [30 degC] 119 g/100 mL water


In high-hardness brines such as CaCl2, Williston, Michigan, and Zechstein brines, caustic soda cannot be used to effectively raise the pH due to the high level of cations, which combine with hydroxyl ions to precipitate hydroxides such as Ca(OH)2 and Mg(OH)2.

Toxicity and handling

Bioassay information is available upon request. Handle as an industrial chemical, wearing protective equipment and observing the precautions described in the safety data sheet (SDS).

Avoid exposure and handle only when fully protected. Care should be taken when mixing. Caustic soda should be added slowly to the mud system through a properly designed chemical barrel. Do not mix caustic soda with other chemicals or through the mud hopper. When using the chemical barrel, fill to the desired level with water, then add dry caustic soda.

Packaging and storage

Caustic soda is packaged in 50-lbm [22.7-kg], multiwall paper sacks with plastic liners. Other packaging includes fiberboard or steel drums of various sizes as well as other sack sizes. Store at room temperature in a dry, well-ventilated area. Keep in original container. Keep container closed. Keep away from heat, sparks, and flames. Store away from incompatibles.