Many substances, both reactive and inert, are added to drilling fluids to perform specialized functions. The most common functions are:
Alkalinity and pH Control
Designed to control the degree of acidity or alkalinity of the drilling fluid.
Most common are lime, caustic soda and bicarbonate of soda.
Bactericides
Used to reduce the bacteria count. Paraformaldehyde, caustic soda, lime and starch preservatives are the most common.
Calcium Reducers
These are used to prevent, reduce and overcome the contamination effects of calcium sulfates (anhydrite and gypsum). The most common are caustic soda, soda ash, bicarbonate of soda and certain polyphosphates.
Corrosion Inhibitors
Used to control the effects of oxygen and hydrogen sulfide corrosion. Hydrated lime and amine salts are often added to check this type of corrosion. Oil-based muds have excellent corrosion inhibition properties.
Defoamers
These are used to reduce the foaming action in salt and saturated saltwater mud systems, by reducing the surface tension.
Emulsifiers
Added to a mud system to create a homogeneous mixture of two liquids (oil and water). The most common are modified lignosulfonates, fatty acids and amine derivatives.
Filtrate Reducers
These are used to reduce the amount of water lost to the formations. The most common are bentonite clays, CMC (sodium carboxymethylcellulose) and pre-gelatinized starch.
Flocculants
These are used to cause the colloidal particles in suspension to form into bunches, causing solids to settle out. The most common are salt, hydrated lime, gypsum and sodium tetraphosphates.
Foaming Agents Most commonly used in air drilling operations. They act as surfactants, to foam in the presence of water.
Lost Circulation Materials
These inert solids are used to plug large openings in the formations, to prevent the loss of whole drilling fluid. Nut plug (nut shells), and mica flakes are commonly used.
Lubricants
These are used to reduce torque at the bit by reducing the coefficient of friction. Certain oils and soaps are commonly used.
Pipe-Freeing Agents
Used as spotting fluids in areas of stuck pipe to reduce friction, increase lubricity and inhibit formation hydration. Commonly used are oils, detergents, surfactants and soaps.
Shale-Control Inhibitors
These are used to control the hydration, caving and disintegration of clay shale formations. Commonly used are gypsum, sodium silicate and calcium lignosulfonates.
Surfactants
These are used to reduce the interfacial tension between contacting surfaces (oil/water, water/solids, water/air, etc.).
Weighting Agents
Used to provide a weighted fluid higher than the fluids specific gravity. Materials are barite, hematite, calcium carbonate and galena.
