Drilling fluids are mixtures of natural and synthetic chemical compounds used to cool and lubricate the drill bit, clean the hole bottom, carry cuttings to the surface, control formation pressures, and improve the function of the drill string and tools in the hole.

There are five main types of pesticides to formulate. They may be classified according to their solubility properties

Invert emulsion or oil-base, drilling fluids are used in drilling troublesome shale formations, water-sensitive production zones, and highly pressured hot formations. Recently, they have been used for penetration rate advantage as well. Invert emulsion fluids contain special surfactants that permit the formation of the water-in-oil emulsion and maintain its stability. These are called simply "emulsifiers".

When encountering shale during drilling operations, water in the drilling fluid may interact with the clay materials within the formation, causing the shale to swell. This can lead to instability in the wellbore, and dispersion of shale into the drilling fluid (sloughing), eventually leading to hole washout.

The history of corrosion inhibitors and neutralizers and their invention, development, and application in the petroleum industry is documented in the literature. Early corrosion inhibitor applications in each of the various segments of the industry, including oil wells, natural gas plants, refineries, and product pipelines, are reviewed.