There are many different types of specialty chemicals used in the oil industry, each with its own specific function. Some of the most common types of oil specialty chemicals include:

1. Drilling fluids: These are used to lubricate drill bits and transport drill cuttings to the surface during the drilling process. Drilling fluids can also help to stabilize the wellbore and prevent damage to the formation.
2. Corrosion inhibitors: These are used to protect metal pipes and equipment from corrosion caused by exposure to water, salt, or other corrosive substances.
3. Scale inhibitors: These are used to prevent the buildup of mineral deposits (such as calcium carbonate or barium sulfate) in pipes and equipment.
4. Demulsifiers: These are used to break down emulsions (mixtures of oil and water) that can form during the production and processing of crude oil.
5. Surfactants: These are used to reduce the surface tension between oil and water, allowing them to be more easily separated during processing.
6. Friction reducers: These are used to reduce the friction between fluids and the walls of pipes, allowing for more efficient transport of fluids through the pipeline.
7. Asphaltene inhibitors: These are used to prevent the buildup of asphaltenes (complex organic molecules found in crude oil) that can clog pipes and equipment.
8. H2S scavengers: These are used to remove hydrogen sulfide (a toxic gas that can be released during the production and processing of crude oil) from oil and gas streams.
9. In the oil and gas industry, biocides are used to control the growth of microorganisms in drilling fluids, pipelines, and storage tanks. Microorganisms can cause a range of problems in oil and gas operations, including corrosion, fouling, and reduced production rates. Biocides can help to prevent these problems by killing or inhibiting the growth of microorganisms.

Biocides used in the oil and gas industry include a wide range of chemicals, such as chlorine, formaldehyde, glutaraldehyde, and quaternary ammonium compounds. The choice of biocide will depend on a variety of factors, including the type of microorganisms present, the severity of the problem, and the specific application.

These are just a few examples of the many different types of specialty chemicals used in the oil industry. The specific types of chemicals used will depend on the particular application and the properties of the crude oil or natural gas being produced or processed.