Formation fluid refers to the naturally occurring liquids and gases contained in geologic formations.Schlumberger Oilfield Glossary - Formation fluid
/ref> Fluids introduced during the drilling process are called

drilling fluid In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also us ...

s.Schlumberger Oilfield Glossary - Drilling fluid
/ref> Fluids in an oil or gas reservoir are called reservoir fluids. The fluids flowing from the

wellhead A wellhead is the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment. The primary purpose of a wellhead is to provide the suspension point and ...

of an oil or gas well are called

production fluid Production fluid is the fluid mixture of oil, gas and water in formation fluid that flows to the surface of an oil well from a reservoir. Its consistency and composition varies. Fluids may be described by a multitude of characteristics including ...

References

Oilfield terminology {{geology-stub