1. n. [Drilling Fluids]

A permeable material used in a filtration device through which filtrate passes and on which the filter cake is deposited, commonly a specifically designed filter paper or permeable disk used in a static filter press that meets API standards. The filter medium can be the cylindrical, permeable core or disk used in a dynamic filtration test or permeable rock downhole on which a filter cake is deposited in a wellbore.

Synonyms: filter media

See: capillary suction time test,  dynamic filter press,  filter press,  fluid-loss control,  fluid-loss-control material,  high-pressure, high-temperature filtration test,  low-pressure, low-temperature filtration test,  particle-plugging apparatus,  relative filtrate volume,  static filtration,  wastewater cleanup,  water clarification