1. n. [Drilling Fluids]

A group of mud additives specifically designed to lower the volume of filtrate that passes through a filter medium. Specific materials are available for all types of water- and oil-base mud systems and are evaluated in static filtration tests or in various dynamic filtration tests.

See: dynamic filter press,  dynamic filtration,  filter medium,  filtrate volume,  fluid-loss control,  high-pressure, high-temperature filtration test,  low-pressure, low-temperature filtration test,  oil-base mud,  static filtration,  water-based drilling fluid

2. n. [Well Completions]

A chemical additive used to control the loss of fluid to the formation through filtration. In cementing operations, loss of the aqueous phase can severely affect the performance of the slurry and set cement. In almost any operation, loss of fluid to the reservoir formation carries a high risk of permeability damage.