1. n. [Drilling Fluids]

An additive for oil- and synthetic-base muds that provides high viscosity at low shear rates, which is useful when drilling high-angle and horizontal wells and can be critical for cuttings carrying and to prevent sag and settling of weighting material. Products used include dimeric and trimeric fatty acids, imidazolines, amides and synthetic polymers.

Alternate Form: rheology modifier