Frictional resistance for a fluid to flow. There are two models of this parameter that are commonly used. They are (1) the Newtonian model where resistance is proportional to flow rate and (2) Bingham Plastic where flow resistance is linear after an initial shear is exceeded. This model is almost universally used to characterize drilling fluid. The initial shear associated with zero flow rate assists with the suspension of drill cuttings during trips.
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