Ratio of shear stress to shear rate. NOTE 1 In the SI system, viscosity is expressed in pascal seconds (Pa⋅s). NOTE 2 If the shear stress is expressed in the CGS system (dynes per square centimetre) and the shear rate is expressed in reciprocal seconds, the viscosity is expressed in poise, P. 1 P = 1 dyn·s/cm2 = 1 g⋅cm−1⋅s−1 = 10−1 Pa⋅s.
Source: API RP 13C, Recommended Practice on Drilling Fluids Processing Systems Evaluation, Upstream Segment, Fourth Edition, December 2010. Global Standards
Measure of a fluid’s tendency to resist flow.
Source: IADC UBO / MPD Glossary, December 2011. Global Standards