The viscosity of drilling mud will change with a change in the shear rate because in some degree drilling fluids are shear-thinning. Because of its nature of drilling mud, people create the new term of viscosity called “**Effective Viscosity**” to compensate the change in shear rate of viscosity. By definition, the effective viscosity means the viscosity of Newtonian fluid that gives the same shear stress at the same shear rate.

**The following equation is the effective viscosity equation.**

** **

Where

µea = effective viscosity in the annulus, centi-poise

Ka = consistency factor in the annulus, poise

Dh = hole diameter, inch

Do = Outside diameter of pipe, inch

na = power law constant of drilling mud in the annulus

Va = annular velocity in the annulus, ft/sec

**Please see the following example for more understanding.**

Ka = 6.63 poise

Dh = 8.5 inch

Do = 5 inch

na = 0.514

Va = 7 ft/sec

µea = 42.53 centi-poise

**Reference: Drilling Hydraulic Books**

what is consistency factor in the annulus ? how to calculate it?

thanks

You should get from the mud report.