Hershel Bulkley Rheology - Audit
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Hershel-Bulkley rheology model, release 2a, issued 3 July 2013.
This worksheet takes Fann viscometer readings at 3, 6, 300rpm and 600 rpm. It outputs values of τ0 (the shear stress at zero shear rate), n and K for the Herschel-Buckley model and plots the consistency curve of Shear Stress against Shear Rate.
For a given shear rate of interest, the shear stress and viscosity are also calculated.
Θ3 dial reading, Pστ5 =
Θ6 dial reading, Pστ10 =
Θ300 dial reading, Pστ511 =
Θ600 dial reading, Pστ1022 =
Shear rate of interest, Γi sec-1 =
(You can enter a shear rate of interest to calculate the shear stress and viscosity)
Shear stress at zero shear rate;
Calculate n and K. Note that the Herschel-Bulkley value for K is not represented by K as a variable name here. This conflicts with the Drillers.com Standard Variable Names standard, also the variable name K is a standard Mathcad variable, used for chemical concentration. The variable P_K is used instead as the units for K are the same as the units for stress, psi or kgf/m2. K is also called the Consistency Index and equals the shear stress at a shear rate of 1 sec-1.
Shear stress at sec-1 =
Viscosity η at
If n = 1, the fluid is Newtonian.
If n > 1, the fluid is Dilatent.
If n < 1, the fluid is non-Newtonian (most muds).
Shear stress Pστ = KΓn
Plot shear stress (Pστ) vs shear rate (Γ)
Click here when any values are modified to update the result.
Version 1 of this worksheet was released on 7 October 2008 by Steve Devereux.
Version 2 refined the results, added units, added a calculation for shear stress and viscosity at a shear rate of interest. 2a added some further small refinements. This was released on 3 July 2013 by Steve Devereux.
Formulae from the Dowell Fluids Handbook.