NOTICE: Our Mathcad database got attacked and infected with a virus. Unfortunately, we've had to shut it down until further notice.
You can safely browse the pages, as the Mathcad server was separate to this main website, and was only accessible here. (We used something called an iFrame, which is like a window into a different website).
UPDATE 28th of January 2020: the virus happened just over a week ago. We've temporarily cut and pasted the text parts of the Mathcad pages rather than having blank pages there.
UPDATE 3rd of February 2020: We've been unable to recover the Mathcad worksheets and offer them in a format that provided total security to users. They were published a decade ago, and our IT people say that they would need a complete re-creation with the latest code and security fixes.
APPEAL: These 44 pages were created, and offered as a free resource for over a decade. We know from our website analytics that more than 1000 users visited each month. If only half of these regular visitors donated $20, we would have enough to create an even better solution. As you know, time is money, have these Mathcad pages saved you $20 in time over the years? We expect that they have, not to mention the learning opportunities provided to new engineers entering the industry.
Please, donate at least $20 as a one-off payment, to bring back the drillers Mathcad back as an always free to use resource!
NO! I can't or won't donate to the restoration fund. I'm happy to spend a few minutes to offer a testimonial to help encourage the effort. These worksheets do have value. Offer Feedback.
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.