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Mud Hydraulics Fundamentals 25

Bingham Plastic Fluids
The plastic viscosity (PV) of Bingham plastic fluids can be calculated
using the following formula:
μ = 300 ðθ N 2 − θ N 1 Þ (2.6)
p
N 2 − N 1
where

= dial reading of Fann VG meter at rotary speed N 1
θ N 1
= dial reading of Fann VG meter at rotary speed N 2
θ N 2
If the rotary speeds of the Fann VG meter are chosen to be N 1 =300
rpm and N 2 = 600 rpm, Eq. (2.6) degenerates to μ p = θ 600 − θ 300 ,
where θ 600 and θ 300 are the dial readings of the Fann VG meter at the
rotary speeds of 600 rpm and 300 rpm, respectively.
The yield point (YP) of Bingham plastic fluids can be calculated using
the following formula:

− μ N 1 (2.7)
τ y = θ N 1 p
300
If the rotary speed of the Fann VG meter is chosen to be N 1 = 300 rpm,
this equation degenerates to τ y = θ 300 − μ p .

Power Law Fluids
The flow behavior index of Power Law fluids can be calculated using the
following formula:

θ N 2
log
n = θ N 1 (2.8)
N 2
log
N 1
If the rotary speeds of the Fann VG meter are chosen to be N 1 = 300 rpm
and N 2 = 600 rpm, Eq. (2.8) degenerates to

θ 600
n = 3:322 log (2.9)
θ 300
The consistency index of Power Law fluids can be calculated using
the following formula:
K = 510 θ N n (2.10)
ð1:703NÞ