Page 173 - Shale Shakers Drilling Fluid Systems

156 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

FIGURE 7-5. Vessel with small sedimentation height.

where V t = Terminal or settling velocity
2
a = Bowl acceleration, in./sec =
0.0054812 x bowl diameter x rpm 2
D = Particle diameter, micron
p s = Solid (particle) density, grams/cm 3
pj = Liquid density, grams/cm 3
(i = Liquid viscosity, centipoise
2
(dyne-sec/100 cm )
Stokes' Law shows that as fluid viscosity and den-
sity increases, the settling rate decreases.
It is impossible to separate a drilled solid par-
ticle of equivalent mass by settling.

where d ds = Diameter of drilled solids particle
d b = Diameter of barite particle
p ds = Density of drilled solids particle
p b = Density of barite
p = Density of liquid

Assuming barite has a specific gravity of 4.25
and drilled solids 2.65, the equivalent diameter
ratio for settling in a 14-pound per gallon mud
(specific gravity = 1.68) is:

or

In a drilling fluid weighing 14 ppg, a 50-micron
barite particle will settle at the same rate as an
81-micron drilled solid particle. All solids, includ-
ing low-gravity and barite particles 2 microns and
smaller (colloidal), can have a detrimental effect
on drilling fluid viscosity. That is, a low, specific-
gravity particle that has an equivalent spherical
diameter that is 1.6 times that of a barite particle,
will settle at the same rate as the barite particle. The
low-gravity solid will have the same mass as the FIGURE 7-6. A simple centrifuge.