Page 167 - Shale Shakers Drilling Fluid Systems

150 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

Generally, a barite particle (specific gravity = (specific gravity = 2.65) in an 11.5 ppg mud with
2
4.25) will settle at the same rate as a drilled sol- PV = 20 cp and YP = 12 lbs/100 ft ?
ids particle (specific gravity = 2.65) that is 1 ^ Using Stokes' Law, the settling velocity is:
times the barite particle's diameter. This may be
verified by applying Stokes' Law.

Example #1. A viscosified seawater fluid with a
specific gravity of 1.1, PV = 2.0 centipoise, and YP For equivalent settling rates, V s = V s. And for ji, =
2
= 12.0 lbs/100 ft , is circulated to clean out a ji 2 (the same fluid, therefore, the same viscosity).
cased wellbore. What size low-gravity solids will
settle out with 5-micron barite particles? With 10-
micron barite particles, what is the settling veloc-
ity in rig tanks?
Using Stokes' Law, the settling velocity is:

For equivalent settling rates, V s = V s. And for |i, =
jj, 2 (the same fluid, therefore, the same viscosity).

Thus, a 10-micron barite particle will settle at the
same rate as a 15-micron low-gravity particle, and
a 50-micron barite particle will settle at the same
rate as a 75-micron low-gravity particle.
Stokes' Law shows that as fluid viscosity and
density increase, separation efficiency decreases.
If the drilling fluid weight is 14.0 pounds per
gallon (specific gravity = 1.68):

Thus, a 5-micron barite particle will settle at the
same rate as a 7-micron low-gravity particle, and
a 10-micron barite particle will settle at the same
rate as a 14-micron low-gravity particle.
Settling velocity for a 5-micron barite (or 7-
micron drilled solid) particle is:
Therefore, in drilling fluid weighing 14 pounds per
gallon, a 10-micron barite particle will settle at the
same rate as a 16-micron drilled solid particle, and
a 50-micron barite particle will settle at the same
rate as an 80-micron (or 81.4) drilled solid particle.
It is important to remember that the efficiency
of a separator is viscosity dependent. The median
and for a 10-micron barite (or 14-micron drilled cut, or D 50 cut point, increases with viscosity as
solid) particle:
shown by Stokes' Law:

Example #3. A 4-inch cone will separate half of
Example #2. What are the equivalent diameters the 12-micron low-gravity (specific gravity = 2.6)
of barite (specific gravity = 4.25) and drilled solids particles in water (that is, the D 50 cut point is 12