Page 190 - Shale Shakers Drilling Fluid Systems

CHAPTE R TE N
Calculating Drilled
Solids Concentrations
Drilled solids concentration in a slurry (drilling
fluid or discharge from solids control equipment)
may be determined from the following equation:
where p B = Density of high-gravity solids (barite is the equation:
4.2 gm/cc)
p lg = Density of low-gravity solids
V lg = Volume percent of low-gravity solids
p f = Density of filtrate
V s = Volume percent of undissolved solids
MW = Mud weight, ppg
For freshwater drilling fluid, assuming the den-
sity of the drilled solids is 2.6 gm/cc, the density
of the barite is 4.2 gm/cc, and the water density
is 1.0 gm/cc, the equation becomes:
If the retort solids are 13% volume and the mud
weight is 11 ppg, the percent of low-gravity solids
is 6% volume. If the fluid contains 2.5% volume
of bentonite, the drilled solids concentration is
3.5% volume.
In saline water-based drilling fluid, the salt dis-
solved in the water phase increases the filtrate
density and also remains in the retort cup after the
water evaporates from the sample. The density of
the filtrate (p f) may be calculated from the concen-
tration of the salt:
where NaCl = Concentration of NaCl in filtrate,
mg/liter
KCl = Concentration of KCl in filtrate,
mg/liter
CaCl 2 = Concentration of (CaCl 2) in
filtrate, mg/liter
173
Organic = Concentration of organic material
in filtrate, Ib/bbl
To account for the increase in total solids in
a saline drilling fluid, the total volume percent
of suspended solids, V s, may be calculated from
where V w = Volume of water (in cc) recovered
from the retort
PROCEDURE FOR DETERMINING
ACCURATE, LOW-GRAVITY SOLIDS
The following procedure requires an oven, pycno-
meter, and an electronic balance to weigh samples.
A pycnometer can be made by removing the beam
from a pressurized mud balance. Any type of bal-
ance may be used to determine weight, however,
electronic balances are more convenient.
Determine Volume of Pycnometer
1. Weigh the pycnometer (assembled)
2. Fill with distilled water
3. Determine the water temperature
4. Reassemble the pycnometer and pressurize
5. Weigh the pycnometer filled with pressurized
water
6. Determine the density of water using a den-
sity/temperature water table
7. Subtract the pycnometer weight from the weight
of the pycnometer filled with water to determine
the weight of water in the pycnometer
8. Divide the weight of water in the pycnometer
by the density of water to determine the
volume of the pycnometer