Page 194 - Shale Shakers Drilling Fluid Systems
P. 194
CALCULATING DRILLED SOLIDS CONCENTRATIONS 177
or fluid contains 47.3 gm of solids for every 87 gm
of water. The total liquid discard rate is 4391.9 gm/
min. The solids discarded by the screen that are
associated with the drilling fluid are: (47.3 gm
solids/87 gm water) (4391.9 gm/min) or 2387.8 gm/
The discard density is 2.78 gm/cc so the weight min or 315.6 Ib/hr.
percent barite is 27.07% weight. The weight of dry The weight fraction of barite in the drilling fluid
discard from the shaker screen is 1239 Ib/hr. The is 77.4% wt. and the weight fraction of low-gravity
quantity of barite discarded is (0.2707) x 1239lb/hr), solids in the drilling fluid is 22.4% wt. Of the sol-
or 377lb/hr. The low-gravity solids discard rate is ids discarded from the screen associated with the
1239 Ib/hr - 377 Ib/hr or 861 Ib/hr. "whole" drilling fluid, 244 Ib/hr are barite and 71.2
Ib/hr are low-gravity solids.
Previously, the dry solids discarded by the
CALCULATING SOLIDS DISCARD shaker screen were calculated to be 377 Ib/hr
barite and 861 Ib/hr low-gravity solids. Subtract-
AS WHOLE DRILLING FLUID
ing the solids associated with the drilling fluid
from the solids removed by the screen yields the
The drilling fluid contains 13% volume of solids.
This percentage in the liquid phase of the shale discarded solids in excess of those associated with
the drilling fluid.
shaker discard could be associated with the "whole"
drilling fluid.
The weight percent of dry solids discarded from • Barite: 377 Ib/hr - 244 Ib/hr = 133 Ib/hr.
the shaker screen was calculated to be 68.11%; so • Low gravity solids: 861 Ib/hr - 71.2 Ib/hr
31.89% of the discard must be liquid. Assume that = 798.8 Ib/hr.
this liquid is composed of drilling fluid with the
solids distribution of the drilling fluid in the pits. This indicates that the 200 mesh screen is remov-
The liquid discard rate is (13,772 gm/min)(0.3189) ing some excess barite and almost 800 Ib/hr of
or 4391.9 gm/min. This liquid should contain 13% drilled solids.
volume solids. Note that the technique of using the concentra-
Since the drilling fluid contains 13% volume tion of barite in the discard does not allow an
solids, a 100 cc sample contains 87 cc of liquid. accurate measurement of the quantity of drilling
In this 100 cc sample the water fraction would fluid in the shaker discard. Some measurements
weigh 87 gm. With an 11.2 ppg (1.343 gm/cc den- even indicate that less barite is in the discard than
sity) drilling fluid, the 100 cc sample should weigh in the "whole" drilling fluid. Shaker screens can pass
134.3 gm. Since the liquid weighs 87 gm, the solids much of the small barite and remove it from the
must weigh 47.3 gm. In other words, the drilling liquid before it is discarded by the shaker screen.
