BAKER HUGHES - Drilling Fluids Reference Manual

MECHANICAL SOLIDS CONTROL
Figure 10 - 14 Weighted Fluid: Two Stage Centrifuging
The dewatering system operates by destabilizing the fluid chemically, which causes coagulation of
the solids, and then by chemically flocking the solids. “Flocked” solids and liquid are then
separated by use of a centrifuge or screwpress to achieve maximum concentration of the solids in
the discard and maximum return of the solids-free liquid to the fluid system.
The benefits vary when utilizing a dewatering system depending on the fluid type. Besides the
primary benefit of reduced haul-off, reduction in fluid maintenance can be realized for two reasons,
(1) the amount of solids carried in the fluid can be controlled without total dependence on chemical
thinners and, (2) any soluble materials in the liquid phase will be returned to the system after the
flocculation process. However, it should be noted that some additives are removed depending on
the ionic charge of the chemical flocculants and the concentration used. This will reduce the cost
of fluid built to replace that lost with the solids.
Calculations Used in Solids Control Evaluations
The following equations are based on the fact that the specific gravity (S.G.) of the fluid is equal to
the sum of the specific gravity times the volume fraction of each of its components. In these
simplified equations, the fluid will consist of three basic components – liquid, low-gravity solids,
and high-gravity solids.
S M = (V W )(S W ) + (V LG )(SLG) + (V HG )(S HG )
1. Average spec ific gravity of solids in water-base fluids.
• Freshwater fluid
S
a
=
[ 0.12(
D )]
V
m
s
−V
w
BAKER HUGHES DRILLING FLUIDS
REVISION 2006 10-22
REFERENCE MANUAL