BAKER HUGHES - Drilling Fluids Reference Manual

MECHANICAL SOLIDS CONTROL
Dispersion of Surface Area - Removal of particles of very fine size produces greater viscosity
reductions than does the removal of an equivalent volume of coarser particles due to differences in
2
surface area. For example, a cubic foot of formation has 6 ft of surface area, whereas this same
piece of formation broken up into cubic micron-size particles would have a combined surface area
of 1,828,800 ft 2 or 42 acres. The volume % solids that would result from incorporation of these
particles in a fluid would be the same in both cases, but a considerable change in the volume of
water to wet the surface would occur. Obviously, a solids problem can develop without an increase
in solids volume if the particles are degraded into smaller sizes. Table 10-2 describes the increase
in surface area as a solids cube is broken down into smaller pieces.
Number of Cube
Divisions
Total Number
Pieces
Individual Cube
Size, inches
Total Surface Area,
square inches
0 1 1 6
1 8 1/2 12
2 64 1/4 24
3 512 1/8
48
4 4096 1/16 96
5 32768 1/32 192
6 262144 1/64 384
7 2.0972 x 10 6 1/128 768
8 1.6772 x 10 7 1/256 1536
9
8
1. 3421 x 10 1/512 3072
10 1.0737 x 10 9 1/1024 6144
15 3.5184 x 10 13 1 /32768 1966081
Table 10 - 2 The Disintegration of Solids
Current Solids Control Techniques
The methods by which drilled solids can be removed are as follows:
• Displacement – reduces solids by discarding the solids laden fluid and replacing it with a
drilled solids free fluid
• Dilution - additions of clean/clear fluids which is the most expensive method of controlling
drill solids
• Mechanical removal – accomplished with shale shakers, desanders, desilters, centrifuges, etc.
• Settling – restricted
to low-viscosity, low-density fluids and requires a large settling pit to
allow particles the necessary time to settle out of suspension.
The higher the concentration of drill solids in a discard, the more favorable the displacement or
mechanical removal method. The purpose of mechanical control is to minimize dilution
BAKER HUGHES DRILLING FLUIDS
REVISION 2006 10-6
REFERENCE MANUAL