Page 247 - Shale Shakers Drilling Fluid Systems
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EQUIPMENT GUIDELINES 229
19. The degasser (if needed) should be installed 23. Two different pieces of solids equipment should
immediately downstream of the shaker and up- not simultaneously operate out of the same suc-
stream of any piece of equipment requiring feed tion compartment. Note: Different means, for
from a centrifugal pump. example, degasser and desander or desander
and desilter.
Degassers are used to remove entrained hy-
drocarbon gasses from drilling fluid. Another If a desander and a desilter take suction from
benefit of degassers is to prevent air or gas the same compartment and then discharge
from entering centrifugal pumps, where even into the next compartment, some fluid will be
small quantities significantly reduce pump effec- desanded and some will be desilted. This is
tiveness. As liquid (or drilling fluid) is thrust to referred to as connecting the equipment in
the outside of the impeller chamber, air or gas parallel. Desanders are usually used to de-
collects at the center. Eventually, enough air or crease solids loading in the desilters. If these
gas will collect to completely block the suction two pieces of equipment operate in parallel
and no liquid will be able to enter the pump. and a significant amount of solids are being
processed, the desilters will probably plug.
20. The solids removal equipment should be ar- In some poorly designed systems, where an
ranged sequentially so that each piece of equip- insufficient number of compartments are avail-
ment removes successively finer solids. Although able, the degasser and the desander may be
every piece of equipment may not be used or connected in parallel. This assumes that only
needed, general arrangements are as follows: the degasser, and not the desander, will be
Unweighted Mud Weighted Mud used on weighted drilling fluid. Obviously, if
Gumbo Remover Gumbo Remover they are connected in this manner (parallel),
Shale Shaker Shale Shaker both cannot operate simultaneously.
Degasser Degasser
Desander Mud Cleaner 25. If two of the same piece of solids control equip-
Desilter Centrifuge ment are used simultaneously, the same suction
Centrifuge and discharge compartment should be used for
Dewatering Units both. Example: If two desilter units are used,
both should be properly rigged up and have the
Including the degasser in the unweighted mud same suction and discharge compartments.
list was not agreed upon by the entire com-
mittee. Influx of gas into the drilling fluid This situation is frequently encountered with
normally requires the addition of a weighting desilter banks. In the upper part of a borehole,
agent to the drilling fluid. Very few unweighted many hydrocyclones are needed to handle the
drilling fluids are degassed. volume (based on 50 gpm per 4-inch hydro-
cyclone, 1200 gpm will require 24 cones).
21. The overflow for each piece of solids control While some of these cones can be mounted
equipment should discharge to the compartment on mud cleaners (the screen is blanked to
downstream from the suction compartment for discard all underflow), all cones should use
that piece of equipment. This is termed proper the same suction compartment and discharge
piping, plumbing, or fluid routing. downstream to the next compartment.
Another problem can arise when a separate
The compartments do not need to be large. rig pump is used to increase annular velocity
Simple partitions in a larger tank can fre- in risers. The additional flow rate onto the
quently be added to improper systems to im- shale shakers may require adding additional
prove their performance. Since a backflow is units in parallel. The degasser capacity require-
desired between compartments, the partitions ments may demand additional degassers be
do not require a complete seal.
added to the mud tank system. These degassers
should also be connected in parallel.
22. Improper fluid routing always leads to solids-
laden fluid bypassing the removal device.
26. The degassers, desanders, desilters, and mud
Unfortunately, improper routing is all too com- cleaners should process 10096 of the mud en-
mon on drilling rigs. In the 1980s, approx- tering their individual suction compartments. In
imately 90% of the rigs had flaws in their a properly designed system, the processing rate
removal system, and the situation has not im- should be at least 10-2596 more than the rig cir-
proved much in the 1990s. culating rate. (See Rule 5 for Hydrocyclones.)
