Page 139 - Drilling Technology in Nontechnical Language

130 Drilling Technology in Nontechnical Language Second Edition

Next comes the sand trap. The sand trap is a tank that usually sits
underneath the shale shakers. Flow from the shale shakers goes into the
sand trap. The purpose of the sand trap is to give temporary protection to
the rest of the system if a shale shaker screen splits. In this case, the larger
solids will settle in the sand trap, and they can be later dumped through a

large butterfly valve on the bottom of the sand trap.
Mud from the sand trap flows out at the top through a cutout in the

top rim of the tank. The mud will then flow into another tank. This mud,

having routed through the shale shakers and sand trap, will still contain
smaller rock particles. This second tank will be used to feed a centrifugal
pump that will pump the partially cleaned mud into a hydrocyclone system.
A hydrocyclone is a simple but ingenious bit of kit with no moving
parts. It is comprised of a cone with a small hole at the bottom (narrow)
end. At the top of the cone is an inlet pipe, positioned so that mud entering
the cone does so in such a way that it swirls around the inside diameter. An
outlet pipe exits upwards, but the bottom end of this pipe sticks into the top

of the cone (see fig. 5–16).

Fig. 5–16. Hydrocyclone—principle of operation
Picture courtesy of Baroid.

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