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The Drilling
fluid (mud) Mixing System
Drilling fluid is very
expensive, modern day operation can have as many a 7000 bbls of
fluid on the rig at one time, the active system (that's the one
that is being circulated there could me as many as four systems
on the rig at one time?) needs to be kept in good condition, The
fluid returning from the well will first be directed to the
solid control system where as much of the solid as possible will
be remove, it will then flow back to the active tank (pits)
where sooner or later it will need to be reconditioned
built.
If the fluid needs
reconditioning it will be drawn from the pits using a
Centrifugal
pump. The centrifugal pump consists of a rotating impeller
mounted inside a casing, unlike positive pressure piston pumps,
e.g. "the rig mud pumps", centrifugal pumps provide constant
“head.” Consequently, the pump and associated piping system must
be correctly sized and designed to deliver the required flow
rate and desired head. Fluid enters the casing at the
center (the eye of the impeller). As the impeller spins, the
fluid is accelerated to the circumference by the curved impeller
vanes. The accelerated fluid exits the impeller and enters the
pump casing where kinetic energy is converted into pressure
energy.
Pump Performance Curves, illustrate that the head generated by
centrifugal pumps decreases very little as the flow rate is
increased. Conversely, the flow rate through mixing system is
not affected much by head.
However the
pump should be sized to provide the correct head at the flow
rate dictated by the pump rate or system designed operating
pressure .

Here we see very
basic lay out where the mixing pumps are piped in to the low
pressure system, not there are two suction lines lines the lower
being the mixing suction to the mixing pumps
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