STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

630 Drilling and Well Completions
suction pipe. Minimizing the effect of inertia requires a reduction of the suction
velocity and mud weight. It is generally practical to use a short suction pipe
with a large diameter.
When a desirable suction condition cannot be attained, a charging pump
becomes necessary. This is a common solution used on many modern rigs.
Cooling Mud
Mud temperatures of 150' can present critical suction problems. Under low
pressure or vacuum existing in the cylinder on the suction stroke, the mud can
boil, hence decreasing the suction effectiveness. Furthermore, hot mud accelerates
the deterioration of rubber parts, particularly when oil is present. Large mud
tanks with cooling surfaces usually solve the problem.
Gas and Air Separation
Entrained gas and air expands under the reduced pressure of the suction
stroke, lowering the suction efficiency, Gas in water-base mud may also deteriorate
the natural rubber parts used. Gases are usually separated with baffles or by
changing mud composition.
Settling Pits
The normally good lubricating qualities of mud can be lost if cuttings,
particularly fine sand, are not effectively separated from the mud. Adequate
settling pits and shale shakers usually eliminate this trouble. Desanders are
used occasionally.
Discharge Manifold
A poorly designed discharge manifold can cause shock waves and excessive
pressure peaks. This manifold should be as short and direct as possible, avoiding
any sharps turns. The conventional small atmospheric air chamber, often
furnished with pumps, supplies only a moderate cushioning effect. For best
results, this air chamber should be supplemented by a large atmospheric air
chamber or by a precharged pulsation dampener.
Priming
Pump Operation
A few strokes of the piston in a dry liner may ruin the liner. When the pump
does not fill by gravity or when the cylinders have been emptied by standing
too long or by replacement of the piston and liner, it is essential to prime the
pump through the suction valve cap openings.
Cleaning the Suction Manifold
Suction lines are often partly filled by settled sand and by debris from the
pits, causing the pump to hammer at abnormally low speeds. Frequent inspection
and cleaning of the suction manifold is required. The suction strainer can also
be a liability if it is not cleaned frequently.