Downhole sucker-rod pumps: Difference between revisions

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Tight clearances (less than 0.003 in.) may cause producing problems, whereas loose clearances (greater than 0.008 in.) may result in excessive leakage by the pump. Good field-pump records are essential to make good pump recommendations.
Tight clearances (less than 0.003 in.) may cause producing problems, whereas loose clearances (greater than 0.008 in.) may result in excessive leakage by the pump. Good field-pump records are essential to make good pump recommendations.
Slippage in sucker-rod pumps takes two forms: static and dynamic slippage.
• Static slippage is the dominant factor and occurs only during the upstroke of the pump; it is caused by the pressure differential across the plunger-barrel fit. The high hydrostatic pressure present in the tubing string, acting on top of the plunger with the traveling valve closed, forces liquid to slip past the plunger into the pump chamber between the traveling and the standing valves.
• Dynamic slippage, on the other hand, takes place both on the up-, and the downstroke of the pump and is caused by the plunger’s movement; its magnitude being proportional to the plunger velocity i.e. the pumping speed used. The direction of liquid slippage is different for the up-, and downstroke: during upstroke liquid falls below the traveling valve while during the downstroke liquid flows upwards and decreases the amount of liquid passing through the traveling valve.
An extensive series of theoretical and experimental investigations [ 13 – 16 ] on pump slippage resulted in the following main conclusions.
• Early formulas greatly overestimate the amount of liquid slippage. Typical values, based on experimental data are about two times greater for plunger fits less than 0.006” and more than three times greater for fits larger than 0.006”. This implies that pumps with fits larger than those selected on the basis of earlier predictions can be used without experiencing too high pump leakages.
• The eccentricity of the plunger’s lateral position in the barrel has a great effect on liquid slippage (also proved by [ 17 ]), a fact that most previous formulas disregarded. For a completely eccentric position leakage rates 2.5 times greater than for concentric cases can be expected.
• Most previous correlations disregarded the effect of dynamic leakage in the pump.


== Compression ratio ==
== Compression ratio ==
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