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Oilfield Glossary
Oilfield Glossary
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volumetric efficiency

1. n. [Drilling]
The ratio of the actual output volume of a positive displacement pump divided by the theoretical geometric maximum volume of liquid that the pump could output under perfect conditions. Inefficiencies are caused by gaseous components (air and methane) being trapped in the liquid mud, leaking and noninstantaneously sealing valves in the pumps, fluid bypass of pump swab seals, and mechanical clearances and "play" in various bearings and connecting rods in the pumps. This efficiency is usually expressed as a percentage, and ranges from about 92% to 99% for most modern rig pumps and cement pumps. For critical calculations, this efficiency can be determined by a rigsite version of the "bucket and stopwatch" technique, whereby the rig crew will count the number of pump strokes required to pump a known volume of fluid. In cementing operations, displacement is often measured by alternating between two 10-bbl displacement tanks.
See: swab
2. n. [Production Testing]
The relationship between actual pump displacement and the pump displacement under ideal conditions. The relationship can be expressed as percentage. A reduction in pump volumetric efficiency is an indication of an operational problem in the well. In sucker-rod pumps, the gas lock and gas interference phenomena can significantly reduce the volumetric efficiency of the pump.