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.