4. n. [Drilling]
The shortest distance from the surface location of a well to the vertical projection of the bottom of the well (or other point in the well) to the Earth's surface. Horizontal wells often have total displacements of 1000 ft [305 m] or more from the surface location, and the world record exceeds 10 km [6.2 miles] of displacement.
5. n. [Drilling]
The act of removing one fluid (usually liquid) from a wellbore and replacing it with another. This is accomplished by pumping a spacer fluid that is benign to both the first and second fluid, followed by the new fluid, down the drillstring and out the bottom of the drillstring or bit. While the spacer and second fluid are pumped into the top of the wellbore, the first fluid is forced out of the annulus between the drillstring and the wellbore or casing. In some cases, this general procedure may be reversed by pumping in the top of the annulus and taking fluid back from the drillstring. Since this is the reverse of the normal circulation path, this is referred to as "reversing out" or "reverse circulation."
6. n. [Drilling]
The act of forcing a cement slurry that has been pumped into a casing string or drillstring to exit the bottom of the casing or drillstring by pumping another fluid behind it. Cement displacement is similar to definition 5 above, with the noted exception that the cement slurry would not normally be pumped out the top of the annulus, but would instead be placed in a particular location in the annulus. This location might be the entire annulus on a short casing string, or filling only a bottom portion of the casing on longer casing strings.