Displacement:
1.The weight of a fluid (such as water) displaced by a freely floating or submerged body (such as an offshore drilling rig).
If the body floats, the displacement equals the weigh of the body.
2.
Teplacement of one fluid by another in the pore space of a reservoir.
For example, oil may be displaced by water.
3. 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.”
