1. n. [Drilling Fluids]

A sample of mud from the deepest or current drilling depth of a well. The term refers particularly to a mud sample that has experienced stagnant conditions at the bottom of the hole, including the temperature, pressure, and other conditions at that depth. A bottoms-up sample is commonly collected after a trip out of the hole or if an influx of formation fluid is suspected.

See: bottoms-up,  mud-aging cell,  mud-in sample,  mud-out sample,  pilot test,  trip out