1. n. [Drilling Fluids]
The particle size that has a specified chance of being removed by an item of solids control equipment. Most commonly, D10, D50 and D90 cut points are specified corresponding to 10, 50 and 90% chances of removal, respectively. Taken together, they approximate the separation curve. If the percent is not specified, it is normally taken to be the D50 value. For example, if the D50 of a shaker screen is 100 microns, then a particle of this size has an equal chance of being removed or staying in the system. Larger particles are more likely to be removed and smaller ones more likely to be retained in the underflow.
See: crude oil