Circulation sub Definition


Circulation sub:

A downhole tool typically used with motors or assemblies that restrict the allowable fluid-circulation rates.

When operated, the circulation sub allows a higher circulation rate to be established by opening a path to the annulus in the top section of the tool string.

This is especially useful in applications such as drilling in slim-diameter wells, where a higher circulation rate may be necessary to effect good cuttings transport and hole cleaning before the string is retrieved.