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Oilfield Glossary
Oilfield Glossary
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Tools

circulation sub

1. n. [Well Workover and Intervention]
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.