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Oilfield Glossary
Oilfield Glossary
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underbalance

1. n. [Drilling]
The amount of pressure (or force per unit area) exerted on a formation exposed in a wellbore below the internal fluid pressure of that formation. If sufficient porosity and permeability exist, formation fluids enter the wellbore. The drilling rate typically increases as an underbalanced condition is approached.
Antonyms: overbalance