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Drilling Industry Glossary

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Underbalanced Drilling

Underbalanced drilling, or UBD, is a procedure used to drill oil and gas wells where the pressure in the wellbore is kept lower than the formation pore pressure. As the well is being drilled, formation fluid flows into the wellbore and up to the surface. The circulating fluid for underbalanced drilling can be lower density mud, air, nitrogen, mist, foam, etc.

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