Underbalanced Drilling

“Underbalanced drilling” means drilling under conditions where the hydrostatic head of the drilling fluid column is intentionally designed to be lower than the pressure of the formation being drilled.

Source: Alaska Oil and Gas Conservation Commission, Definitions, Alaska Admin. Code tit. 20, § 25.990, December 7, 2012. Regulations


Underbalanced Drilling (UBD)

A drilling activity employing appropriate equipment and controls where the pressure exerted in the wellbore is intentionally less than the pore pressure in any part of the exposed formations with the intention of bringing formation fluids to the surface.

Source: IADC UBO / MPD Glossary, December 2011. Global Standar

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