Hessari - petroleum University of technology(PUT)

underbalanced Drilling (UBD) operations reduce the hydrostatic pressure of the drilling fluid column so that the pressure in the wellbore is less than the formation pressure. Underbalanced drilling is used increasingly worldwide as an alternative technique to conventional overbalanced drilling to reduce invasive near wellbore formation damage problems and increasing rate of penetration. In this work, at first, UBD and its advantages and disadvantages is explained, then necessity of application UBD in SN oilfield is investigated, at last but not at least one important case is studied, that is stability Analysis. For stability analysis the FLAC software is used, which simulates the behavior of structures built of, rock or other materials which may undergo plastic flow when thir yield limit is reached.

Drilling, Underbalanced, UBD. Wellbore stability