Critical Thinking

Producing flow using a snubbing unit failed as

Producing wells in Middle East are faced with downhole corrosion problems as they mature. External and internal corrosion of production casing and tubing can lead to underground blowout as it was the case in well 159. Well 159 was drilled in 1959 in Bahrain and was completed within the shallow sandstone reservoir. Thirty-six years after the well was completed, a routine annulus survey was conducted and indicated tubing leak in 5” production casing. Several attempts were made to work the well over to get near the producing perforations after pulling part of the original completion. These conventional methods failed and attempt to kill and cement off flow using a snubbing unit failed as well.

In the interval within the shallow aquifer from 300′ to 700′, casing had shown signs of severe corrosion. The casing was parted and shifted below 681′ and the wellbore was no longer accessible from the surface below this depth. Blowout flow rate was estimated at 8 MMscfpd of gas. This caused significant safety problems (Flak L.H. et al, 1995): 1) sour gas venting out of the charged aquifer in offset well cellars; 2) subsurface charging and associated shallow gas hazard. Relief well 515 was drilled as a solution to kill underground blowout in well 159, plug and abandon well 159 and then serve as a replacement well. Few challenges have to be considered in pre-planning process (Flak L.H. et al, 1995):

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1)      Surface separation of blowout and relief wells limited by shallow reservoir depth to 85′;

2)      No borehole surveys of any kind available on the blowout;

3)      Safely drilling and casing of the shallow actively charged aquifer;

4)      Maintain well control and borehole stability of the relief wellbore;

5)      Near well intercept (

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