Well control was gradually regained during December 2003, after a period of worsening and pressure build-up in the well and annulus.
The wellbore path (A-8-B) was then plugged and prepared for a new sidetrack / new wellbore path (A-8-C).
Summary of the investigation report:
The investigation indicates several direct causes of the incident and the worsening situation before well control was regained.
The direct causes of the incident/worsening situation were:
1. Drilling in permeable hard formations in an area that was expected to be depressurized.
2. Loss of mud to the formation in greater volumes than experienced in other Valhall wells.
3. Worsening of the situation in connection with running the drill string in/out, as well as circulation of the well without closing the BOP.
4. Plugging of the drill string due to "gunk".
The investigation shows that the underlying causes of the kick are multiple and complex and cannot be linked to a common factor/system. This applies e.g. to the following:
We would like to thank all of the involved parties in BP who have been very accommodating in connection with the investigation.
We have asked BP for the company's evaluation of the proven deviations and observations by October 15, 2004.
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