Being an environmentally sensitive area, wells drilled in the Barents Sea are subject to comprehensive well planning, particularly with respect to well control issues. On the Obelix field, which is a limestone prospect in the Barents Sea, an extensive quantitative risk-based well control study was undertaken in order to establish robust operational routines for facing major risks and uncertainties.

An advanced dynamic computer model was used to evaluate potential well control scenarios which could occur. Drilling into caves can lead to severe mud losses and introduce large influx volumes in the well. An important part of the study was therefore to include a discussion of possible scenarios, e.g. mud loss and influx detection critiera and evaluate procedures for mitigating severe losses. The advanced well control model was then used to evaluate the consequences of large influx volumes. Since the well was relatively shallow with a potential for large influx volumes, gas migration issues and consequences related to that was evaluated thoroughly. It was important to stress the need for rapid well control response in case of such events.

The model was also used to evaluate maximum casing shoe pressure for various kick volumes, and the typical dynamics to be seen when applying a given well control method for safely bringing up the kick. Special focus was on evaluating the dynamics of large influx volumes e.g. with respect to separator capacity.

The paper aims at presenting a way of working, where the initial work focus on obtaining an overall quantitative risk assessment with respect to well control. Critical factors are then identified in order to direct more detailed studies.

The paper also demonstrates that advanced models are necessary in order to support operational choices and procedures. The holistic approach which combines modelling and practical insight is regarded as a valuable improvement to better well control planning.

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