The Heidrun field, situated on the Norwegian Continental Shelf (Figure 1), is scheduled to come on stream in August 1995. Heidrun will be developed using a tension leg platform (TLP). The reserves are estimated to 119 M Sm3 (750 M STB) of oil and 45 GSm3 (1.6 TSCF) of gas. Heidrun consists of three main reservoirs, the Fangst Group, the Tilje Formation and the Are Formation where the Fangst Group contributes more than 70% of the total reserves. A total of seven Fangst oil producers will be pre-drilled and pre-completed to accelerate the build up period. These wells are all planned as gravel packed wells with high deliverability.

To optimize the completion design and maximize flowrate potential for the producers, a new approach to evaluate well performance was developed. The individual well deliverabilities were computed as a probability distribution directly reflecting the uncertainties related to the input variables rather than the more conventional single flow rate.

The results showed that the flowrate was likely to be restricted by the completion configuration rather than the reservoir deliverability. As a result, the current tubing size was increased and the Fangst well design rate was raised. By increasing the design rate, the pre-plateau period was reduced. This increased the NPV of the Heidrun project significantly.

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