Oil and gas industry is increasingly approaching more challenging situations where it is of primarily importance to carefully assess the technical solutions to maximize productivity, to evaluate the economic worth of investment and identify all the risks and opportunities involved in the project.

A challenging subsea well is planned to be drilled and completed in a deep offshore field in the Adriatic Sea (Italy).

This project includes all the challenges and criticalities related to: deepwater wells, sour environment, gas lift wells, multilateral and intelligent wells.

The objective of the study was to provide decision support for the selection of the most suitable multilateral and completion design addressing, through a probabilistic approach, all the uncertainties regarding reservoir characteristics, well design and productivity in terms of duration and cost.

A multidisciplinary working team, including drilling and completion engineers, geologists and reservoir engineers, has been created in order to assess all the aspects of the project with its opportunities and criticalities.

Different scenarios have been compared with regards to the available technologies for multilateral and intelligent completions.

The first step of the analysis was the identification of the uncertainties (opportunities and risks) related to technical, organizational or environmental issues, successively reported in a probabilistic time and cost model.

A dedicated fault tree approach was deemed useful to focus on the combination of events leading to a potential branch loss and to calculate the associated probability.

All uncertainties were then combined with production profiles into a technical unit cost ($/bbl).

This paper describes workflow and results. The results provide the managers with a comprehensive picture of a complex issue to make the investment right decision at a given confidence level.

This should provide a guideline to engineers, geologists and managers on the risked approach for the development of complex projects.

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