The main design criteria of an innovative semisubmersible drilling rig are presented. Among other distinctive features, the "functional availability" is illustrated as the most effective fault tolerance systemic approach of the state of the art. The basic tool to implement functional availability is the "Fault isolation through distribution" with ensuing beneficial effects bot technical and economical on the major onboard systems.

Consistent, reliable performance quality-level and overall operational safety enhancement are the direct result of such an approach, alongside with a substantial increase of operational flexibility.

This applies as well to the easy and quick conversion of the rig into an early production unit (and back) in P modes:

Production & Drilling Mode, keeping drilling equipment onboard with a 40 - 60,000 BBPD oil production capacity

Production Only Mode, removing main drilling equipment, with a resulting oil production capacity of 80 - 110,000 BBPD, without considering possible associated gas.

The unit has been designed to fully comply with the stringent Norwegian Petroleum Directorate rules for floating production units, including all extra requirements for fire protection (also structural).

A modular approach to production and drilling equipment and facilities enhances easy, safe, quick installation & removal.

Finally a concise description of the technical nature of the maiden assignement of the rig is supplemented, with a variety of operational duties on the Snorre Field off Norway, which could extended, from 1990, untill 1998.

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