Upgrading existing Drilling Units has been considered an attractive option for offshore oil exploitation, since costs and time to be spent at shipyards can be lower than for new building. Moreover, use of a Dynamic Positioning System and automated drilling facilities are essential for the performance of the Unit when operating in ultra deep waters.

The demand of drilling offshore Brazil was the motivation to evaluate the feasibility of upgrading a Mobile Drilling Unit to operate in water depths up to 2500 m, with slender drilling risers.

This paper focuses on the main aspects considered during the basic design phase of the upgrading of a Semi-submersible Drilling Unit as follows:

  • Additional utility systems;

  • New Bilge and Ballast system;

  • Drilling facilities;

  • Increase in Payload;

  • DP system with addition of thrusters;

  • Naval architecture, including blisters, pontoons enlargements, thrusters locations and new compartmentation;

  • Upper hull arrangement;

  • Structural reinforcements;

  • Model testing;

  • Power demand and Generation;

  • Integration between systems;

  • Class Notation.

With all those aspects addressed, the objective of providing a design of a Unit feasible to operate in ultra deep waters has been reached, from safety, structural, stability, station keeping, arrangement and drilling performance points of view.

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