Integrated Design Based 6th Generation Deepwater Drillships {minus} Design & Engineering, Construction, Commissioning & System Integration Testing and Sea Trials
Authors: Claassen Laurens , Lee Young Chul , Hendriks Sjoerd , Kumar Rakesh 
Published: May 2011

Drilling operations in the deepwater plays of the world typically require a 5th or 6th generation Mobile Offshore Drilling Unit (MODU). The 6th generation deepwater drillships based on integrated design are entering service in 2011. Functional specifications have been incorporated into a newbuild drillship of an integrated class with improved capabilities, making operations more efficient and cost effective compared to non-integrated drillships. The advantages of the design include reduction of capital expenditure, vessel dimensions, dynamic positioning power requirements and environmental footprint. Presented here is the effort encompassing design, construction, commissioning and sea trials of a deepwater drillship, initiated in the 1990s and resulting - by the time of writing this paper - in a total of seven ships of this class.

Introduction

Currently, the 6th generation drillships are being added to the worldwide drillship fleet. These vessels have followed the trend of the 5th generation, by evolving into larger and larger units. In the deepwater areas, 5th and 6th generation vessels are typically mobilized for operations: drilling and testing exploration, appraisal and development wells, running completions, performing workover and intervention operations. The size of these vessels affects cost effectiveness: larger vessels come at higher initial investment (capex) and operational costs (opex), but also at a higher cost in terms of sustainability and environmental impact. The integrated drillship designs aim to curb the growth of vessel dimensions and associated cost, with a design philosophy focusing on functionality and fit for purpose design, while maintaining flexibility in operational scenarios.

A typical example of this philosophy is the P10,000 design, saving weight and equipment to reduce vessel size as an effective tool against tight economic circumstances of the current market. In this paper, the compact design approach will be presented and typical examples of the results of this approach. The design philosophy is to focus on the intended function of the vessel, aiming at a vessel as compact as possible without compromising the operational integrity of the rig. An example of a design philosophy that has led to the growth of design dimensions of the 5th and 6th generation drilling units, is the incorporation of future early production capability. Requirements for this capability include crude oil storage capacity, additional topsides, and offloading systems. The crude oil storage option has numerous consequences for the design, all boosting the dimensions, capex, opex and as a result the break-even day rate. When the hull volume below the main deck is sacrificed for crude oil storage, the drilling equipment has to be located in topside modules above the main deck. These topsides raise the center of gravity of the vessel, compromising stability, which in turn must be counterbalanced by an increase in vessel width. However, in the existing fleet the storage facilities are hardly ever utilized. If the design focus would have been more on the actual functionality of the rig, substantial size and cost reductions would have been possible.

In the context of this paper, Builder refers to Hyundai Heavy Industries and Designer refers to GustoMSC. The contents of this paper is the point of view with regard to general design and shipbuilding methods of Designer and Builder only, and not of a specific rig owner.