SS: Spar Technology - The Internationalization of the Spar Platform
Authors: Sablok Anil K. , Barras Steven Alexander 
Published: July 2009

One of the key features of the Spar platform is its low motion response characteristics. This results in a high degree of functional flexibility that has enabled the Spar to be employed in a variety of different applications such as wet tree host, dry tree wellhead, with or without platform drilling facilities and with or without production facilities. The Spar has also been employed as wellhead only platform, utilizing Tender Assisted Drilling in place of a Spar mounted drill set. While all but one of the Spars in service today operate in the US Gulf of Mexico (the one exception being the Kikeh Spar in Malaysia), new designs have been developed for the Spar platform to further extend its use, both in terms of function and geographic location, in order to meet the needs of other oil and gas producing regions as they extend their E&P activities into deeper waters and more harsh environments. These designs range from relatively simple modifications, such as the incorporation of crude oil storage in the hull to facilitate the use of dry tree completions and motion sensitive riser systems in infrastructure-remote locations, to more significant modifications, such as the reconfiguration of the Spar as a power and control buoy platform, or as a deep water Arctic platform, which requires the Spar to function as an ice-breaker in sheet ice conditions, while also allowing it to be disconnected to avoid larger icebergs.

The functional requirements, export infrastructure, operating environments and construction and installation capacity vary significantly across regions. Each of these variations has the potential to drive alterations to the Spar hull configuration. This paper discusses the most significant requirements of a number of key regions where Spar technology can provide significant value, and addresses these requirements in terms of the resulting Spar configuration and how the Spar design has been, or can be, adjusted to meet the local challenges and requirements. The specific regions covered are the ultra deep waters of the Gulf of Mexico, S.E. Asia, West Africa, North Sea, Brazil and the Arctic regions of East Canada and the Barents Sea. A variety of Spar configurations are presented to address nominal solutions for each of the regions, each based on either the Classic, Truss or Cell Spar technology.

Introduction

The Spar platform exhibits low motion response characteristics in response to environmental loads when compared to other floating structures. This is due to the deep draft design and high stability which results from the inherent separation of the center of gravity and center of buoyancy. The center of gravity is lowered by installing heavy ballast at the platform keel.

The low motions of the Spar platform enable the use of motion-sensitive rigid risers such as top tensioned and steel catenary risers in water depths ranging from as shallow as 300 m to over 3,000m.

Broadly there are three Spar types: Classic, Truss and Cell. These are shown in Figures 1 to 3. However, there are a number of available variations of each Spar type which address a range of required functionality and operating environment, for example, the Closed Centerwell Spar represents one key variation of the Truss Spar design. Presently there are seventeen Spars in service, three Classic Spars, thirteen Truss Spars and one Cell Spar. All except the Kikeh Truss Spar offshore Malaysia are deployed in US Gulf of Mexico (GOM).

While the basic Spar concept dates back several decades, the Classic Spar represents the first reference point for modern Spar technology, with the Neptune Spar marking the first Spar application, having been installed in 1996. The Classic Spar hull comprises three main components as shown in Figure 4.