The "Box Spar" Floating Production, Drilling, Storage, and Offloading Vessel for the Gulf of Mexico and Brazil
Authors: Halkyard John , Choi Guibog , Prislin Igor , Steen Atle , Hawley Phil 
Published: October 2008

A new alternative for large deepwater field development is described. This "Oil Box" (aka "Box Spar") is a multifunction floater capable of drilling, production and storage. It is distinguished from other Floating Drilling, Production, Storage and Offloading vessels by its unique hull form and oil storage system. It's main advantages are flexibility derived from the floatover deck option, use of proven top tensioned riser technology, and motion characteristics which make it operable in a wide range of environmental conditions.

Introduction

Large oil and gas discoveries have been made in the ultra-deep waters of the Gulf of Mexico. These discoveries are on a par with those found in the other "hot" frontier areas of West Africa and Brazil. The high costs of drilling and producing these ultra deep water fields using conventional approaches naturally yields an incentive to consider new methods and paradigms for field development. One approach being promoted by several contractors for West Africa is the "multifunction" vessel, which can do drilling, production, storage and offloading. These Floating Drilling, Production, Storage and Offloading vessels (FDPSO) have the advantage of reducing the need for costly MODU operations for development drilling and completions, and they allow dry tree operations and workovers. The FDPSO combines the functions of a wellhead platform and an FPSO, reducing thetotal costs for facilities.

A disadvantage of the FDPSO approach is that the vessel's schedule is driven by the longest lead time component, usually the process facilities. While combining all functions on one vessel might save some money, project economics might be improved if, for example, the drilling function could be fast tracked with a smaller wellhead platform. Some operators also perceive added risk in "placing all the eggs in one basket".

Most FDPSO designs are based on conventional mono-hull construction. These are suitable for subsea wells and flexible risers in most environments, but these hulls are not ideal for rigid risers and steel catenary risers in harsh environments or those subject to cyclonic events.

A new FDPSO design has been developed to address these issues. This "Oil Box" (formerly known as the "Box Spar") was originally intended for West Africa (Ref. 1). Recently, the configuration has been optimized for improved motions and is capable of operations in Brazil and the Gulf of Mexico as well. This paper will present a description of the Oil Box as configured for West Africa and as modified for Gulf of Mexico applications. We will also present the current status of development and an economic assessment of the Oil Box for a typical field development scenario.

Design Criteria

Table 1 lists the design criteria used for designs described here.

Table 1 Design Criteria (Available in full paper)

Survival environments used for this paper are summarized in Table 2. Two 100-year environments are listed for each location. The environment labeled "current" corresponds to the 100-year current with a 10-year wind/wave environment, and similarly the 100-year "storm" corresponds to a 100-year wind/wave together with a 10-year current.