Deepwater Facility Selection
Authors: Ronalds Beverley F. 
Published: October 2008

A large number of factors influence the choice of production system for a particular oil and gas field. This paper outlines the key drivers that govern the selection process for one subset of systems-surface facilities for deepwater production- and verifies them using a comprehensive database of deepwater platforms. Regional variations-natural, industrial, political and experiential-are seen to be particularly important in the selection process. For fields benefiting from platform drilling and/or workover, the water depth and well count are key drivers.

The matrix approach to system comparison presented in the paper also highlights future technology developments across a range of disciplines required for more efficient hydrocarbon production in ultra-deepwater. Both new platform types, and enhancements of existing facilities to extend their applicability, are described. Overall, subsea well systems are anticipated to find increasing application as water depths increase.

Introduction

Offshore oil and gas fields may be developed using a variety of production systems. The configuration of the optimum system for a particular application depends on a myriad of factors [1]. First, the selection criteria used to determine the "best" solution must be defined-these are likely to be lifecycle financial value as well as other more subjective measures. The field characteristics are important, including site, regional, global and company parameters, as are the elements of the preferred production plan to deplete the reservoir. The hardware components required to deliver the production plan have inherent advantages and limitations that must be correlated with each other and to the field and production parameters; system selection involves optimising these synergies. Potential risks associated with the system must also be recognised. However, of these many factors, only a few become the key drivers that govern the final selection decision, although these key drivers vary according to the field and production characteristics. The system selection process is greatly facilitated when the key drivers are understood.

This paper describes a sequence of key drivers for facility selection in deepwater. It is presented in tabular form and justified using a database of past, current and sanctioned deepwater platforms. Anticipated innovations are also discussed briefly to appreciate how these might influence both the range of facility choices available, and the selection process.

Deepwater Facilities

"Deepwater" is defined in the study to be greater than 300m (nearly 1,000ft), giving a reasonable sample size of 89 facilities. This cut-off enables all compliant towers to be included, along with some important North Sea platforms. Conventional shallow water fixed platform technology is ignored even though both jackets and concrete gravity structures have been installed in water depths greater than 300m. Subsea tiebacks to existing facilities are also excluded. This leaves six proven deepwater platform types-FPSOs, semisubmersibles, spars, compliant towers, TLPs and mini-TLPs [2-4]. Here, the mini-TLP is differentiated from conventional TLPs by supporting subsea trees, with the first three mono-column TLPs being of this type. Table 1 summarises key statistics of the various facility types; a detailed comparison is presented in [1].