Technology Gaps and Preferred Architectures for Deepwater FPSOs
Authors: Bensimon Luis F. , Devlin Paul V. 
Published: October 2008

FPSOs are one of the promising deepwater facilities. A critical look at the technology, challenges and gaps was performed on a systematic basis. The findings and recommendations for areas of further FPSO work are reported.

INTRODUCTION

Integrated, ship-shaped Floating Production Storage and Offloading system, typically known, as FPSOs are some of the most promising floating systems for exploitation of ultradeepwater fields.

Over the past 20 years FPSOs have proven to be a reliable, cost-effective solution for offshore field development. Nowadays there are nearly 70 FPSOs or FSOs in operation worldwide [1]. Some in extremely harsh conditions like the West of Shetlands [2], and some in very deep waters such as the Marlin South field in over 1400m water depth [3].

As part of the DeepStar Phase V, Systems engineering Committee, CTR-5902, "Floating Production Technology Gaps", the feasibility of integrated Floating Production, Storage and Offloading (FPSOs) systems for water depths up to 10,000-ft in the Gulf of Mexico, was investigated. The main goals of the study were:Identify state-of-the-art technology for FPSOs as ultra-deepwater floating production systems for the Gulf of Mexico.Develop basic FPSO system geometry for each of the base design cases.Identify potential technology gaps that could preclude the use of FPSOs in waters up to 10,000 feet.Identify high-impact enhancements to the FPSO technology as it applies to production of ultradeepwater fields.Value and rank these potential technology gaps and enhancement opportunities.

The "Functional Analysis System Technique" (FAST) approach was used for mapping all functional aspects of the entire system, from reservoir access to hydrocarbon export to shore. All base cases were "run" through the master FAST diagram and all potential gaps in the technology or areas in need of improvement were identified.

CAPEX and OPEX costs for all FPSO bases cases were estimated based on the respective selected system's architecture.

Base Cases

Two reservoir sizes were considered in the study, a smaller one with 150MMbbls reserve and a large reservoir with 700MMbbls reserve. General reservoir data used in the study is presented in Table 1.

The small reservoir case was studied for a water depth of 6,000ft. The large reservoir was studied for a 6,000ft and a 10,000ft water depth.

In both cases a Tension Leg Riser (TLR) system was the riser system of choice for connecting the FPSO to the subsea equipment. In general terms, the TLR system consists of steel catenary risers (SCRs) spanning from the subsea equipment to a subsurface tension-leg moored steel buoy. Flexible pipe jumpers make the connection between the SCRs at the buoy and the FPSO.

Three base cases were selected resulting in a combination of the small and the large reservoir, in 6,000-ft and 10,000-ft water depth, as shown in Table 2. Other characteristics of the selected base cases are included in tables 3 to 5.

Two FPSO vessel sizes were selected, namely a 135,000- dwt vessel for the small reservoir scenario, and a 280,000-dwt vessel for the large one.