An FPSO with Surface Wells and Workover System in Deepwater
Authors: Ishida Kozo , Otomo Kazuhisa , Hirayama Hiroaki , Okamoto Norihiko , Nishigaki Makoto , Ozaki Masahiko 
Published: October 2008

A new and unique Floating Production Storage and Offloading (FPSO) concept termed the CVAR-FPSO is under development by a Japan National Oil Corporation headed Joint Industry Project. The concept, using Compliant Vertical Access Risers (CVAR) and including the ability to complete and workover a well independently, offers enormous economic and operational benefits during all phases of a deepwater oil field development (Fig. 1).

The central attribute of the CVAR-FPSO is the use of CVARs. These compliant but rigid risers, fitted with syntactic buoyancy, connect wells from the seafloor to the surface Xmas trees mounted on the weathervaning vessel turret, and can compensate for vessel motion. The CVAR, being vertical access to the wells, also allows a full range of completion and workover operations to be performed from the FPSO.

The CVAR-FPSO would make its potential maximum in calm and deepwater, Brazil, West Africa, Indonesia, etc. Here offshore Brazil ultra deepwater is especially focused. This paper describes operational and economical benefits of the CVAR-FPSO for offshore Brazil ultra deepwater. The main benefits are 1) Completion and workover capability, 2) Artificial lift options are easily installed. 3) Weathervane capability, 4) the CVAR-FPSO takes over advantages of a conventional FPSO, low cost, large storage, etc. And this paper also focuses on the workover system of the CVARFPSO concept for offshore Brazil ultra deepwater. Here, the workover system consists of derrick, fluid transfer system and riser centering system. The configurations of the workover system are very sensitive to environmental conditions, operational requirements and economics. And also well system and riser system are explained.

The development concept involves the drilling and temporary abandonment of wells by a Mobile Offshore Drilling Unit (MODU). The CVAR-FPSO is then moved onto location, CVAR risers are connected from subsea tiebacks to each Xmas tree in the turret, and wells are completed from the CVAR-FPSO. Re-completions, maintenance, workovers, logging are performed from the CVAR-FPSO through the life of the wells. This oilfield development strategy with the CVAR-FPSO offers economic and operational benefits.

Introduction

The FPSO has become a widely used oil production platform worldwide, being used in a many different seas, for many different reservoir types. This wide range of applications is due to the inherent benefits of the system, including the ability to produce, store, offload, the ease of adaptability to different reservoir and sea conditions, re-usability, applicability as Extended Well Test (EWT) or Early Production System (EPS) and relatively short system implementation lead times.

However, current FPSO implementations have disadvantages, as all use subsea completions, connected to the FPSO via a turret or buoy. Subsea completions are more complex and expensive than surface completions, with wellknown reliability issues. These complexities, in terms of the necessary sophisticated completion design, the control system and related umbilicals, and the large number of independent lines to the surface for production, control, gas lift and injection, while not prohibitive by any means, have to be shown consideration.