Competitive CVAR-FPSO concepts with Dry trees in ultra-deepwater; Weathervaning CVAR-FPSO for Brazil and Indonesia vs. Non-weathervaning for West Africa

Abstract A new FPSO concept termed CVAR-FPSO is under development by a JNOC headed Joint Industry Project (JIP). The concept, using Compliant Vertical Access Risers (CVARs), dry trees, a workover rig, and including the ability to complete and workover wells, offers enormous economic and operational benefits to deepwater oil field development. The JIP introduced the CVAR-FPSO - "OTC 12990 An FPSO with Surface Wells and Workover System in Deepwater" at the OTC2001. The original CVAR-FPSO design for Indonesia and Brazil allows weathervane with a turret, fluid transfer system, and riser centering system, which are the most expensive facilities of the FPSO. However, the CVAR-FPSO doesn't require these expensive facilities in West Africa, because a spread mooring system works without weathervaning there. Hence, CVAR-FPSO with CVAR, a spread mooring system and a skidding W.O. rig delivers much more practical and economical performances in West Africa. The central attribute of the CVAR-FPSO is the use of CVARs. These compliant but rigid risers connect wells from the seafloor to the dry trees mounted on the FPSO, and the compliancy can compensate for vessel motion. The CVAR, being vertical access to the wells, also allows completion and workover operations to be performed from the FPSO. The field development concept involves the drilling and temporary abandonment of wells by a MODU. The CVAR-FPSO is then moved onto location. CVARs are installed, and wells are completed from the CVAR-FPSO. CVAR-FPSO would be more economical and practical with the following system; weathervane system in Indonesia and Brazil, and non-weathervane system in West Africa. 1. Introduction The JIP introduced the original CVAR-FPSO design which allows weathervane with a turret, fluid transfer system, and riser centering system (we call it CVAR-FPSO I afterward). Here, we introduce CVAR-FPSO with CVARs, a spread mooring and rig skidding (we call it CVAR-FPSO II afterward). CVAR-FPSO I works in Indonesia and Brazil, while CVAR-FPSO II works in West Africa. Each Figure. 1 and Figure 2 shows CVAR-FPSO I and II. Background of introduction of the CVAR-FPSOs is the following. An FPSO has become a widely used oil production platform worldwide, being used in 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.