Parque das Conchas (BC-10) Steel Lazy Wave Riser Installation: Pre-Abandonment, Recovery and Transfer Challenges

Abstract

Abstract The Parque das Conchas (BC-10) project is located in deepwater, in block BC-10, off the coast of Brazil. It comprises a number of subsea fields tied back to a centrally located turret moored Floating Production Storage and Offloading (FPSO) host in some 1800 meters of water. This paper describes the installation engineering challenges for the 7 Steel Lazy Wave Risers (SLWR) and the dynamic sections of the 3 umbilicals that are part of the Phase 1 scope of the project. To decouple the schedule risk of the installation of the subsea systems from the FPSO arrival schedule, a pre-abandonment, recovery and transfer method of the SLWR and umbilical in lazy wave configuration was chosen. Successful installation of SLWR by this method to the FPSO turret required the design of a suitable pre-abandonment layout taking into consideration the installation sequence and careful assessment of the risks involved particularly in terms of clearance and interference issues with FPSO mooring lines and the already transferred SLWRs/ umbilicals. Pre-abandonment, recovery and transfer by keel haul of this " worlds first?? SLWR system had a number of challenges that had to be overcome. These include determining the pre-abandonment route of SLWR, lay tension to balance curve stability, lazy wave ‘hump’ stability while on seabed, lay stresses on flex joint, etc. The recovery and transfer operations had challenges associated with clearance monitoring with mooring lines and already installed risers as well as maintaining the design touch down points. The pre-abandonment layout was developed using Shell's in-house design tool for high level assessment followed by detailed engineering installation analysis by Subsea7 using Orcaflex. This enabled the development of analytical procedures to assess and mitigate the risks involved in pre-abandonment, recovery and transfer operation of SLWR. Subsea7's construction vessel ‘Seven Oceans’ performed the SLWR and dynamic umbilical installation activities. This paper describes how this complex riser operation was modeled and successfully executed. Introduction The Parque das Conchas (BC-10) project is located off the coast of Brazil in the Campos Basin in water depths from 1190 meters to 1940 meters. Shell is the operator with a 50% working interest in a Joint Venture with Petrobras (45%) and ONGC (15%). During Phase I of the project, the Ostra, Abalone and Argonauta B-West fields were tied-back via SLWR's to the turret-moored FPSO in approximately 1800m water depth as presented in Figure 1. Argonauta O-North is planned to be developed as part of Phase II of the project.