Bundle Hybrid Offset Riser (BHOR): An Advanced Solution for Improved Riser Tower Systems Installability and Operability in Deepwater West of Africa

Abstract

Several riser system configurations have been developed to assist the recovery of hydrocarbon reserves from deepwater reservoirs. Vertical hybrid riser systems present a number of attractive features and are currently proposed for various West of Africa deepwater developments. The paper describes the Bundle Hybrid Offset Riser (BHOR) concept of a vertical hybrid riser which incorporates bundle arrangements of multiple conduits conceived to enhance the flow assurance performance of the system to allow for the delivery of the production stream to the surface treatment facilities under the production conditions which are anticipated during the field life. Gas lift capability is also incorporated in the bundle arrangement. The passive thermal insulation properties of the system are then addressed by presenting the ability of the concept to accommodate both syntactic and gel materials. Further to the above, the BHOR concept fabrication and installation scenario is discussed in relation to the specific features and constraints which characterize the West of Africa deepwater conditions. Moreover, the paper addresses both the mechanical and structural design issues associated to the proposed system configuration with specific focus on the anticipated improvements in the dynamic and fatigue behavior both under in-place conditions and during installation by tow. Finally, the paper describes the operational advantages offered by the Active Circulation System (ACS) based on hot fluid circulation from the top of the riser down to the gas lift injection point which is incorporated in the BHOR concept to provide hydrate blockage removal capability following either accidental conditions or prolonged shut-downs exceeding the cool down system capacity.