Single Independent Riser: A Cost Efficient Ultra-Deep Water Riser

Abstract

Hydrocarbon fields discovered in ever deeper waters and uncertainties regarding oil prices are driving the need for cost efficient riser concepts tailored for ultra-deep waters. The Single Independent Riser (SIR) is an innovative hybrid riser configuration optimized for Ultra-Deep water field development. This paper will provide a general overview of the SIR with a specific focus on its installation method and the associated tools that were developed. The SIR is based on a hybrid solution composed, from bottom-up, of a rigid part vertically tensioned by means of distributed or continuous buoyancy and a flexible jumper. This configuration features improved dynamic behavior for the rigid riser section under fatigue and extreme environmental conditions thanks to its compliant shape. The configuration of the flexible jumper ensures displacements of the rigid riser section are significantly decreased compared to that of an SHR. In addition, its design makes it adapted to any water depth beyond 1000 m. The SIR is also inherently safer as it is less sensitive to buoyancy loss than a riser tensioned by mean of a buoyancy tank. This design is highly versatile and can easily be staggered to comply with design constraints, congested lay out and installation scheme. The relevancy of the SIR has been assessed on the basis of several case studies derived from actual projects as well as on-coming prospects. The considered cases include a wide range of environments such as West of Africa, East of Africa, Brazil and riser types, both for pipe in pipe and single pipe arrangements, in order to confirm the suitability of the design. Extreme, wave fatigue, VIV fatigue, interference analyses were conducted through these assessments. In parallel, a dedicated installation method was developed to address the specificities of the design and to cover both dry and wet flexible jumper connections. In the frame of this study, specific installation tools were designed to reduce the need for offshore assets during installation. This paper will first provide a general overview of the SIR, illustrating the arrangement of the various components and providing outcomes of engineering studies confirming the relevancy of the design. A second part will focus on its installation method and the associated tools that were developed.