Following the successful installation of a first set of Single Hybrid Risers (SHRs) in a West of Africa oil field, this paper addresses the main lessons learned from the first set and how these were implemented into the design, fabrication, installation of a second set of risers to be installed in a new field by mid 2005. It also addresses the necessary modifications incorporated into several risers for production service applications while the first set of risers was developed specificly for gas/water injection purposes. The production service risers are denoted Pipe-in-Pipe SHRs (PIP-SHRs).
Production systems, due to their fluid characteristics and operating requirements and combined with the long flowlines / deep water nature typical of West African Oil Fields, require insulation of the flowline / riser system and gas lift / chemical injection features for risers. These functional requirements introduce technical challenges particularly for design and installation.
This paper initially presents an overview of the first set of Injection SHRs, more details of which can be found in Ref  and some key advantages of the SHR concept for Fields of this type.
The paper then presents the Operator-defined Functional Requirements particular to the Production SHRs (PIP-SHRs) of the second set of risers, describes some of the design processes involved in implementing these requirements and the resulting configuration.
Details are also presented concerning how aspects of the first set of Injection SHRs have been developed and optimized for implementation into the second set of Injection and PIPSHRs, and furthermore how lessons learnt have allowed optimization of the Field Layout surrounding the FPSO.
Finally, an overview of installation procedures for the first set of Injection SHRs are presented, and in particular how the specific technical challenges pertinent to the PIP-SHRs have been accommodated by adjustments to these procedures.
The injection SHR is a free-standing top-tensioned single pipe riser, connected to a floating vessel via a flexible pipe. It conveys either gas or water down to the flowline and onto the subsea manifolds / wellheads in order to maintain reservoir pressure. The SHR consists of the following components (see figure 1a):
A steel buoyancy tank located 50-75m below sea surface which provides sufficient tension to limit riser inclination.
A chain tether which links the buoyancy tank to the top assembly.
A riser top assembly which transfers the tension from the tether to the linepipe, receives the flexible end and ensures continuity between the flexible and the rigid pipe riser string (figure 1b).
A rigid pipe riser string for which length varies with the water depth.
A riser bottom assembly at the base of the rigid pipe riser string which is connected to a gravity foundation via a flexible joint (outside the fluid flow path) and to the flowline via an M-shape rigid jumper (figure 1c).
A gravity foundation that takes the overpull created by the buoyancy tank.