Hybrid Riser Towers – Not just for Deepwater
EVENT: OTC Asia
1 Mar 2018
Most people know the Hybrid Riser Tower solution, combining the use of steel pipes in a freestanding bundle and multiple flexible jumpers for connection to a floating host vessel, from the 3 towers installed in 2001 offshore Angola in 1,350m water depth to the Girassol FPSO.
Little known is the fact that the first bundled riser tower, in a slightly different arrangement preceding Girassol, was actually installed by Placid in Green Canyon (1988), and the same riser tower was later re-deployed by Ensearch in Garden Banks (1994, now decommissioned), both in the Gulf of Mexico in less than 650m water depth to a semi-submersible production platform.
This paper describes the adaptation of the bundled hybrid riser tower concept for subsea connection to a FPSO in Indonesia in only 90m water depth. The ‘mini’ riser tower, comprising 6 risers in the bundle and installed in 2013, made full use locally available materials, fabrication labours, skills and facilities, and installation capabilities in the region. This project, and its successful implementation, paves the way for more SE Asian operators to maximise local contents, optimise costs and exercise better project control for their upcoming developments.
This hybrid riser tower solution can lend itself readily for HPHT field developments, or aggressive production fluids, when conventional riser solutions such as bonded or unbonded flexible pipes, and corrosion resistance alloy (CRA) clad steel catenary risers cannot handle the fluid properties or the shallow water depths, respectively. Work is underway to use high quality thermoplastic composite pipe (TCP) as the jumpers in a hybrid tower to overcome the chemical issues.