This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 16630, "Bundle Hybrid Offset Riser: An Advanced Solution for Improved Riser-Tower-Systems Installability and Operability in Deep Water West of Africa," by Giovanni Chiesa, Saibos S.A.S.; Floriano Casola, Saipem S.A.; and Francois Regis Pionetti, Saibos S.A.S., prepared for the 2004 Offshore Technology Conference, Houston, 3-6 May.
Several riser-system configurations have been developed to assist hydrocarbon recovery from deepwater reservoirs. Vertical hybrid-riser systems were pro-posed for various deepwater developments west of Africa. The bundle-hybrid-offset-riser (BHOR) concept of a vertical hybrid riser uses bundle arrangements of multiple conduits to enhance flow assurance for delivering the production stream to the surface treatment facilities at production conditions anticipated during the field life. The bundle arrangement includes gas lift capability.
Development of hydrocarbon resources in deep and ultradeep waters requires suitable gathering and transportation systems to deliver the production stream to the surface treatment facilities from remote subsea wells. Flow-assurance management becomes more important as reservoir exploitation moves toward deep water. The riser system is critical for flow-assurance management because of the following aspects.
- Significant temperature drop following depressurization along the riser conduits may affect the arrival temperature of the produced fluids at the surface receiving facilities.
- Gas lift injection capability boosts produced fluids to the surface, particularly when the gas content of the produced fluid is low; the gas lift stream must be delivered to the bottom of the riser conduits under certain pressure and flow-rate conditions that minimize the temperature drop along the riser length.
- Production conduits filled with wet gas following shutdown can lead to potential hydrate formation during restart, or produced fluids can enter the gas lift line through the injection orifice, potentially blocking the line in the event of low temperatures.
- Methanol-injection capability can eliminate hydrate on restart.
- Full depressurization of the flowline can dissipate a flowline blockage
