Hydraulic and earth engineering – Marine structure or fabrication thereof – With anchoring of structure to marine floor
Reexamination Certificate
1997-12-23
2001-10-30
Taylor, Dennis L. (Department: 3672)
Hydraulic and earth engineering
Marine structure or fabrication thereof
With anchoring of structure to marine floor
C166S359000, C405S195100
Reexamination Certificate
active
06309141
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a heave resistant, deepwater platform supporting structure known as a “spar.” More particularly, the present invention relates a deepwater catenary riser system suitable for deployment with such spars.
Efforts to economically develop offshore oil and gas fields in ever deeper water create many unique engineering challenges. One of these challenges is providing a suitable surface accessible structure. Spars provide a promising answer for meeting these challenges. Spar designs provide a heave resistant, floating structure characterized by an elongated, vertically disposed hull, having a very deep draft. Most often this hull is cylindrical, buoyant at the top and with ballast at the base. The hull is anchored to the ocean floor through risers, tethers, and/or mooring lines.
Vertical access production risers can connect production facilities on the platform to wells on the seafloor therebeneath. The production facilities receive and initially process the well fluids which are then sent into a subsea pipeline network through an export riser. While the ability to service the wells through a vertical riser is served by the production risers, these export lines derive no analogous benefit and it is desirable to avoid the complications required for motion compensated support attendant such vertical deployment. For this reason, export riser requirements are often addressed with deepwater steel catenary risers that may be supported directly by the platform.
Access to the catenary risers directly at the moonpool would be desirable to facilitate an officiant layout for processing facilities and bringing the risers onto the platform through the moonpool would serve to protect the risers from possible collision damage with service vessels. However, the very deep draft of the spar inhibits deploying the catenary risers through a central moonpool. Catenary risers may also be deployed for import risers connecting the spar to remote or satellite wells.
Thus, there is a clear need for catenary riser system suitable for deployment in a spar type offshore structure. Further there is a need for such a catenary riser system that is compatible with deploying vertical access production wells and/or drilling risers from the spar platform.
SUMMARY OF THE INVENTION
The present invention is a spar platform having a deck supported by a buoyant tank assembly having a first buoyant section connected to the deck and defining a central moonpool and a second buoyant section disposed beneath and axially vertically aligned with the first buoyant section. A buoyant section spacing structure connects the first and second buoyant sections in a manner providing a horizontally extending vertical gap therebetween and a counterweight spacing structure connects the counterweight to the buoyant tank assembly. A flexjoint receptacle connected to the exterior base of the second buoyant section receives a receptacle connection on the exterior of the riser to support a catenary section of the riser between the receptacle connection and the seafloor. An exterior section of the riser mounts to the exterior of the second buoyant section and an ingress section passes through the horizontally extending vertical gap to the moonpool. An interior section of the riser then extends to the deck through the moonpool within the first buoyant section.
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Allen Donald Wayne
Balint Stephen W.
Cox Bobby Eugene
Henning Dean Leroy
Shell Oil Company
Taylor Dennis L.
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