Hydraulic and earth engineering – Marine structure or fabrication thereof – Floatable to site and supported by marine floor
Reexamination Certificate
1999-01-21
2001-04-03
Lillis, Eileen D. (Department: 3673)
Hydraulic and earth engineering
Marine structure or fabrication thereof
Floatable to site and supported by marine floor
C405S224200, C441S004000, C166S345000
Reexamination Certificate
active
06210075
ABSTRACT:
BACKGROUND OF THE INVENTION
Offshore hydrocarbon production systems generally include a plurality of wells extending to undersea deposits of oil, with trees located on the sea floor, wherein each tree includes a plurality of valves and pipe couplings. Risers extend up from the trees to apparatus floating at the sea surface that has oil handling equipment. One low-cost production apparatus comprises a spar buoy or spar in the form of a body having a height that is a plurality of times its average width, and usually at least 5 times as tall as wide. The small width of the spar results in only moderate drift in reaction to winds, currents, and waves, which results in only moderate bending of the risers and fluid-carrying pipes therein. To keep the spar upright, its upper portion is made highly buoyant while its lower portion contains considerable ballast to weight it and thereby lower its center of gravity. There are several occasions when it would be desirable to disconnect a spar buoy from the risers that extend down to the sea floor. Some of these include disconnection when icebergs approach, and disconnection to permit use of a workover vessel such as a semi-submersible platform that carries pipes that can extend to the tree to carry tools to clean out wax deposits. In deep seas, expensive workover vessels must be used, with conduits that can extend down to trees at the sea floor. An offshore hydrocarbon production system that facilitated installation of the spar and its disconnection, especially to enable a workover vessel to work on the risers, trees and undersea pipes, would be of value.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, an offshore installation is provided that uses a spar at the sea surface that is coupled through risers extending to the sea floor, which facilitates detachment of the spar in the event of an approaching iceberg or when conduits such as risers must be cleaned, and which simplified set-up of the system and ballasting of the lower end of the spar. The system includes a subsea buoy lying under the spar and attached to the spar. The subsea buoy can be made negatively buoyant to ballast the lower end of the spar and keep the spar upright. The subsea buoy can be made positively buoyant to hold up risers while the spar moves away from the vicinity of the installation. The upper ends of the risers can be attached to buoyancy cans that can slide vertically with respect to the subsea buoy to keep the risers taut, and with trees at the upper ends of the buoyancy cans. If a workover vessel is to be used, it can connect to the trees at the upper ends of the risers, without pipes from the workover vessel having to extend all the way down to the sea floor.
The subsea buoy can be hung from the lower end of the spar by a chain or other tension member which allows the spar to tilt by more than the subsea buoy, so as to minimize bending of the risers at the bottom of the subsea buoy. Flexible hoses extend from the upper end of the subsea buoy, as from the trees on the buoyancy cans, to the lower end of the spar, where the hoses connect to spar pipes extending up to handling equipment at the upper end of the spar. The use of a hanging ballast for a spar, can be used in any spar installation, where the hanging weight lies closer to the surface than the sea floor.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
REFERENCES:
patent: 3196958 (1965-07-01), Travers et al.
patent: 3677310 (1972-07-01), Dobler et al.
patent: 3778854 (1973-12-01), Chow
patent: 3982401 (1976-09-01), Loggins
patent: 4130076 (1978-12-01), van Bilderbeek
patent: 4234047 (1980-11-01), Mott
patent: 4284143 (1981-08-01), Scherrer et al.
patent: 4371037 (1983-02-01), Arnaudeau
patent: 4630681 (1986-12-01), Iwamoto
patent: 4637335 (1987-01-01), Pollack
patent: 4702321 (1987-10-01), Horton
patent: 4906139 (1990-03-01), Chiu et al.
patent: 5098323 (1992-03-01), Poldervaart et al.
patent: 5558467 (1996-09-01), Horton
patent: 5758990 (1998-06-01), Davies et al.
patent: 5881815 (1999-03-01), Horton, III
patent: 6027286 (2000-02-01), Pollack
patent: 2040599 (1971-01-01), None
patent: 1533973 (1978-11-01), None
Imodco Inc.
Lagman Frederick L.
Lillis Eileen D.
Rosen Leon D.
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