U.S. patent application number 09/789688 was filed with the patent office on 2001-10-04 for low heave motion semi-submersible vessel.
Invention is credited to Ludwigson, Robert.
Application Number | 20010026733 09/789688 |
Document ID | / |
Family ID | 22676968 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026733 |
Kind Code |
A1 |
Ludwigson, Robert |
October 4, 2001 |
Low heave motion semi-submersible vessel
Abstract
A semi-submersible vessel 10 adapted to resist heave motion that
includes a plurality of support columns 16, each of which has an
upper end 19 and a lower end 23. A deck 39 is interconnected
between the plurality of support columns 16 at locations upon the
columns 16 proximate the upper ends 19 thereof. The deck 39 is a
box-shaped structure. A ring-pontoon 43 is connected to the
plurality of support columns 16 at locations proximate the lower
ends 23 of each of the columns 16. Each support column 16 has a
longitudinal axis 29 that is inclined upwardly and inwardly from
the ring-pontoon 43 to the deck 39 and the longitudinal axis is
oriented substantially radially from a center point 13 of the
vessel 10. An angle of columnar inclination of the support columns
16 approaches at least five degrees from vertical. The ring-pontoon
43 is rectangular-shaped, and in one variation, is substantially
square-shaped and has corner pontoon portions 49 interconnected by
elongate pontoon portions 56. The square-shaped ring-pontoon has a
centerline 73 intersecting center points 79 of vertically taken
cross-sections 76 of the square-shaped pontoon 43. The elongate
pontoon portions 56 comprise four box-shaped structures 59, each of
which has a substantially four-sided vertically taken
cross-sectional configuration.
Inventors: |
Ludwigson, Robert;
(Goteborg, SE) |
Correspondence
Address: |
Tracy W. Druce
KILPATRICK STOCKTON LLP
Suite 300
11130 Sunrise Valley Drive
Reston
VA
20191-4329
US
|
Family ID: |
22676968 |
Appl. No.: |
09/789688 |
Filed: |
February 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60184463 |
Feb 23, 2000 |
|
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|
Current U.S.
Class: |
405/224.2 ;
114/264 |
Current CPC
Class: |
B63B 35/44 20130101;
B63B 39/005 20130101; B63B 1/107 20130101; B63B 39/00 20130101;
B63B 2001/128 20130101; B63B 2039/067 20130101 |
Class at
Publication: |
405/224.2 ;
114/264 |
International
Class: |
B63B 035/44 |
Claims
What is claimed and desired to be secured by Letters Patent is as
follows:
1. A semi-submersible vessel adapted to resist heave motion, said
semi-submersible vessel comprising: a plurality of support columns,
each column of said plurality of support columns having an upper
end and a lower end; a deck interconnected between said plurality
of support columns at locations proximate said upper ends of each
of said columns of said plurality of support columns; a
ring-pontoon connected to said plurality of support columns at
locations proximate said lower ends of each of said columns of said
plurality of support columns; each of said plurality of support
columns having a longitudinal axis inclined upwardly and inwardly
from said ring-pontoon to said deck.
2. The semi-submersible vessel as recited in claim 1 wherein said
longitudinal axis of each of said plurality of support columns is
oriented substantially radially from a center point of said
vessel.
3. The semi-submersible vessel as recited in claim 2 wherein an
angle of incline of said longitudinal axis of each of said
plurality of support columns is at least five degrees from
vertical.
4. The semi-submersible vessel as recited in claim 2 wherein said
ring-pontoon is substantially rectangular-shaped.
5. The semi-submersible vessel as recited in claim 2 wherein said
ring-pontoon is substantially square-shaped having corner pontoon
portions connected by elongate pontoon portions, and said
square-shaped pontoon having a centerline intersecting center
points of vertically taken cross-sections of said square-shaped
pontoon.
6. The semi-submersible vessel as recited in claim 5 wherein each
of said lower ends of said columns of said plurality of columns is
substantially connected at a corner pontoon portion of said
square-shaped ring-pontoon.
7. The semi-submersible vessel as recited in claim 6 wherein said
deck is positioned substantially inboard of said centerline of said
ring-pontoon.
8. The semi-submersible vessel as recited in claim 6 wherein said
elongate pontoon portions comprise four box-shaped structures, each
of said box-shaped structures having a substantially four-sided
vertically taken cross-sectional configuration.
9. The semi-submersible vessel as recited in claim 6 wherein a
center-point of said lower end of each of said columns of said
plurality of columns is positioned inboard of said centerline of
said ring-pontoon.
10. The semi-submersible vessel as recited in claim 9, further
comprising: a substantially triangularly-shaped tank having a
height substantially equal to a height of said ring-pontoon, said
substantially triangularly-shaped tank positioned at a location
inboard of a corner pontoon portion and of a said lower end of a
column connected to said ring-pontoon at said corner pontoon
portion.
11. The semi-submersible vessel as recited in claim 9, further
comprising: each of said support columns being subdivided into four
quadrants by cruciform bulkheads, each of said bulkheads being
oriented at substantially the same inclination as said longitudinal
axis of said support column; and each of said bulkheads being
arranged as extensions of inward sides of said ring-pontoon.
12. The semi-submersible vessel as recited in claim 9, further
comprising: each of said support columns being subdivided into four
quadrants by cruciform bulkheads, each of said bulkheads being
oriented at substantially the same inclination as said longitudinal
axis of said support column; each of said bulkheads being arranged
as extensions of longitudinally oriented bulkheads contained within
said ring-pontoon; and said longitudinally oriented bulkheads
dividing said pontoon box-shaped structures into at least two
compartments.
13. The semi-submersible vessel as recited in claim 9, further
comprising: an external periphery of said ring-pontoon being
substantially octagonally shaped.
14. The semi-submersible vessel as recited in claim 9, further
comprising: an internal periphery of said ring-pontoon being
substantially octagonally shaped.
15. The semi-submersible vessel as recited in claim 9, further
comprising: an external surface of a corner pontoon portion being
substantially rounded and forming an extension of a lower end of a
respective column connected at said corner pontoon portion.
16. The semi-submersible vessel as recited in claim 9, wherein said
deck is configured as a box-shaped structure.
17. The semi-submersible vessel as recited in claim 9, wherein said
semi-submersible vessel is adapted for accommodating the production
of hydrocarbons from at least one sub-sea well-head that is
connected to said semi-submersible vessel by at least one
substantially rigid pipe laying along the sea floor and extending
upwards in a catenary to said semi-submersible vessel.
18. The semi-submersible vessel as recited in claim 9, wherein said
semi-submersible vessel is adapted for accommodating the production
of hydrocarbons through a substantially vertical rigid riser
terminating at a well-head positioned proximate said deck and which
in turn is connected to production equipment by a jumper-hose.
19. A method for providing a semi-submersible vessel adapted to
resist heave motion, said method comprising: providing: a plurality
of support columns, each column of said plurality of support
columns having an upper end and a lower end; a deck interconnected
between said plurality of support columns at locations proximate
said upper ends of each of said columns of said plurality of
support columns; and a ring-pontoon connected to said plurality of
support columns at locations proximate said lower ends of each of
said columns of said plurality of support columns; locating a
predominance of a buoyancy capacity of said ring-pontoon proximate
said lower ends of said columns of said plurality of support
columns; and inclining each of said plurality of support columns
upwardly and inwardly from said ring-pontoon to said deck.
20. The method as recited in claim 19, further comprising:
orienting a longitudinal axis of each of said plurality of support
columns substantially radially from a center point of said
vessel.
21. The method as recited in claim 19, further comprising:
configuring said ring-pontoon into a substantially rectangular
shape.
22. A semi-submersible vessel adapted to resist heave motion, said
semi-submersible vessel comprising: a plurality of support columns,
each column of said plurality of support columns having an upper
end and a lower end; a deck interconnected between said plurality
of support columns at locations proximate said upper ends of each
of said columns of said plurality of support columns; a
ring-pontoon connected to said plurality of support columns at
locations proximate said lower ends of each of said columns of said
plurality of support columns; at least four of said plurality of
support columns having a longitudinal axis inclined upwardly and
inwardly from said ring-pontoon to said deck and said longitudinal
axis being oriented substantially radially from a center point of
said vessel.
23. A semi-submersible comprising: a superstructure deck; a ring
pontoon having four box-structures having a substantially
four-sided cross-section and formed into a symmetrical square ring;
four columns inclined inwards toward the upper end with an angle of
inclination of at least five degrees from vertical; and a
longitudinal axis of said pontoon box-structures being located
outside of lower end center-points of said columns.
Description
RELATED PATENT APPLICATIONS
[0001] This patent application claims priority to U.S. Provisional
Application No. 60/184,463 filed Feb. 23, 2000. Said application in
its entirety is hereby expressly incorporated by reference into the
present application.
TECHNICAL FIELD
[0002] The present invention relates generally to off-shore
semi-submersible platforms, and more specifically to
semi-submersible platforms where low heave motion is required.
BACKGROUND ART
[0003] Offshore platforms of the so called semi-submersible type
typically include a superstructure deck carried upon columns
supported by submersible pontoon system. The pontoon system can
include either two or more elongate and usually parallel pontoon
bodies, each of which normally extend beyond the columns. An
alternative configuration for the submersible portion of the
structure is a ring-pontoon construction. The ring-pontoon type of
construction typically consists of four box-shaped structures
formed together into a square ring.
[0004] While semi-submersibles with parallel pontoons normally have
a number of braces between the pontoons and/or columns for taking
up structural loads caused by wave-forces acting on the pontoons,
ring-pontoon type semi-submersibles have the advantage of not
requiring such braces. In the case of the ring-pontoon type
semi-submersible, the structure of the pontoon ring itself forms a
sufficiently strong and rigid structural member that interconnects
the columns. As a result, no braces are needed. On the downside,
however, the traditional ring-pontoon design for semi-submersibles
has resulted in a pontoon geometry that detrimentally produces
higher heave motions than counterpart semi-submersibles of similar
capacities that have parallel pontoons. Such a traditional
ring-pontoon configuration may be appreciated in FIG. 4 where a
portion of one is superimposed on the left-hand side thereof. Still
further, the traditional ring-pontoon configuration suffers from
higher resistance characteristics when moved through the water,
give that at least two sides of the ring-pontoon are oriented
transversely to the direction of travel thereby creating
significant drag when the semi-submersible is being moved between
locations.
[0005] Ring-pontoon styled semi-submersibles have normally been
used for the production of hydrocarbons. In this connection, the
semi-submersible is held stationary at a location for long periods
of time. These periods may extend over a number of years, and as a
result the resistance experienced when the semi-submersible is
moved is of negligible importance. On the other hand, as a result
of the strong and rigid structural characteristics provided by the
ring-pontoon, stresses induced in the platform are minimized and
accordingly, so is the risk of cracks being caused in the
platform.
[0006] When used in the production of hydrocarbons,
semi-submersible platforms have normally been connected to sub-sea
wellheads with flexible hose-type riser(s). Recently, however,
there have been two developments in this area. First, there has
been an increased interest or demand for so-called steel catenary
risers. In this configuration, a substantially rigid steel, or
other metal, pipe is configured so that a portion of the pipe lies
along the sea floor and another portion extends upwards toward the
water's surface in a catenary curve to a semi-submersible vessel.
Due to the rigidity of the pipe, large heave motions (substantially
vertical movements caused in a platform) of the semi-submersible
result in considerable fatigue loading on such steel catenary
risers. For ring-pontoon styled semi-submersibles, the larger
heave-motions experienced have meant that steel catenary riser
configurations have been less feasible to use in combination with
such ring-pontoon designs in comparison to semi-submersibles having
parallel pontoons.
[0007] In some circumstances, it is preferred to have dry wellheads
located above the sea surface. These dry wellheads are connected to
the sea floor through vertical rigid risers. The dry wellhead may
be connected to production equipment on the platform by a "jumper
hose", or in certain applications, by telescoping devices utilized
for holding the dry wellheads. In areas that experience large
waves, the magnitude of resulting heave-motions caused in
semi-submersibles has meant that the stroke of such telescoping
devices and the length of such jumpers necessitated by the movement
is too great for practical utilization with dry wellheads and rigid
risers in combination with semi-submersibles.
[0008] In view of the above described deficiencies associated with
the use of known designs for semi-submersible offshore platforms
not specifically designed to give low heave motions, the present
invention has been developed to alleviate these drawbacks and
provide further benefits to the user. The aim of the present
invention is to provide a configuration for a ring-pontoon styled
semi-submersible platform less susceptible to heave-motion which in
turn facilitates the use of steel catenary risers and/or rigid
risers associated with dry wellheads. These enhancements and
benefits are described in greater detail hereinbelow with respect
to several alternative embodiments of the present invention.
[0009] Certain aspects of the invention are discussed in
presentation papers included herewith as pages A-1 through A-6 and
to be considered part of this provisional patent application
filing.
DISCLOSURE OF THE INVENTION
[0010] The present invention in its several disclosed embodiments
minimizes the drawbacks described above with respect to
conventionally designed semi-submersible platforms, and
incorporates several additional and beneficial characteristics
consequent of the new designs. The present invention uniquely and
advantageously combines ring-pontoon design with inclined columns
to produce a semi-submersible vessel or platform having superior
heave characteristics.
[0011] It has, for conventional two-pontoon semi-submersibles, been
learned that the heave-motion is improved if the displacement of
the submerged pontoons are moved away from the center of the
semi-submersible. For two-pontoon type semi-submersibles, this has
resulted in "dog-bone" shaped pontoon geometry.
[0012] The same principles instruct that a uniform configuration
along the length of the elongate portions of a ring-pontoon should
be modified to transfer buoyancy from the mid-length region of the
elongate region of the elongate portions to the end region(s)
thereof. This has been uniquely accomplished by effectively
"stretching" the ring-pontoon structure in the present invention,
while maintaining a substantially constant upward buoyant factor
for the platform as a whole. As a result, the cross sectional area,
taken vertically across the ring-pontoon, is reduced. As can be
best appreciated in FIG. 4, this effectively achieves a transfer of
a portion of the buoyance previously experienced mid-length of the
elongate portion of the pontoon (A), and moves it to end regions
thereof (B' and B") nearer the columns. As a result, passing waves
create less heave motion in the semi-submersible platform.
[0013] Another unique feature of the present invention is the
inclination of each column from corners of the ring-pontoon
inwardly toward a center point of the vessel. Traditionally,
inclined columns have been known, on two-pontoon type
semi-submersible vessels. In the present invention, the
dual-direction inclination of the columns further contributes to
the semi-submersible's capabilities for resisting heave motion
induced as waves pass.
[0014] The beneficial effects described above apply generally to
the exemplary embodiments disclosed herein of the heave-resistant
semi-submersible vessel design(s). The specific structures through
which these benefits are delivered will be described in detail
hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will now be described in greater detail in the
following way, by example only, and with reference to the attached
drawings, in which:
[0016] FIG. 1 is an elevational view of a heave-resistant
semi-submersible vessel constructed according to the present
invention.
[0017] FIG. 2 is a substantial cross-sectional view taken along
line 2-2 of FIG. 1 showing bulkheads of the support columns
configured as extensions of interior sides of the ring-pontoon.
[0018] FIG. 3 is a substantial cross-sectional view taken along
line 2-2 of FIG. 1 showing bulkheads of the support columns
configured as extensions of longitudinally oriented bulkheads
contained within the ring-pontoon.
[0019] FIG. 4 shows the semi-submersible vessel of FIG. 3, with an
illustration of a conventionally designed, non-inclined columnar
system superimposed on a left-hand side thereof and in which the
traditionally configured columns are substantially vertically
oriented and the elongated portions of that traditional
ring-pontoon have larger cross-sectional areas.
[0020] FIG. 5 is a perspective view of an exemplary embodiment of a
semi-submersible vessel constructed according to the present
invention.
[0021] FIG. 6 is a schematic of the box-shaped structural portion
of the elongate pontoon portion demonstrating a vertical
cross-section thereof.
MODE(S) FOR CARRYING OUT THE INVENTION
[0022] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention that
may be embodied in various and alternative forms. The figures are
not necessarily to scale, some features may be exaggerated or
minimized to show details of particular aspects or components.
Therefore, specific structural and functional details disclosed
herein are not to be interpreted as limiting, but merely as a basis
for the claims and as a representative basis for teaching one
skilled in the art to variously employ the present invention.
[0023] With reference to the figures, a semi-submersible vessel 10
adapted to resist heave motion is shown. The semi-submersible
vessel 10 includes a plurality of support columns 16, each of which
has an upper end 19 and a lower end 23. A deck 39 is interconnected
between the plurality of support columns 16 at locations upon the
columns 16 proximate the upper ends 19 thereof. Preferably, the
deck 39 is configured as a box-shaped structure. A ring-pontoon 43
is connected to the plurality of support columns 16 at locations
proximate the lower ends 23 of each of the columns 16. Each support
column 16 has a longitudinal axis 29 that is inclined upwardly and
inwardly from the ring-pontoon 43 to the deck 39 and the
longitudinal axis is oriented substantially radially from a center
point 13 of the vessel 10. Though described in terms of a
longitudinal axis 29 of the columns, in general, it is also the
structural component of the column 16 itself that is oriented at
such an inclination. While the angle of inclination may vary widely
and still produce the beneficial characteristics described herein,
a preferred version of the invention embodies an angle of columnar
inclination of the longitudinal axis 29 of each of the support
columns 16 approaching at least five degrees measured from
vertical.
[0024] While it is preferred that the ring-pontoon 43 be
rectangular-shaped, it is especially preferred that the
ring-pontoon 43 be substantially square-shaped and have corner
pontoon portions 49 interconnected by elongate pontoon portions 56.
The square-shaped ring-pontoon has a centerline 73 intersecting
center points 79 of vertically taken cross-sections 76 of the
square-shaped pontoon 43. The elongate pontoon portions 56
constitute four box-shaped structures 59, each of which has a
substantially four-sided vertically taken cross-sectional
configuration.
[0025] As shown, each of the lower ends 23 of the columns 16 is
connected at a corner pontoon portion 49 of the square-shaped
ring-pontoon 43.
[0026] In a variation of the design, a center-point 26 of the lower
end 23 of each of the columns 16 is positioned inboard 46 of the
centerline 73 of the ring-pontoon 43.
[0027] A substantially triangularly-shaped tank 93 is included that
has a height 96 substantially equal to a height 83 of the
ring-pontoon 43. The triangularly-shaped tank 93 is positioned at a
location inboard 46 of a corner pontoon portion 49 and of the lower
end 23 of a column 16 connected to the ring-pontoon 43 at that
corner pontoon portion 49. In a preferred embodiment, and as
illustrated, there are four such triangularly-shaped tank 93, one
each located inboard at the four corner pontoon portions 49.
[0028] In one embodiment, each of the support columns 16 is
subdivided into four quadrants 36 by cruciform bulkheads 33. Each
of the bulkheads 33 are oriented at substantially the same
inclination as the longitudinal axis 29 of the support column 16.
Still further, in this embodiment, each of the bulkheads 33 are
arranged as extensions of interior sides 69 of the ring-pontoon 43.
Alternatively, the bulkheads 33 may be arranged as extensions of
longitudinally oriented bulkheads 63 contained within the
ring-pontoon 43. In this instance, the longitudinally oriented
bulkheads 63 divide the box-shaped portions 59 of the ring-pontoon
43 into at least two compartments 66.
[0029] In one embodiment, both an external periphery 86 and an
internal periphery 89 of the ring-pontoon 43 are substantially
octagonally shaped in vertical cross-section.
[0030] In another embodiment, an external surface 53 of a corner
pontoon portion 49 is substantially rounded and forms an extension
of a lower end 23 of a respective column 16 connected at that
corner pontoon portion 49.
[0031] Regarding utilization aspects of the present invention, in
one embodiment, the semi-submersible vessel 10 is adapted to
accommodate its own incorporation into production processes for
hydrocarbons coming from a sub-sea well-head. In one instance, the
well-head is connected to the semi-submersible vessel 10 by a
substantially rigid pipe laying along the sea floor and extending
upwards in a catenary to the semi-submersible vessel 10. Similarly,
the semi-submersible vessel 10 is also adapted for accommodating
the production of hydrocarbons through a substantially vertical
rigid riser terminating at a well-head positioned proximate the
deck 39 and which in turn is connected to production equipment by a
jumper-hose.
[0032] In an alternative embodiment, the present invention takes
the form of a method for providing a semi-submersible vessel
adapted to resist heave motion. The method includes the steps of
providing, as described above, a plurality of support columns 16,
each having an upper end 19 and a lower end 23. A deck 39 is
interconnected between the plurality of support columns 16 at
locations proximate the upper ends 19 thereof. A ring-pontoon 43 is
connected to the support columns 16 at locations proximate the
lower ends 23 of each of the columns 16. A primary characteristic
of the invention includes locating a predominance of a buoyancy
capacity of the ring-pontoon 43 proximate the lower ends 23 of the
columns 16. The design method also includes inclining each of the
plurality of support columns 16 upwardly and inwardly from the
ring-pontoon 43 toward the deck 39.
[0033] The longitudinal axis 29 of each of the plurality of support
columns 16, an in turn the support column 16 itself, is oriented
substantially radially from a center point 13 of the
semi-submersible vessel 10. As indicated above, the ring-pontoon 43
is configured into a substantially rectangular shape, and
preferably a square shape.
[0034] A semi-submersible vessel adapted to resist heave motion and
various of its components have been described herein. These and
other variations, which will be appreciated by those skilled in the
art, are within the intended scope of this invention as claimed
below. As previously stated, detailed embodiments of the present
invention are disclosed herein; however, it is to be understood
that the disclosed embodiments are merely exemplary of the
invention that may be embodied in various forms.
INDUSTRIAL APPLICABILITY
[0035] The present invention finds applicability in the offshore
platform industries, and more specifically in those parts of that
industry in which such offshore platforms are required to have low
heave-motion characteristics.
* * * * *