Note: Descriptions are shown in the official language in which they were submitted.
CA 02400903 2002-08-22
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METHOD AND APPARATUS FOR INCREASING
FLOATING PLATFORM BUOYANCY
BACKGROUND OF THE DISCLOSURE
The present invention relates generally to floating platform systems for
testing and
producing hydrocarbon formations found in deep (600-10,000 feet) offshore
waters. More
particularly, the invention relates to a method and system for changing the
buoyancy of the
floating platform to accommodate changes in platform payload and water depth
requirements
without redesigning the platform hull.
The exploration for oil and gas deposits in offshore waters, and recovery of
the oil and
gas therefrom is very expensive. Large capital expenditures are required and
thus only large oil
and gas deposits justify such expenditures. Smaller oil and gas deposits
usually do not justify
large capital investments and therefore are deemed to be uneconomical to
produce.
Various methods aiid offshore production systems have been utilized to locate
and
recover offshore oil and gas deposits. Production systems such as converted
Mobile Offshore
Drilling Units ("MODU") and Tendon Leg Platforms (TLP) are typically used in
deep waters.
Even these systems, however, can be quite expensive to manufacture and
install.
There continues to be a need for improved platform and drilling systems,
particularly for
use in deep waters, which would justify the economic investment to produce
even relatively
small oil and gas fields. Drilling and production platforms, such as TLP's,
are engineered for use
in particular offshore environments and to support a maximum payload. The
specifications for
the platform are based on assumptions which may or may not prove to be
accurate once the
platform is installed and in use for a period of time. Other factors, such as
the discovery of
recoverable oil and gas from adjacent deposits may alter the payload
requirements for a platform
already in use. Thus, being able to increase the payload a platform can
support without
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redesigning the hull would be highly desirable and significantly reduce the
cost of producing
offshore oil and gas deposits. Cost reductions can also be had by eliminating
the need for
completely redesigning the hull and node structure of the platform to
accommodate different
payload requirements. The buoyancy of a floating platform may be increased by
extending
the column length of the platform rather than redesigning the hull, thereby
saving time and
engineering costs associated with redesigning the platform hull.
It is therefore an object of the present invention to provide a floating
platform adapted
to support an increase in payload capacity without redesigning the structural
design of the hull
of the platform. The increase in payload capacity is accommodated by attaching
a column
extension to the lower end hull of the platform while in the fabrication yard.
It is another object of the present invention to provide a floating platform
whereby the
payload capacity of the platform maybe increased after the platform is located
in the field.
Such an increase in payload capacity is provided by attaching a buoyancy
module to the
platform hull rather than redesigning the hull and node structure of the
platform.
SUMMARY OF THE INVENTION
Certain exemplary embodiments can provide a floating platform comprising a
hull
supporting one or more decks in a body of water above the water line, anchor
means securing
the hull to the seabed, said hull including buoyancy means for supporting said
one or more
decks of said platform above the water line and pontoons secured on a lower
end of said hull
and supplemental buoyancy means mounted on said hull; below the pontoons to
increase the
buoyancy of said platform.
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Certain exemplary embodiments can provide a method for increasing the payload
capacity of a floating platform having a hull; the method comprising securing
supplemental
buoyancy means provided below pontoons secured on a lower end of the hull of
said
platform.
Embodiments provide a floating platform for recovery of oil and gas from
offshore
oil and gas fields. The platform supports one or more decks above the water
surface to
accommodate equipment for drilling and processing oil, gas and water recovered
from the oil
and gas field. In an embodiment, the platform includes a hull having a portion
located
substantially below the water surface, and including a portion which extends
above the water
surface. The platform hull includes a base and is anchored to the seabed by
one or more
tendons secured to the base of the hull at one end thereof and to the seabed
at the opposite
ends of the tendons. The payload carrying capacity of the platform is
increased without
redesigning the
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structural design of the platform hull by attaching a column extension to the
bottom of the hull
of the platform.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features, advantages and objects
of the
present invention are attained can be understood in detail, a more particular
description of the
invention briefly summarized above, may be had by reference to the embodiments
thereof which
are illustrated in the appended drawings.
It is noted, however, that the appended drawings illustrate only typical
embodiments of
this invention and are therefore not to be considered limiting of its scope,
for the invention may
admit to other equally effective embodiments.
Fig. 1 is a side view of a floating platform anchored to the seabed;
Fig. 2 is a side view of the floating platform of the invention including a
buoyancy
extension attached to the bottom of the hull of the platform;
Fig. 3 is a partial side view of an alternate embodiment of the platform of
the invention
depicting a buoyancy module mounted to the bottom of the hull of the platform;
Fig. 4 is a top plan view of the platforin of the invention shown in Fig. 3;
Fig. 5 is a partial exploded view of the connector means for securing the
buoyancy
module of the invention to the hull of the platform; and
Fig. 6 is a side view of the platform of the invention illustrating riser or
flow line support
?0 means mounted on the buoyancy module of the invention.
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DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring first to Fig. 1, the floating platform of the invention is generally
identified by
the reference numeral 10. The platform 10 includes a central column or hull 12
which provides
positive buoyancy and vertical support for the platform 10. One or more decks
14 are supported
on the hull 12 above the water surface 16. Drilling and/or production
equipment necessary for
the recovery and processing of oil, gas and water recovered from the oil and
gas field are secured
on the deck 14.
The hull 12 extends upward from the base or keel of the hull 12. The base node
of the
hull 12 includes pontoons 18 extending radially outward from the hull 12. The
platform 10 is
anchored to the seabed by tendons 20 secured at one end thereof to the
pontoons 18 and at the
opposite ends thereof to foundation piles (not shown in the drawings) embedded
in the seabed.
The hull 12 provides sufficient buoyancy to support the payload of the
platform 10, which
payload includes the deck 14, drilling and/or completion equipment, production
facilities,
production and drilling risers and sufficient excess buoyancy to develop the
tendon pre-tension.
The platform 10 is designed for the environmental and depth conditions at the
offshore
location of an oil and gas deposit of interest. At other locations, other
platforms may be required
to efficiently recover the oil and gas from other subsea deposits. Such other
platforms may be
required to carry a greater payload than the platform 10 is designed to
support. The increased
payload, however, may be accominodated by increasing the buoyancy of the
platform 10. An
increase in buoyancy may be accomplished by extending the length of the hull
12 rather than
redesigning the structural design of the hull and base node structure of the
platform 10. Likewise,
the payload requirements for a platform may increase after installation, in
which case a buoyancy
module 32, as shown in Fig. 3, may be mounted to the bottom of the hull 12 of
the platform 10.
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Referring now to Fig. 2, the column extension 22 is a relatively short
cylindrical chamber
having an outside diameter approximately equal to the outside diameter of the
hull 12. The
column extension 22 is welded to the bottom of the hull 12 at weld 23 at the
fabrication or
construction site of the platform 10.
Referring now to Fig. 3, an alternate embodiment of the invention depicts a
buoyancy
module 32 mounted to the bottom of the hull 12. In the embodiment of Fig. 3,
the buoyancy
module 32 is added to the offshore platform 10 while it is located in the
field. to increase the
payload capacity of the platform 10 so that additional equipment may be
installed on the deck
of the platform 10 or so that the platform 10 may be installed at a deeper
water site. The
buoyancy module 32, like the column extension 22 shown in Fig. 2, is a
relatively short
cylindrical chamber having a diameter approximately equal to the diameter of
the hull 12.
Mounting posts 24 secure the module 32 to the hull 12. The mounting posts 24
may be welded
or otherwise fixed to the hull 12 and module 32.
Alternatively, the mounting posts 24 may be pre-installed about the periphery
of the hull
12, by welding or other connection means, so that the module 32 may be
installed at a later time
after the platform 10 is anchored offshore, as required, to increase the
payload capacity of the
platform 10. The buoyancy module 32, shown in Fig. 3, is likewise provided
with mounting posts
26 for cooperating engagement with the posts 24 mounted on the hull 12. As
more clearly shown
in Fig. 5, the mounting posts 24 are adapted to be received or telescoped into
the posts 26.
Various connections means, such as grout, mechanical connectors or welding,
may be employed
to lock the post 24 and 26 together and thus secure the buoyancy module 32 to
the bottom of the
hull 12. This manner of connection has the added benefit of permitting the
module 32 to be more
easily detached from the hu1112 in the event the payload requirements of the
platform 10 change
and the buoyancy module 32 is no longer needed or to substitute a larger
module in the event
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greater buoyancy is required. Two or more modules 32 may also be connected in
piggy-back
manner in vertical alignment with the hull 12 in the event additional buoyancy
is required.
The column extension 22 and buoyancy module 32 may be provided with the
necessary
plumbing, including a fill port 28 and vent 30, for connection with the
ballast system of the
platform 10. Additional riser hangers, such as porches 33, for hanging risers
or flow lines 34
therefrom, as shown in Fig. 6, may be installed on the column extension 22 or
module 32, as
required.
The shape of the column extension 22 and module 32 is depicted as a closed
cylinder or
plug for illustrative purposes. It is understood that the extension 22 and
module 32 may comprise
various shapes. If, for example, the hull 12 includes a moon pool, the
extension 22 and module
32 may be provided with an axial passage for matching alignment with the
profile of the moon
pool. The extension 22 and module 32 in such an arrangement would have a shape
or profile
similar to a donut. Likewise, the extension 22 and module 32 may include
radial extensions or
arms matching the profile of the pontoons 18, which arms may be secured to the
bottom of the
pontoons 18.
While one or more preferred embodiments of the invention has been shown and
described, other and fiu-ther embodiments of the invention may be devised
without departing
from the basic scope thereof, and the scope thereof is determined by the
claims which follow.
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