Ships – Floating platform – Float assembly
Reexamination Certificate
1999-10-08
2001-04-10
Avila, Stephen (Department: 3617)
Ships
Floating platform
Float assembly
Reexamination Certificate
active
06213045
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a flotation assembly, such as an off-shore floating platform or other structure, and also to a method related to the same. More particularly, the present invention relates to such an assembly and method where an auxiliary flotation support section or sections are provided for floating support to the assembly in a particularly effective manner.
1. Background of the Invention
For many years, the oil and gas industry has used off-shore fixed platforms resting on the sea floor, to drill and extract oil from under the ocean. More recently, the need to explore and produce in deeper waters requires the employment of floating platforms, since a fixed platform could not be designed for operation at those greater depths.
In many respects, the considerations and problems relating to the design, construction and operation of floating off-shore platforms are analogous to those of the design, building and operation of ships. Therefore, it was only natural that those who were engaged for the design of such floating platforms had a background in, or at least derived much of their information from, the ship building industry, particularly since there already exists a large body of design and fabrication expertise in that industry which would be directly applicable to the task of designing, constructing and operating floating platforms.
Thus, the current method of providing flotation for off-shore platforms is to construct a steel structure, commonly called a “hull”, that displaces an amount of water equal to its own weight plus the pay load. Generally the upper support surface of the hull is located about 40 to 60 feet above the water level, and the hull would normally extend downwardly below the water surface from 100 to 200 feet. The hull must resist the external pressure of the water below the water line, and this is accomplished by using steel plates, reinforced as needed with internal ribs, stiffeners, bulk-heads and bracing. Further, the entire structure must have sufficient structural strength to withstand the external loads imposed on them from the wind, waves, and possibly other sources.
2. Related Art
A search of the U.S. patent literature has disclosed a number of patents related to flotation support structures of various kinds, some of these being related to off-shore drilling, and these are the following:
U.S. Pat. No. 5,435,262 (Grinius et al.) discloses a semi-submersible off-shore platform comprising a hull having a plurality of stabilizer buoys. Each of the buoys is coupled to the hull and is positioned adjacent to the peripheral edge of the hull. There is a system for stabilizing the semi-submersible platform.
U.S. Pat. No. 4,422,803 (Wetmore) discloses an off-shore structure which has at least two similar prefabricated concrete modular subassemblies interconnected in a vertical manner to define a horizontal interface between each pair of subassemblies. There are vertically disposed sheer resistant pin means between the subassemblies and the cement at the interface to secure them together.
U.S. Pat. No. 2,552,899 (Manes), shows a “floating drilling rig” that is provided with tanks that provide flotation as it is moved to the drilling site.
U.S. Pat. No. 3,572,041 (Graaf) disclosed a spar type floating production facility for under water oil and gas wells. There is a spar section
13
which supports what is called a “super structure component
14
” that is located above the water surface
16
. The upper part of the spar section
13
consists of
6
large diameter, hollow vertical columns
101
-
106
which are interconnected by a large diameter, hollow grid
107
and a small diameter, hollow upper grid
108
.
U.S. Pat. No. 4,126,011 (Lamy et al) relates to an off-shore tower structure, and deals primarily with the method of fabrication. It appears that there is a support structure adapted to rest on the bottom of the body of water and there is another member extending upwardly in the body of water. The platform is made up of two pieces which are floatable. The patent describes in detail the method for assembling and positioning the same.
U.S. Pat. No. 4,234,270 (Gjerde et al) shows a support element
6
of cells
10
that surround the upper end of the structure and holds the platform above the sea surface.
U.S. Pat. No. 4,310,052 (Rivertz) show an upright platform supporting member
7
, that is provided with surrounding elements
6
that appear to serve as floats.
U.S. Pat. No. 4,702,648 (Stageboe et al) shows a platform structure in which there is an anchoring base
2
, that rests on the sea floor. The upper, floating section which is also formed of joined cylinders is joined to the lower location by a tension element. The upper section is formed of relatively elongated cylinders, some of which are long enough to act as supports for the platform.
U.S. Pat. No. 4,740,109 (Horton) shows a compliant buoyant tower which is shown in
FIG. 19
, as being kept upright by a group of elongated cylinders
96
, composed of tank like elements
98
.
U.S. Pat. No. 4,766,836 (Behar et al) shows an off-shore tower which is formed of a central buoyant element and a series of tank elements secured around the central element. The outer elements are used for storage.
U.S. Pat. No. 5,038,702 (Bowes) shows what is called a “semi-submersible platform” which is supported on columns with pontoons extending between an outboard of the columns. This is provided with pitch stabilization and motion phase control devices such that when the platform is in the “drilling mode”, the platform is able to ride with the storm waves.
U.S. Pat. No. 5,088,858 (Massoudi) relates primarily to a method of manufacturing and installing what is termed an “artificial island”, such as a column, pile, harbor, and also a drilling platform capable of Withstanding icebergs, etc. There is a structure
1
having a polygonal construction which has a number of anchors
7
. This is surrounded by what is called an “annulus” of pontoons
16
. There is a detailed description of the method of installing this, and this can be summarized by reading claim
1
, beginning on line
17
of column
10
.
U.S. Pat. No. 5,375,550 (Innis) shows a floating platform where there is a plurality of cylindrical air filled platform modules, each having an open bottom end and a closed top end cap
18
of a square configuration. The trapped air chambers are interconnected to increase stabilization of the platform, and the caps
18
collectively provide the support platform.
U.S. Pat. No. 5,435,262 (Grinius et al.) shows a semi-submersible off-shore platform having stabilizer buoys
108
attached to the upper surface of the hull.
U.S. Pat. No. 3,933,108 (Baugh), shows a system for attaching floats to the riser. The purpose is to make the riser sections sufficiently buoyant to substantially reduce the need for tensioners or other similar apparatus for applying tension to the riser column.
SUMMARY OF THE INVENTION
It is long been recognized that the use of steel in the construction of off-shore platform hulls requires that a large mass of steel be used, thus producing a high weight-to-buoyancy ratio. In other words, many pounds of steel must be used to produce relatively few pounds of buoyancy. Thus, the hull must be sized to float not only the pay load but also to float itself.
Further, steel is prone to corrosion from the marine environment. In spite of coatings, and due to the need for cathodic protection, the maintenance costs of steel structures is high, adding significantly to life cycle cost. Accordingly, it is an object of the present invention to provide a flotation assembly which is particularly adapted for off-shore platforms and other such structures, which maintains the benefits of current design and construction of off-shore platform hulls and other such structures and yet which provide a lower weight-to-buoyancy ratio and other related benefits.
More specifically, the present invention enables the effective use of other materials, such as fiber reinforced plastic, that are more corrosion resi
Avila Stephen
Hughes Robert B.
Hughes & Schacht, PLLC
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