U.S. patent application number 09/758306 was filed with the patent office on 2002-07-11 for column-stabilized offshore vessel.
Invention is credited to Dixon, Paul C., Malcolm, Bruce G..
Application Number | 20020090270 09/758306 |
Document ID | / |
Family ID | 25051269 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020090270 |
Kind Code |
A1 |
Malcolm, Bruce G. ; et
al. |
July 11, 2002 |
Column-stabilized offshore vessel
Abstract
The invention relates to a semi-submersible vessel designed to
operate in water depths of 200 to 10,000 feet. The vessel has a
ring pontoon with an outer and inner configuration of the pontoon
forming a triangle. Three corner columns are fixedly attached at
their lower ends to the ring pontoon. The upper ends of the
stabilizing columns carry an upper deck designed to support
drilling and production operations. The vessel uses no diagonal or
horizontal braces, nor auxiliary supporting columns. The triangular
shape of the vessel minimizes environmental forces acting on the
vessel, thus improving its stability at any operational draft. The
vessel can be fully constructed and outfitted quay (dock) side.
Inventors: |
Malcolm, Bruce G.; (Katy,
TX) ; Dixon, Paul C.; (River Ridge, LA) |
Correspondence
Address: |
THOMAS S. KEATY
KEATY PROFESSIONAL LAW CORP.
2140 WORLD TRADE CENTER
NO. 2 CANAL STREET
NEW ORLEANS
LA
70130
US
|
Family ID: |
25051269 |
Appl. No.: |
09/758306 |
Filed: |
January 10, 2001 |
Current U.S.
Class: |
405/195.1 |
Current CPC
Class: |
B63B 2001/128 20130101;
B63B 1/107 20130101; B63B 35/4413 20130101; B63B 2039/067
20130101 |
Class at
Publication: |
405/195.1 |
International
Class: |
E02B 001/00 |
Claims
We claim:
1. A semi-submersible vessel, comprising: a buoyant generally
triangularly-shaped pontoon; a plurality of vertical stabilizing
columns fixedly attached to said pontoon, each column having an
intercostal connection with a respective corner of said pontoon;
and a platform supported by upper ends of said columns for
conducting offshore operations therefrom.
2. The vessel of claim 1, wherein said pontoon is a ring
pontoon.
3. The vessel of claim 2, wherein an outer perimeter of said ring
pontoon forms a triangle.
4. The vessel of claim 2, wherein an inner perimeter of said ring
pontoon forms a triangle.
5. The vessel of claim 1, where said pontoon comprises a plurality
of pontoon sections, each end of each pontoon section being fixedly
attached to an adjoining pontoon section and to at least one of
said stabilizing columns.
6. The vessel of claim 5, wherein each of said columns is attached
to said pontoon along at least one side.
7. The vessel of claim 5, wherein each of said pontoon section has
a generally rectangular cross section.
8. The vessel of claim 1, wherein each of said stabilizing columns
has a generally square cross-section, and wherein outer corners of
each of said stabilizing columns is outwardly convex to reduce drag
forces acting on the vessel.
9. A semi-submersible vessel, comprising: a buoyant ring pontoon
having an outer perimeter defining a triangle; a plurality of
vertical stabilizing columns fixedly attached to said pontoon, each
column being connected along at least one side to an intersecting
corner of the ring pontoon sides; and a platform supported by upper
ends of said columns for conducting offshore operations
therefrom.
10. The vessel of claim 9, wherein the ring pontoon has a
non-continuous connection to each of said stabilizing columns.
11. The vessel of claim 9, where said pontoon comprises a plurality
of pontoon sections, each end of each pontoon section being fixedly
attached to an adjoining pontoon section and to at least one of
said stabilizing columns.
12. The vessel of claim 9, wherein an inner perimeter of said ring
pontoon forms a triangle.
13. The vessel of claim 9, wherein each of said stabilizing columns
has a generally square cross-section, and wherein outer corners of
each of said stabilizing columns are outwardly convex to reduce
drag forces acting on the vessel.
14. The vessel of claim 11, wherein each of said pontoon sections
has a generally rectangular cross-section.
15. The vessel of claim 9, wherein each of said columns is attached
to said pontoon along at least one side.
16. The vessel of claim 9, wherein each of said columns is attached
to said pontoon along more than one side.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to an offshore drilling and production
vessels, and more particularly to a semi-submersible vessel for
conducting offshore operations in water depths from 60 feet to
10,000 feet, such as the Gulf of Mexico, the North Sea and the
like.
[0002] In recent years, oil and gas drilling and production
operations have been conducted at increasingly greater distance
from the shoreline, making oil and gas prospecting more expensive.
Small companies or individual operators find it difficult to
compete with major oil companies partly due to increased
fabrication and deployment costs associated with large
semi-submersible units or jack-up rigs. Usually, such units are
deployed at rich reserve sites, where the prospect of substantial
production amount is anticipated.
[0003] However, there exists a substantial number of marginal field
production in deep water, for instance in depths from 3,500 to
7,500 feet. It is not very cost effective to deploy a conventional
permanently positioned unit in a marginal field. As a result, the
operators use mobile offshore production units (MOPUs) to operate
in such environment. At present, the total worldwide fleet of MOPUs
is comprised of approximately 135 floating units. The present
invention is directed to providing a more cost-effective solution
to marginal field production in deep water.
[0004] Various designs of floating structures are known in the art
for supporting the mineral exploration and production operations,
as well as providing living accommodations to the crew and storage
for the necessary equipment. For instance, in deep waters, over
7500 feet, it is conventional to deploy floating semi-submersible
vessels, as opposed to fixed bottom anchored structures.
[0005] The majority of semi-submersible vessels utilize buoyant
pontoons, or lower hulls that support a plurality of vertically
extending columns, the upper portions of which carry a working
platform with one or more decks. Some semi-submersible vessels have
a single caisson, or column, usually denoted as a buoy, while
others use three or more columns extended upwardly from buoyant
pontoons.
[0006] In many such structures, vertical and/or diagonal braces are
used between the columns, the braces contributing to the water
plane area of the vessel. The braces usually have much smaller
diameters than those of the supporting columns and are therefore
more vulnerable to the environmental and mechanical damage. If the
connecting braces are damaged, the entire structure becomes
jeopardized.
[0007] One example of a three-column structure is shown in U.S.
Pat. No. 3,246,476 issued on Apr. 19, 1966 to Wolff for
"Submersible Vessel for Submarine Operations." The semi-submersible
vessel of the '476 patent, in some of its embodiments, has three
stabilizing columns connected at the bottom to a triangular base.
The base has connecting braces joining the main base members at
midsections and forming a triangular inner base. Auxiliary vertical
columns are provided for supporting the upper deck.
[0008] There also exist numerous designs of semi-submersible
vessels using diagonal braces in addition to horizontal stays.
These tend to reinforce the support structure of the platforms and
resist destructive forces of the ocean waves. One of the designs
using diagonal braces in a ring pontoon is shown in U.S. Pat. No.
6,015,245 to Frimm et al. The '245 patent has six columns
interconnected by a number of pontoons forming a generally
rectangular base. One of the disadvantages of the additional
columns and braces is increase in the water plane area of the
vessel, which adversely affects the weight, wave resistance and
overall cost of the vessel.
[0009] Another consideration that is taken into account when
designing semi-submersible vessels is resistance of the vessels to
motions induced by waves. The vessels must have sufficient
capability to withstand wave motions to allow the mineral
exploration and production operations to be carried out in safety
with minimal downtime to maximize efficiency. The present invention
contemplates provision of a column-stabilized semi-submersible
vessel with improved safety features, cost efficiency and
resistance to wave induced motions.
SUMMARY OF THE INVENTION
[0010] It is, therefore, an object of the present invention to
provide a semi-submersible vessel with improved safety
features.
[0011] It is another object of the present invention to provide a
column-stabilized semi-submersible vessel with a ring pontoon.
[0012] It is a further object of the present invention to provide a
semi-submersible vessel that uses no additional braces assuring
minimal increase in water plane area, while resisting spreading and
twisting forces acting on the global structure.
[0013] These and other objects of the invention are achieved
through a provision of a semi-submersible vessel for use in water
depths from 200 to 10,000 feet and particularly advantageous for
use in depths of 3,500 to 7,500 feet. The vessel comprises three
vertical stabilizing columns connected at their lower ends to a
ring pontoon. The pontoon has three sections that form a triangle.
The corners of the triangle are attached to the vertical columns.
The upper ends of the columns carry a working platform or deck,
from which mineral exploration and production operations are
conducted.
[0014] The vessel has a relatively small water plane area since it
does not require any diagonal braces to reinforce the support
column structure. The ring pontoon resists column twisting that may
be caused by wave and current forces. In addition to added
resistance to spreading and twisting forces acting on the overall
structure the ring pontoon offers cost efficiency in fabrication
and deployment. Where most floaters need heavy lift vessels in
order to integrate the topside platform with the hull, the
semi-submersible vessel of the present invention it does not
require offshore integration in its capital cost range.
[0015] To minimize drag forces induced by wave motions, the columns
are provided with outwardly convex, rounded corners. This design
reduces drag force transmitted when mooring or moving the vessel
while maximizing the storage for an optimum design. The pontoon
hulls may have compartments for storing ballast, drill water and
other necessary supplies, while the columns may house reserve mud
tanks, ballast tanks, force air ventilation supply and other
necessary machinery and equipment. Living quarters and service
equipment may be mounted on the platform.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Reference will now be made to the drawings, wherein like
parts are designated by like numerals, and wherein FIG. 1 is a
perspective view of the semi-submersible vessel in accordance with
the present invention.
[0017] FIG. 2 is an outboard profile illustration of the vessel in
accordance with the present invention.
[0018] FIG. 3 is an outboard profile of the vessel of the present
invention taken at a different angle from the view of FIG. 2.
[0019] FIG. 4 is a schematic view of the ring pontoon of the
semi-submersible vessel of the present invention.
[0020] FIG. 5 is a schematic view showing an example of connection
of the bottom of the columns to the ring pontoon; and
[0021] FIG. 6 is a cross-sectional view of a column taken along
lines 6--6 of FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Turning now to the drawings in more detail, numeral 10
designates the semi-submersible vessel of the present invention.
The vessel comprises a buoyant ring pontoon 12 having sections 14,
16, and 18. The pontoon sections are connected together to form a
triangle, which may be an equilateral triangle or other geometric
shaped triangle. The outer perimeter of the ring pontoon 12 defines
a generally triangular shape. A central open space 20 defines an
inner perimeter of the pontoon 12 and follows in configuration the
outer configuration of the pontoon 12. Both the outer perimeter of
the ring pontoon 12 and the inner perimeter of the ring pontoon 12
form an equilateral triangle. Each pontoon section 14, 16 and 18
has a generally rectangular cross section; each section is defined
by a top plate 22, 24 and 26, respectively, a pair of vertical side
plates 28, 30, 32, 34, 36 and 38, respectively and a bottom plate
(not shown).
[0023] The corners of the triangular pontoon have flat vertical
plates 40, 42 and 44 for attaching to respective mating surfaces of
the columns, as will be described below. The pontoon sections may
be divided into a plurality of watertight compartments for
accommodating ballast.
[0024] Secured to the corners 40, 42 and 44 of the pontoon sections
14, 16 and 18 are vertical stabilizing columns 50, 52 and 54. The
columns 50, 52 and 54 extend at right angles to the horizontal axis
of the ring pontoon 12. Each column 50, 52 and 54 has a generally
square cross-section (see FIG. 6).
[0025] To improve the drag characteristics of the vessel, that is
to minimize drag, the exterior corners of each column is formed
with rounded vertical corners 60, and 62. The rounded corners 60
and 62 are attached to sides 65, 66 and 67 of each column by
welding and the like. The side 64 of each column 50, 52 and 54
contacts a respective mating side 40, 42, or 44 of the ring pontoon
12.
[0026] The radius of the outward curvature may be 1/4 or greater of
the width of the generally square column. Such rounded corners
minimize drag forces, while still providing the necessary strength
and storage to the corner columns. Additionally, the vertical flat
panels of the columns are less expensive to fabricate as compared
to conventional round columns of the prior designs.
[0027] The side 64 of each of the columns 50, 52 and 54, is made of
a flat plate to allow mating attachment of the column to a corner
of the ring pontoon 12, as shown in FIG. 5.
[0028] In the preferred embodiment, the buoyant pontoon 12 is
intercostal to the columns, i.e. it is made of separate parts, not
continues with the columns 50, 52 and 54. As a result, construction
of the vessel is simplified and made more cost-effective. The
sections 14, 16 and 18 of the pontoon 12 close the area between the
three columns 50, 52 and 54 to provide the necessary buoyancy and
strength.
[0029] The upper portions of the columns 50, 52 and 54 carry a
platform 70 adapted for supporting mineral exploration and
production operations. During offshore operations, parts of the
columns 50, 52 and 54, as well as the ring pontoon 12 are submerged
below the water surface to an operational draft, while the upper
portions of the columns 50, 52, 54 and the platform 70 are elevated
to a level above maximum expected wave for a particular location.
The ballast chambers in the pontoon 12 provide the necessary room
for introducing ballast, for example, sea water to partially
submerge the structure.
[0030] The platform 70 is of a modular type and is attached to the
upper ends of the columns 50, 52 and 54 in such a way that the
entire deck could be removed for replacement by a different type of
deck, designed for other purposes. For instance, the platform 70
may be equipped for oil recovery, then substituted by a platform
suitable for gas production, work over operations or drilling.
Generally, the hull is independent from topside to allow easy
changing of the deck for different job requirements.
[0031] The main or upper deck platform 70 is a simple grillage beam
structure designed to support the processing equipment and
facilities. This approach eliminates the need for special equipment
support structure and allows individual items of equipment to be
simply put in place and connected by piping and electrical line to
achieve the process facility. Such design saves both time and
cost.
[0032] The operational draft of the vessel 10 is generally higher
than a survival draft. When the vessel 10 encounters particularly
harsh conditions, wave and hydrostatic forces act on the pontoon
and on the columns, causing the vessel 10 to move vertically and
angularly, subjecting the vessel to heave and pitch motions of the
wave. These forces which cause vertical and angular motions of the
vessel result in the vessel shifting in relation to a vertical
axis. The columns 50, 52 and 54, being relatively large in
cross-section help stabilize the vessel and to reduce wave-induced
motions acting on the vessel.
[0033] Mounted on the main deck 72 of the platform 70 are a pair of
winches 74, one at each column 50 and 24 (FIG. 1). Since the need
for the permanent winches, chain lockers, chain and wire line
storage has been eliminated through the use of pre-set mooring
technology, the vessel 10 has lower operational costs, which
advantageously affects the cost of the minerals recovered with the
use of the vessel 10.
[0034] The vessel 10 provides a facility for conducting mineral
exploration in relatively deep waters of up to 10,000 feet. The
vessel 10 is equipped with at least one crane 76, although more
than one crane is usually provided. A heliport 78 is erected in one
corner of the triangularly-shaped platform 70. The helicopter
landing pad is used for delivering personnel and supplies to the
vessel 10 when in operation. Drilling and production operations are
conducted through the platform 70 in a manner well known to those
skilled in the art.
[0035] Flexible lines (not shown) from sub sea oil and gas wells
may be connected from the sub sea wellhead to the pontoon sections,
or lower hulls 14, 16 and 18. Connection of the flexible lines at
the lower hull allows existing technology to be effectively
utilized and by connecting below the total vertical center of
gravity, additional stability capability is not required. The
vessel 10 must only provide sufficient buoyancy to counteract the
platform weight, the weight of the process facility mounted on the
main deck 72, the mooring line loads and the flexible line loads
from the wells and the export or sales line(s). This design reduces
the amount of displacement and the amount of steel required to
fabricate the vessel 10.
[0036] The compartments formed in the ring pontoon 12, in addition
to holding salt water ballast, may be equipped for housing pumps,
storing drill water, diesel oil and other necessary materials. The
columns 50, 52 and 54 may be also compartmentalized to hold reserve
mud tanks, brine tanks, base oil tanks, ballast tanks, vents,
ventilation supplies and return pipes for lower hull and column
machinery compartments. Water is allowed to enter the ballast
chambers by gravity and may be expelled from the chambers by
compressed gas or air.
[0037] Other equipment necessary for offshore operations, such as,
sewerage treatment unit, portable water tanks, storage tanks can be
positioned in other compartments within the columns 50, 52 and 54.
The upper hull, or platform 70 structure may be designed to house
drilling and ship service equipment, power generation and storage
for liquid mud, sacks, and other variable materials and
equipment.
[0038] The vessel 10 uses no diagonal or horizontal braces, or
intermediate columns, instead relying on the ring pontoon and the
three large columns to provide the displacement, stability and
strength to the vessel having improved motion characteristics.
There are no on-deck mooring winches; mooring is accomplished with
suction piles that are pre-set at location. As a result, the vessel
10 is very mobile and may be leased/rented by an operator and
brought to a location with minimum expenditure for deployment. Once
the site is depleted, the vessel 10 may be easily moved to another
desired location.
[0039] The vessel 10 may be deployed at varying depths, from 200 to
10,000 feet of water. It is envisioned, however, that the vessel 10
will find its greater application for use in 3,500 to 7,500 feet
water depth. The column height may be up to 110 feet, with
waterline passing at about 60 to 80 feet.
[0040] The triangular shape of the vessel 10 minimizes
environmental forces acting on the vessel, thus improving its
stability at any operational draft. The vessel can be fully
constructed and outfitted quay (dock) side. The design lends itself
to easy size modification; it may be scaled to accommodate the more
demanding processing requirements.
[0041] The vessel 10 has adequate stability to be floated to the
desired location, where it is partially submerged moored and left
for both normal operations and for extreme environmental
conditions. The vessel may be towed to another location at a deep
or shallow water draft since it is designed to be transported like
a ship. It is also capable of being dry towed to other locations
throughout the world if more cost efficient to the owner/operator.
In comparison to other floating structures, for instance Spar-type,
it has better design characteristics for relocation and re-use at a
new site.
[0042] Many changes and modifications can be made in the design of
the present invention without departing from the spirit thereof.
We, therefore, pray that our rights to the present invention be
limited only by the scope of the appended claims.
* * * * *