U.S. patent number 3,720,066 [Application Number 04/878,460] was granted by the patent office on 1973-03-13 for installations for submarine work.
This patent grant is currently assigned to Compagnie Francaise D'Entreprises Metalliques. Invention is credited to Robert H. Vilain.
United States Patent |
3,720,066 |
Vilain |
March 13, 1973 |
INSTALLATIONS FOR SUBMARINE WORK
Abstract
An offshore drilling platform has a column which can be
articulated by a universal joint to a base anchored to the seabed.
The column is subdivided into a plurality of superposed ballasting
compartments. Means are provided for external control, from a
compressed air source, of the flooding or emptying of at least one
of the compartments. One compartment close to the articulated end
of the column can be flooded during positioning the structure so
that the water compresses the air before it. Means are provided to
allow the air to escape thereafter or be further pressurized to
drive out the water. Floats which can be partly filled with water
can be arranged radially around the column and emptied during the
setting up operation. Oil dashpot type shock-absorber means can be
provided for damping impact against the base.
Inventors: |
Vilain; Robert H.
(Maisons-Alfort, FR) |
Assignee: |
Compagnie Francaise D'Entreprises
Metalliques (Paris, FR)
|
Family
ID: |
25372075 |
Appl.
No.: |
04/878,460 |
Filed: |
November 20, 1969 |
Current U.S.
Class: |
405/202;
114/264 |
Current CPC
Class: |
B63B
35/4406 (20130101) |
Current International
Class: |
B63B
35/44 (20060101); B63b 035/44 (); B65d 087/08 ();
E02d 017/00 () |
Field of
Search: |
;61/46.5,46 ;114/.5 ;9/8
;137/154 ;220/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
World Oil (publ) Feb. 1, 1968 pp. 38-39.
|
Primary Examiner: Shapiro; Jacob
Claims
What is claimed is:
1. A structure of the offshore drilling platform type, having a
column, coupling means at one end of said column to make it
securable in articulated fashion to a base anchored to the seabed,
the column being subdivided into a plurality of superimposed
ballasting compartments, and air valve means arranged on said
column to regulate air from a source of compressed air so as to
control the flooding and emptying of at least one of said
compartments and wherein proximate said coupling means at least one
of said compartments comprises water valve means for flooding said
at least one compartment with water during positioning of the
structure so that said latter water compresses before itself the
air contained therein thereby counteracting the external
hydrostatic pressure on the compartment, and air valve means for
allowing said air to escape thereafter.
2. A structure according to claim 1 including, in combination with
a system of external floats for providing hydrostatic compensation,
three superimposed compartments within the column, of which one is
adapted to be always flooded and located substantially level with
said system of floats, another is located in the lower portion of
the column adjacent to said base and has first water valve means
permitting it to be filled with water in the course of positioning
of the structure, and the third is located in the upper portion of
the column and includes second water valve means enabling it to be
filled at the end of the column positioning operation.
3. A method of positioning the column of a structure as claimed in
claim 1, said column having at least one lower compartment and at
least one upper compartment, comprising the steps of first allowing
water to flood the lower compartment and compress the air before it
so as to counteract external hydrostatic pressure on said
compartment and thereby avoid distortion of the wall as the column
is sunk, of then allowing the air to escape until a given height of
compressed air remains in that compartment, of thereafter at least
partly filling the upper compartment with liquid, and of finally
reversibly effecting the escape of the compressed air remaining in
the lower compartment at a rapid rate to avoid hammering effects
during the final phase of positioning.
4. A structure according to claim 1, comprising a buoyancy system
formed by a plurality of floats arranged radially about the column,
float valve means on one or more of said floats to enable it to be
at least partly filled with water while the structure is towed to
its ultimate location to provide stabilization about the axis of
the column, and to be emptied during the phase of positioning the
structure.
5. A structure according to claim 4, comprising a pipe connected to
said second water valve means and a pump connected to said pipe and
adapted to fill the upper compartment with water drawn from the
lower compartment.
6. A structure according to claim 1, wherein said coupling means
comprises a coupling block fixable to the base at three points at
least, and a universal joint between the coupling-block and the
column.
7. A structure according to claim 6, wherein the coupling means
includes remote-controlled radially disposed jack-actuated latching
means for fixing the coupling block to the base.
8. An offshore platform comprising a structure according to claim
6, and a said base including shock-absorbing means for damping
impact shocks when the coupling-block contacts the base.
9. A platform according to claim 8, wherein said shock-absorbing
means are of the oil dashpot type.
10. A method according to claim 5, wherein said air valve means is
adapted to cooperate with said coupling means in such manner as to
achieve reversibly rapid positioning of the column on the base.
Description
The present invention relates to structures of the offshore
platform type for submarine work, of the kind in which the platform
proper is carried on a supporting column which is articulated,
notably by means of a universal joint, to a base set down on the
seabed.
Already known are means for floating and towing the platform and
its column up to its location and for then fixing the column to the
base, the column being first tilted over by water-ballast, then set
in a vertical position and guided towards the base by means of
guide-cables. It has further been advocated to ballast the column
at its base and to provide it at the platform end with buoyancy
floats for hydrostatic stabilization, whereby the base-ballast,
together with the overall weight of the system, substantially
balances the hydrostatic thrust exerted by the floats so as to
relieve the universal joint or other securing means as much as
possible.
The invention relates to a number of features for taking better
advantage of the characteristics of these types of platform and for
permitting easy transport of such platforms to the work site and
for facilitating and increasing the reliability of the process of
setting them up by providing reversible maneuvers.
One of these features, which relates specifically to the setting up
of the column (and possibly the base), consists in providing the
same with ballast compartments and with means permitting external
control, by means of a compressed-air source, of the emptying of at
least one of said compartments if need be, notably in order to
enable the order of operations to be reversed should this prove
necessary.
In one embodiment, a compartment is provided in the column, between
the buoyancy float and its end to be fixed to the base. During the
setting-up operation, water is allowed to flow into this
compartment and to compress the air contained therein, this air
being then allowed to exhaust or being on the contrary
repressurized in order to drive out the water by the means referred
to, if need be. An upper provisional flooding compartment may
possibly be provided to complete the submerging operation.
In accordance with another feature, a plurality of buoyancy floats
are arranged about the column, some of which are flooded during the
towing up to the work-site and emptied for the setting-up
operation, notably for the ultimate phase thereof.
Yet another feature relates to at least three latches arranged
radially and symmetrically about the axis of the column, for the
purpose of securing the coupling-block at the lower end of the
column to the base.
The description which follows with reference to the accompanying
non-limitative exemplary drawings will give a clear understanding
of how the invention can be carried into practice.
In the drawings:
FIG. 1 shows in schematic side elevation one embodiment of a
platform with an oscillating column in accordance with the
invention, in its erect position;
FIG. 2 is a schematic separate plan view of the base of this
column;
FIGS. 3 and 4 show on an enlarged scale, fragmentally and in
greater detail, in section and in plan view respectively, said base
and a portion of the column coupling-block, the whole in accordance
with this invention;
FIG. 5 illustrates in schematic section the initiation of the
column lowering operation, starting from the towing position;
and
FIGS. 6 through 9 portray four different stages in the operation of
lowering and securing the column to the base.
Reference is first had to FIG. 1 which shows a preferred embodiment
of an offshore platform with an oscillating column intended to be
set up in an offshore location, according to this invention, which
comprises the following essential parts:
A base 1 intended to be set down on the seabed and to be weighted
with concrete or in any other convenient way, and constructed, for
example as described below;
an articulation system, notably of the universal joint type, for
securing the column to said base and basically comprising a lower
coupling-block 2 capable of being fixed to the base, the universal
joint proper with its ring 3 and an upper block 4 forming part of
the column; and
the column proper 5, consisting basically of a suitably
compartmented cylindrical steel shell, i.e. comprising, at the top,
the mooring plateform 6 with, below the latter, the living quarters
and working premises 7 and the machine-rooms 8 and, further below
still, buoyancy floats 9 which in the erected position of the
column exert an upward thrust in order to stabilize the column and
allow guiding cables to be dispensed with.
In accordance with a feature of this invention, a number of these
floats are arranged around the column, and one or more of them are
at least partly flooded during the towing phase in order to
stabilize the system about its axis (FIGS. 5 to 9).
Adjacent the coupling-block 4, the lower end of the column includes
a ballast compartment 10 tending to counterbalance the buoyancy
force of the floats 9.
The interior of the column is furthermore divided into a plurality
of ballast compartments A, B, C in conjunction with flooding and
emptying means to be described hereinafter, the partition walls 11,
12, 13 of which compartments are shown on the drawings.
In what follows the base, and thereafter the column, with their
associated positioning means and operations, will be examined in
succession.
Referring first to the base 1, the same is constructed essentially
with a metal framework comprising a baseplate 14 with partitions
for possible ballast compartments 15 (concrete, etc.) and at least
one flooding compartment, located for instance at the center at 16
or at any other convenient place, the whole arrangement being
surrounded by floats 17.
The complete base may be square or rectangular shape (FIG. 2), its
dimensions varying according to the height of the column. For a
column approximately one hundred meters long, the sides of the
square would be approximately 20 to 25 meters long and the loaded
weight approximately 1,000 to 1,500 tons, these figures being given
for purely indicative purposes only.
Underneath the base is provided a suitably reinforced plate forming
an erosion arrester (FIG. 1) to prevent erosion of the seabed by
the hydrostatic undermining effect of the sea.
On top of the base are provided means for securing the lower
coupling-block 2 and means for securing guiding cables preferably
provided to guide the column at least during the ultimate phase of
the operations, which cables are shown only in FIGS. 3, 8 and 9, at
19, in order not to clutter the drawings unnecessarily.
The means for making the lower coupling-block 2 of the column fast
with the base 1 are provided at three points at least, arranged
radially and symmetrically, i.e. at 120.degree. about the axis of
the system. They consist for example of connecting elements 20
(FIGS. 3 and 4) formed with holes 21 for receiving bolts 27 carried
on the lower coupling-block 2.
The elements 20 comprise guides 54 for correctly locating the lower
coupling-block 2 during assembly.
The base includes a further two guiding elements 22 for attaching
the guide-cables 19, and these elements consequently include
shackling means 23, the whole arrangement being covered with masks
24 for facilitating penetration into elements formed with openings
25 therein and carried by the lower coupling-block 2 (FIG. 3).
FIGS. 3 and 4 show that in order to enable it to cooperate with the
elements 20 and 22 just described, the coupling-block includes a
substantially triangular shaped base from which the three bolts 27
may protrude, while a cross-member 26 carries the elements formed
with the openings 25 therein.
It is a further feature of this invention that provision is made
for remote-control means of the bolts 27 once the coupling-block
has been positioned and located by the elements 20, 54, which means
are possibly of the hydraulic type and include jacks 28. Additional
means associated with the base 1 are provided for damping any
shocks which may occur when the lower coupling-block 2 contacts
base 1, and such shock-damping means may be of the hydraulic type
such as the shock-absorbers 29 and be actuated at 30 in conjunction
with an oil reservoir 31 (FIG. 3).
Considering next the procedure to be adopted for submerging a base
as hereinbefore specified and anchoring it to the seabed at the
start of operations, this may be accomplished by providing the base
with suitable flooding valves so that after it has been floated up
to its final position it can be gradually weighted and caused to
slowly submerge while it is suspended by a cable from an
appropriate floating system.
The submerging process may be controlled by means powered by
compressed air, an example being the means to be described below
with respect to the column and which if necessary will allow the
operation to be reversed by causing the water to be expelled by the
inrush of compressed air into the float (notably in the event of an
error requiring the operation to be repeated).
Flooding is first effected in the external floats 17 until the base
is lowered on the seabed at a sufficiently slow speed, after which
the setting onto the seabed is completed by flooding central
compartment 16 or other appropriate compartments by remotely
controlling appropriate valves.
Considering now the special means in accordance with this invention
for submerging the column 5 and causing it to rest with its
coupling-block 2 on the base 1, a possible embodiment thereof will
now be described.
The column, comprising compartments A, B, C for example, is
preferably towed into position, for instance with two or three of
its floats 9 at least partly filled with water in order to
stabilized the structure about its longitudinal axis, and for
instance also with compartment B filled with water, which
compartment is substantially level with the floats 9 (FIG. 5). The
preferred procedure is then as follows:
In the first stage the water is caused to enter compartment C
through at least one manually or remotely controlled valve 40
located on the same side as coupling-block 2, 3, 4, but without
expulsion of the air contained therein, whereby compartment C is
set under pressure and a final position of equilibrium is achieved
(FIG. 6) with coupling-block 2, 3, 4 positioning itself at a
certain distance from base 1.
In the second stage, the air contained at the top of compartment C
is caused to exhaust at a suitable rate, for instance through a
conduit 41 having port at 42 via a valve 43, and this is continued
until a closer position is achieved (FIG. 7) in which a certain
quantity of compressed air of height h is allowed to subsist in
C.
In the third and final stage, the setting up of the column on its
base is completed by causing the following to take place in any
convenient order: at least partial flooding of upper compartment A,
emptying of floats 9, and exhausting of the residual air remaining
at the top of compartment C (FIGS. 8 and 9).
The process of compressing the air in compartment C as a result of
the flooding is particularly advantageous, for the air pressure
generated thus counters the hydrostatic pressure exerted on the
column and consequently relieves the strain on the plates.
Further the reserve air h, upon being allowed to exhaust in the
third stage of the submerging operation allows the coupling-block 2
to contact the base 1 without the hammering that would tend to
occur under the effect of the swell during this ultimate phase. The
shock of impact is in any event damped by the shock-absorber means
referred to above.
In accordance with another important feature of this invention,
means are provided, in combination with the means for exhausting
the air from compartment C, for re-admitting air under pressure,
for example at 44 through a possibly multi-way valve 43, towards
the conduit 41, or through another valve or another conduit (see
FIGS. 5 to 9). In this way, should difficulties be encountered
during the submerging operation, a reversibility feature is
resorted to, i.e. the possibility of reverting to the initial
configuration by exhausting the compartment C.
Any convenient means may be devised by the specialist in the art
for performing the above stages in the submerging operation, and
such means may be directly or remotely actuated by any convenient
hydraulic, pneumatic, electric or other control means.
The first stage is accomplished by opening the valve 40, the valve
43 remaining closed (FIGS. 5 to 9), whereby the upper part of
compartment C is set under pressure.
The second stage is performed by opening discharge valve 43 and
exhausting the air from compartment C until the residual supply of
height h remains therein, said valve being then closed anew (FIG.
7).
The third stage requires for example a pump 45 for drawing in water
and conveying it through a conduit 46, 47 into compartment A, by
way of a valve 48. This pump draws the water from compartment C
when it is set in operation and when valve 48 is opened.
Simultaneously the air is allowed to escape from compartment A
through a valve 49 which is caused to open (FIG. 8). The height of
the water level reached in compartment A depends on the immersion
depth to be obtained.
With regard to emptying of the floats 9, this can be done in any
convenient way, for instance by admitting air under pressure
thereinto and temporarily opening liquid discharge valves 50.
Lastly, with regard to obtaining the ultimate downward movement,
accomplished by emptying the residual air in compartment C, this is
initiated by actuating the exhaust valve 43 once more.
Once the final position has been reached, that is to say with
coupling-block 2 resting on base 1, the water level in upper
compartment A may establish itself at the same level as the surface
of the sea.
No reference has been made in the foregoing to the manner of
handling the guide-cables 19 (shown in FIGS. 8 and 9 only). These
cables may be employed as follows:
When the column is tilted over (FIG. 5) and is in the configuration
of FIGS. 6 and 7, these cables are in position along its entire
length. At the bottom of the column, adjacent the coupling-blocks,
these cables are threaded through the rings 25 on lower
coupling-block 2, 26 and their ends are coiled up temporarily
pending attachment to the shackles 23 on guiding elements 22. When
the configuration of FIG. 8 is reached, divers secure the cables to
shackles 23 and the cables are then pulled taut. This provides
excellent guiding means for coupling-block 2, which can thus
descend into its ultimate position (FIG. 9) while receiving
additional guidance from the ramps 54 of the three elements 20.
Any convenient means may be provided for tightening the cables 19,
such as counterweights 52 supported at the top of the column and
associated to pulleys or pulley-blocks 53 (FIGS. 8 and 9).
The oil or drilling pipes, or other piping or devices to be run
through the column 5 are not shown on the drawings, but it is to be
understood that the passage of such pipes, notably through
universal joint 3, is accomplished in any convenient manner.
An offshore drilling platform or structure devised as hereinbefore
disclosed offers numerous advantages over the prior art platforms
of this kind, and the following in particular:
the positioning operations can be remotely controlled by the sole
actuation of valves or the like;
the building up of dangerous hydrostatic pressures can be avoided
during the column submerging operation, these pressures being
balanced by the compression of the air;
it is possible to obtain a sufficiently rapid rate of descent
during the ultimate positioning phase (through escape of the air
under residual pressure) to avoid any hammering effects;
dangerous shocks are prevented by virtue of the shock-absorber
means provided;
latching of the lower coupling-block on to the base can be remotely
controlled from the platform by means of the jack which actuates
the latching elements; and
appropriate utilization of the air under pressure permits of
reversing the operations and hence of reverting to the starting
configuration at any time if need be.
It goes without saying that many changes and substitutions of parts
may be made to the specific embodiments described hereinabove
without departing from the spirit and scope of the invention, and
that, broadly speaking, the above-disclosed basic principles may be
applied likewise to structures of a different kind and furthermore
that variants may be adopted in regard to the nature, number and
succession of the setting-up operations.
* * * * *