U.S. patent number 3,643,446 [Application Number 05/025,943] was granted by the patent office on 1972-02-22 for marine platform foundation member.
This patent grant is currently assigned to Texaco Inc.. Invention is credited to George E. Mott.
United States Patent |
3,643,446 |
Mott |
February 22, 1972 |
MARINE PLATFORM FOUNDATION MEMBER
Abstract
The invention relates to an anchor or foundation member for
positioning a buoyant platform at an offshore location
characterized by a sloping or irregular floor surface. The anchor
includes initially separable members which are floated to an
operating or anchoring site. A coupling member depending from the
anchor is adapted to engage the lower end of the elongated, buoyant
structure for retaining the latter in place at the water's surface.
The coupling member is adjusted into vertical alignment with a
connector depending downwardly from the marine structure. While
being held in the upwardly aligned position by an enclosing
retainer, a hardenable fluid such as cement is introduced to
solidify and form the coupling and retainer member into a singular
body.
Inventors: |
Mott; George E. (Metairie,
LA) |
Assignee: |
Texaco Inc. (New York,
NY)
|
Family
ID: |
21828913 |
Appl.
No.: |
05/025,943 |
Filed: |
April 6, 1970 |
Current U.S.
Class: |
405/202; 114/264;
175/7 |
Current CPC
Class: |
B63B
21/502 (20130101); E02B 17/027 (20130101); E21B
41/10 (20130101); B63B 35/4406 (20130101); B63B
2021/505 (20130101) |
Current International
Class: |
E02B
17/00 (20060101); E02B 17/02 (20060101); E21B
41/10 (20060101); B63B 21/00 (20060101); B63B
21/50 (20060101); B63B 35/44 (20060101); E21B
41/00 (20060101); E02b 017/00 (); E02d
027/04 () |
Field of
Search: |
;61/46.5,46,52 ;166/.5
;175/7,8,9 ;9/8 ;114/.5D |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shapiro; Jacob
Claims
I claim:
1. A subsea mooring for an elongated buoyant marine structure
disposed in a generally upstanding position in a body of water,
said structure having a submerged portion extending toward the
ocean floor and having connecting means at said structure's lower
end, which subsea mooring anchor includes;
a. a coupling member having a vertically upstanding connector
adapted to engage said structure connecting means whereby to anchor
and restrain lateral movement of said structure in response to
displacing forces acting thereagainst,
b. and a separable retainer positioned at the floor of said body of
water in engagement with said coupling member to maintain the
vertical attitude of said upstanding connector,
c. said separable retainer including means forming a cavity
therein,
d. and said coupling member including a body confined within said
means forming said cavity, said body being initially slidably
retained in said means forming said cavity to permit said connector
to be aligned to a vertically upstanding attitude,
e. and said means forming said cavity being communicated with a
source of a solidifiable fluid whereby to introduce a flow of said
fluid to said means forming said cavity whereby to solidify said
coupling body within said cavity.
2. In a subsea mooring anchor as defined in claim 1 wherein said
retainer includes; a cap having opposed upper and lower surfaces,
said means forming said cavity extending through said cap and
terminating at respective upper and lower surfaces, said opening at
said upper surface being constricted and adapted to receive said
connector, and a seating base connected at said cap lower side
whereby to maintain said coupling in said means forming said
cavity.
3. In a subsea mooring anchor as defined in claim 1 wherein said
retainer includes a cap having opposed upper and lower surfaces,
said means forming said cavity including an opening at said pad
upper surface that widens along an upper contoured wall into said
cavity, said body connector being registered in said constricted
opening and said body further including a contoured surface
conformed to the contour of said cavity upper surface whereby to
permit sliding movement of said body in said cavity when said
contoured surfaces are in engagement.
4. In a subsea mooring anchor as defined in claim 1 wherein said
retainer includes buoyancy means incorporated therein and adapted
to be adjusted whereby to vary the buoyancy of said retainer.
5. Subsea mooring for a buoyant marine structure, buoyantly
positioned in an offshore body of water, which mooring
includes;
a coupling member having a connector extending outwardly from said
mooring when the latter is positioned at the floor of said offshore
body of water,
a cap member having opposed upper and lower surfaces,
a buoyant seating member detachably engaging the cap lower surface
to define a cavity therebetween, and said coupling member being
initially operably confined within said cavity and being slidably
movable therein whereby to align said connector in a substantially
upright disposition, and
means for immobilizing said coupling member within said cavity to
fixedly establish said coupling in said upright disposition when
said mooring is at said floor.
6. In a subsea mooring as defined in claim 5 including; guide means
on said cap and seating members respectively and operable to
remotely guide said respective members into engagement when at said
floor.
7. In a subsea mooring as defined in claim 6 wherein said guide
means includes; means projecting upwardly from said seating member,
and having a flexible cable attached thereto, and passage means
formed in said cap member, said flexible cable being registered in
said passage means and extending to the water's surface whereby
said cap is slidably lowerable along said flexible cable to engage
said seating member when the latter is at said floor.
8. Method for positioning a mooring anchor for a floatable marine
structure in an offshore body of water, which structure includes a
connecting end adapted to operably engage said mooring anchor, the
latter including separably joined connector, cap and seating
members, which method includes;
positioning said mooring anchor at the surface of said offshore
body of water,
detaching said seating member from the anchor and controllably
lowering said member to the floor of said body of water,
guidably submerging said connector to engage said seating
member,
guiding said cap to said floor whereby to engage said seating
member and position said connector therebetween,
introducing a flow of a solidifiable material to said anchor to
contact said respective connector, cap and seating members for
unitizing said members upon solidification of said material into a
hardened mass.
Description
BACKGROUND OF THE INVENTION
In the drilling for and producing of oil, gas, and other petroleum
based fluids from offshore sites, it has been found desirable under
certain conditions to utilize floatable rather than fixed
platforms. Such a platform is usually tethered by an elongated
rigid structure as to be self-buoyant, while being connected at its
lower end to an anchoring or foundation member. Operations such as
drilling and producing of oil and gas wells can then be achieved
from a work deck supported atop the buoyant structure.
Because of its great size and weight, particularly in deep water
locations, positioning of the foundation member constitutes a
substantial engineering problem. Toward at least partially
overcoming this problem, it has been determined that the anchor or
foundation member, can be economically floated into place and
thereafter submerged at a desired site. With the anchor thus
partially imbedded into the ocean substratum, the platform or rigid
connecting structure is operably engaged at its lower end to the
anchor. The connection means joining said structure and foundation
member, must be sufficiently flexible to absorb displacing forces
such as wind, water currents, waves and the like. Further, said
connection must be versatile as well as being readily adapted to
encountering adverse weather conditions at the water's surface.
Additional problems inherent to the use of such an anchoring
arrangement, particularly in deep water, are topographical
irregularities which characterize the ocean floor. Such
irregularities comprise not only a generally uneven surface, but
may be in essence a gradual or steep grade. For example, certain
sections of the Continental Shelf or the Outer Shelf are at such an
exaggerated grade as to prohibit an ordinary foundation base from
assuming a level attitude.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical elevation illustrating an offshore buoyant
platform of the type contemplated anchored in place at the ocean
bottom.
FIGS. 2 and 3 are segmentary views in partial cross section and
enlarged scale of the anchor member shown in FIG. 1.
FIG. 4 is a view in partial cross section of the coupling member
shown in FIGS. 2 and 3.
FIGS. 5a to 5e inclusive illustrate the sequential steps embodied
in positioning the presently disclosed marine structure at a
submerged offshore site.
The invention therefore provides a novel anchor or subsea
foundation for an offshore, buoyant marine platform. The anchor
further includes provision for being fastened to the ocean floor
whereby to tether and uprightly position a buoyant structure above
the floor well site. The anchor embodies a plurality of discrete
members which are separable prior to installation at the job site,
but which are subsequently cemented into a unitary element when at
the ocean floor.
Referring to FIG. 3, prior to being unitized the anchor includes a
coupling segment having means depending from the upper end thereof
to engage and operably hold the lower end of a floatable marine
structure. The coupling element, comprising a ball or hemispheric
unit is movably held within a cavity formed within the anchor
member. When ultimately positioned to most advantageously engage a
floating structure, the cavity formed within the anchor is filled
with a hardenable material to fixedly imbed the coupling member,
and to establish its upright position to best accommodate said
structure.
As shown in FIG. 1, in a typical offshore installation utilizing
the present anchor or foundation member, a buoyant marine platform
10 is utilized for drilling one or more subterranean wells into the
ocean stratum. In FIGS. 1 and 2, the surface of the latter is shown
at an exaggerated slope or grade. Platform 10 includes a working
deck 11 holding a derrick 12, draw works and other equipment
peculiar to an oil drilling and/or producing operation. Deck 11 is
normally supported 50 or 60 feet beyond the water's surface to
maintain the equipment out of the reach of high waves during severe
weather conditions.
Deck 11 is supported at its desired height by an elongated
supporting structure 13 which includes one or more legs that extend
downwardly from the water's surface to the ocean floor. Said
structure 13 is made buoyant by the use of a ballasting system
incorporated into the structure. Said system, although not
presently shown in detail, includes longitudinally spaced buoyancy
tanks whereby the respective tanks are controlled to regulate their
degree of buoyancy and consequently the attitude of structure
13.
Under normal operating conditions, by regulating the buoyancy of
the anchor member 14, and by adjusting the buoyancy of support
structure 13, the latter is caused to assume a generally vertical
disposition to a desired water depth at the offshore site.
Thereafter, the structure's lower end is engaged with the imbedded
anchor 14 and retained by one or more flexible lines. Thus the
platform, including deck 11 and support structure 13, can oscillate
in the body of water during a predetermined degree of displacement
while still maintaining sufficient stability to carry on operations
at the deck level.
In the shown arrangement, platform 10 is anchored in place. However
it is appreciated that the entire structure 13 is subjected to
continuous tidal movement within the range of several feet up to
approximately 30 feet of height, depending on the location of the
offshore site. It is therefore necessary, in order to achieve the
desired degree of stability in the platform's vertical disposition,
that the lower end of support structure 13 be operably retained
rather than merely connected firmly to anchor 14.
Referring to FIG. 2 the floor positioned anchor 14 comprises a
plurality of discrete, though cooperatively arranged elements. Said
elements include basically a coupling 16, held within a retainer,
the latter comprising ballastable seating base 18 and cap 19. The
latter embodies tanks which can be flooded to provide the necessary
weight to anchor 14 whereby to submerge and hold the anchor at the
ocean floor or permit it to float.
Referring to FIG. 4, an embodiment of the coupling 16 includes a
body 21 adapted by virtue of its contoured outer surface to be
movably confined within retainer 19. Body 21 is slidably held
within cavity 23 to permit connecting post 22 to assume a desired
upright disposition. Preferably, such disposition is finalized with
connector post 22 aligned in a substantially vertical direction.
When so positioned, said connector post 22 will slidably engage a
corresponding sleeve 25 in the lower end of the support structure
13.
Body 21 of coupling member 16 includes any of several geometric
configurations which, in the instance of the present device, can be
spherical, hemispherical or similarly shaped. The function of
curved body 21 within the scope of the invention is to afford
coupling member 16 a degree of universal movement within confining
cavity 23 prior to being cemented in place. It is appreciated that
although body 21 is illustrated in a generally spherical
configuration, such a geometric shape is to permit sliding movement
between the body 21 upper surfaces, and the adjacent surrounding
walls of cavity 23. Such movement could be achieved in a manner of
fashion by the mating of nonspherical although similarly contoured
rubbing surfaces.
Connecting post 22 depending upwardly from the surface of body 21,
is firmly imbedded in the latter. A hub 24 at the lower end of
connector post 22 defines an intermediate collar between the post
22 lower end and the surface of said body 21. Connector post 22
comprises a generally elongated, uniform diameter cylindrical
element of sufficient diameter to register within sleeve 25 of
structure 13.
Prior to being cemented at the ocean floor, body 21 is upwardly
supported in sliding contact with the walls of cavity 23. Thus, by
exerting upward tension on cable 45 and post 22, seating section 18
can adjust its attitude on a contoured ocean floor regardless of
the topography of the latter.
Toward achieving a more firm connection between coupling 16 within
retainer cavity 23, the outer surface of body 21 is provided with a
series of surface depressions 26. Said depressions can also assume
the form of a series of spaced projections extending outwardly of
the surface whereby affording the cement a greater holding
area.
Body 21 is fabricated of formed steel plate so contoured and welded
together to permit the surface thereof to be slidably received
within the corresponding anchoring surface of cavity 23. Further,
the body interior is compartmented by transversely positioned
gussets or panels 27 and 28 respectively arranged to define
individual chambers 29 and 29a. Said panels are appropriately
placed to stiffen or strengthen the walls of the body. The
respective chambers can be further provided with valving whereby to
flood the chambers for submerging said coupling member.
Cap member 19 assumes the general structural features of a
controllably floatably member having integral compartments such as
30 which are connected to a buoyancy system. The cap section is of
sufficient proportion such that when deballasted or evacuated of
water, said member will support coupling member 16 at the water's
surface whereby to facilitate surface transportation and
installation of the unit.
Cap member 19 is provided with a recessed cavity 23 defined by a
surface contoured in accordance with the corresponding upper
configuration of coupling member body 21. Cavity 23 opens at the
upper surface of cap 19 in a constricted opening 32. Said cavity is
preferably formed with an inwardly contoured and tapered wall which
terminates at said constricted opening 32. Constricted opening 32
is of sufficient diameter to permit free movement of the connector
22 as the body member 21 is slidably adjusted within cavity 23.
The underside of retainer cap 19 is further provided with two or
more aligning indentations 33 which are adapted to receive
corresponding projections 34 depending from the upper surface of
seating member 18. Thus, the respective upper and lower surfaces of
cap 19 and seating base 18, are readily guided into mating
engagement at the ocean floor by a remotely controlled operation.
Passage 36 in cap 19 extends upwardly from aligning indentations
33. The flexible cable 37, having the lower end connected to the
tip of connector post 22 is guided by and extends through passage
36. Said cable functions to slidably guide the cap 19 and seating
base 18 into engagement subsequent to said base 18 being lowered to
a drill site at the ocean floor.
Seating member 18 includes an upper surface which not only
supportably engages body 21 and coupling 16 to hold it within
cavity 23 but also engages the underside of cap 19 to form a
unitary member therewith. Seat 18 in the base is fabricated in the
form of a steel bargelike construction embodying evacuable buoyancy
compartments 42 which are connected to a buoyancy control system
whereby said base can be controllably submerged.
The operation of cementing coupling member 16 within retainer
cavity 23 is facilitated by one or more cement passage 39 which
communicates with cavity 23 through cap 19 and seating member 18.
Said conduits terminate at the upper surface of cap 19 and are
connectable to a flexible conduit means 43 which in turn extends
upwardly through the water for carrying fluidized cement to the
anchor.
Referring to FIGS. 5a through 5c inclusive in the normal operation
of the disclosed mooring with respect to positioning a floating
platform 10 as shown in FIG. 1, support structure 13 includes an
elongated leg or legs having means at the lower end to operably
engage at least one connecting post 22 depending upwardly from the
coupling member body 21. Foundation element 14, including coupling
member 16 and retainer 19 are towed to a predetermined position for
lowering to the ocean floor. Both cap 19 and seating base 18
comprising retainer 19, are supported at the ocean's surface by
exhausting water from buoyancy tanks in each of said members.
At the proposed under water site, seating base 18 is disconnected
from cap 19 and submerged by exhausting ballast from internal tanks
42. Guide line 45 is connected to post 22 depending upwardly from
the anchor 14, which guide line passes through passage 36 to the
top of platform 10. Seating member 18 will imbed itself by its own
weight at least partially into the ocean stratum together with stub
piles 51 and 52 carried on the said member. Depending on the
contour of the ocean floor, said seating member will be offset or
canted at an angle from the horizontal in accordance with the
composition of the substratum and the general slope of the ocean
floor. Cavity segment 38 is thereby upwardly exposed to receive
body 21.
Coupling 16 is next disconnected from cap 19 and guidably supported
by central guide cable 45.
The coupling is next flooded to reduce its buoyancy at the water's
surface and is thereafter controllably lowered to register within
the open cavity 38 of seating member 18.
In the event that guide cable 45 is acted on by an appreciable
force as would be the instance of a heavy cross current or currents
running through the water, the guide cable will tend to assume a
curved configuration whereby to offset the connector post in the
direction of the water current. Under such circumstances, coupling
16 can be provided with a pair of laterally extending, detachable
arms. With the latter slidably engaging cables 37, sideward
displacement of coupling 16 will be restrained as it descends.
With coupling 16 and seating member 18 located at the ocean floor,
the buoyancy of cap member 19 is progressively decreased. The upper
ends of the respective cables 45 are retained above the water's
surface, being attached to a winch or jacking mechanism at the
upper side of platform 10. At the ocean floor, cap member 19 will
be guided into alignment with the prepositioned post 22 by virtue
of the aligning projections 34 and openings 33. On becoming
properly seated, cap member 19 will form a closure about cavity 38
to form a substantially spherical or hemispherical enclosure for
body 21.
By exerting an upward tension on cable 45, connector 21 will be
urged into vertical alignment. When so positioned, fluid cement is
introduced by way of conduit 43 and passage 39 to cavity 23. As the
cavity fills with cement, between body 21 and the cavity walls, the
cement will overflow through opening 32. Subsequent hardening of
the cement will thereby immobilize connector 22 in a vertical
attitude to receive its complementary member on structure 13.
Obviously many modifications and variations of the invention, as
hereinafter set forth, may be made without departing from the
spirit and scope thereof, and therefore, only such limitations
should be imposed as are indicated in the appended claims.
* * * * *