US3643446A

US3643446A - Marine platform foundation member

Info

Publication number: US3643446A
Application number: US25943A
Authority: US
Inventors: George E Mott
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1970-04-06
Filing date: 1970-04-06
Publication date: 1972-02-22
Anticipated expiration: 1989-02-22
Also published as: GB1330289A; NO135678C; CA942514A; FR2099064A5; NL7104503A; IE35050B1; NO135678B; DE2116852A1; IE35050L; JPS515203B1; ES389970A1

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.

Description

[ 5] Web. 22, 11972 MARINE PLATFURM FUUNDATIflU/N MEMBER Primary ExaminerJacob Shapiro Attorney-Thomas l-l. Whaley and Carl G. Ries [57] 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 waters 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 hardenablc fluid such as cement is introduced to solidify and form the coupling and retainer member into a singular body.

3 Claims, 9 Drawing lFigua-cs PATENIED FEB 2 2 I972 SHEET 1 [IF 2 MARINE PLATFORM FOUNDATION MEMBER 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 waters 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. l 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 Sc 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 is utilized for drilling one or more subterranean wells into the ocean stratum. In FIGS. l 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 l2, draw works and other equipment peculiar to an oil drilling and/or producing operation. Deck lll 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 113 which includes one or more legs that extend downwardly from the waters surface to the ocean floor. Said structure 113 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 con trolled 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 l4l, 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 ll 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 i3 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 platforms vertical disposition, that the lower end of support structure ll3 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 llo, held within a retainer, the latter comprising ballastable seating base 18 and cap R9. The latter embodies tanks which can he flooded to provide the necessary weight to anchor I-tl 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 to includes a body 21 adapted by virtue of its contoured outer surface to be movably confined within retainer l9. Body 2i is slidably held within cavity 23 to permit connecting post 22 to assume a desired upright disposition. Preferably, such disposi tion 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 211 is illustrated in a generally spherical configuration, such a geometric shape is to permit sliding movement between the body 2ll 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 beingcemented at the ocean floor, body 2i 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.

r sz sf a 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 compartrnented 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 waters 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.

Theunderside 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 remotelycontrolled 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 nected 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 sur face 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. 50 through 50 inclusive in the normal operation of the disclosed mooring with respect to positioning a floating platform 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 oceans 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 waters 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. 1

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 beguided 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 V 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 22in 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.

Iclaim:

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 structures 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,

(1. 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 ]l 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 re' gistered 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. ln 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 waters surface whereby said cap is slidably lowerable along said flexible cable to engage said seating member when the latter is at said floor.

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 se parably 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.

Claims

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.

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.