US3693361A

US3693361A - Method and apparatus for transporting and launching an offshore tower

Info

Publication number: US3693361A
Application number: US29831A
Authority: US
Inventors: Albert M Koehler
Original assignee: Brown and Root Inc
Current assignee: Brown and Root Inc
Priority date: 1970-04-20
Filing date: 1970-04-20
Publication date: 1972-09-26
Anticipated expiration: 1989-09-26

Abstract

A method and apparatus for transporting an offshore tower to a preselected marine site upon an annular floatation collar encompassingly connected to the upper end of the offshore tower and one or more floatation chambers connected to the outer periphery of the base of the tower. At the preselected site the tower is removed from the base flotation system and pivots about the center of gravity of the offshore tower into a generally vertical posture within the body of water. The annulus is then at least partially ballasted to lower the tower to a position adjacent the bed of the body of water while maintaining the vertical posture of the central axis of the offshore tower with respect to the plane of the surface of the body of water. The tower is then pinned to the bed of the body of water to stably support the tower and retain the vertical orientation thereof with respect to the surface of the body of water, notwithstanding an irregular geography of the bed of the body of water. In one embodiment the floatation system, connected to the base of the outer periphery of the offshore tower, comprises a pair of floation chambers spaced symmetrically on opposite sides of a plane intersecting the central axis of the offshore tower and lying normally with the plane of the surface of the body of water. In this embodiment one of the floatation chambers is at least partially flooded to induce a rotation of the offshore tower 130* about its center of gravity prior to releasing the floatation chambers from the base of the offshore tower.

Description

Koehler 51 Sept. 26, 1972 1 1 METHOD AND APPARATUS FOR TRANSPORTING AND LAUNCHENG AN OFFSHORE TOWER [72] Inventor: Albert M. Koehler, Houston, Tex.

[73] Assignee: Brown 8: Root, lnc., Houston, Tex.

[22] Filed: April 20, 1970 21 Appl. No.: 29,831

[52] US. Cl. ..61/46.5, 9/8, 1l4/0.5 F [51] Int. Cl ..E02b 17/00, B63b 35/44 [58] Field of Search ..61/46.5, 52, 82, 81; 114/05 D, 0.5 F; 9/8

[56] References Cited UNITED STATES PATENTS- 3,017,934 l/1962 Rhodes etal. ..9/8 X 3,118,408 l/l964 Knapp ..1l4/0.5 D 2,906,500 9/1959 Knapp et al ..61/46.5 X 3,496,897 2/1970 Poconowskietal....1l4/0.5 D 3,360,810 l/1968 Busking 9/8 FOREIGN PATENTS OR APPLICATIONS 649,506 0/1962 Canada ..61/82 Primary ExaminerJacob Shapiro Attorney-Burns, Doane, Benedict, Swecker & Mathis [57] ABSTRACT A method and apparatus for transporting an offshore tower to a preselected marine site upon an annular floatation collar encompassingly connected to the upper end of the offshore tower and one or more floatation chambers connected to the outer periphery of the base of the tower. At the preselected site the tower is removed from the base flotation system and pivots about the center of gravity of the offshore tower into a generally vertical posture within the body of water. The annulus is then at least partially ballasted to lower the tower to a position adjacent the bed of the body of water while maintaining the vertical posture of the central axis of the offshore tower with respect to the plane of the surface of the body of water. The tower is then pinned to the bed of the body of water to stably support the tower and retain the vertical orientation thereof with respect to the surface of the body of water, notwithstanding an irregular geography of the bed of the body of water.

In one embodiment the floatation system, connected to the base of the outer periphery of the offshore tower, comprises a pair of floation chambers spaced symmetrically on opposite sides of a plane intersecting the central axis of the offshore tower and lying normally with the plane of the surface of the body of water. In this embodiment one of the floatation chambers is at least partially flooded to induce a rotation of the offshore tower 130 about its center of gravity prior to releasing the floatation chambers from the base of the offshore tower.

16 Claims, 19 Drawing Figures PATENTED E m2 3,693,361

- SHEET 2 [IF 4 INVENTCR ALBERT M. KOEHLER QM, BY 5 5 ,5 14/53 ATTORNEYS PATENTED8P26 m2 SHEET 3 0F 4 INVENTOR ALBERT M. KOEHLER W 4 Am,-

' ATTORNEYS METHOD AND APPARATUS FOR TRANSPORTING AND LAUNCHING AN OFFSHORE TOWER BACKGROUND OF THE INVENTION More particularly, the invention relates to an improved launching vessel and launching process for rapidly and conveniently transporting a large, deep water offshore tower to a desired marine site and positioning the tower in a generally vertical posture with respect to the surface of the body of water and fixedly connecting the tower thus positioned to the bed of the body of water.

Towers have a multiplicity of applications in a marine environment such as, for example, supports for radar or sonar stations, light beacons, scientific marine exploration labs and the like. Additionally, offshore towers are frequently utilized in the oil industry in connection with drilling, producing, storing, and distributing operations.

Drilling for oil and gas in formations situated beneath the surface of a body of water has in the recent past become an extremely challenging and important segment of activity in the oil industry. In this connection creative scientists and engineers have made tremendous strides in connection with exploration, drilling,producing, storing and distributing activities in a hostile marine environment. Notwithstanding the successes of the recent past however, significant challenges remain in this infant segment of the oil industry.

In the initial stages of development offshore operations were conducted in locations of relative shallow water depths from a few feet to one or two hundred feet, such as exists along the near shore portions of the Gulf of Mexico. More recently, however, large mineral resources have been detected in water depths ranging from a few hundred to a few thousand or more feet such as exists along the Pacific coast continental shelf and the Arctic regions.

In order to exploit the mineral resources which exist below such a substantial depth of water, tower designs which have been reliable and effectively utilized in the past have undergone considerable redesign for prolonged high stress, deep water use. In this connection, offshore towers being presently designed are enormous structures presenting truly significant engineering challenges, not only from an initial design aspect, but from a subsequent construction,transportation and erection point of view.

At least one method for transporting and erecting an offshore tower which has attained a degree of successful utilization in deep water locations comprises segmenting the tower legs with bulkheads into ballast compartments and floating the tower to an offshore site upon the buoyant tower legs. At the work site the compartments are flooded to sink the tower to the bed of the body of water.

While this technique is frequently adequate, it has recently been desirable to drill through the tower legs, thus isolating the conductor and drilling string from the hostile marine environment. It will .be readily realized, however, that floatation compartment bulkheads obstruct the placement of conductors within the leg of the tower at an offshore site and/or require intricate shipyard fabrication. Further, a lack of universal application or reuse capability often renders such a concept of transportation and erection economically undesirable.

A further known method of transporting and launching offshore towers comprises attaching one or more flotation pontoons to the exterior of the tower structure and floating the tower to a preselected work site resting upon the pontoons. In order to launch the tower the pontoons are released which permit the offshore tower to settle upon the bed of the body of water.

It will be realized, however, that floats or pontoons supporting a drilling tower must transmit enormous buoyancy forces. Releasing the pontoons from the weight of the tower immediately unleashes these buoyancy forces which correspond to the previous weight of the supported tower with the resultant effect of an almost explosive throwing and thrashing of the flotation chambers. This violent action in conjunction with the enormous pontoon sizes required to support current deep water offshore towers renders the operation extremely hazardous to personnel and equipment located within the erection vicinity.

At least one further known method of transporting and launching an offshore tower comprises floating the tower to an offshore site resting upon pontoons. At the preselected site the pontoons are flooded'to ballast the tower into the body of water.

Ballasting the flotation chambers, however, shifts the center of gravity of the offshore tower somewhat unpredictably, thus placement of the tower precisely upon a desired subsea site becomes somewhat difficult.

It would therefore be highly desirable to provide a safe, convenient and efficient method and apparatus for transporting offshore towers of large dimensions to a suitable marine working site and controllably lowering the tower within the body of water accurately to a preselected waterbed site. Additionally, it would be advantageous to be able to safely detach the transport apparatus from the tower so as not to interfere with subsequent drilling operations and thus permit the reuse of the transport apparatus in subsequent operations. Further, it would be desirable to provide a method and apparatus wherein the upper end of the offshore tower projecting above the surface of the body of water may be continuously controlled to prevent undesirable and uncontrollable movement which may be at least potentially dangerous to personnel and equipment.

Further, it would be desirable to provide a method and apparatus for launching an offshore tower and pinning the tower to the bed of the body of water wherein the vertical posture of the tower with respect to the surface of the body of water may be conveniently assured notwithstanding an irregular geography of the immediate bed of the body of water. Additionally, it would be desirable to provide a method and apparatus for erecting an offshore tower accurately upon a preselected water bed site.

OBJECTS OF THE INVENTION It is therefore a general object of the invention to provide a method and apparatus which will obviate or minimize problems of the type previously described.

It is a particular object of the invention to provide a method and apparatus for controllably transporting and launching a deep water offshore tower within a body of water.

It is a further object of the invention to provide a method and apparatus for transporting and launching an offshore tower whereby the apparatus may be removed from the launched tower for reuse in subsequent operations.

It is a still further object of the invention to provide a method and apparatus for launching an offshore tower which will minimize the hazards to equipment and personnel during the launching operation.

It is another object of the invention to provide a method and apparatus for transporting an offshore tower to a preselected working site and erecting the offshore tower, utilizing the transport apparatus, within the body of water in a vertical posture with respect to the surface plane of the body of water, notwithstanding an irregular geometry of the bed of the body of water.

It is a still further object'of the invention to provide a method and apparatus for transporting and erecting an offshore tower wherein the upper end of the tower projecting above the surface of the body of water is continuously controlled to prevent excessive oscillation or dipping beneath the surface of the body of water during the launching operation.

It is yet another object of the invention to provide a method and apparatus for stably transporting and launching an offshore tower which is universal in application and may be adopted to accommodate a plurality of tower designs and configurations.

It is yet a further object of the invention to provide a method and apparatus for transporting and launching an offshore tower which will not interfere with subsequent drilling operations and will be economically attractive.

It is yet a still further object of the invention to provide a method and apparatus for accurately erecting an offshore tower upon a preselected subsea site.

THE DRAWINGS Other objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein: I

FIG. 1 is an isometric view of an offshore tower positioned in a transport posture along the surface of a body of water and having attached at its upper end an annular floatation collar and attached at the outer periphery of the lower end of the tower a pair of flotation vessels;

FIG. 2 is a plan view of an annular floatation collar forming a portion of the invention;

FIG. 3 is a cross-sectional view taken along section line 3-3 of FIG. 2;

FIG. 4 is a side elevational view of a flotation chamber forming a portion of the invention;

FIG. 5 is a cross-sectional view taken along section line 5-5 of FIG. 4;

FIGS. 6-14 disclose in a schematic array a method of transporting and erecting an offshore tower according to a preferred embodiment of the invention; and

FIGS. -19 disclose in a schematic array a method and apparatus for transporting and erecting an offshore tower according to an alternate embodiment of the invention.

DETAILED DESCRIPTION Referring now to the drawings and more particularly to FIG. 1 thereof, there will be seen an offshore tower 20 resting in a generally horizontal posture substantially above or along the surface 22 of a body of water 24. The tower includes generally vertical legs 26 which are encompassed by a plurality of girder rings 28 and a shell of cross braces 29 which support the tower legs against bucking when the tower is in the erected posture. The top or upper end of the tower 30 is provided with a platform 32 forsupporting drilling and/or production equipment, etc. (not shown). The base or lower end of the tower 34 is provided with skirt pile casings 36 for the reception of piles (not shown) suitable for pinning the offshore tower to the bed of the body of water 24. The specific tower structure 20, per se, does not form a part of this invention but merely represents one of a multiplicity of contemplated offshore tower designs which may be transported and launched by the present invention Intimately surrounding the top portion 30 of the offshore tower is a generally hollow annular flotation vessel 40, being of sufficient dimensional proportions to buoyantly support the upper end 30 of the offshore tower in a posture substantially above the surface 22 of the body of water 24. The base of the tower 34 is similarly buoyantly supported by a pair of similar flotation vessels 42 (note FIG. 7) and 43 positioned upon opposite sides of a planar surface 46 intersecting the central longitudinal axis 48 of the offshore tower and lying substantially perpendicular to the planar surface of the body of water 22. The

flotation vessels

42 and 43 are releasably connected to the outer periphery of the base of the tower 34 by, for example, a plurality of supporting braces and studs 50 which are releasably connected to the offshore tower and will be more fully described hereinafter.

Referring now to FIG. 2, there will be seen a preferred embodiment of an annular floatation collar having an outer periphery generally in the form of a symmetrical geometrical configuration which may range depending upon the geometry requirements of the tower from a circle to a triangle. The annulus 40 I may be continuously open throughout the interior thereof or segmented into individual compartments by one or more bulkheads (not shown). Further, the annulus may be separated into a first half 52 and a second half 54 having compatibly juxtaposed faces and apertured flanges 56 for the ready connection of the two halves by a plurality of conventionally threaded fasteners 58. While the flange and threaded fastener arrangement has been described as a means for releasably connecting and separating the annular floatation collar 40, other conventional mechanical fastening connections, such as hinges, cutting and welding, etc. will be apparent to those skilled in the art.

FIG. 3 is a cross-sectional view of the annulus 40 of FIG. 2 taken along section line 3-3 and discloses the circular character of the annular floatation collar shell 60. While this circular configuration is preferred, other geometric configurations from circular to triangular are fully contemplated as desired for the particular offshore tower application.

The bottom surface 62 of the annular flotation collar 40 is provided with a ballast fill or jettisoning discharge valve 64 which may be remotely controlled by a pneumatic, hydraulic or electrically actuated control mechanism (not shown) from an adjacent control and towing vessel 70 (note FIG. 1). Valve 64 serves to permit the ingress and egress of water within the interior of the annular floatation collar 40 and thus serves to regulate the buoyancy of the annulus.

In a similar manner connected to the upper surface 72 of the annular floatation collar 40 is a vent valve 74 and a blow valve 76 which may, like valve 64, be remotely controlled by electrical, pneumatic or hydraulic actuators regulated from the towing and control vessel 70.

While a single ballast fill or jettisoning discharge valve 64, vent valve 74 and blow valve 76 have been disclosed in FIG. 3, in those instances where the interior of the annular floatation collar 40 is segmented with a plurality of bulkheads across the interior of the vessel to form a plurality of compartments therein, it is con templated that a ballast fill or discharge valve, vent valve, and blow valve may be radially tapped into each compartment to facilitate the control of the buoyancy of the collar 40.

While specific connecting braces and/r struts have not been illustrated, it will be realized that suitable connecting means between the annular floatation collar 40 and the upper portion 30 of the offshore tower are contemplated. For example, metallic bands having explosive couplings junctions for ready release may be utilized, or horizontal supports and diagonal cross bracing struts which may be weldingly connected between the floatation collar 40 and the upper portion of the tower 30 and subsequently severed, and the like will be required to maintain the stationary posture of the flotation collar 40 about the upper end of the offshore tower during the flotation and erection operations.

Referring now to FIG. 4, there will be seen a flotation vessel 43 adapted to be connected to the outer periphery of the base 34 of the offshore tower 20, as illustrated in FIG. 1, which includes a generally longitudinally extending cylindrical shell 80 having hemispherical caps 82 sealingly closing the ends thereof to establish a watertight flotation vessel.

FIG. discloses a cross-sectional view of the flotation vessel 43 taken along section line 55 in FIG. 4 and discloses the generally circular character of the shell 80. It will be realized, however, that other geometric configurations of the flotation vessel 43 are fully contemplated and that the presently illustrated embodiment has been found to be effective because of the elimination of sharp angled junctions which potentially create stress difficulties when the flotation vessel is required to withstand a large amount of pressure.

The floatation vessel 43 is provided with a ballast fill or discharge valve 84 in a lower posture through the skin of the vessel 80. The valve 84, as previously discussed in conjunction with the valve 64 of the annular floatation collar 40, may be controllably actuated from a remote location such as, for example, the control and towing vessel 70 by pneumatic, hydraulic or electric actuators. The upper portion of the vessel 43 is provided with a vent valve 86 and a blow valve 88 which operate in conjunction with the ballast fill and discharge valve 84 in a manner which will be more fully discussed hereinafter to control the buoyancy of the floatation vessel 43.

The

floatation vessels

42 and 43 may be releasably connected to the outer peripheral surface of the lower end 34 of the offshore tower 20 by means of a connecting network 50 of braces 90, support arms 92 and crossing struts 94. The free ends of the braces 90 may be coped to intimately engage with compatible outer surface portions of the offshore tower and may be fixedly welded thereto. The base ends of the braces 90 are fixedly connected to stiffening brackets 91. Alternatively, depending upon the loads required to be supported, the connecting network 50 may be extended within the interior of the lower portion of the offshore tower and connect through a supporting network (not shown) to the upper interior surface of the tower.

While braces and struts have been previously described which may be physically severed as, for example, by explosive collars in order to remove the 'flotation vessels 42 from the outer periphery of the tower, other releasable attaching mechanisms are contemplated such as, for example, hydraulically actuated C-clamps, explosive detachable metallic straps or hands, and the like.

METHOD OF TRANSPORTING AND LAUNCHING Referring now.specifically to FIGS. 6-14, there will be seen in a schematic array, a generally sequential depiction of transporting an offshore tower to a select marine site, controllably and accurately erecting the tower upon the bed of the body of water and retrieving the transport and launch apparatus.

More particularly, and referring to FIG. 6, there will be seen an offshore tower 20 floatably resting at its upper end 30 upon an annular floatation collar 40 and similarly supported at its lower end 34 upon

floatation vessels

42 and 43 in a stable triangular bearing posture as best seen in FIG. 7 upon the surface 22 of a body of water 24.

A control and tow vessel connected to the upper end 34 of the tower serves to tow the thus horizontally disposed tower 20 to a previously selected offshore site.

Upon reaching the desired marine site, the vessel 70 may be disconnected from the forward portion 30 of the tower and the tower rest upon the surface of the body of water with the

flotation vessels

42 and 43 as best seen in FIG. 8 positioned substantially beneath the outer periphery of the base of the tower 34. The flotation vessels are spaced approximately equidistantly from a plane 46 intersecting the central longitudinal axis 48 of the offshore tower, said plane 46 lying normally with the plane of the surface of the body of water. The

flotation vessels

42 and 43 thus positioned support the major portion of the offshore tower and thus the center of gravity C.G. thereof above the center of buoyancy CB and the surface 22 of the body of water.

It will be readily recognized that this relationship of the CB. and CG. is by definition unstable. However, the outrigger character of the triangular arrangement of the flotation collar 40 and vessels 42 makes this arrangement stable enough to be effectively utilized to transport the tower to the desired drilling site while minimizing the amount of drag produced by the tower structure extending within the body of water.

Prior to releasing the

flotation chambers

42 and 43 from the periphery of the tower and righting the tower within the body of water, it is desirable to substantially remove the flotation vessels from their posture beneath the offshore tower. Violent thrashing of the vessels produced by a sudden release of the buoyant forces is thereby minimized.

In this connection and as best sequentially illustrated in FIGS 8-10, one of the flotation vessels 43 is partially ballasted by the opening of the ballast fill and discharge valve 84 and vent valves to permit the ingress of water into the interior of the vessel 43. This will induce a rotational roll of the vessel 20 about the center of gravity of the offshore tower 20, as best seen in FIG. 9. Ballasting of vessel 43 shifts the center of gravity and the center of buoyancy of the towerslightly to the right and simultaneously displaces the CB. out of vertical alignment with respect to the C.G.

A rotational couple is thus created having an increasing moment arm D until the CB. and C.G. lie in the same horizontal plane. Further rotation in the same direction will diminish the moment arm D until vertical alignment is achieved wherein the C.B. lies above the C.G. as best seen in FIG. 10. The tower 20 will thus have rolled l80and the greater part of the base of the offshore tower is now positioned beneath the body of water. It will be readily recognized by those skilled in the art that the above described roll is accomplished with insignificant lateral shifting of the offshore tower. Further, flotation vessel 43 may be pressurized to offset the crushing load imposed upon the vessel '43 during the roll operation.

Upon release, the

flotation vessels

42 and 43 may be completely blown of any fluid taken during the transport and launch operation by closing the vent valves 86 and opening the blow valves 88 to jettison fluid out of the jettisoning discharge valves 84. Upon obtaining maximum buoyancy all of the valves 84, 86 and 88 are closed and the vessels are ready to be towed back to port for reuse. Further, following release of the

flotation vessels

42 and 43, it will readily be realized, and as best illustrated in FIG. 11, that the offshore tower 20 will begin to pivot about the center of gravity C.G. of the tower 20 and the annular flotation collar 40 into the body of water 24. The tower will translate downwardly along vertical line 41 which passes normally from the surface of the body of water through the C.G. of the tower and floatation collar. Insignificant deviation from this line is due to drag and acceleration forces created by the displaced water.

Thus in order to accurately locate the tower 20 upon a preselected waterbed site the C.G. of the tower and flotation collar is positioned vertically above the desired waterbed site. The

flotation collars

42 and 43 are released and the tower 20 will right itself and settle to the waterbed along vertical line 41 accurately to the preselected subsea location.

Moreover, it is significant to note that because of the continuous nature of the buoyancy annulus 40 and the encompassing relationship thereof with the upper end of the offshore tower 20, as the collar translates along the surface of the body of water and the vertical position is approached, an increasing portion of the flotation annulus facing the base of the offshore tower will come into contact with the water and thus minimize the tendency of the top 30 of the tower 20 from being pulled downwardly into the body of water. In this specific connection, it has been found by experimental model testing that side to side oscillation of the tower thus launched is minimized to the extent of being practically imperceptible.

The offshore tower 20, as best seen in FIG. 12, thus launched will be supported at its upper end by the annular buoyancy collar 40 with the central axis 48 of the tower positioned perpendicularly to the surface of the body of water 24 and directly over the preselected waterbed site. In this connection, it will be readily apparent to one skilled in the art that the above described tower posture, as particularly illustrated in FIG. 12, is only achievable if the buoyancy collar 40 is dimensioned to have a buoyancy greater than the effective weight of the offshore tower 20 when the tower is righted within the body of water.

In order to affix the offshore tower to the bed of the body of water, the annular floatation collar 40 is ballasted by opening ballast fill valve 64 and vent valve 74 in the annular collar 40. The annulus will then take water and permit the tower 20 to vertically descend within the body of water. Vertical descent is controlled, however, by selective jettisoning and filling such that the tower 20 may be controllably lowered until one portion of the outerperiphery of the base of the tower comes into contact with the bed 25 of the body of water 24.

The vertical descent of the tower 20 is then halted, as illustrated in FIG. 13, and a plurality of conductor piles are driven through the jacket legs and into the bed of the body of water to pin the tower with respect to the bed in a posture wherein the central axis 48 remains perpendicular to the surface 22 of the body of water.

Following the pinning operation, the annulus 40 may then be split and recovered for subsequent transport and launch operations. Piles 96 are then driven through the pile casings 36 and grouted thereto to fixedly connect the tower in a vertical posture to the bed of the body of water notwithstanding the sloping character of the water bed 25.

Referring now to FIGS. 15-19, there will be seen an alternative method of launching an offshore tower according to an alternate embodiment of the invention. Referring specifically to FIG. 15, there will be seen an offshore tower 20 positioned in a generally horizontal posture along the surface 22 of a body of water 24 disposed at its upper end 30 upon an annular floatation collar 40 and at its lower end upon a flotation vessel 98.

A control and transport vessel 70 is releasably connected to the upper end of the offshore tower and serves to tow the tower to a preselected marine site. Upon reaching the offshore site a second vessel 100 is connected to the floatation vessel 98 and lays away in a direction approximately from the direction of tow by the control barge 70. Such counter pulling induces the removal of the floatation barge 98 from beneath the base 34 of the offshore tower 20, as illustrated in FIG. 16, and thus precipitates a downward rotation of the base of the tower 34 into the body of water 24, as best illustrated in FIG. 17. Alternatively, the tower 20 may be jacked off of the barge 98 by conventional jacking techniques.

The tower then pivots about the annular C.G. into a generally vertical posture wherein the central axis 48 is held generally vertical with respect to the surface 22 of the body of water 24.

Further, following removal of the flotation vessel 98, it will readily be realized, and as best illustrated in FIG. 11, that the offshore tower 20 will begin to pivot about the center of gravity C.G. of the tower 20 and the annular floatation collar 40 into the body of water 24. The tower will translate downwardly along vertical line 41 which passes normally from the surface of the body of water through the C.G. of the tower and flotation collar. Insignificant deviation from this line is due to drag and acceleration forces created by the displaced water.

Thus in order to accurately locate the tower 20 upon a preselected waterbed site the C.G. of the tower and flotation collar is positioned vertically above the desired waterbed site. The flotation vessel 98 is removed and the tower 20 will right itself and settle to the waterbed along vertical line 41 accurately to the preselected subsea location.

Moreover, as previously mentioned, the continuous nature of the annular flotation vessel 40 and the increasing contact with the' surface of the water and spreading of the buoyancy forces minimizes the tendency of the upper portion of the tower to oscillate on the surface of the body of water and prevents the top of the tower from being pulled downwardly into the body of water.

As illustrated in FIG. 18, the floatation annulus is controllably ballasted until the bottom portion of the offshore tower 20 in at least one point contacts the bed of the body of water 25. Pinning conductor pilings 95 may then be driven through the tower jacket legs to pin the tower to the bed 25 of the body of water with the central axis 48 thereof lying normally with respect to the surface plane of the body of water.

In order to firmly attach the offshore tower 20 in this vertical posture, as best illustrated in FIG. 19, a plurality of piles 96 are driven through the pile casings and grouted thereto to relatively permanently establish'the tower upon the bed of the body of water to facilitate subsequent drilling and production operations.

SUMMARY OF THE MAJOR ADVANTAGES It will be seen that the present invention provides an improved method and apparatus for transporting and launching an offshore tower.

Particularly significant is the provision of a annular floatation collar encompassing the upper portion of an offshore tower which permits a free axial rotation of the tower and enhances the stability of the upper end of the tower during the righting operation.

A significant method aspect of the invention is the step of axially rotating the tower on the water surface about the C.G. without significant lateral translation prior to releasing the floatation vessels connected to the base thereof to minimize uncontrolled motion of the tower and the vessels upon release thereof.

A further significant aspect of the invention is the three-point bearing floatation arrangement which provides stability for transporting the tower to an offshore site notwithstanding the C .6 being above the CB.

Further, the transportation and launch apparatus may be recovered and reused for subsequent operations and will not interfere with subsequent drilling, production, storage or distribution.

Another significant aspect of the invention is the process of erecting the offshore tower, utilizing the transport apparatus within the body of water in a vertical posture with respect to the surface plane of the body of water notwithstanding an irregular geometry of the bed of the body of water.

A further advantage of the invention is the provision of erecting an offshore tower while simultaneously maintaining control of the upper end thereof to prevent excessive whipping or submergence thereof during he launching operation.

A still further major advantage of the present invention is the method of accurately placing an offshore tower upon a preselected subsea site with a minimum amount of time and effort.

Although the invention has been described with reference to preferred embodiments, it will be appreciated bythose skilled in the an that additions, deletions, modifications, substitutions and other changes not specifically'described may be made which will fall within the purview of the appended claims.

What is claimed is:

1. An offshore tower apparatus comprising:

an offshore tower including,

a base portion for resting upon the bed of a body of water, and an upper portion operable to extend above the surface of the body of water for stably supporting a platform above the surface of the water; i a substantially hollow annular flotation collar releasably connected around the outer periphery of the upper end of the offshore tower for buoyantly supporting the upper end of the offshore tower substantially above the surface of the body of water when the tower is in a horizontal posture during transportation to a marine site and for increasingly contacting the surface of the body of water when the tower is being righted in the body of water thus minimizing turbulence during the righting operation, said substantially hollow annular flotation collar being dimensioned to have a buoyancy greater than the total effective weight of the offshore tower when said offshore tower is righted within the body of water; and floatation means releasably connected to the exterior of the base of the tower for at least buoyantly supporting the base of the tower substantially above the surface of the body of water during the transport operation.

2. An offshore tower apparatus as defined in claim 1, wherein:

said substantially hollow annular flotation collar being generally circular in cross-section.

3. An offshore tower apparatus as defined in claim 1 and further comprising:

means for selectively ballasting or blowing the interior of said substantially hollow annular flotation collar.

4. An offshore tower apparatus as defined in claim 1 wherein the said flotation means comprises:

a pair of generally cylindrical hollow tanks connected to the outer periphery of the base of the offshore tower and being spaced upon opposite sides of a plane extending through a central axis of the offshore tower and lying normal to the surface of the body'of waterwhereby said annular flotation collar and said pair of flotation vessels form a stable triangular bearing transport apparatus.

5. An offshore tower apparatus as defined in claim 4,

and further comprising:

means for controllably ballasting or blowing the interior of at least one of said pair of generally cylindrically hollow tanks.

6. An offshore tower apparatus as defined in claim 1,

wherein said floatation means comprises:

a generally rectangular tank having the long sides thereof, lying approximately normally to a plane intersecting the central axis of the offshore tower and lying normal to the surface of the body of water, and said tank beingdimensioned with sufficient buoyancy to maintain the based the tower above the surface of the body of water.

7. An offshore tower apparatus comprising:

an offshore tower including,

a base portion for resting upon the bed of a body of water, and A an upper portion operable to extend above the surface of the body of water for stably supporting a platform above the surface of the body of water;

an annular flotation collar releasably connected about an upper end of the offshore tower for buoyantly supporting the upper end of the offshore tower substantially above the surface of the body of water when the tower is in a horizontal posture during transportation to a marine site and for providing a substantially constant buoyant force during a 180 rotation of the offshore tower in a horizontal posture with respect to the body of water prior to righting the offshore tower in the body of water and for increasingly contacting the surface of the body of the water when the tower is being righted in the body of the water thus minimizing turbulence during the righting operation, said substantially hollow annular floatation collar being dimensioned to have a buoyancy greater than the total effective weight of the offshore tower when said offshore tower is righted within the body of water; and I a pair of flotation vessels connected to the base portion of the offshore tower, symmetrically disposed on opposite sides of a plane intersecting a central axis of the offshore tower and lying normal to the surface of the body of water, whereby said pair of floatation vessels in combination with said annular flotation collar forms a stable triangular floating system for transporting and launching the offshore tower. 8. An offshore tower apparatus as defined in claim 7 and further comprising:

means for controllably ballasting and blowing the interior of said annular floatation collar for regulating the buoyancy thereof; and

means for ballasting or blowing at least one of said pair of cylindrical floatation vessels for controlling the buoyancy thereof.

9. A method of transporting an offshore tower to a marine site and launching the offshore tower within the body of water in a generally vertical posture having the base thereof fixed to the bed of the body of water and having the upper end thereof extending above the surface of the body of water to stably support a platform above thesurface of the body of of water, comprising the steps of:

floating an offshore tower to a desired marine site resting upon an annular flotation collar at the upper end thereof and a pair of spaced flotation vessels symmetrically disposed upon opposite sides of a plane intersecting the central axis of the offshore tower and lying perpendicular to the surface of the body of water, said flotation vessels being connected to the outer periphery of the base of the offshore tower; at least partially ballasting one of said pair of floatation vessels connected to the outer periphery of the base of the tower, rotating the offshore tower about the center of gravity thereof; releasing said pair of flotation vessels from the outer periphery of the base of the offshore tower; pivoting the offshore tower about the center of gravity thereof into a generally vertical posture within the body of water whereinthe central tower axis lies normally with the plane of the surface of the body of water; ballasting the annular floatation collar to vertically descend the tower to a position wherein at least one portion of the outer periphery of the base approximately contacts the bed of the body of water notwithstanding the particular geography of the bed; pinning the offshore tower to the bed of the body of water to stably support the offshore tower and maintain the'normal alignment of the central axis of the offshore tower to the plane of the surface of the body of water; removing the annular floatation collar from the upper end of the offshore tower; and driving a plurality of piles through pile casings surrounding the base of the tower into the bed of the body of water to fixedly connect the tower to the bed of the body of water. g 10. A method of accurately locating and erecting at a preselected waterbed site an offshore tower within a body of water in a generally vertical posture, comprising the steps of:

supporting an offshore tower at a marine site horizontally at the upper end thereof by a first floatation means and at the lower end thereof by a second floatation means; positioning the center of gravity of the combined offshore tower and the first flotation means vertically over the desired waterbed site; and releasing the buoyant support from the offshore tower lower end permitting the tower to rotate about the center of gravity thereof and the first flotation means and vertically descent to the bed of the body of water along a line intersection said center of gravity and lying normally with the surface of the body of water. 11. A method of accurately erecting an offshore tower as defined in claim 10 wherein said step of supporting includes:

ing the base of the offshore tower, contacting the surface of the body of water to minimize turbulence during the righting operation;

ballasting the annular collar connected about the 12. A method of accurately erecting an offshore 5 upper end of the offshore tower to lower the tower as defined in claim wherein said step of supoffshore tower in a generally vertical mode to a porting includes: position adjacent the bed of the body of water thus suspending'the lower end of the offshore tower from orienting the central axis of the offshore tower apa pair of spaced flotation vessels releasably conproximately normal to the surface of the body of nected directly with the upper outer periphery of water notwithstanding the particular geography of the lower end of the offshore towerwhen the base the water bed;

of the offshore tower is substantially submerged pinning the offshore tower to the water bed to rigidly beneath the surface of the body of waters support the tower upon the water bed and main- 13. A method of transporting an offshore tower to a tain the central axis of the tower in a posture normal to the surface of the body of water; and

disconnecting the annular floatation collar from the upper end of the offshore tower for subsequent reuse. 15. A method of transporting an offshore tower to a predetermined marine site and launching the offshore tower within thebody of water in a generally vertical posture, comprising the steps of:

floating an offshore tower to a desired marine site upon an annular collar at the upper end thereof and upon a pair of generally hollow flotation vessels at the lower end thereof being symmetrically spaced on opposite sides of a plane extending through the central axis of the offshore tower and lying normal to the surface of the body of water thus forming in conjunction with the annular collar at the upper end of the offshore tower a triangular flotation arrangement for stably floating the offshore tower to a desired marine site upon a 35 three-point bearing pad of'buoyancy vessels;

rotating the offshore tower in a generally horizontal posture about the center of gravity thereof approximately 180;

disconnecting the pair of flotation vessels from the lower end of the offshore tower; and

pivoting the offshore tower about the center of gravity thereof into a generally vertical posture within the body of water.

16. A method of transporting an offshore tower to a predetermined marine site and launching the offshore tower within the body of water in a generally vertical posture, comprising the steps of:

floating an offshore tower to a desired marine site upon an annular collar at the upper end thereof and upon a pair of generally hollow flotation vessels at the lower end thereof symmetrically spaced on opposite sides of a plane extending through the central axis of the offshore tower and lying normal to the surface of the body of water, thus forming in conjunction with the annular collar at the upper end of the offshore tower a triangular flotation arrangement for stably floating the offshore tower to a desired marine site upon a three-point bearing pad of buoyancy vessels;

removing the floatation vessels from beneath the lower end of the offshore tower, including the steps of rotating the offshore tower about the center of gravity thereof approximately 180 by at least partially ballasting one of said pair of spaced flotation vessels to induce the rotation of the marine site and launching the offshore tower within a body of water, comprising the steps of:

floating the offshore tower in a generally horizontal posture to a marine site while buoyantly supporting the offshore tower substantially above the sur face of the body of water upon an annular flotation collar connected around the upper end thereof and upon other means for flotation attached substantially beneath the outer periphery of the lower end thereof;

rotating the offshore tower while in the horizontal posture about the center of gravity thereof approximately 180;

disconnecting the other means for flotation from the other periphery of the lower end of the offshore tower;

pivoting the offshore tower about the center of gravity thereof and the attached flotation collar into a vertical posture within the body of water while simultaneously supporting the upper end of the offshoretower at the surface of the body of water by the annular flotation collar, which collar during said pivoting motion translates along the surface of the body of water with an increasing portion of the collar, facing the base of the offshore tower, contacting the surface of the body of water to minimize turbulence during the righting operation.

14. A method of transporting an offshore tower to a marine site and launching the offshore tower within a body of water, comprising the steps of:

floating the offshore tower in a generally horizontal posture to a marine site while simultaneously supporting the offshore tower substantially above the surface of the body of water upon an annular flotation collar connected around the upper end thereof and upon other means for flotation attached substantially beneath the outer periphery of the lower end thereof; removing the said other means of flotation provided substantially beneath the outer periphery of the lower end of the offshore tower;

pivoting the offshore tower about the center of gravity thereof and the attached flotation tower into a vertical posture within the body of water, while simultaneously supporting the upper end of the offshore tower at the surface of the body of water by the annular flotation collar, which collar during said pivoting motion translates along the surface of the body of water with an increasing portion of the collar, fac-

Claims

1. An offshore tower apparatus comprising: an offshore tower including, a base portion for resting upon the bed of a body of water, and an upper portion operable to extend above the surface of the body of water for stably supporting a platform above the surface of the water; a substantially hollow annular flotation collar releasably connected around the outer periphery of the upper end of the offshore tower for buoyantly supporting the upper end of the offshore tower substantially above the surface of the body of water when the tower is in a horizontal posture during transportation to a marine site and for increasingly contacting the surface of the body of water when the tower is being righted in the body of water thus minimizing turbulence during the righting operation, said substantially hollow annular flotation collar being dimensioned to have a buoyancy greater than the total effective weight of the offshore tower when said offshore tower is righted within the body of water; and floatation means releasably connected to the exterior of the base of the tower for at least buoyantly supporting the base of the tower substantially above the surface of the body of water during the transport operation.

2. An offshore tower apparatus as defined in claim 1, wherein: said substantially hollow annular flotation collar being generally circular in cross-section.

3. An offshore tower apparatus as defined in claim 1 and further comprising: means for selectively ballasting or blowing the interior of said substantially hollow annular flotation collar.

4. An offshore tower apparatus as defined in claim 1 wherein the said flotation means comprises: a pair of generally cylindrical hollow tanks connected to the outer periphery of the base of the offshore tower and being spaced upon opposite sides of a plane extending through a central axis of the offshore tower and lying normal to the surface of the body of water whereby said annular flotation collar and said pair of flotation vessels form a stable triangular bearing transport apparatus.

5. An offshore tower apparatus as defined in claim 4, and further comprising: means for controllably ballasting or blowing the interior of at least one of said pair of generally cylindrically hollow tanks.

6. An offshore tower apparatus as defined in claim 1, wherein said floatation means comprises: a generally rectangular tank having the long sides thereof, lying approximately normally to a plane intersecting the central axis of the offshore tower and lying normal to the surface of the body of water, and said tank being dimensioned with sufficient buoyancy to maintain the base of the tower above the surface of the body of water.

7. An offshore tower apparatus comprising: an offshore tower including, a base portion for resting upon the bed of a boDy of water, and an upper portion operable to extend above the surface of the body of water for stably supporting a platform above the surface of the body of water; an annular flotation collar releasably connected about an upper end of the offshore tower for buoyantly supporting the upper end of the offshore tower substantially above the surface of the body of water when the tower is in a horizontal posture during transportation to a marine site and for providing a substantially constant buoyant force during a 180* rotation of the offshore tower in a horizontal posture with respect to the body of water prior to righting the offshore tower in the body of water and for increasingly contacting the surface of the body of the water when the tower is being righted in the body of the water thus minimizing turbulence during the righting operation, said substantially hollow annular floatation collar being dimensioned to have a buoyancy greater than the total effective weight of the offshore tower when said offshore tower is righted within the body of water; and a pair of flotation vessels connected to the base portion of the offshore tower, symmetrically disposed on opposite sides of a plane intersecting a central axis of the offshore tower and lying normal to the surface of the body of water, whereby said pair of floatation vessels in combination with said annular flotation collar forms a stable triangular floating system for transporting and launching the offshore tower.

8. An offshore tower apparatus as defined in claim 7 and further comprising: means for controllably ballasting and blowing the interior of said annular floatation collar for regulating the buoyancy thereof; and means for ballasting or blowing at least one of said pair of cylindrical floatation vessels for controlling the buoyancy thereof.

9. A method of transporting an offshore tower to a marine site and launching the offshore tower within the body of water in a generally vertical posture having the base thereof fixed to the bed of the body of water and having the upper end thereof extending above the surface of the body of water to stably support a platform above the surface of the body of of water, comprising the steps of: floating an offshore tower to a desired marine site resting upon an annular flotation collar at the upper end thereof and a pair of spaced flotation vessels symmetrically disposed upon opposite sides of a plane intersecting the central axis of the offshore tower and lying perpendicular to the surface of the body of water, said flotation vessels being connected to the outer periphery of the base of the offshore tower; at least partially ballasting one of said pair of floatation vessels connected to the outer periphery of the base of the tower, rotating the offshore tower 180* about the center of gravity thereof; releasing said pair of flotation vessels from the outer periphery of the base of the offshore tower; pivoting the offshore tower about the center of gravity thereof into a generally vertical posture within the body of water wherein the central tower axis lies normally with the plane of the surface of the body of water; ballasting the annular floatation collar to vertically descend the tower to a position wherein at least one portion of the outer periphery of the base approximately contacts the bed of the body of water notwithstanding the particular geography of the bed; pinning the offshore tower to the bed of the body of water to stably support the offshore tower and maintain the normal alignment of the central axis of the offshore tower to the plane of the surface of the body of water; removing the annular floatation collar from the upper end of the offshore tower; and driving a plurality of piles through pile casings surrounding the base of the tower into the bed of the body of water to fixedly connect the tower to the bed of the body of water.

10. A method of accurately locatinG and erecting at a preselected waterbed site an offshore tower within a body of water in a generally vertical posture, comprising the steps of: supporting an offshore tower at a marine site horizontally at the upper end thereof by a first floatation means and at the lower end thereof by a second floatation means; positioning the center of gravity of the combined offshore tower and the first flotation means vertically over the desired waterbed site; and releasing the buoyant support from the offshore tower lower end permitting the tower to rotate about the center of gravity thereof and the first flotation means and vertically descent to the bed of the body of water along a line intersection said center of gravity and lying normally with the surface of the body of water.

11. A method of accurately erecting an offshore tower as defined in claim 10 wherein said step of supporting includes: suspending the lower end of the offshore tower from at least one floatation vessel releasably connected directly beneath the outer periphery of the lower end of the offshore tower.

12. A method of accurately erecting an offshore tower as defined in claim 10 wherein said step of supporting includes: suspending the lower end of the offshore tower from a pair of spaced flotation vessels releasably connected directly with the upper outer periphery of the lower end of the offshore tower when the base of the offshore tower is substantially submerged beneath the surface of the body of water.

13. A method of transporting an offshore tower to a marine site and launching the offshore tower within a body of water, comprising the steps of: floating the offshore tower in a generally horizontal posture to a marine site while buoyantly supporting the offshore tower substantially above the surface of the body of water upon an annular flotation collar connected around the upper end thereof and upon other means for flotation attached substantially beneath the outer periphery of the lower end thereof; rotating the offshore tower while in the horizontal posture about the center of gravity thereof approximately 180*; disconnecting the other means for flotation from the other periphery of the lower end of the offshore tower; pivoting the offshore tower about the center of gravity thereof and the attached flotation collar into a vertical posture within the body of water while simultaneously supporting the upper end of the offshore tower at the surface of the body of water by the annular flotation collar, which collar during said pivoting motion translates along the surface of the body of water with an increasing portion of the collar, facing the base of the offshore tower, contacting the surface of the body of water to minimize turbulence during the righting operation.

14. A method of transporting an offshore tower to a marine site and launching the offshore tower within a body of water, comprising the steps of: floating the offshore tower in a generally horizontal posture to a marine site while simultaneously supporting the offshore tower substantially above the surface of the body of water upon an annular flotation collar connected around the upper end thereof and upon other means for flotation attached substantially beneath the outer periphery of the lower end thereof; removing the said other means of flotation provided substantially beneath the outer periphery of the lower end of the offshore tower; pivoting the offshore tower about the center of gravity thereof and the attached flotation tower into a vertical posture within the body of water, while simultaneously supporting the upper end of the offshore tower at the surface of the body of water by the annular flotation collar, which collar during said pivoting motion translates along the surface of the body of water with an increasing portion of the collar, facing the base of the offshore tower, contacting the surface of the body of water to minimize turbulence durinG the righting operation; ballasting the annular collar connected about the upper end of the offshore tower to lower the offshore tower in a generally vertical mode to a position adjacent the bed of the body of water thus orienting the central axis of the offshore tower approximately normal to the surface of the body of water notwithstanding the particular geography of the water bed; pinning the offshore tower to the water bed to rigidly support the tower upon the water bed and maintain the central axis of the tower in a posture normal to the surface of the body of water; and disconnecting the annular floatation collar from the upper end of the offshore tower for subsequent reuse.

15. A method of transporting an offshore tower to a predetermined marine site and launching the offshore tower within the body of water in a generally vertical posture, comprising the steps of: floating an offshore tower to a desired marine site upon an annular collar at the upper end thereof and upon a pair of generally hollow flotation vessels at the lower end thereof being symmetrically spaced on opposite sides of a plane extending through the central axis of the offshore tower and lying normal to the surface of the body of water thus forming in conjunction with the annular collar at the upper end of the offshore tower a triangular flotation arrangement for stably floating the offshore tower to a desired marine site upon a three-point bearing pad of buoyancy vessels; rotating the offshore tower in a generally horizontal posture about the center of gravity thereof approximately 180*; disconnecting the pair of flotation vessels from the lower end of the offshore tower; and pivoting the offshore tower about the center of gravity thereof into a generally vertical posture within the body of water.

16. A method of transporting an offshore tower to a predetermined marine site and launching the offshore tower within the body of water in a generally vertical posture, comprising the steps of: floating an offshore tower to a desired marine site upon an annular collar at the upper end thereof and upon a pair of generally hollow flotation vessels at the lower end thereof symmetrically spaced on opposite sides of a plane extending through the central axis of the offshore tower and lying normal to the surface of the body of water, thus forming in conjunction with the annular collar at the upper end of the offshore tower a triangular flotation arrangement for stably floating the offshore tower to a desired marine site upon a three-point bearing pad of buoyancy vessels; removing the floatation vessels from beneath the lower end of the offshore tower, including the steps of rotating the offshore tower about the center of gravity thereof approximately 180* by at least partially ballasting one of said pair of spaced flotation vessels to induce the rotation of the base of the tower about the center of gravity thereof, an disconnecting said spaced floatation vessels from the outer periphery of the base of the tower; and pivoting the offshore tower about the center of gravity thereof into a generally vertical posture within the body of water.