US3496897A

US3496897A - Apparatus for transporting a floatable marine platform

Info

Publication number: US3496897A
Application number: US730163A
Authority: US
Inventors: Ivo C Pogonowski; Fuad T Saadeh
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1968-05-17
Filing date: 1968-05-17
Publication date: 1970-02-24
Anticipated expiration: 1987-02-24
Also published as: NL6907608A; JPS5124198B1; GB1257358A; FR2008781A1; DE1925142A1

Description

Feb. 24,1976 LC .P(-DG ONOWISKI ETAI- 3,496,897

APPARATUS FOR TRANSPORTING A FLOATABLE MARINE PLATFORM Filed May 17, 1968 States Unite ABSTRACT OF THE DISCLOSURE The invention relates to a method and apparatus for transporting and launching a deep water floatable marine platform. The method embodies the use of at least two floatable support stages. An elongated marine platform is fioatably supported on the respective stages, at a plurality of bearing pads or points. The stages in turn are spaced apart to permit independent movement thereof in response to undulations in the body of water. One or more of the stages are fixedly positioned at one end of the marine platform, While at least one other stage pivotally supports the opposite end of said platform to permit the desired independent movement of the respective stages without imposing a strain on the supported platform.

BACKGROUND OF THE INVENTION The usual practice in the construction and transportation of large marine platforms such as submergible well drilling platforms, is to build the platform in whole or in parts at a shore installation, and thereafter move the entire unit or units to an offshore position for anchoring. The two most practical and widely used ways for achieving this include either physically carrying the completed unit to its ultimate location or in the alternative, floating the unit to position. Both methods are desirable under particular conditions. Where the unit is light enough to be carried on barges and within the capabilities of the available lifting cranes, such transportation is desirable. However, with bulky and less manageable marine platforms it has become customary to construct the units in a manner that they will be self buoyant. Thus, the various members constituting the platform structure are so arranged and fabricated as to incorporate buoyant chambers which might be controlled to either immerse or float the structure.

With the present tendency toward relatively deep water installations, the overall size of appropriate marine platforms is becoming steadily larger. Thus the latter mentioned method of fioatably transporting such a unit to its working location is preferred. However the drawbacks to this mode of transportation are similar to those associated with any land built vessel. The latter for example must be deposited into a body of water adjacent to the building site and thereafter floated to its location. This of course presupposes that the waterway adjacent to the building site is of a sufficient depth to support the platform as to permit its movement.

For platforms of the type presently considered, the unit when positioned comprises a singular, large diameter column which extends vertically through a body of water from the floor to the surface, and is stabilized by a base structure. The latter is usually anchored to the ocean floor to fixedly position the entire structure. To adequately and safely support an upright column having an order of magnitude of 600 to 1,000 feet, it is necessary that the expanse of the base structure must be at least several hundred feet. It will thus be appreciated that a base member having for example, a length of approxi- 3,496,897 Patented Feb. 24, 1970 mately 400 feet, could not feasibly be floated in a near shore body of water since the depth would be insuflicient to accommodate the unit.

It is therefore a primary object of the invention to provide a method and apparatus for supporting and transporting a marine drilling platform between its point of fabrication and a submerged working position. A fur ther object is to provide a platform of the type described which might be safely launched from floatable support stage or barges in a manner to avoid damaging the platform or the barges. A still further object is to provide means for facilitating the launching and submerging of a marine platform whereby the latter is progressively lowered to its ultimate position while pivotally supported on at least one floatable support member. Still another object is the provision of means and apparatus for transporting a marine platform in a manner to avoid undue stress in the latter caused by the unsynchronized movement of the floating support in response to water undulations.

FIGURE 1 is an elevation view illustrating the invention including spaced apart fioatable stages supporting an offshore drilling platform. FIGURE 2 is an end view taken line 2-2 in FIGURE 1. FIGURE 3 is a segmentary view on an enlarged scale of a portion of the drilling platform shown in FIGURE 1. FIGURE 4 is an end view of FIGURE 3. FIGURE 5 is a segmentary view on an enlarged scale and in cross section of one of the stages shown in FIGURE 1, and FIGURE 6 is similar to FIGURE 1 illustrating the drilling platform in a partially submerged position.

The present method and apparatus, in brief, affords a convenient means to safely and economically transport and position a large, floatable offshore platform. The latter when disposed in an inclined position, is supported at opposed ends by two or more spaced apart stages. Each stage or barge is particularly adapted to permit the platform to ride safely and securely regardless of water turbulence or undulation. The platform is so received at, at least one end, to loosely engage the sup-porting barge such that the latter might rock independently of other barges in response to movement of the water. Thus, the supported marine platform is not subjected to undue stresses or strain as a result of sudden movement of the barges.

The apparatus as shown in FIGURE 1, includes essentially a pair of spaced apart floating stages or barges 10 and 11, each of which supports a portion of the load comprising marine platform 12. The platform, together with the two stages, might be readily floated through a body of water having a depth not substantially exceeding the depth of the stage when depressed, without the platform touching the water substratum. Preferably, the respective stages are so arranged that the upward support is provided to the platform at opposed ends. This however is a matter of convenience and the positioning of the stages will be such as to accommodate the particular structure and disposition of the platform.

While the presently illustrated marine platform is adapted to be adequately supported by two spaced apart stages, it is understood that the same function can be achieved with three or more stages so arranged to provide the non-rigid connection between the stages and the platform thus assuring the desired independence of movement.

It is further understood that the marine platform shown and here described constitutes but a single embodiment of the many types of such platforms which may be similarly supported and transported. Since most such platforms comprise a plurality of rigidly assembled structural members, the positioning of the stages and bearing joints to provide the desired freedom of movement, is a matter of practical design. For the purpose of the following description the marine platform is shown and described to best illustrate the disclosed method, which platform is adapted for immersion in a body of water to be supported on the ocean floor and a portion above the ocean surface for positioning the usual drilling equipment and acces sories.

Again referring to FIGURES 1 and 2, the platform is shown in a reclining position with the normally upright central member at a substantially horizontal attitude. More precisely, the platform comprises an elongated central support column 13 formed of a series of tubular end welded members and being of a substantially uniform diameter throughout. When properly placed for operation, platform 13 extends uprightly from the ocean floor to position the top thereof above the water surface. Although not presently shown, the normally upright member 13 may embody one or more conductor pipes, buoyancy and storage tanks, and similar equipment ancillary to an oil well drilling operation.

Column 13 when in its immersed operating position is maintained uprightly by a relatively broad base comprising a series of integral

structural members

14, 16, 17 and 18 so arranged and connected to afford the necessary support to withstand water and wind forces acting against the column. A plurality of intermediate reinforcing

members

19, 21, 22 and 23 connect the lower end of column 13 to the respective base members. The column is laterally stabilized at one or more levels by peripherally spaced reinforcing legs, 24 and 26 for example, which extend from the base, and are fastened to the outer wall of column 13.

Following usual construction techniques, the various structural members of the platform including the base and the legs are joined by welding. They are further provided as above noted, with controllable buoyancy members such as tanks built into the various members and so connected to piping means to regulate the condition of the tanks and consequently the attitude of the platform when in the water.

As shown in FIGURES 1 and 3, the upper end of column 13 is provided with an arm or brace assembly 27 which is fastened to the column primarily as a temporary expedient for transporting the platform. After use, the assembly may be either removed, or left in place in anticipation of a subsequent move. Arm assembly 27 includes basically a plurality of

compression elements

28 and 29 which are end welded or otherwise affixed to the outer wall of column 13 and extend therefrom. The remote ends of the respective compression elements terminate in a joint 31 such as a bearing knuckle 31, anvil or similar member having a contoured underside adapted to slideably engage a complementing seat. The arm structure may be further provided with a guide brace 32, formed in a generally arcuate shape and fastened at one end adjacent to knuckle 31 and at the other end to the column 13. The respective compression and

arcuate members

28, 29 and 32 as shown in FIGURE 4 are split, or assume a general V configuration having the extremities fastened to opposed outer walls of column 13 and terminating at knuckle member 31. Arm or brace assembly 27 might be welded or bolted to the outer wall of column 13, the latter is in turn reinforced by plates or circular bands 25 to accommodate and distribute the load concentration on column 13 when pivotally supported at arm 27.

Floatable stages or barges 1t) and 11 supporting platform 12, by and large follow the normal construction for such units and comprise in essence a relatively expansive tank embodying buoyant means for controllably varying the level and attitude thereof in a body of water. For example, stage is so positioned to support the base structure of the marine column, in a rigid or semirigid manner to permit, although minimize movement of the column with respect to said barge. Thus base member 17 might be rigidly secured to barge 10; alternately it might be so supported in a manner to permit movement of the stage in response to water undulations. Lower element 17 of the base assembly is supported with the latter positioned approximately adjacent to the bottom of stage 10. In such a position, while being transported, the marine platform may be at least partially submerged thereby af fording a degree of self support.

Stage or barge 10 may as mentioned, be provided with internal buoyancy control such that the flooding of discrete chambers will regulate the rate of descent and attitude of the stage as well as of the platform to enhance the seaworthiness of the unit. In the present arrangement, a single fioatable stage 10 is utilized to support the lower or heavier end of the marine platform 12. This support can be supplemented with other similar stages should the length of member 17, or the physical size of the stage warrant additional floating support.

Barge 10 is provided with an articulated support as sembly such as 50 which pivotally attaches to the lower part of the stage underside as by an elongated hinged joint 51. Said assembly 50 comprises essentially a pair of arms 52 disposed on opposed ends of the stage. While a single arm is here shown in the figures, it is understood that a corresponding arm assumes a similar position on the opposite end of the stage such that both arms of the assembly work simultaneously. Each arm is rigidly connected at the lower end to a pivotal hinge such as pin 51. The remote end of each arm is further provided with a cradle 53 or similar receptive member adapted to receive and support one end of the marine platform 12.

Cradle 53 for example may include a journal surface positioned in direct contact with the member to be supported. Thus, when the latter is of a cylindrical shape, an upper clamping bracket 53 grasps the platform member firmly in a rolling grip and yet allows the barge to pitch or roll slightly in response to undulated movement of the water.

The entire arm assembly 50 is preferably connected to a suitable source of power to be operated as a unit, whereby the arms may be pivoted about pin 51 to adjust position of the supported end of the platform in the water. However, each arm may also be individually powered and controlled to be operated with respect to the stage.

Stage 11, positioned remote from stage 10 is similar in basic construction to the latter. Stage 11 however incorporates the additional feature of being so adapted to embody a seat 33 or socket which cooperates With a corresponding bearing pad of the platform to permit in effect limited universal movement between the two.

Seat 33 is adapted to receive anvil 31 or other appropriate form of bearing pad. Said seat includes

upstanding side walls

34, 36 defining the seat outer edge, which side walls may be tapered inwardly to readily receive and guide anvil 31 as the latter is lowered into place onto the stage. As shown in the figures, the entire seat 33 within stage 11 is positioned at a low level in the stage or barge preferably such that the seat itself is below the center of buoyancy of the barge thus providing the latter with a substantial degree of stability under heavy loading conditions.

To properly function as the journal surface for bearing pad 31 extending from the platform 12, seat 33 comprises primarily a foundation or contact surface which may be adapted to provide either a smooth surface, or a pliable cushion type surface.

In the instance of the smooth surface the contoured face of the foundation includes a metallic foundation block 37 having an upward facing, contoured opening conforming to the contoured face of the anvil 31. As the latter is seatably positioned in the foundation block, movement of either the platform 13 or barge 11, results in a sliding relationship between the anvil and its mating contoured seat, thus providing maximum bearing along the contoured face of the anvil in contact with the foundation block 37.

In an alternate embodiment of the foundation member not presently shown, the latter may be provided with a layer of displaceable material such as stone aggregate, gravel or the like which will sufficiently yield under the pressure of the contoured anvil 31 to form a seat of the proper shape.

The relationship of anvil 31 within seat 33, whether the latter be of the smooth contoured type or of the cushion type, is to permit in effect limited universal sliding movement of the anvil in the seat. This action permits the platform to move or adjust independently of the undulations of any one support stage or barge 11 as the latter is subject to movement of the water.

To permit automatic effective adjustment of platform 13 on the respective supporting stages and 11, the slideable connection between the latter and the bearing pads is supplement with restraining lines 39 and 41. The tension in such restraining lines is such as to permit the desired limited movement, and yet prohibit the stage from being displaced entirely from its supporting relationship with the platform as the stage is towed.

The nature of the sliding joint formed between anvil 31 and corresponding seat 33 is such as to provide a minimum degree of friction between engaging members and allow the desired freedom of movement. Thus, anvil 31 particularly at the lower curved face may comprise replaceable metallic convex shoes or wear surfaces. This wear surface is applied to a rigid contoured body such as a hemispherical shape formed of a steel shell, which in turn attaches to the

respective compression members

28 and 29.

The seat or foundation block 41 upon which anvil 31 bears may be adapted as previously mentioned for forming a pliable cushion into which the anvil might work itself while being lowered into position. Alternately, the foundation block 41 may be lined, as is shoe 31, with a metallic material either in strip form or as a solid metallic sheet. In the instance of the latter the sliding relationship between the contacting members might be improved by use of a suitable lubricant such as a heavy grease injected between the faces of the anvil 31 and its foundation block 37 to form a thin lubricating layer.

It will be appreciated that under ordinary conditions wherein the platform is being either towed at sea, or merely standing in a body of water, the engaging surfaces of anvil 31 and its seat will be in a virtually continuous state of relative movement. Thus the rigid type surface joint embodies certain advantages since the deformable or pliable cushion type seat which will tend to be displaced under the great weight of the platform assembly thereby presents the possibility of Wearing away or displacing entirely the pliable cushion.

From the foregoing it is seen that the present arrangement suggests many advantages in the transportation and the setting of an offshore type platform in either deep or shallow water. The number and the positioning of the bearing pads will of course be contingent on the particular size and shape of the platform. For example bearing pads 37 and 38 in the present instance are located preferably at opposed ends of base support member 17 While a third bearing pad is located at the terminus of central column 13. Thus, the structure is ideally supported by bearing pads spaced apart to provide a triangular form of three point support. This type support of course is the most stable and the least likely to impose stress on the platform being supported.

In the instance of a platform utilizing two, three or more legs, the latter might be provided with a suitable bracing arrangement to maintain the single point of sup port at one end of the platform.

It should also be appreciated that the number of stages utilized for supporting a platform most efficiently and with the least strain imposed on the latter, would be contingent on the dimensions of the platform base, or the width of the entire platform. For example on a relatively small unit, conceivably two stages might be readily utilized, one being supportably positioned beneath the platform base while a second platform is disposed at the upper terminus of the platform. Where of course the base is of sufficient width to warrant more than one stage or support barge, each of the latter will move independently one of the other thereby continuing the three point support and the minimization of the strain on the supported platform.

Further, the description has heretofore disclosed the novel arrangement in terms of the upper bearing pad or anvil 31 as 'being the sole connection adapted to universal movement in response to undulations of the water. However this does not preclude the use of a similar support point or bearing pad at each of the points at which the platform is supported. Each of the support stages might be provided with a recessed seat as described with respect to stage 11 to receive an anvil-like bearing pad.

In the actual practice of the method and the apparatus used therefor, platform 12 is normally constructed on land and thereafter either partially or completely floated onto one or more of the support platforms as herein noted. In the instance of a single column elongated platform as shown in the figures, the width or length of the base would ordinarily preclude the entire platform from being floated in the water prior to being put on the supporting stages. Therefore transfer of the platform to the respective support stages is achieved while the platform is on the land at the construction site.

It should be further appreciated that the various bearing points of the platform are so arranged and positioned to provide a relatively uniform weight distribution between the respective stages to facilitate both the transportation and the subsequent handling of the platform.

In the instance of an elongated type platform as presently shown, maximum utilization of the water buoyancy might be achieved by at least partially immersing a portion of the platform base to provide a degree of buoyancy to supplement the buoyant effect of the respective support stages. In such position, the platform will receive maximum self-support and thereby avoid the possibility of straining of the platform central column when the latter is supported at its terminals.

In the instance of the upper, or bearing pad adjacent at the top of column '13, the base end is elevated above the stages 10, or the latter are submerged and then floated to rise beneath the base bearing pads. Thereafter, the platform upper end is raised to align anvil 31 over seat 33, thence lowered into place. When so positioned the respective retaining lines at the joints are adjusted to maintain the stages and bearing pads in the proper engaged position and yet permitting the desired freedom of movement therebetween.

As used in the above description, the terminology first and second stages refers of course to the support members which are fioatable and similarly submergible, characteristic of a barge having controlled buoyancy features. Further, the terminology bearing pad relates to the particular balance points within the platform structure which, when supported, will permit the platform to be transported in the most stable and controllable manner.

With respect to disengaging agent of the platform for the bearing pads, at a desired offshore platform site, the platform is preferably lowered into place to rest the base on the ocean fioor. By controlling the buoyancy of the platform, column 13 will be maneuvered into a substantially upright position with the upper end of column 13 extending above the water surface.

With the platform so positioned, anvil 31 or arm assembly might be removed or alternately left in place depending on the position of the same with respect to the normal platform accessories which will be supported at the upper end of the column such as the derricks, draw-works, storage facilities, etc.

Obviously many modifications and variations of the invention as herein set forth may be made without departing from the spirit and scope thereof.

We claim:

1. In the waterborne transport and positioning of an elongated offshore marine platform within a body of water, said platform being formed of at least one elongated member having opposed ends, and being normally disposed for operation in a substantially upright attitude Within said body of water;

a first stage element fioatably supporting one end of said elongated marine platform at at least one bearing pad,

a second stage element fioatably supporting the opposed end of said platform at another bearing pad spaced from said first mentioned bearing pad,

said bearing pads on said elongated platform being each operably engaged wtih a corresponding support element, each element of which includes a seat adapted to receive a bearing pad to permit restrained pivotal movement of said pad on said seat,

at least one of said bearing pads including a brace depending from said platform elongated member and an anvil carried at the remote end of said brace, said anvil being operably received on said floating support element,

whereby said platform is maintained by said terminal support in a substantially horizontal disposition at the waters surface, while avoiding imposition of undue physical strain into said platform as the result of movement of said respective support elements in response to water undulations.

2. In the waterborne transport and positioning of an elongated offshore marine platform within a body of water, said platform being formed of at least one elongated member having opposed ends, and being normally disposed for operation in a substantially upright attitude within said body of water;

said bearing pads on said elongated platform being each operably engaged with a corresponding support element, each element of which includes a seat adapted to receive a bearing pad to permit restrained pivotal movement of said pad on said seat,

at least one of said bearing pads including a brace depending from said platform elongated member, and

an anvil carried at the remote end of said brace, said anvil being operably received on said fioatably supporting stage element, said latter mentioned support element including a seat defined by upstanding walls and a foundation member, said anvil being disposed in said seat and in sliding engagement with said foundation member,

3. In an apparatus as defined in claim 2 wherein said foundation member includes a substantially solid block contoured in accordance with the contour on said anvil, whereby said anvil when disposed in said foundation block defines a bearing area across the face of said anvil regardless of the relative positions thereof in said foundation block.

4. In an apparatus as defined in claim 3 wherein said foundation block and said anvil are similarly contoured to define a bearing area across the face of said anvil regardless of the relative position thereof in said foundation block.

5. In an apparatus as defined in claim 2 wherein said latter mentioned fioatable supporting stage includes a seat defined by upstanding Walls and a foundation base, said foundation base including a pliable cushion formed of a material adapted to being displaced and assuming the contour in said displaced position of said anvil face when the latter is operably engaged with said seat.

6. In an apparatus as defined in claim 2 wherein at least a portion of the upstanding walls of said seat are inwardly tapered to a conjuncture at the said seat.

7. In an apparatus as defined in claim 2 wherein said seat for receiving said anvil is positioned at a depressed location in said floatable support stage at a point below the center of gravity of said stage.

References Cited UNITED STATES PATENTS 2,581,098 1/1952 Guenzel 6146.5 3,323,478 6/1967 Hunsucker 114-.5 3,347,052 10/1967 Steitle et al. 114.5

TRYGVE M. BLIX, Primary Examiner U.S. Cl. X.R. 6146.5