US3516259A - Offshore structure method and apparatus - Google Patents

Description

June 23, 1970 A. J. ToKoLA OFFSHORE STRUCTURE METHOD AND APPARATUS 5 Sheets-Sheet 1 Filed sept. 12, 196e l M d RO 7E@ gw?. l n..t m L y A 4 ",a/w

a 51:11 J 4 a n .ww/ Qu l* 4 n u l u 4 1 (l 2 1 w June 23, 1970 A. J. ToKoLA OFFSHORE STRUCTURE METHOD AND Filed sept. 12. 196s APPARATUS 5 Sheets-Sheet 2 pump/A9056 INVENTOR.

ALPO J TOKOLA A. J. TOKOLA l OFFSHORE STRUCTURE METHOD AND APPARATUS 5 Sheets-Sheet 3 Filed Sept. 12. 196s INVENTOR ALPO .I TOKOLA June 23, 1970 A. J. ToKoLA 3,516,259

OFFSHORE STRUCTURE METHOD AND AP'PARATUS Filed Sept. 12, 1966 .l 5 Sheets-Sheet 4 lid mvENToR ALPO JT TOKOLA June 23, 1970 A. J. ToKoLA OFFSHORE STRUCTURE METHOD AND APPARATUS 5 sheets-'sheet 5 Filed slept. 12. 196e INVENTOR. ALP@ I TOKOLA BY Unted States Patent O 3,516,259 OFFSHORE STRUCTURE METHOD AND APPARATUS Alpo J. Tokola, Lafayette, Calif., assignor to Kaiser Steel Corporation, Oakland, Calif., a corporation of Nevada Filed Sept. 12, 1966, Ser. No. 578,681 Int. Cl. E02d 21/00 U.S. Cl. til-46.5 6 Claims ABSTRACT F THE DISCLOSURE Method of constructing and installing an offshore supporting structure and the resulting structure wherein the structure is initially provided 'with a plurality of legs disposed in a polygonal arrangement and in a spaced relationship to one another and wherein at a preselected time and after installation of the structure at an offshore site the tops of all but one of the legs of the structure are caused to be terminated at a level substantially below a selected Water level at the site.

The present invention relates to off-shore supporting structures and to methods of constructing and conducting various operations from such structures. Such structures are particularly adapted for supporting oil and gas well drilling and production units and for use as 1wharves and moorings. While one embodiment of this invention is adapted for all climatic conditions, the invention nds its greatest utility in permanent or fixed type supporting structures located in climates lwhere appreciable oating ice is encountered during various months of the year.

With the discovery of extensive oil and gas fields under continental shelves and under bays and seas, offshore well drilling operations have assumed increasing importance over the entire world.

Since the time that the first true olf-shore drilling structure became operational some years ago in relatively shallow water, there has been a steady increase in the number and size of off-shore structures and drilling units as well as the depth of water in which they can effectively operate such that today the investment in off-shore drilling structures amounts to many millions of dollars. A number of these structures are capable of drilling Wells in many hundreds of feet of water. Many of these off-shore structures are exceedingly large, massive and expensive. These are desirably prefabricated to a major extent on land and they can then be self-floated or carried on barges in a horizontal position to the drilling site where they are lowered to the bottom in a vertical position and secured in the desired drilling location by means of piles extending into the bottom earth to a considerable distance. The piles can be either welded to the above-ground structure, in a semi-permanent arrangement, or cemented in with concrete to form a fully permanent installation. In this connection a discussion of the installation of an offshore marine structure of one particular design is contained in the patent to Borrmann, No. 3,209,544, granted Oct. 5, 1965 for Marine Structure. While Borrmann is mainly concerned with the stability of his supporting structure in various towing and upending operations, he discusses the present practice of extensive piling which is required in all of the legs of his supporting structure to give the required strength. lt will be noted that in all cases Borrmann maintains multiple leg support at the top of the structure which must be piled at the bottom not only to resist the tilting and shifting of the structure that can result from wind and `wave action but also to withstand the `forces exerted by floating ice when the structure is used in cold climates.

When the Borrmann supporting structure, which is 3,516,259 Patented June 23, 1970 representative of certain structures in use today, is used in cold climates, oe ice in cold weather will pack against the multiple leg structure and exert great forces thereon.

Frequently this oe ice will not only be several feet thick but also miles in extent whereby it reaches a tremendous mass. The packing of the ice at and about the legs of the structure in the manner of a log jam results in the overriding of loose ice slabs upon other loose or packed ice. As a consequence there can be a deleterious build up in the thickness of the ice adjacent the structure which further increases the mass of the surrounding ice and the :forces exerted on the legs of the supporting structure as well as other operational hazards. It is, therefore, necessary in the case of the Borrmann marine structure to pile very extensively at the bottom to prevent the structure from tipping over or shifting under the influence of the ice floes and even when piled to a maximum the ice may still pack to a suicient mass to cause structural damage adjacent the top of the support even if the bottom remains stable, despite the serious stresses thereon.

In the olf-shore supporting structures and methods according to the present invention, at least during periods of cold weather when the usual fioe ice is expected, the structure will advantageously expose to the ice a single leg upon which a production platform, a drilling rig or the like is supported, the other legs of the structure being cut olf below the expected low ice level. The iioe ice encountering the single and preferably cylindrical leg will usually either be simply diverted away from the structure upon finding no pocket in the supporting legs of the structure within which it can become lodged or it will be readily crushed and split so that materially reduced forces are exerted upon the structure and the bottom piling can be kept to a minimum while maintaining a broad stable base.

Since piling is an on-site operation, it is quite expensive and time consuming. By practice of the instant invention, considerable savings in time and money in the olf-shore drilling structures and methods can be effected in that the instant invention provides within practical limits minimum piling as against the costly maximum piling required in the normal multiple leg supporting structures, such as used by Borrmann, particularly where such structures are to be installed and operated in a climate in which oating ice is encountered.

The advantages stated above with respect to combattmg floe ice in cold weather operations are also present to a lesser degree in warm weather operations where a single above water leg extends from the supporting structure. ln such construction, the broad base bottom supnort is still retained for purposes of stability but the piling need be only suicient to resist the action of wind and wave on the single exposed leg extending through the upper water where the maximum wave action is encountered. Again, with the other legs cut olf below the level of extensive wave action the piling may be kept to a minimum and the cost of the installation greatly reduced.

The off-short supporting structure according to the present invention may be constructed with three or four, or more if desired, main and preferably cylindrical columns or legs of, for example, steel piping 8 feet to 20 feet in diameter and of a thickness on the order of l inch. The length of the legs is such that they will desirably be from about 40 to 50 feet above high water where the structure is to be erected in the open ocean, and down to as little as l0 feet above high water when the structure is to be located inside protected bays. The spacing between the legs and the bracing therebetween will vary widely with the depth of the water in which the structure is to be erected. For example, the spacing may vary from 30 feet in shallow water to as much as 250 feet for water of 1,000 foot depth. The bracing between the legs of the structure may likewise be of cylindrical pipe suitably welded or otherwise secured to the main legs of the structure.

The fabrication of the major components of the supporting structure is preferably performed on land in a suitable yard or drydock. The fabricated structure may be self-floated at the construction yard with its columnar legs in a substantially horizontal position and for this purpose the ends of the legs are appropriately sealed against entrance of water to lend buoyancy to the structure. The floating structure is then towed in a horizontal position to the olf-shore site where water is admitted to the legs to tilt the strucure into the desired erect or partially erect position in which it is finally controllably lowered and brought into proper contact with the bottom at the desired location.

Alternatively, smaller structures need not be sealed and self-floated but may be floated on barges to the drilling site and dropped by a derrick into the desired vertical supporting position at the site.

Although drilling site factors such as soil conditions alternate modes of operation, etc. will influence to some extent the amount of piling which must be utilized to give the bottom strength required for the off-shore supporting structure, still and all considerably less piling will be needed than in the case of the structures in use today. In the first manner of operation a large drilling platform is constructed upon all of the legs of the structure and the drilling carried out from this platform during the period of mild weather before substantial ice is encountered. With the drilling completed, the legs of the structure, other than a single leg left to support a production platform, are cut off below the water line and the lowest expected ice level. The structure then can operate in the winter months with but a single leg presented to the floating ice to minimize the stress on the supporting structure.

With this manner of operation the structure is pinned and piled to have a bottom strength sufficient to effectively resist the forces of the wind and waves acting upon the drilling platform and all of the various legs of the supporting structure as well as the forces of the floating ice acting on the single fully exposed leg remaining in the production mode. The structure is therefore piled to resist whichever of these forces is the greater. This piling will, in any event, be considerably less than the piling required if all of the legs of the structure were exposed to floe ice. As explained heretofore, a multiple leg construction results in tremendous forces being exerted on the structure from the great mass of ice which packs and overrides as it engages the multiple legs.

A second manner of operating with the off-shore structure according to this invention involves the cutting oif of all but the single leg substantially immediately after the structure is lowered to the bottom and piled. In this instance the legs to be cut-off are still desirably fabricated initially in long lengths for several reasons, including the need for stability of the structure as it is towed to the off-shore site and the need for the tops of these legs being accessible above water to facilitate the insertion of piling therethrough. In this manner of operation, the single remaining leg has a lightweight drilling rig mounted thereon and the main auxiliaries for the drilling operation, including the supplies and the power supply units, are carried on a service barge or tender associated with the installation. This mode of operation requires that the resulting structure be piled to resist the greater of (1) the forces resulting from wind and wave action on the single leg, and (2) the forces exerted by ice on the single leg. In this instance a lesser piling requirement may result than in the first manner of operation if the wind and Wave forces on the multiple leg structure are greater than the force exerted by ice on the single leg.

The multiple lower leg and single upper or fully exposed leg conliguration is also desirable to lessen the piling requirements for mooring dolphins and the like used for otf-short wharves where tankers or other vessels may dock, as for the loading of oil, gasoline and other materials. Such wharf structures present problems similar to those discussed above for drilling and production units in that the amount of piling which is required will depend upon the forces which are exerted on the upper part of the supporting structures. These forces are considerably less in the case of the single upper leg with structural stability maintained by spaced short legs on the bottom. One aspect of this invention therefore is directed to wharves and mooring dolphins employing supporting structures constructed in accordance with the teachings hereof.

The foregoing and other objects and features of the invention will be apparent to those skilled in the art from the following specification and the appended drawings in which:

FIG. 1 is a side elevational view of a self-floated, prefabricated supporting structure being towed to an offshore site;

FIG. 2 is a view partially in section of the structure of FIG. 1 being rotated into a vertical position at the olf-short site;

FIG. 3 is an elevational view of the supporting structure and a Idrilling platform thereon when installed at an off-short drilling site;

FIG. 4 is an elevational view of the supporting structure with all but a single leg cut olf below the water line and expected low ice level;

FIG. 5 is a view of an alternate drilling arrangement in which a drilling rig is mounted on a single supporting leg and wherein main auxiliaries for the rig are disposed on or carried by a service barge or tender;

FIG. 6 is an elevational view of a permanent production unit on a single supporting leg evolved from the drilling operation of either FIG. 3 or FIG. 5;

FIG. 7 is a broken and enlarged vertical sectional View through the main supporting leg of the structure, as at 7-7 of FIG. 4;

FIG. 8 is a plan view of a supporting structure, looking in the direction of the arrow 8 of FIG. 2;

FIG. 9 is a plan view similar to FIG. 8 on a different scale and showing modified leg dimensions;

FIG. 10 is a plan view of a supporting structure using a four-leg configuration;

FIG. 1l is an enlarged transverse sectional view generally taken along the line 11-11 of FIG. 2 and with parts omitted for the sake of simplicity;

FIG. 12 is an enlarged transverse sectional view taken on the line 12-12 of FIG. 2;

FIG. 13 is an enlarged detailed sectional view taken generally along the line 13-13 of FIG. l1;

FIG. 14 is a generally diagrammatic representation of a mooring wharf employing supporting structure according to the present invention;

FIG. l5 is an elevational view of the mooring wharf of FIG. 14;

FIG. 16 is an elevational view of the principal service structure of the wharf of FIG. 14;

FIG. 17 is an elevational view of a mooring dolphin of the wharf of FIG. 14 taken in the direction of the arrow 17; and

FIG. 18 is a partial elevational view of the mooring dolphin of FIG. 17 taken from the plane 18-18 of FIG. 14.

With further reference to the drawings and in particular FIGS. 1, 2, 8, 11 and l2 of the drawings, the prefabricated supporting structure 20 therein illustrated and representing one preferred embodiment of this invention comprises three columnar legs 21, 22 and 23 in the form of abutting sections of hollow pipe which may be, by way of example only, 8 feet to 20 feet in diameter and of a wall thickness of the order of 1 inch. These columns or legs 21-23 are preferably disposed at the apexes of an equilateral triangle, as shown in FIG. 8, and are secured together in substantial parallel relation by means of bracing pipes 24 extending therebetween and with the uppermost portion of every bracing pipe 24, for example, that connecting to leg 23, being disposed below the expected low level of the ice to be encountered at the olf-shore site. Temporary bracing pipes interconnect the tops ofthe legs 21-23.

The prefabricated structure 20 may be carried to the off-shore site in a horizontal position on suitable barges, or may be self-floated as in FIG. 1 wherein the legs 21 and 22 float in the water in a substantially horizontal plane with the leg 23 being supported in the air thereabove by the bracing pipes 24 and 25. The self-floated structure 20 may be towed to the off-shore site by one or more tugs 26.

The construction of the columnar' legs 21-23 may take many forms and that specifically shown and described herein is to be considered only exemplary of one optional form of such construction. As illustrated, the legs 21-23 are provided with transverse and apertured diaphragm plates 27 at the top and 28 at the bottom and `with intermediate diaphragm plates 29 throughout their lengths. The diaphragm plates 27 are welded or otherwise secured to the upper ends of the legs 21-23 in watertight relation. The diaphragm plates 27 at the top and 28 at the bottom have openings 31 therethrough for the passage of piling pipe and the diaphragms 29 have like openings 32 therethrough for the passage of the piling. The openings 31 and 32 are symmetrically disposed and are vertically aligned for the passage of vertical piling pipe therethrough. The openings in plates 27 and 28 are, of course, covered or closed by appropriate means when the structure provided with the same is to be self-floated during launching and towing.

The diaphragm plates 27 and 29 are also provided with central openings 33 therethrough in which may be disposed optional pipes 34 sealably closed at their bottoms by appropriate means. The diaphragms 27-29 are rigidly secured to the columnar legs 21-23, as by welding, and are likewise rigidly secured to the central pipes 34 to strengthen the column structure. The pipes 34 are therefore concentric with the columnar legs 21-23 and provide an annular space 35 therebetween through which extend the piling pipes, as will be later described. The spaces within the central pipes 34 may be used for any desired storage purpose at the off-shore site, such as for Water, fuel, produced oil, etc.

To render the bottom ends of the columnar legs 21-23 watertight and as indicated particularly in FIGS. 11 and 13, the openings 31 through the diaphragm plate 28 are covered by circular plates 36 mounted against the bottoms of the diaphragms 28 by bolts 37 drawn up against sealing rings 38. The plates 35 may be formed of plastic or other readily frangible material so that the piles may be driven directly therethrough.

To control the tilting of the supporting structure at the drilling site, the bottom ends of the columnar legs 21-23 are desirably provided with valves 41 and entrance to the interiors of the bracing pipes 24 may be secured through valves 42. The valves 41, 42 may optionally be of appropriate pneumatic, hydraulic or electrically operated types and controlled lby lines leading from associated tenders or platforms at the top of the water. Likewise, air pressure lines may communicate with the chambers 35 interiorly of the columnar legs 21-23 by suitable connections, not shown, adjacent the top ends of the legs. Control of the pressure within the legs and of the valves 41 and 42 maintains precise control over the tilting and lowering action of the supporting structure at the oit-shore site. As shown in FIG. 2, water has been admitted to a considerable portion of the lower end of the legs 21 and 22 and to a lesser extent of the legs 23, the structure 20 being in the process of erection into a vertical position at the olf-shore site. When vertical, the structure is dropped or allowed to settle to the bottom 43 at which time the lower ends of the legs 21-23 rest on the bottom 43 while the upper ends of the legs extend above the water level 44 in the manner shown in FIG. 3.

With the supporting structure resting on the bottom, as in FIG. 3, the columnar legs 21-2-3 are adjusted to the de-sired vertical positions and leveled to take care of any irregularity in the bottom, in a manner well known in the art. Filing is now passed through the legs 21-23 into the bottom 43 and secured to the legs. The piling 45 can be in the form of pipes of substantially the diameter of the openings 31, 32 through the diaphragms 27, 28 and 29 and it is through the piling pipes 45 that future drilling operations may be effected, although it is obvious that drilling may be accomplished outside of the columnar legs where desired.

To emplace the piling 45 and in the event diaphragms 27 at the top of legs 21-23 are imperforate, diaphragms 27 are cut at the job site to provide openings in alignment with and of the same size of the openings 31 and 32 in diaphragms 28 and 29. In addition to openings 31 in diaphragms 27 which can be made at the job site, as noted above, the diaphragms 27 may also have central openings cut on the job site if necessary of the size of the openings '33 so as to provide for passage of pipes 34. The piling pipes 45 are then passed downwardly into the legs 21-23 through the newly cut openings in the diaphragms 27, the openings 32 in the diaphragms 29 and the openings 31 in the diaphragms 28. When the lower end of a piling pipe engages a plate 36 closing an opening 31 it is driven or forced through this plate and into the ground forming the bottom 43. Preferably, the piling pipes are driven into the ground a suicient distance to perform their desired supporting function but where the character of the ground material is such that the piling pipes cannot be driven, holes may be previously drilled, the bottoms of the piling pipes inserted in the holes and cemented in the ground, in the manner disclosed in the Borrmann patent. The piling pipes 45 preferably terminate adjacent the tops of the columnar legs 21-23 and in semi-permanent installations, they may be secured to the legs by welding thereat to facilitate disassembly of the piles when the supporting structure is to be disassembled or moved. However, in ordinary installations a permanent mounting is secured as illustrated in FIG. 7, where the piling pipes 45 are shown cemented to the columnar leg 23 and its internal pipe 34 by means of concrete 46 which may completely fill the space 35 between the leg 23 and the internal pipe 34 about the piling pipes 45.

The piles 45 carry the weight of the supporting structure 20 and whatever superstructures are mounted thereon and prevent tilting and shifting of the supporting structure upon the application of external forces thereto due to wave action, oe ice, wind pressure and like elemental forces. The amount of piling necessary to provide the desired strength and stability to the supporting structure will depend, as previously explained, on the type of operation carried out during use of the supporting structure and the various climatic and environmental conditions to be encountered. FIGS. 3 and 5 represent alternate drilling operations using the structure according to the present invention, with the end result in both cases of securing a permanent production installation as in FIG. 6.

In the drilling operation of FIG. 3, the supporting structure 20 is preferably towed to the drilling site and erected in warm or mild weather after the disappearance of surface ice so that the full-height, multiple-leg structure of FIG. 3 is not subjected to the action of ice oes. After erection and levelling and with piling 45 in place, a large heavy-duty drilling platform 47 is mounted on all of the legs 21-23. Thereafter a drilling derrick 48, hoisting crane 49 and housing 51 for personnel, auxiliaries,

power, etc., are all installed on platform 47 so that the platform 47 is substantially selfcontained for drilling operations and need be visited only periodically by a supply barge or tender. The full-height, multiple-leg structure of FIG. 3 Will be subjected to Wind and Wave action during the drilling operation and the piling 45 must be of sufficient depth and strength to accommodate the weight of the supporting structure, the platform 47 and the drilling accessories thereon while at the same time preventing tilting and shifting of the supporting structure 20' under the expected forces, and stresses exerted by the elements. The drilling operations are desirably conducted directly through the piling pipes 45 at any and all of the legs 21-23 and the drilling rig 48 is desirably shiftable in location for that purpose. Additional well holes may be drilled exteriorly of the legs 21-23 when desired. The schedule is such as to complete the drilling operation prior to the ad'vent of winter and the coming of oe ice to the drilling site.

When the drilling operation with the structure of FIG. 3 is completed, the drilling derrick and auxiliaries are removed by suitable barges and the platfonm 47 likewise dismantled and removed. The legs 21 and 22 are now cut down to the level 52 indicated in FIG. 4 which is substantially Ibelow the lowest level of floating ice expected at the drill site. The original lengths of the legs 21-23 Will be determined by the depth of the water 44, the tide at the drill site, the expected wave action and other factors. In the open ocean it is desirable that the height of the legs 2-1-23 be about 40 to 50 feet clear of high Water, while inside bays and other protected Water they may be as low as 10 feet above high water. The level 52 to which the pipes 21, 22 are cut should be at least l to l2 feet below the low water level whereby the upper ends of these legs will terminate substantially below the low water level at the site to adequately clear floe ice encountered at the drill site and may be cut just above the connection of the bracing pipes 24 thereto, as shown in FIG. 4. The leg 23` may remain its original length or `be somewhat foreshortened if desired and there is mounted thereon a production facility 53, as shown in FIG. 6. The Wells which were drilled from the platform 47 are now to be considered producing wells which are pumped or otherwise controlled from the facility 53 through relatively permanent pipelines, barges or tankers not shown, to an on-shore storage or refining installation. The structure of FIG. 6y is the producing structure which is maintained permanently while the Wells are producing and which is subject to exposure of the winter ice at the drill site. With only a single cylindrical leg 23 being contactable or engageable by floe ice, the stresses exerted on the overall supporting structure 20I by the ice are materially minimized since the ice slabs will either be readily diverted away from leg 23 and structure 20 without becoming fully engaged or locked to the structure 20 or be readily cracked and crushed at the rounded leg 23 so that minimum shifting and tilting forces are exerted on the supporting structure in its nal evolution of FIG. 6.

With the space 35 in the leg 23 filled with concrete 46, as in FIG. 7, the leg 23 offers major resistance to structural damage to itself while at the same time the legs 21 and 22 and the bracing pipes 24 provide a wide, stable base for the production facility 53 and its supporting leg 23.

In the above description it has been assumed that the piling necessary to support the installation of FIG. 3 will be suicient to enable the single leg 23 to resist the action of floe ice in the nal production construction of FIG. 6. However, if the piling 45 required to resist the action of oe ice is greater than that required to resist the action of wind and Iwave in the FIG. 3 construction, the original piling for the structure should be that required for the winter operation. In either case, the piling will still be considerably less than that required to provide for winter 8 operation with all of the legs 21-23 at their full height and exposed to the action of floe ice. There is therefore a considerable savings in time and cost in the lessened piling requirement for winter operation with the production construction of FIG. 6'.

An alternate drilling operation is shown in FIG. 5. In this operation the legs 21 and 22 are cut off substantially immediately after the supporting structure 20` is erected and the piling 45 emplaced.

With this mode of operation a drilling derrick 54 isI supported on the top of the single leg 23 and the supplies, power, etc. are carried on a tender or barge 55 which remains anchored adjacent the supporting structure. With this arrangement there is no prior construction or assemblage of a large heavy-duty drilling platform which with its auxiliaries must be disassembled at the conclusion of the drilling operation and prior to the pumping operation as in the case of the mode of operation of FIGS. 3` and 6. When drilling is completed with the arrangement of FIG. 5 the drilling rig 54 is removed and the production facility S3 simply mounted on the leg 23 and substituted for rig 54.

The arrangement of FIG. 5 may also be used where it is desired to drill further the next year after winter production from the structure of FIG. 6, the production facility 53 having a drilling rig like 54 added thereto.

Using the arrangement of FIG. 5 initially instead of the platform drilling arrangement of IFIG. 3 can result in a further saving in the piling needed for the supporting structure where the piling required for the full length legs 21-23, platform 47 and associated auxiliaries is greater than the piling required for the single leg Winter operation of FIG. 6.

Where the supporting structure is to be used in a more moderate climate Where winter ice does not present a problem, the drilling structure of FIG. 5 can still eiect a considerable savings in the extent of piling required since the action of the environmental elements on the structure of FIG. 5 will be considerably less than the action on the structure of FIG. 3. Again, in addition to the savings in the piling required the cost of the platform and the assembly and disassembly is avoided. Against this, however, must be weighed the cost and inconvenience of the floating tender or barge 55. Thus the economics of the different operations as determined by the character of the drilling sites, the climatic conditions and the extent of the drilling to be carried out will dictate the most practical mode of operation to be used in practicing the instant invention. In this connection it is to be observed that where the structure 20 of FIGS. 3, and 6- or 5 is installed and used in the open sea where minimal floe ice conditions exist, if at all, legs 21 and 22 would be cut olf below the mean water level in the manner aforedescribed and as far below the surface as is practical to minimize the effects of major wind and wave action on the structure at the particular drill site while at the same time taking into account the various economic and drill site conditions involved.

The supporting structure 20A of FIG. 9 is substantially the same as the supporting structure 20 of FIG. 8 except that the legs 21A and 22A have been reduced in diameter over the legs 21 and 22 of the structure 20. In the structure 20A, since the leg 23A will be the main supporting leg to carry, for example, the production facility 53, it can be made larger in diameter than legs 21A and 22A. Since the legs 21A and 22A do not encounter the surface ice and are used to supply a broad, stable base for the structure they have been made of reduced diameter.

The supporting structure 20B of FIG. 10 shows a rectangular configuration for the supporting legs 21B, 22B, 22B and 23B at the corners of the rectangle. The supporting structure 20B may be operated under the conditions of any or all of FIGS. 3, 5 and 6, the legs 21B, 22B and 22B' being cut oif to the level 52, leaving only the leg 23B for FIG. 5 and FIG. 6 type operations.

FIGS. 14-18 illustrate further applications of the instant invention and how supporting structures according to the present invention may be utilized for the construction of wharves and for mooring dolphins. Any combination of units may be utilized in that all of the structures may be of the cutoff, single leg configuration of FIGS. 4 and 6 or one or more may employ all full length legs as in the example illustrated in FIGS. 14-16. In the exemplication shown the wharf is composed of a central, all-full-length leg supporting structure 61 and auxiliary single leg supporting structures at each side thereof 62, 63, 64, 65, 66 and 67. The supporting structure 61 has a platform 68y thereon at the desired height above high water and the supporting structures 62-67 have smaller platforms 69 on their single long legs, with the platforms 68 and 69 connected by conventional hanging catwalks 71. The supporting structures may carry suitable bumpers 72 illustrated on the structures 61, 64 and 65 which are engaged by vessels 73, 73A moored to the wharf by suitable mooring lines such as lines 74 connected to the structures 63 and 66 for the vessel 73, and by lines 74A connected to the structures 62 and 67 for the vessel 73A. The central platform 68 may carry suitable auxiliaries and accessory gear 75 and 76 and may serve to load the vessels 73, 73A from on-shore installations through suitable lines diagrammatically illustrated at 77.

In the case of the supporting structure `61 all of the legs thereof are of full height and will be subjected to the action of wind, waves and the ice encountered in a cold winter climate. Therefore, the piling 78 for the supporting structure 61 must be sufficiently heavy to resist the forces exerted on the full-height, exposed multiple-leg structure by the elements and will be considerably more extensive than that required on single exposed leg structures where, as previously explained, the forces to be resisted are considerably less. Therefore, the use of full-height, multipleleg supporting structures 61 will be minimized in the wharf and, desirably, none would be used, there being illustrated a single one in the figures to cover the case where an exceptionally large heavy-duty platform 68 may be required.

The other supporting structures `62-67 have a single leg projecting into the paths of Wind, waves and ice as illustrated in FIGS. l5, 17 and 18. Therefore, the piling 79 for these supporting structures may be considerably lighter than the piling 78 required for the full-length, multiple-leg supporting structure 61.

Even though the arrangements of FIGS. and l5 contemplate cut-off of the legs 21 and 22 as soon as the supporting structures are erected and piled, it is desirable to construct the prefabricated structure with full length legs as shown in FIGS. 1 and 2. This not only gives symmetry and stability in the towing operation but also facilitates the insertion of the piling pipes through the accessible upper leg ends. However, by operating finally with a single exposed leg the extent of piling required to give the necessary support and to resist tilting and shifting of the supporting structure is still materially less than where the full-length, multiple-leg construction is employed. Further, while the invention has been discussed with particular reference to structures provided with simple elongated hollow columnar legs certain of which are cut off or severed below a predetermined water level, these legs may be made in the form of telescoping sections. In this instance all of the telescoping legs of the structure except one would be retracted instead of being sheared off whereby the tops of the telescoped legs would terminate at the -desired distance below the 'water level. In addition, where telescoping legs are employed in the case of the modes of operation exemplified in FIGS. 3 and 6, the legs that are telescoped for winter operation could be distended or expanded for summer operation.

While certain preferred embodiments of the invention have been specifically illustrated and described it will be understood that the invention is not limited thereto as many variations will be apparent to those skilled in the art and the invention is to be given its broadest interpretation within the terms of the following claims, wherein,

What is claimed is:

1. The method of constructing, floating and installing an offshore supporting structure which comprises: fabricating a supporting structure comprising a plurality of columnar legs of a length substantially greater than the depth of the water at the proposed offshore operating site, said legs `being disposed in a polygonal arrangement and in spaced relation to each other and having bracing members therebetween; floating said fabricated structure to the offshore site; sinking said structure at said site whereby said structure will stand on the bottom at said site with the legs thereof being substantially vertical and having their upper ends exposed above high water level; piling said structure; securing the piling; erecting a well drilling platform on said structure and drilling a well from said platform, removing said platform, causing the tops of all but one of said legs as well as the upper portions of said bracing members to be terminated at a substantial distance below the low water level at said site whereby said terminated legs and said bracing members can normally clear floating objects at the installation site; and then erecting a working structure on top of one of said legs for carrying out an operation with but one leg of said structure being exposed to the action of the elements.

2. The method defined in claim 1 including: erecting on said one of said legs after the top terminating operation on the other legs a producing structure.

3. The method of constructing and installing an olfshore supporting structure which comprises: fabricating a supporting structure comprising a plurality of hollow columnar legs of a length substantially greater than the depth of the water at the proposed offshore operating site, said legs being disposed in a polygonal arrangement and spaced relation to each other and having bracing members therebetween; moving said fabricated structure to the offshore site; sinking said structure at said site whereby said structure will stand at the bottom of said site with the legs thereof being substantially vertical and having their upper ends exposed above high water level; piling said structure through said legs from the accessible upper ends thereof into the earth beneath the legs; securing the piling extending through each leg to that leg; erecting a well drilling platform on said legs, drilling a well from said platform; removing said platform, causing the tops of all but one of said legs as well as the upper portions of said lbracing members to be terminated at a substantial distance below the water level at said site whereby said terminated legs and said bracing members can normally clear fioating objects at the installation site; and thereafter erecting a working structure on top of one of said legs for carrying out an operation with but one leg of said structure being exposed to the action of the elements.

4. The method defined in claim 3 including: erecting on said one of said legs after the terminating operation on the other legs a producing structure.

5. An offshore wharf structure comprised of a series of spaced supporting structures, certain of said supporting structures comprising: a plurality of substantially vertical columnar legs disposed in a polygonal arrangement and a hoizontally spaced relation with bracing members arranged therebetween, said legs having their lower ends resting on the bottom, one only of said legs of said certain structures extending substantially above the water surface at the offshore location, the tops of the other of said legs of said certain structures terminating below the water surface and below the expected lowest level of major wave action and any normally expected ice oating at said offshore location; piling associated with each leg of said certain structures and extending through the said legs and into the earth therebeneath; means connecting said piling to each of the legs with which it is associated; a working platform mounted on said one leg of each of said certain structures that extends substantially above the water surface; each of said certain structures being supported and stabilized by all the piled legs thereof while presenting only said one leg thereof to the forces exerted by the elements, one of said supporting structures adjacent the middle of said wharf structure having all of its legs exposed above the water surface and carrying a large working platform thereon, and the piling for the legs of said middle supporting structure being of greater extent than the piling for said exposed one-leg structures to resist the action of the elements on said multiple exposed leg structure.

6. An offshore wharf structure comprised of a series of spaced supporting structures, certain of said supporting structures comprising: a plurality of substantially vertical hollow columnar legs disposed in a polygonal arrangement and a horizontally spaced relation with bracing members arranged therebetween, said legs having their lower ends resting on the bottom, one only of said legs of said certain structures extending substantially above the high water level at the offshore location, the tops of the other of said legs of said certain structures terminating below the expected lowest level of ice floating at said offshore location; piling extending through each of said legs of said certain structures and into the earth therebeneath; means connecting said piling to the legs through which it extends; a working platform mounted on said one leg of each of said certain structures that extends substantially above the high water level; each of said certain structures being supported and stabilized by all of the piled legs thereof while presenting only said one leg thereof to the forces exerted by the elements, one of said supporting structures adjacent the middle of said wharf structure having all of its legs exposed above the high water level and carrying a large working platform thereon; and the piling for the legs of said middle supporting structure being of greater extent than the piling for said exposed one-leg structures to resist the action of the elements on said multiple exposed leg structure.

References Cited UNITED STATES PATENTS 2,653,796 9/1953 McGee et al. 61-465 X 2,772,539 12/1956 Sandberg 6l-46.5 2,941,370 6/1960 Walker 61-46.5 3,145,538 8/1964 Young 61-46 3,209,544 10/1965 Borrmann 61-46.5 2,429,952 10/1947 Willey 61-46 3,348,382 10/1967 Blenkarn et al. 61-46 3,362,170 l/1968 Manning 61-46.5

JACOB SHAPIRO, Primary Examiner U.S. Cl. X.R. 61-52, 48

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