US3797256A

US3797256A - Jack-up type offshore platform apparatus

Info

Publication number: US3797256A
Application number: US00287256A
Authority: US
Inventors: R Giblon
Original assignee: George G Sharp Inc
Current assignee: George G Sharp Inc
Priority date: 1972-09-08
Filing date: 1972-09-08
Publication date: 1974-03-19
Anticipated expiration: 1991-03-19
Also published as: GB1446751A; DE2345274A1; FR2199038A1; JPS5911008B2; FR2199038B1; BE804607A; NO142456C; ES418566A1; NO142456B; NL7312471A; IT994202B; JPS4968501A

Abstract

Floatable, jack-up type offshore drilling platform apparatus has ''''multiple-stage'''' feature permitting use in water depths greater than 300 feet, e.g. 600 feet or more, under 100-year storm conditions. Either a mobile type rig or a self-erecting permanent type platform structure is provided. Apparatus includes a floatable upper or working platform to be jacked out of water, one or more lower support platforms each functioning as a weight support and as a lateral bracing structure when the apparatus is erected, a plurality (three or more) of 300 feet long upper support legs permanently attached at their lower ends to each lower platform and whose upper ends are slidable through, but attachable to the next platform thereabove, and a plurality of independently movable lower support legs whose upper ends are slidable through, but attachable to the lowermost platform and whose lower ends rest on the sea bottom. Lower stages widen progressively for increased stability. Stages telescope, the lower platforms nesting with the upper platform, and all support legs projecting above water level, when rig is collapsed and floating. Buoyancy tanks on lowermost legs permit use of winch and cable devices or low-powered jacks for raising and lowering same, and buoyancy tanks in each lower platform permit use of low-powered jacks for raising and lowering platforms, including upper platforms. Telescopic air or compressed gas operated jack, 145 feet long and having expansible movement of 105 feet, is attached at lower end of each lower support leg in one embodiment, and is also useful on modified form of jack-up offshore platform for intermediate depths.

Description

United States Patent [1 1 Giblon Mar. 19, 1974 a 1 1 JACK-UP TYPE OFFSHORE PLATFORM APPARATUS [21] Appl. No: 287,256

Primary Examiner-Jacob Shapiro Attorney, Agent, or Firm-Brooks Haidt & Haffner 5 7 ABSTRACT Floatable, jack-up type offshore drilling platform apparatus has multiple-stage feature permitting use in water depths greater than 300 feet, e.g. 600 feet or more, under IOO-year storm conditions. Either a mobile type rig or a self-erecting permanent type platform structure is provided. Apparatus includes a floatable upper or working platform to be jacked out of water, one or more lower SUPPOI'lI platforms each functioning as a weight support and as a lateral bracing structure when the apparatus is erected, a plurality (three or more) of 300 feet long upper-support legs permanently attached at their lower ends to each lower platform and whose upper ends are slidable through, but attachable to the next platform thereabove, and a plurality of independently movable lower support legs whose upper ends are slidable through, but attachable to the lowermost platform and whose lower ends rest on the sea bottom, Lower stages widen progressively for increased stability. Stages telescope, the lower platforms nesting with the upper platform, and all support legs projecting above water level, when rig is collapsed and floating. Buoyancy tanks on lowermost legs permit use of winch and cable devices or low-powered jacks for raising and lowering same, and buoyancy tanks in each lower platform permit use of low-powered jacks for raising and lowering platforms, including upper platforms. Telescopic air or compressed gas operated jack, 145 feet long and having expansible movement of 105 feet, is attached at lower end of each lower support leg in one embodiment, and is also useful on modified form of jack-up offshore platform for intermediate depths.

30 Claims, 35 Drawing Figures PATENIEUHAR 19 m4 3797256 sum 02 or 10 PATENTEDMAR 19 m4 3797'. 256

sum ns'nF 1o PATENTED "AR 1 9 I974 snm oa ur 1o cal-197L256 PATENTEDMAR 1 9 m4 sum "10 0F 10 JACK-UP TYPE OFFSHORE PLATFORM APPARATUS This invention relates to offshore platform structures of the type from which operations, such as oil-well drilling operations, are conducted in coastal waters and other sea areas. More particularly, the invention relates to such platform apparatus as is of a self-erecting, socalled jack-up type and which is floated to an offshore site and set by hoisting its operations platform to a height above the level of the water after its support legs have been lowered to rest on the sea bottom.

BACKGROUND OF THE INVENTION AND THE PRIOR ART It is currently believed that the depths of water in which such jack-up rigs may be positioned and used are limited to about 300 feet and that, when drilling is to be conducted in deeper waters, especially in hurricaneprone locations such as the Gulf of Mexico and in other locations such as the North Sea where severe wave and wind action may be expected, either a so-called semisubmersible" type platform, or a floating type platform such as a drillship or barge, must be used. However, jack-up type platforms have certain advantages over semi-submersible or ship type platforms, which could be utilized if jack-ups could be safely positioned and used in the deeper water. For example, drilling operations may be conducted from a jack-up rig virtually continuously as compared with operations from a semisubmersible or a floating type platform, both of which are more susceptible to severe wind and wave action caused by storms and the like. Thus, downtime is minimized, resulting in lower average costs of drilling operations. Moreover, the initial cost of a jack-up type platform is far less than that of a semi-submersible rig, which is considered to be the next best type of platform, but the most expensive, from which to conduct deepwater operations.

Although semi-submersibles are used in depths up to about 1,000 feet and drillships can be used in even deeper .waters, when on site ready for drilling, semisubmersible platforms and drillships are subject to considerable rolling, heaving and pitching motion, and to drifting off location due to winds, tides, currents and the like. Both must rely upon heavy anchors and/or electronically controlled thruster devices to keep them accurately in position over the hole being drilled in the sea bottom. Downtime, when it is not possible to drill because of sea conditions, may average from 12 to 25 percent of the time. Moreover, semi-submersibles require frequent adjustment of ballast due to displacement differentials resulting from changes in equipment and consumdables, and are more limited with respect to the amount of consumables they can carry as com pared with drillships and jack-up platforms.

Considering that the working platform is positioned some fifty or sixty feet above the water when the structure is erected, existing mobile jack-up rigs usable in depths up to about 300 feet of water have support legs, extending from the sea bottom to the elevated platform, which may be almost 400 feet long. Such length is considered a maximum due to the higher bending moments generated by increased length when the structure is supported on the sea bottom, and due to stability problems when the rig is floating as are attributable to the upward projection of the raised legs some 350 feet and the resulting dynamic forces created when the rig rolls in a seaway.

Moreover, although self-erecting platforms may have been installed as permanent platforms in shallow water, it has been believed that such floatable jack-up type apparatus cannot be successfully employed for providing a self-erecting, permanent platform or template in deep water of 300 feet or more for reasons including those for which mobile jack-up type rigs have not been used in working such depths. Thus, it has been believed necessary to build such structures in place by floating either the prefabricated template or its separate components, such as its extremely long support legs, to the drill site inhorizontal position and then, by appropriate ballasting and flooding, to tip the template or leg to a vertical position and sink it to the ocean floor. Conventional piling is driven using additional special equipment brought to the site, and a working platform is built on the support at the appropriate elevation above sea level. It is apparent that such known technique for erecting a permanent platform in deep water is a very costly and time-consuming procedure.

Jack-up type offshore platform structures and supporting leg assemblies as are known are, for one reason or another, inadequate to provide either a mobile or permanent type offshore platform from which undersea drilling operations can be conducted in waters deeper than about 300 feet. The striking evidence of this is that, insofar as is known, nojack-up type rig is presently used in such circumstances. Of the known jack-up rig arrangements, some provide underwater bracing which, when the rig is erected, extends laterally between their support legs at a depth corresponding approximately to the midpoint of their lengths, with or without additional similar lateral bracing adjacent the sea bottom. In this regard, US. Pat. Nos. to Suderow 3,013,396, Rechtin 2,771,747, and Samuelson 2,589,146 are probably most pertinent. However, the support legs which are braced by the usually unattached lateral bracing extend continuously from the upper or working platform to the sea bottom and are therefore subject to the aforementioned length limitation, or are telescopic leg or piling arrangements which are inadequate to provide the required stability for operation in depths-greater than 300 feetjFor example, in the aforementioned Suderow patent the submerged lateral bracing structure which is provided is in effect,

slung below the upper platform, and is not intended to itself contribute to the support of the weight of the overall structure. It is not apparent from this or any prior concepts that, by rearrangement of the lateral bracing structure .with respect to the leg structure extending thereabove and therebelow, the bracing can additionally serve as a major point of weight support of the erected structure as a whole, which can then have at least twice the height of known structures of the type. Nor is it apparent that greater height can be provided by additional tiers of such support bracing structure.

Moreover, and although the disposition of buoyancy tanks on the support legs of such structures is known,

as described for example in Suderow US. Pat. No.

3,980,446 and Rybicki US. Pat. No. 3,367,119, it has not been appreciated how such feature, or the additional disposition of buoyancy tanks on such rearranged lateral bracing structure itself, cancontribute to the capability of these structures of being placed in depths of water over 300 feet, as well as to the stability of the rig when floating. The referred to Suderow and Rybicki patents also generally disclose so-called wave-transparent constructions for such support legs, as is also a feature of the apparatus to be described herein.

Similarly, and although the leg assemblies for such jack-up structures have been previously made in the form of telescopic columns which are extended and retracted by internal or external jack mechanisms such as described for example in Suderow US. Pat. No. 2,984,075 and Suderow US. Pat. No. 2,961,837, it has not been apparent that such support legs can incorporate as a part of their overall lengths a very elongated pair of telescoping cylinders which function in uncomplicated manner as pneumatic jacks for equalizing the support provided by each leg and consequently the level disposition of the working platform, and for lifting the entire structure, including the working platform, after the legs have been poistioned on the sea bottom.

OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is intended by the present invention to provide a floatable jack-up type offshore platform apparatus having a plurality of support legs, each of length within the aforementioned maximum limitation of about 400 feet, which can be safely towed or selfpropelled at sea to a drill site, and set on the sea bottom and operated safely in water depths significantly greater than 300 feet, e.g. in water depths of 600 feet or more, under extreme conditions of wind and sea, such as so-called lOO-year storm conditions and the like.

Although the invention was made in connection with efforts to improve mobile-type offshore platforms which are positioned temporarily for relatively short periods of, say, several months and then refloated and moved to another location, in a modified form the invention also appears well-suited for use as a permanent-type offshore platform structure which would be intended for installation at a particular site for a relatively long period of perhaps more than years, but which would be of a self-erecting type. Such permanent offshore platforms are utilized as drilling and production platforms for gas and oil wells which have been located previously by exploration drilling operations conducted from mobile jack-up or floating type platforms. These permanent drilling and production platforms, called templates, are normally of heavier construction because they will remain on site for such considerable periods of time, and are usually pinned to the ocean floor by means of piles. To avoid the very high costs, and to shorten the erecting time involved in the building of such permanent platforms, it is intended by the present invention to provide a permanent type offshore platform structure which is of the self-erecting type, yet which can be placed safely in deep water for such long periods of time. Thus, the self-erecting permanent type platform can be towed to the site with all equipment aboard, including fuel, drilling mud, drill pipe, casings and the like, as well as the equipment required for the self-erectin g of the unit, and fully erected within a comparatively short time of a week or so as compared to several months for a built-in-place structure.

More particularly, and whether the jack-up type apparatus is of the mobile or permanent type, it is intended that it be seaworthy and capable, in its erected condition, of withstanding the most severe wind, wave and ocean current conditions as are experienced in the North Sea and the Gulf of Meixco. That is, it is believed that apparatus in accordance with the invention can safely experience winds up to 120 knots, waves as high as 100 feet, and currents in excess of 4 knots on the surface as would be created by 120 knot wind, as occur in the North Sea. Since hurricane conditions are less severe, the apparatus should also operate safely in the Gulf of Mexico.

It is further intended by the present invention to provide features in jack-up type offshore platforms which will reduce the power requirements for raising and lowering the platform support legs, lateral bracing, and perhaps of the working platform itself. Thus, a winch and cable arrangement, rather than conventional but more expensive hydraulic or mechanical jacks, can be used, or the sizes and therefore the costs of the conventional type jacks can be reduced.

Moreover, certain of the inventive features-may be utilized to provide a jack-up type offshore platform especially adapted for use in intermediate water depths in the range of from about 300-450 feet under normally anticipated wind and sea conditions, and possibly as deep as 500 feet in relatively calm waters when severe storms are not anticipated. These platform structures might also be either of the mobile or permanent platform type.

. Briefly describing the floatable jack-up type off-shore apparatus which is provided by the invention, the apparatus may be characterized as having a plurality of stages, in vertical tandem arrangement, each supported on another when the rig is fully erected on the sea bottom and arranged for telescopic collapse with the other stages when the rig is in floating condition. In the erected condition, the uppermost stage supports an upper platform at an elevation of about 50 or feet above the water level from which workoperations, such as oil-well drilling operations, are conducted. The upper platform is buoyant for floating the entire apparatus.

In addition to the floatable upper or working platform, the apparatus includes one or more so-called lower'platforms, each preferably having only a trusslike construction for carrying out its function as both a structural support and a lateral bracing structure when the apparatus has been erected. A plurality of three or more so-called upper support legs are permanently attached at their lower ends to project upwardly from each of the lower platforms, their upper ends being slidable through, but attachable to the next platform thereabove. In addition, a plurality of three of more independently movable, so-called lower support legs for directly supporting the structure on the sea bottom are mounted on the lowermost of the platforms, their upper ends being slidable through, but attachable to the platform, and their lower ends resting on or penetrating the sea bottom when the structure is erected.

ries of upper support legs and in the group of lower sup-' port legs will be at least 250 feet long, or perhaps as long as the present state of the art will permit in such floatable rigs, and thus the rig will be capable of being placed in depths corresponding to multiples of such length. The support legs, as well as the lower platforms, are all of essentially open latticework construction, such that they may be characterized as wavetransparent and thus minimize wave forces thereon.

Although each of the lower platforms to which the referred to support legs are attached may have entirely rigid construction, in one embodiment limited vertical movement of the leg structure at each corner of the platform, with respect to the platform itself, is afforded by an associated vertically slidable portion of the platform to which the leg structure is attached. This limited movement is to provide leveling adjustment at the plat form to compensate for irregularities of elevation of the sea bottom as might otherwise cause the referred to lower platform to have a canted rather than level disposition, as where one or more legs would be disposed at a higher or lower elevation than intended. The movement of each movable portion is independent of any movement of the others and is powered by hydraulic jack actuators, disposed between the movable portion and the main body of the platform, and controlled from the upper or working platform.

In the preferred embodiment, each of the lower platforms is provided with buoyancy tanks, so that it is at least partially buoyant at all times for the purpose of reducing its effective weight, and therefore the power required to submerge and raise it. These buoyancy tanks are effectively provided at the lower ends of the aforementioned upper support legs which are permanently attached to the platform. Additional buoyancy tanks can be'provided to render each lower platform floatable so as to reduce the displacement requirements of the floatable upper platform when the rig is floating, these additional buoyancy tanks being floodable to assist in submerging the platform.

Buoyancy tanks are also provided on the lower ends of the lower support legs, and preferably also on their upper ends, to render each leg partially buoyant and thereby reduce the power requirements for submerging and raising the leg. Thus, less expensive and more dependable winch and cables can be used to raise and lower each of these independently movable lower support legs. Alternatively, remotely controlled, lowpowered, underwater-type jacks can be used, these being situated on the lower platform on which the lower legs are mounted.

If jacks are mounted on the lower platform to raise and lower the lower legs, they may instead be highpowered so that, after the lower legs are set on the sea bottom, they can be operated in unison to raise the lower platform on the lower support legs, thus lifting the upper platform attached to the upper support legs, to the desired elevation above the water surface.

In a modified embodiment, each lower support leg is formed part as a pneumatic or compressed gasoperated jack by telescoping cylinder portions of the leg, preferably at its lower end. These leg jacks are similarly used to set the lower legs and jack up the entire structure to position its upper platform above the water level. Devices are provided for locking the telescoping cylinders together in their several relative positions, and compressed air orgas inlet means, and a valve opening for flooding the cylinders at appropriate times,

are provided. One of the locking devices provides a plurality of annularly spaced apart, radially outward projecting ratchet pawls on the inner cylinder for engaging respective ratchet pins on the interior wall of the outer cylinder to prevent the lower inner cylinder from moving upwardly with respect to the outer cylinder, and respective, radially outward slidable wedges on the inner cylinder associated with each of the ratchet pawls to engage respective stops on the outer cylinder to concurrently prevent movement of the cylinders in opposite direction. Different arrangements of such elongated, air-jack type support legs in the overall structure are contemplated.

The invention may be adapted. for use as a permanently installed type of platform structure, but which may be fully assembled and loaded with equipment in advance, and towed to the site where it is easily selferected in the same manner as a mobile type jack-up rig. In suchembodiment, all of the components are of more rugged or durable construction, and the referred to lower legs preferably have hollow cylindrical, rather than open latticework construction, and are adapted for driving self-contained piles into the sea bottom from its lower end. As in the previous embodiment, the lower ends of these lower support legs are provided with buoyancy tanks to assist in floating the apparatus, but these tanks are flooded for improvement of the stability of the permanent installation after the leg is lowered to the sea bottom. Each hollow cylindrical leg is also at least partially filled with concrete in order to further increase its stability, and to permanently set the driven piles which pin it to the sea bottom.

DETAILED DESCRIPTION OF THE INVENTION These and other objects, features and advantages of the invention will be more fully apparent from the following detailed description thereof, when taken in conjunction with the accompanying drawings in which:

FIG. 1 is an elevational showing, partially in crosssection, of a mobilejack-up type offshore platform apparatus in accordance with the invention, the rig being shown in floating condition; Y

FIG. 2 is a top plan view of the apparatus of FIG. 1, with certain features removed for clarity;

FIG. 3 is an illustration, also partially in crosssection, of theimobile jack-up type drilling rig apparatus of FIG. 1 in its jacked-up condition, supported on the sea bottom ready for drilling, but with drilling equipment and the like removed. for clarity;

FIG. 4 is a further illustration of the apparatus of FIG. 1, also partially in cross-section, showing the apparatus as it would appear during an intermediate stage of the selferecting procedure;

FIG. 5 is a sectional plan view, as seen from lines 5-5 in FIG. 4, illustrating the lower platform structure of the apparatus of FIG. 1;

FIGS. 6, 7 and 8 are diagrammatic side-sectional illustrations of the lower platform structure of FIG. 5, showing several possible conditions of the structure during the self-erecting procedure;

FIG. 9 is an enlarged fragmentary plan view, partially in cross-section, of only one corner of the lower platform structure of FIG. 5, to illustrate its operation;

FIG. 10 is a similarly enlarged fragmentary elevational view as seen from lines"1010 in FIG. 9;

FIG. 11 is an elevational showing, partially in crosssection, of a modified form of mobile, jack-up type offshore platform apparatus in accordance with the invention, the rig being shown in floating condition;

FIG. 12 is an illustration, also partially in crosssection, of the mobile jack-up type drilling rig apparatus of FIG. 11 in its jacked-up condition supported on the sea bottom ready for drilling, but with drilling equipment and the like removed for clarity;

FIGS. 13-17 are enlarged elevational and fragmentary showings, in cross-section, of the lowermost support legs of the apparatus of FIG. 11, to illustrate the various conditions thereof during the self-erecting and refloating procedures, certain features of the support leg being removed for clarity;

FIG. 18 is a further enlarged and fragmentary elevational showing, in cross-section, of the lowermost support legs of the apparatus of FIG. 11 to illustrate a step in the refloating procedure, certain features of the support leg being removed for clarity;

FIGS. 19-22 are still further enlarged and fragmentary, cross-sectional illustrations of the lowermost support legs of the apparatus of FIG. 11 to illustrate the means by which the movable parts thereof are located in position; FIG. 19 being an elevational showing; FIG. 20 being a sectional plan view as seen from lines 20-20 in FIG. 19; FIG. 21 being a fragmentary sectional plan view as seen from lines 21-21 in FIG. 19; and FIG. 22 being a fragmentary side-sectional elevation as seen from lines 22-22 in FIG. 19;

FIG. 23 is an elevational showing, partially in crosssection, of a modified form of mobile, jack-up type offshore platform apparatus, the rig being in floating condition;

FIGS. 24 and 25 illustrate the offshore platform apparatus of FIG. 23 in several stages of the self-erecting procedure;

FIG. 26 is an elevational showing, partially in crosssection, of another modified form of jack-up type offshore platform apparatus in accordance with the invention, but intended for substantially permanent installation at an offshore site, the rig being shown in floating condition;

FIG. 27 is an illustration, also partially in crosssection, of the jack-up type offshore platform apparatus of FIG. 26 in its jacked-up" condition, supported on the sea bottom but only partially readied for drilling, with drilling equipment and the like removed for clar- "y;

FIG. 28 is a further but fragmentary illustration of the apparatus of FIG. 26, also partially in cross-section, showing the apparatus as it would appear during an intermediate stage of the self-erecting procedure;

FIG. 29 is an enlarged, fragmentary and sectional plan view as seen from lines 29-29 in FIG. 27, to illustrate the construction and features of the lower support platform structure of the apparatus of FIG. 26;

FIG. 30 is an enlarged fragmentary side-elevational showing, in cross-section, of only one corner of the apparatus of FIG. 26 to illustrate certain of its features, the apparatus being in floating condition;

FIG. 31 is a fragmentary cross-sectional elevation, to a slightly reduced scale as compared with FIG. 30, showing the same corner of the apparatus at an advanced stage of the self-erecting and positioning procedure;

FIG. 32 is an enlarged plan view in cross-section as seen from lines 32-32 in FIG. 31;

FIG. 33 is a greatly enlarged and fragmentary elevational view, in cross-section, as seen from lines 33-33 in FIG. 32;

FIG. 34 is a view similar to FIG. 33, but showing the apparatus as it appears when finally positioned on the sea bottom; and FIG. 35 is a diagrammatic sidesectional elevation, to a reduced scale, illustrating a further modified form of jack-up offshore platform apparatus in accordance with the invention, in which the apparatus has three stages.

Referring first to the embodiment of the invention as illustrated in FIGS. 1-10, a two-stage mobile, jack-up type offshore platform apparatus in accordance with the invention is generally indicated by reference numeral 50, and includes a floatable working or upper platform 51 on which oil-well drilling apparatus generally indicated by reference numeral 52) is mounted. FIG. 3 shows the platform 51 disposed some 50 to 60 feet above sea level S when the rig 50 is in erected condition at an offshore drilling site. The platform measures about 210 feet by 170 feet, and may also include a helicopter landing deck measuring some feet by 60 feet, as indicated by reference numeral 53. Other conventional features and equipment (not shown) may be disposed on the platform 51 for conducting drilling operations. In addition to the platform 51 (which will also be referred to herein as the upper platform) the apparatus 50 includes four laterally spaced apart, vertically extending, upper support legs generally indicated by numeral 54, a horizontal lower support platform structure generally indicated by numeral 55, and four laterally spaced apart, vertically extending, lower support legs, generally indicated by numeral 56. Although the apparatus 50 is shown as having four upper support legs 54 and four lower support legs 56, and only one lower support platform 55, it will be understood that the apparatus might be provided with only three, or more than four, upper support legs, and three, or more than four, lower support legs,-and that the number of upper legs and lower legs need not be equal.

In addition, and as generally illustrated by FIG. 35, the apparatus may include more than the two stages illustrated in the FIGS. 1-10 embodiment, considering that each additional stage would comprise a plurality of upper support legs such as the legs 54 of FIGS. 1-10, attached to another lower support platform such as the structure 55. Of course, the

platforms

51 and 55 need not have rectangular configuration and, if square or polygonal, need not have their respective corners in vertical alignment. As indicated in FIG. 2, the lower support platform 55 prefereably is larger in length and width than the upper platform 51. v

The lower support platform structure 55 is nestable at the underside of the upper platform 51 when the apparatus or rig is in floating condition, a portion of the lower platform strucutre fitting within an appropriately recessed structure of the upper platform, as generally indicated by reference numeral 55a. Any additional more lower support platform structures of the rig provides a shallower draft for the floating rig as a whole, and improves its movement characteristicsas it iseither self-propelled or towed through the water.

Referring briefly to FIG. 4 as compared with FIGS. 1 and 3, it will be understood that each of the lower support legs 56 is vertically movable with respect to the lower support platform 55, independently of eachother leg 56. Each is slidable through a vertical guide structure 57 of the platform 55 one of the guide structures 57 being disposed at each of the four corners of the structure 55 in the embodiment shown. When positioned either in its fully raised position or in any lowered position with respect to the platform strucutre 55, each lower support leg 56 can be rigidly locked in position by suitable locking devices which are only diagrammatically illustrated at reference numbers 57a in FIGS. 2, 5 and 9, these locking means beingmounted on the respective guide structures 57.

However, each of the upper support legs 54 is rigidly and permanently attached at its lower end 540 to the lower support platform '55 and, at its upper end, is slidable through the upper platform 51. Each may be securely locked in any vertical position, as by a locking device as ordinarily incorporated in the associated jack assembly 58 which is used to raise and lower the leg from the upper platform 51. Thus, the upper support legs 54 are structurally in fixed relation to the lower support platform 55 and when the apparatus is fully erected at a drill site, they are also in structurally fixed relation to the working platform 51, and therefore are subjected to much smaller bending moments than would be the case were the legs, though in fixed relation to the working platform, pin-ended at the sea bottom. Lighter upper support legs can therefore be incorporated in the structure of the present invention, such as might also be smaller in section to absorb lesser forces from the action of waves and undersea currents. The length of each

support leg

54, 56 can be from about 250 feet to the maximum permitted by the state of the art, i.e., presently about 400 feet. It will be noted that the lower support platform 55 functions not only asa direct support for the weight of the leg and platform structure thereabove, but also as a lateral bracing structure for the upper and lower support legs of the apparatus when in erected condition.

Although as previously indicated the lowerplatform or lateral bracing structure 55 to which the upper support legs 54 are attached may be rigid throughout its area, as will be especially apparent from FIGS. 6-10 provision may be made for limited vertical slidable movement of each of its corner portions at which the upper and lower legs are connected. These vertically slidable corner portions are generallyindicatedby ref erence numeral 59, and are movable within a limited range from about feet above their laterally aligned location with respect to the central area 60 of the structure to about ,15 feet therebelow, thus permitting accommodation for differences in penetration of the lower support legs 56 in the sea bottom.

For the purpose of adding buoyancy to the rig when in floating condition as illustrated in FIG. 1 as well as for providing effectively lighter weight when submerged, the lower platform or bracing structure ,55 is provided with respective pairs of

byoyancy tanks

61 and 62 at each of its comer portions, as perhaps best understood by reference to FIGS. 5 and 9. Each buoyancy tank 61 is attached to the lower end of an upper support leg 54, and each buoyancy tank 62 is formed in surrounding relation to one of the aforementioned vertical guide structures 57 through which a lower leg .56 is slidable. Referring particularly to FIG. 9, each set of

buoyancy tanks

61 and 62 form a part of a vertically movablexcomer portion 59 of the structure 55, the cornerportion59 being vertically slidable with respect to the central area or frame portion 60 by means of the four vertical slides 63. In addition, means (not shown) are provided for alternate flooding and emptying of buoyancy tanks 62 when submerging and raising the tanks, may be eliminated.

Jacking of each vertically movable corner portion 59 is controlled by conventional hydraulic jacking actuators 65 at either side thereof which, together with the vertical guides 63, form the connection between each .movable corner59 and the central area frame 60 of the structure. 55.

Referring again to FIGS. 1, 3 and 4, each lowersup- 'port leg 56 has a buoyancy tank at its lower end and,

preferably, a second buoyancy tank 71 atits upper end. As will be best understood from FIG. 3, the upper buoyency tank 71 has the effect of stiffening the lower support leg along the portion thereof which is joined to the lower platform or strucutre 55 when the leg is in its lowered position. The lower buoyancy tanks 70, to-

gether with the buoyancy tanks 71, if included, have size'such that each leg is virtually weightless when submerged as shown in FIGS. 3 and 4. Thus, ordinary winch and cable arrangements 72, mounted atop the upper legs 54 but controllable by winches 72a on the upper platform 51,canbe utilized in raising and lower- ,ing the independently movable lower support legs 56, thuseliminating' very expensive hydraulic or mechanical jacks at each leg as would otherwise be required.

Alternatively, smaller sized hydraulic powered jacks may be used, although the winch and cable arrangement is capable of faster operation.

It will further be noted that the lower platform or lateral bracingstructure 55 is formed as a truss by open latticework construction excepting, of course, for the buoyancy.

tank structures

61 and 62. Similarly, the

upper and

lower support legs

54 and 56 are preferably formed by open latticework construction. Thus, all of the submerged portions of the offshore platform structure are characterized as having wave-transparent construction to minimize, inertial effects of waves and the drag effects of subsurface currents. As a result, the forces acting upon the structure are reduced, either when standing on the sea bottom, or when floating with the lower legs and perhaps the upper legs in a downwardly extending condition. The reduction in such forces on the structure reduces the bending moment in each support leg when extending downwardly from the floating structure, and reduces the overturning moment on the structure as a whole when it is standing on the sea bottom. The legs may therefore have lighter construction than would otherwise be required for a given length.

The apparatus 50 is floated in the condition shown in FIG. 1 to an offshore drill site location, its lower legs 56 being pinned or locked by locking device 57a in their upper positions as shown, and its lower platform structure 55 being in floating or buoyant condition, nested against the underside of the floating platform 51. In this condition the buoyant tanks 62 as well as the buoyant tanks 61 are empty, so that the structure 55 does not detract from, but may add to the buoyancy of the apparatus as a whole. Contributing buoyancy is also furnished by the buoyancy tanks 70 at the lower ends of the lower legs 56. Rather than locking the lower legs 56 in their upper positions, they may be supported therein by the winch and cable arrangements 72.

Referring now to FIG. 4, when the floating unit arrives on site, the general contour of the hard sea bottom 80 on which its lowered legs will rest is first determined using conventional sonar devices or the like. It will be noted that, under usual circumstances, the legs may also be expected to pass through a relatively soft silt bottom 81 before engaging on the hard bottom 80. Lower legs 56 are then lowered from the still raised or floating structure 55 using the respective winch and cable arrangements 72. Each leg 56 is lowered independently of each other. and to an extent such that, together, their lower ends generally conform to the contour of the hard sea bottom 80, whereupon each is pinned or locked to the structure 55 using the locking devices 570. Buoyancy tanks 70 may be partially or fully flooded as the legs 56 are lowered. Alternatively, they may remain empty, unless they are of such size as to render the legs floatable such that the winches and cables 72 could not be used.

As previously noted, the lower ends 5411 of the upper legs 54 are rigidly attached to the lower platform structure 55, so that the structure 55 together with the upper legs 54 can now be lowered with respect to the still floating upper platform 51, by conventional hydraulic or rack and pinion type jacks 58 mounted on the latter. At this time the

buoyancy tanks

62 and 70 are at least partially flooded, making the structure 55 and the lower legs 56 virtually weightless when submerged. Thus, the lower legs 56, lower platform structure 55, and upper legs 54 are lowered as a unit until the lower legs 56 are in contact with the sea bottom. The operation of the jacks 58 is continued, thereby driving the lower legs 56 downwardly through the silt bottom 81 into engagement with the hard bottom 80, and thereafter jacking the upper platform 51 out of the water, on the upper legs 54, to the desired height above sea level.

To accommodate for differences in penetration of the legs in the sea bottom, and ensure disposition of the lower support structure 55 in horizontal position, the appropriate jacking actuators 65 (FIGS. 9 and 10) are actuated together with and for the same distance as the conventional hydraulic jacks located on the upper platform 51, to vertically move the associated comer portion 59 of the structure 55, together with the upper and lower legs attached thereto, upwardly or downwardly to the extent required to compensate for any difference in leg penetration from that which was anticipated. Of course, the upper leg 54 is detached from, and is slidable through the upper platform 51Jduring this operation, and it is therefore apparent that such vertical compensating movement' of each support leg unit must be performed independently of any other such unit.

Referring now particularly to FIGS. 6, 7 and 8, it will be noted that, were there any difference in penetration between the respective legs from that which was anticipated by measurement of the contour of the hard sea bottom 80, all of the vertically slidable corner portions 59 of the structure 55 would remain and be locked in position with respect to the central area 60 in their laterally aligned positions as illustrated in FIG. 6, yet the anticipated penetration of one leg might be less than that required to drive the leg to refusal. Its associated movable corner portion 59a of structure 55, as shown in FIG. 7, would then be moved downwardly, appropriately to adjust the penetration of the leg to support the required load. A maximum distance of downward adjustment movement of fifteen feet is contemplated. Alternatively, and as illustrated at the left hand portion of FIG. 8, if refusal at one leg is reached before the anticipated depth of penetration, the pertinent slidable corner portion 59b may be raised, with respect to the central area 60 of the structure 55, a maximum of 15 feet to accommodate the lesser than anticipated penetration, thus permitting the central area frame 60 to assume a level condition. Where differences both upwardly and downwardly from anticipated penetration must be accommodated, and as illustrated both in FIG. 8 and in FIG. 3, any other lower leg 56 may be concurrently jacked downwardly a compensating distance as much as fifteen feet, using the appropriate jacks 58 located on the upper platform 51. Upon completion of such levelling operations, the upper legs 54 are locked in their positions with respect to the platform 51 using locking devices which are ordinarily a part of the jacking devices 58 or using separate locking devices.

For preloading of the legs as is a normal procedure before conducting operations, or to resist overturning of the platform during storms, any or all of the

buoyancy tanks

70, 71, 61 and 62 may be completely flooded with sea water using conventional flooding valves (not shown) operated from the upper platform 51. Of course, provision such as conventional water eductors or the like (not shown), would be made for emptying these tanks when the rig is to be raised. In addition, it will be noted that each of the lower legs 56 is provided with a dish-shaped footing 56a and, to aid in eliminating suction as would otherwise prevent raising of the lower legs from the sea bottom, conventional water lines and pumping means (not shown) would be provided to pump water below the bottoms of the footings 54a and around the top of the same. Of course, when restoring apparatus 50 to floating condition, the movable corner portions 59 of the structure 55 would be returned to their laterally aligned positions, as shown in FIG. 6, just prior to the nesting of the structure 55 at the underside of the floating platform 51.

It will be noted that the necessary movements of the upper legs 54 and lower legs 56 are imparted by conventional jacks or winches operated on the upper platform 51, and that all other equipment, such as that used for flooding and emptying any buoyancy tanks, relieving suction at the bottom legs, etc., is also operated from the upper platform 51. Pulleys 72b, atop legs 54, are removable.

However, and as previously indicated, the apparatus 50 may be modified by eliminating the movable corner portions 59 of the lower platform structure 55, thus providing a unitary structure to which the upper support legs 54 are attached, and through which the lower support legs 56 are vertically slidable. The lower support legs may be raised and lowered preferably by respective hydraulic jacks (not shown) mounted on the lower platform structure 55, the jacks being of a type operable underwater, or alternatively by winches and cables on the upper platform 51. Because of the buoyancy provided by the tanks 61 and the buoyancy of the lower legs 56, the lower support platform, together with the upper legs, could be raised and lowered by winches and cables on the upper platform or, preferably, by respective, relatively small size hydraulic jacks situated on the upper platform 51.

In positioning this alternative form of the apparatus, the lower support legs 56 would first be lowered to about their midlength position with respect to the lower platform 55, by means of the aforementioned hydraulic jacks mounted on the latter. Next, the lower platform 55 together with the upper and lower support legs would be lowered by means of the aforementioned hydraulic jacks mounted on the upper platform, this jacking down operation being continued until the upper legs are completely extended. The upper legs are then pinned or locked to the upper platform by suitable locking devices, such as those which are'integral with the jacks 58 of the FIG. 1 embodiment. Using the hydraulic jacks mounted on the lower platform, the lower support legs are then lowered into engagement with the hard sea bottom 80. At this time the jacks are operated independently of each other to assure equal loading on the four lower legs, thus keeping both the upper and the lower platforms level. However, the same hydraulic jacks are then operated in unison to jack-up the lower platform on the now lower legs, thus also raising the upper platform out of the water to the desired height above sea level. Buoyancy tanks located at the base of the'upper legs, as well as buoyancy tanks at the base of the lower legs, would then be flooded to enhance stability and prevent overturning of the structure under storm conditions. To remove the platform from the sea bottom, the hydraulic jacks mounted on the lower platform would first be operated in unison to lower the upper platform to its floating condition on the surface of the water, and thereafter independently of each other to lift the lower legs off of the sea bottom, appropriate water jet apparatus being operated to relieve mud suction at the bottomsof the lower legs during the latter operation. The upper legs would then be disconnected from the floating upper platform, and the hydraulic jacks located on the upper platform would be operated to raise the upper legs, the lower platform and the lower legs as a unit, until the lower platform is in nested relation at the underside of the floating upper platform. The lower legs would then be raised individually, such that the lower end of each leg is laterally aligned with the underside of the nested lower platform.

Referring now to FIGS. 11 and 12, a modified form of. mobile, jack-up type offshore platform in accordance with the invention is generally indicated by reference numeral 100 and is shown both in its floating position (FIG. 11) and in its self-erected condition (FIG. 12) at an offshore location. The apparatus 100 has a buoyant upper platform 101 and a partially buoyant or floatable lower support platform or strucutre 102 which, in the floating condition of the rig, is nestable at the underside of the upper platform 101, as indicated in FIG. 11. The apparatus 100 also has four upper support legs 103, each of which is rigidly attached at its lower end to the lower platform 102, and is slidable through appropriate vertical guides 104 in the upper platform 101. Mounted for vertical slidable movement through appropriate vertical guides 105 in the lower platform 102, are respective lower support legs generally indicated by reference numeral 106, four lower legs being provided. As in the previously described embodiments, the lower support platform 102 may be formed essentially of open latticework, truss-type construction, in which case its primary buoyancy will be imparted by its rigidly attached buoyancy tanks 107, to which the lower ends of the upper legs 103 are attached, in turn.

In the embodiment of FIGS. 1 l and 12, the lower half of each lower leg 106 is formed by an elongated, pneumatic or compressed gas operated jack, generally indicated by reference numeral 106a, the upper length portion 106b of the leg having open latticework construction as shown. The jack 106a comprises a pair of telescoping upper and

lower cylinders

109 and 110, respectively, which are vertically slidable one within the other. Although each of the

cylinders

109, 110 is essentially empty, each lower cylinder 110 carries a buoyancy tank 110a at its lower end, the bottom of the buoyancy tank being provided with an inverted dishshaped footing 11%. The upper end 109a of the upper cylinder 109 is closed, and is preferably dome-shaped as shown, whereas the upper end of the lower cylinder 110 is open so that both cylinders are floodable concurrently. The cylinder 109 is attached at its upper end to the remaining upper length portion 106b of the lower support leg 106. The slidable fit 10% between the cylinders need not be watertight, and preferablyis not watertight to eliminate excessive pressure differential between the air pressure in the tank and the outside water pressure.

As in the previously described embodiment the lower support legs 106 are slidable through their respective guides independently of each other. As shown, each of the upper support legs 103 has latticework construction so that it is wave-transparent, for reasons as previously noted. A removable winch and cable arrangement, generally indicated by reference numeral 111, is mounted on the upper end of each upper support leg 103 for use in raising and lowering the respective lower support legs 106. Mechanical locking devices, diagrammatically indicated by reference numeral 112 in FIG. 12, are provided on the lower support platform 102 for pinning the lower support legs 106 in their downwardly extending, as well as in their raised, positions as indicated in FIGS. 12 and 11, respectively.

The telescoping jacks 106a are preferably pneumatically operated by air compressors A situated on the upper platform 101, the air being admitted to, and releasable from the upper cylinder 109 as by an air line 113 Alternatively, tanks of compressed gas such as carbon dioxide, also indicated by reference letter A, could be used to expand the cylinders via lines 113, which could provide more rapid operation. The jacks might be hydraulically operated using sea water although, in such case, the slidable fit 10% between the telescoping sections would be watertight. In the illustrated embodiment the overall height of each leg 106 is 300 feet, the length of cylinder 109 being about 145 feet. The range of expansible movement of the jack 106a is about 105 feet, so that the maximum length of the leg 106 is about 400 feet. The diameter of the outer cylinder 109 is about 26 feet, and the outside diameter of the inner cylinder 110 is about 24 feet 8 inches. Of course, it will be understood that the length of the jack 106a might be as short as about 40 feet affording a range of expansible movement up to about 30 feet, or as long as the leg 106 itself, so as to afford a much greater range of telescopic movement.

As most clearly seen in FIGS. 13-17, immediately above its buoyancy tank 1100 each lower cylinder 110 has a sea water inlet and drain opening 115 having a remotely controlled shutoff valve 116, the opening and closing of the valve 116 being controlled from the upper platform 101. In addition, a locking device 117 is provided for locking the upper and

lower cylinders

109, 110 together when in their telescoped relation as shown in FIG. 13.

Referring now particularly to FIGS. 19 and 20, a locking device, generally indicated by reference numeral 120 and carrying a plurality of ratchet elements 121, is attached atop the lower cylinders 110 for locking the upper and

lower cylinders

109, 110 in any one of several vertically expanded positions relative to each other. Each ratchet pawl 121a is pivotable on a horizontal pivot shaft 120a and is adapted as by the semi-circular end portion 121b at its outer or free end, to engage one of the plurality of vertically spaced aprt, horizontal ratchet pins 122 which are attached, as by welding, adjacent to the interior side wall of the upper cylinder109. The ratchet pins 122 extend between respective pairs of vertical stiffeners 123, which also serve to laterally guide the ratchet pawls 121a so as to maintain the annular alignment of the upper and

lower cylinders

109, 110 by preventing relative rotation between them. Vertically spaced, cylindrical-shaped stiffeners 124 are also provided within the upper cylinder 109, these extending arcuately between the vertical stiffeners 123, and functioning as guides for the vertical movement of the inner, lower cylinder 110. The lower cylinder 110 also has stiffened construction, as indicated by reference numeral 119 in FIG. 19.

The ratchet pawls 121a are advanced and retracted in the radial direction of the lower cylinder in response to pivotal action in the horizontal plane, of a center mounted cam disc 125 on the fixed, criss-cross pattern, box-girderstrueture 126 to which the ratchets 121 are attached, as best seen in FIG. 20. The box-girder construction 126 adds rigidity, yet permits the top of the cylinder 110 to remain open to the passage of water, for operational purposes as will be described. The ratchet pawls 121a are normally retained in their outwardly extended positions as shown in FIG. 19 by the tension springs 127 (see FIG. which are mounted on the box-girder structure 126 and normally urge the disc 125 in counter-clockwise direction, as shown, to press on the ratchet control rods 128. The rods 128 extend between the respective ratchet pawls 121a and the disc 125, the rods being pivotally attached eccentrically with respect to the center of the disc as shown, to hold the ratchet pawls 121a in their outwardly extended positions engaging the respective pins 122 of the upper cylinder, which are respectively positioned adjacent the four, annularly spaced apart locations of the ratchets. Hydraulic cylinders 129 are provided between the box-girder structure 126 and the outer periphery of the disc 125 for disengaging the ratchet pawls 121a at appropriate times, as will be explained. The hydraulic cylinders 129 are operated by control means (not shown) located on the upper platform 101 and act, via their control rods 130, to pivot the disc 125 in clockwise direction as shown, i.e., in direction reverse to that of the bias of springs 127, as will be apparent. As will be noted, the ratchets 121 are intended to operate simultaneously.

Referring now to FIGS. 19 and 21, the locking device 120 also carries a pair of wedge-shaped locking bars 131 mounted for slidable movement below their respectively associated pair of ratchets 121 as will be understood from a comparison of FIGS. 19 and 21. The locking bars 131 are slidable in radial direction within respective guides 132 formed in the structure 126 as seen in FIG. 19. When in their simultaneously locked positions the locking bars 131 project beyond the outer periphery of the lower cylinder 110 to respectively engage the stops as are provided by the upper surfaces of a pair of the pins 122, located below those engaged by the ratchets 121, as also indicated in FIG. 19. Locking engagement of the locking bars with their associated pins 122 is effected and maintained by pivoting of a horizontal arm 133 which is also centrally mounted on the box-girder structure 126. For this purpose, control rods 134 are pivotally attached at their respective ends to the bars 131 and to the outer ends of the arm 133, as shown in FIG. 21. Springs 134a, forming part of each control rod 134, exert radially outward bias to ensure that the locking bars 131 are urged outwardly their full distances to wedge over their associated pins 122. Movement of the slidable locking bars into and out of their locking positions is effected by actuation of conventional two-way hydraulic cylinders 135, which extend between the girder structure 126 and the respective outer ends of the pivotable arm 133 as shown, and which are remotely controlled from the upper or working platform 101.

The pneumatic jacks 106a which form the lowermost halves of the respective lower support legs 106 are utilized both to raise the upper platform 101 to its desired elevation on the upper support legs 103 some feet above the water, and to individually adjust the projecting lengths of each lower leg 106 to achieve a'firm setting on the hard sea bottom and as may involve some penetration thereof. That is, assuming that the rig is initially in floatingcondition over a drill site as shown in FIG. 11, at which time the lower cylinders 110 are fully retracted and locked by the locking pins 117 within the upper cylinders 109, and the lower support legs 106 themselves are locked by locking devices 112 in their raised positions, the procedure for self-erecting the apparatus is as follows:

Referring to any particular lower support leg as illustrated in FIG. 13 and considering that all of the lower support legs 106 are operated in the same manner, the mechanical locking devices 112 are first unlocked to release the connections between the respective lower legs 106 and the lower platform 102, and the respective valves 116 are opened to admit sea water to the lower cylinders 110. The sea water flows upwardly between the cylinders through the sliding fit 109b, and thence through the sea water inlet opening 115. At this time the locking device 117 is unlocked so that the telescoped cylinders are free to expand relative to each other. However, buoyancy tank 110a is sufficiently buoyant to retain the lower cylinder 110 in floating condition within the upper cylinder 109, although its buoyancy is insufficient to prevent the entire lower leg 106 from submerging as the water is admitted. Displaced air from the interior of the cylinders is permitted to escape through air line 113, and the independent downward movement of each leg 106 is effected and controlled by one of the winch and cable arrangements 111. Of course, lowering of the legs rhight alternatively be effected by respective hydraulic or mechanical jacks mounted on the lower platform 102, which would engage each leg 106. In any event, when in their lowered support platform structure 102 by means of mechanical Y locking devices 112, the structure 102 still being in its floating or raised position.

At this time, the hydraulic or other type jacks 140 on the upper platform 101 which respectively engage each of the upper support legs 103 are unlocked and utilized to jack-down all of the upper legs 103 with respect to the floating platform 101, the jacking being continued until the attached lower platform 102 has descended below the still floating upper platform 101 to a'depth corresponding to the full length of the upper support legs 103, a depth of about 300 feet. The interior of the still telescoped cylinders is at this time filled with water as indicated in FIG. 14, and the remotely controlled valves 116 are then closed.

With both its lower support legs 106 and upper support legs 103 in their fully lowered condition, it can be assumed that the lower ends of the still telescoping lower legs are at or near the sea bottom-80, at a depth of about 650 feet, further assuming that the height of each of the platforms101, 102 is 50 feet, the elevation of the underside of the platform 101 above sea level S will be 50 feet, and the length of each

leg

103, 104 is 400 feet.

Compressed air or gas can now be admitted through the air line 113 to force the lower cylinders 110 down onto the sea bottom 80 and to then lift the upper plat form 101 out of the water to its desired elevation as shown in FIG. 16, all of the jacks l06a being operated concurrently after each of the respective lower cylinders 110 have been firmly set in the sea bottom 80. Of course, at this time the internal locking devices of the jacking assemblies 140 on the upper platform 10] are in locked condition with respect to all of the upper legs 103,'and it will be understood that the upwardjacking movement of the pneumatic jacks 106a lifts the upper platform 101, the upper support legs 103, the lower platform 102, and the upper ends 1061) of the lower legs 106, contemporaneously. The elevation differential between the upper end 1100 of the lowercylinder and the lower end 109k of the upper cylinder is sufficient to seal the air within the cylinders and to exert the required force to raise the structure thereabove. As the cylinders expand telescopically, the ratchet pawls 121a of the cylinder locking devices 120 respectively engage the pins 122, to prevent downward movement of the upper cylinders 109 with respect to their associated lower cylinders 110.

When the upper platform 101 has been levelled at its proper height, the compressed air in the upper cylinders 109 is permitted to escape through the air lines 113, so that the cylinders fill with sea water, admitted through the respective slide fits 10% between the cylinders and the openings 115, so that each leg is then in condition as shown in FIG. 17'. It will be noted that the entire weight of the apparatus is then transmitted to the sea bottom through the ratchet locking devices 120. However, in any of the cylinders 109 the displacement of the air by sea water could cause the leg to settle somewhat, such that all of the legs might settle unevenly. In such instances, it may be necessary to pneumatically recharge one or more of the tanks 109 to the extent necessary to level the platform 101.

After the apparatus 100 has been properly set on the sea bottom as shown in FIG. I12 the slidable locking bars 131 of the locking devices (FIG. 19) are extended radially, by pivoting the am 133 as previously explained, so that each of the bars 131 engages the upper surface of its then associated ratchet pin 122 of the outer cylinder of the pair, thus locking the

cylinders

109, 110 securely together and preventing any upward movement of the upper cylinders 109 relative to the lower cylinders 110.

When refloating the platform, the locking bars 131 are first retracted, from their wedged condition, over the ratchet pins 122, by means of the vhydraulic cylinders 135 (FIG. 21) which are controlled from the upper platform 101. Compressed air is then admitted to the upper cylinders 109 via the compressed air lines 113, thus relieving the weight load from the ratchet locking devices 120. The ratchet pawls 121a are then retracted utilizing the hydraulic cylinders 129 as shown and described in connection with FIG. 20.

After the cylinder locking devices 120 are disengaged, the air is released from the pneumatic cylinders 109, permitting the leg portions 106]) and thev cylinders 109 of the lower legs 10.6 to settle downwardly, thus lowering all of the structure therebaove, and refloating the upper platform 101. The pneumatic jacks 106a are then telescoped and filled with water.

The hydraulic jacks on the upper platform 101 are then simultaneously actuated to raise all of the upper'legs 103 and, thus, the structure 102 and lower legs 106 therebelow. Referring to FIG. 18, each of the pneumatic jacks 106a is equipped with a suction relieving device, generally indicated by reference numeral 141, for relieving any suction below and surrounding its footing 110b. The suction relieving device 140 is a water jetting arrangement comprising a water supply line 142 which extends fror'nthe upper platform 101 through the upper end 109a of the upper cylinder 109, and a coiled spring supported hose 142a for continuing the water path to thewater supply line 143 attached within the lower cylinder 110, as shown. The water supply line 143'extends downwardly through the buoyancy tank 110a, at the-lower end of which it has lateral branches 143a which distribute the jetting water to a plurality of jet orifices 143b through which the water appears at the underside of the dish-shaped footing 1l0b. Additional water jet orifices 143 c also distribute the water jetting action to the exterior of the cylinder 110 as it rests within the sea bottom 80. Thus, any natural suction, as would otherwise prevent raising of any lower leg 106, can be relieved.

At or about the time when the lower platform structure 102 has reached the underside of the floating upper platform 101, the valves 1 16 inthe lower legs are opened so that the pneumatic jacks 106a will be drained, The jacks 140 are operated until the upper legs 103 and the lower platform 102 are fully raised.

Claims

1. Jack-up type offshore platform apparatus comprising a floatable upper platform, at least one horizontal lower support platform structure nestably arranged in substantially surrounding relation with respect to at least a portion of said upper platform and for disposition in vertically spaced tandem relation below said upper platform when said apparatus is in erected condition, each of said lower support platform structures being of substantially open latticework construction and carrying an attached plurality of upwardly projecting, elongated upper support legs in laterally spaced apart relation to each other and respectively engaging the platform structure thereabove for vertical movement with respect thereto, means for attaching each of said upper support legs at locations along their respective lengths to said platform structure which it engages for vertical movement, said upper platform being mounted for vertical movement on, and having means for its attachment to said upper support legs on that lower support platform structure which is disposed immediately below said upper platform when said apparatus is in said erected condition, a plurality of elongated lower support legs respectively mounted in laterally spaced apart relation to each other on the lowermost of said lower support platform structures for vertical movement independently of each other to project downwardly from the platform when said apparatus is in said erected condition, and means for attaching each of said lower support legs at locations along their respective lengths to said lowermost support platform structure, whereby when said apparatus is in said erected condition, each said lower support platform structure supports and transmits to the support legs therebelow all of the weight of the structure thereabove.

2. Jack-up type offshore platform apparatus according to claim 1 wherein each of said lower support legs has a buoyancy tank attached to the lower end thereof for rendering the leg at least partially buoyant, and wherein said apparatus further comprises winch and cable means operable from said upper platform for raising and lowering at least said lower support legs with respect to said lowermost lower supPort platform structure.

3. Jack-up type offshore platform apparatus according to claim 2 wherein each of said lower support platform structures has buoyancy tank means rendering the structure at least partially buoyant, and said winch and cable means is further attachable to each of said upper suport legs for raising and lowering their associated lower support platform structure with respect to said upper platform.

4. Jack-up type offshore platform apparatus according to claim 2 wherein said winch and cable means includes pulley means temporarily mounted atop said upper support legs on which said upper platform is mounted for vertical movement.

5. Jack-up type offshore platform apparatus according to claim 2 wherein each of said lower support legs further has a buoyancy tank attached near the upper end thereof.

6. Jack-up type offshore platform apparatus according to claim 1 wherein said lateral spacing apart of the legs of each of said pluralities of upper and lower support legs is greater than that of any of said pluralities of legs thereabove when said apparatus is in said erected condition.

7. Jack-up type offshore platform apparatus according to claim 6 wherein each of said lower support legs has a buoyancy tank attached thereto for rendering the leg only partially buoyant, and wherein said apparatus further comprises respective low-powered jacks on the lowermost of said lower support platform structures and engaging each of said lower support legs for raising and lowering the same with respect to said lowermost support platform structure, each of said low-powered jacks having power sufficient to raise its said associated lower support leg only when the leg is rendered partially buoyant by its said attached buoyancy tank.

8. Jack-up type offshore platform apparatus according to claim 6 which further comrises respective high-powered jacks on said lowermost lower support platform structure, and engaging each of said lower support legs, each of said jacks being operable independently of each other for raising and lowering each of said lower support legs with respect to said lowermost support platform structure to position and set the support legs on a sea bottom, and said jacks being operable concurrently for raising and lowering said lowermost support platform structure on said lower support legs when the same are set on said sea bottom to commensurately raise and lower all of said apparatus thereabove.

9. Jack-up type offshore platform apparatus according to claim 1 wherein each of said upper and lower support legs is at least 250 feet long.

10. Jack-up type offshore platform apparatus according to claim 1 wherein at least the lower end portion of the length of each of said lower support legs has elongated cylindrical shape, and said apparatus further comprises a floodable buoyancy tank on said lower end of each of said lower support legs, a plurality of annularly spaced apart, tubular pile guides extending vertically through each of said buoyancy tanks, a corresponding plurality of vertically extending pile driver guides attached to the interior of each of said lower end portions and respectively in vertical alignment with said pile guides, and removable pile driver means suspended substantially from said upper platform and positionable within each of said support leg lower end portions for engaging each of said respective pile driver guides for driving a pile positioned within its said associated pile guide, each of said tubular pile guides having plate means attached substantially adjacent to its lower end and providing a constricted opening for supporting a pile within the guide, said plate means being rupturable by said pile when the latter is driven.

11. Jack-up type offshore platform apparatus according to claim 1 wherein each of said lower support platform structures has buoyancy tank means rendering the structure at least partially buoyant.

12. Jack-up type offshore platform apparatus comprising a floatable upper platform, at least one horizontal lower support platform structure nestably arranged with respect to said upper platform for disposition in vertically spaced tandem relation below the latter when said apparatus is in erected condition, each of said lower support platform structures carrying an attached plurality of upwardly projecting, elongated upper support legs in laterally spaced apart relation to each other and respectively engaging the platform structure thereabove for vertical movement with respect thereto, means for attaching each of said upper support legs at locations along their respective lengths to said platform structure which it engages for vertical movement, said upper platform being mounted for vertical movement on, and having means for its attachment to said upper support legs on that lower support platform structure which is disposed immediately below said upper platform when said apparatus is in said erected condition, a plurality of elongated lower support legs respectively mounted in laterally spaced apart relation to each other on the lowermost of said lower support platform structures for vertical movement independently of each other to project downwardly from the platform when said apparatus is in said erected condition, and means for attaching each of said lower support legs at locations along their respective lengths to said lowermost support platform structure, whereby when said apparatus is in said erected condition, each said lower support platform structure supports and transmits to the support legs therebelow all of the weight of the structure thereabove, said lateral spacing apart of the legs of each of said pluralities of upper and lower support legs being greater than that of any of said pluralities of legs thereabove when said apparatus is in said erected condition, at least one of said lower support platform structures having a vertically movable portion associated with each of said attached upper support legs, said upper support legs being respectively attached to said movable portions, and respective connection means between each of said movable portions and the remainder of said one platform structure to provide limited vertical movement of the movable portion from a position above to a position below the elevation of said remainder of the platform structure when said apparatus is in said erected condition.

13. Jack-up type offshore platform apparatus according to claim 12 wherein said other support legs which engage said one platform structure for vertical movement with respect thereto respectively engage said movable portions of the platform structure.

14. Jack-up type offshore platform apparatus according to claim 13 wherein each of said movable portions has a pair of buoyancy tanks, one of said pair of buoyancy tanks being floodable.

15. Jack-up type offshore platform apparatus comprising a floatable upper platform, at least one horizontal lower support platform structure nestably arranged with respect to said upper platform for disposition in vertically spaced tandem relation below the latter when said apparatus is in erected condition, each of said lower support platform structures carrying an attached plurality of upwardly projecting, elongated upper support legs in laterally spaced apart relation to each other and respectively engaging the platform structure thereabove for vertical movement with respect thereto, means for attaching each of said upper support legs at locations along their respective lengths to said platform structure which it engages for vertical movement, said upper platform being mounted for vertical movement on, and having means for its attachment to said upper support legs on that lower support platform structure which is disposed immediately below said upper platform when said apparatus is in said erected condition, a plurality of elongated lower support legs respectively mounted in laterally spaced apart relation to each other on the lowermost of said lower support platform structures for vertical movement independeNtly of each other to project downwardly from the platform when said apparatus is in said erected condition, and means for attaching each of said lower support legs at locations along their respective lengths to said lowermost support platform structure, whereby when said apparatus is in said erected condition, each said lower support platform structure supports and transmits to the support legs therebelow all of the weight of the structure thereabove, each of said lower support legs comprising an independently operated, fluid-powered jack for adjusting its length independently of any other support leg, each of said fluid powered jacks comprising a pair of elongated, substantially empty upper and lower cylinders concentrically arranged for telescoping slidable movement relative to each other and together constituting at least a portion of the length of said associated support leg, said upper cylinder having a closed upper end and an open lower end, and said lower cylinder having a closed lower end and an open upper end, means for introducing fluid under pressure into, and for discharging the same from the interior of said cylinders for inducing said telescoping slidable movement relative to each other, means for admitting and discharging sea water into and from said interior of said cylinders, and means for locking said upper and lower cylinders together at positions along the length of their said relative movement.

16. Jack-up type offshore platform apparatus according to claim 15 wherein said upper and lower cylinders constitute substantially the lower half of the length of said associated support leg.

17. Jack-up type offshore platform apparatus according to claim 16 wherein said means for admitting and discharging sea water into and from said interior spacing between said cylinders comprises means providing a valved opening near the lower end of said lower cylinder.

18. Jack-up type offshore platform apparatus according to claim 16 wherein each of said lower cylinders has a buoyancy tank adjacent to its lower end, said valved opening being disposed for admitting and discharging sea water at a location above said buoyancy tank.

19. Jack-up type offshore platform apparatus according to claim 15 wherein the length of each of said lower support legs is at least 250 feet, and the lenghts of each of said cylinders is at least 40 feet.

20. Jack-up type offshore platform apparatus according to claim 15 wherein said fluid under pressure is compressed air.

21. Jack-up type offshore platform apparatus according to claim 15 wherein said fluid under pressure is compressed gas, and said means for introducing said gas comprises compressed gas tanks mounted on said upper platform.

22. Jack-up type offshore platform apparatus according to claim 15 wherein said means for locking said upper and lower cylinders together comprises ratchet pawl means mounted on one of said cylinders for movement towards and away from the other of said cylinders, ratchet pin means mounted on said other cylinder for engagement by said ratchet pawl means of the first said cylinder to prevent said telescoping movement between said upper and lower cylinders in one direction, radially movable means on one of said cylinders, and stop means on the other of said cylinders for engagement by said radially movable means to prevent said telescoping movement between said upper and lower cylinders in the opposite direction.

23. Jack-up type offshore platform apparatus according to claim 22 wherein said means for locking said upper and lower cylinders together further comprises latch means spaced upwardly from the lower end of said lower cylinder for locking said cylinders in their fully telescoped relation.

24. A support leg for a jack-up type offshore platform apparatus, said leg comprising a pair of elongated, substantially empty upper and lower cylinders concentrically arranged for telescoping slidable movement relative to each other and together constituting at least a portion of tHe length of said support leg, said upper cylinder having a closed upper end and an open lower end, and said lower cylinder having a closed lower end and an open upper end, means for introducing fluid under pressure into, and for discharging the same from the interior of said cylinders for inducing said telescoping slidable movement relative to each other, means for admitting and discharging sea water into and from said interior of said cylinders, and means for locking said upper and lower cylinders together at positions along the length of their said relative movement.

25. A support leg according to claim 24 wherein said upper and lower cylinders substantially constitute the lower length portion of said support leg, and said support leg has an upper length portion having wave-transparent construction.

26. A support leg according to claim 25 which further comprises a buoyancy tank within said lower length portion.

27. A support leg according to claim 26 wherein said buoyancy tank forms said closed lower end of said lower cylinder, and which further comprises an inverted-dish shaped footing at the underside of said buoyancy tank, and water jet means for relieving suction forces adjacent to said footing as would otherwise resist the raising of said support leg when resting on a sea bottom.

28. Jack-up type, mobile offshore platform apparatus comprising a floatable upper platform, a first plurality of elongated, substantially vertical upper support legs mounted in laterally spaced apart relation to each other on said upper platform for vertical movement with respect thereto, a horizontal lower support platform structure extending laterally between, and rigidly attached to the lower ends of all of said first plurality of legs, and having buoyancy tank means rendering the platform structure and said upper support legs at least partially buoyant, means on said upper platform for jacking the platform upwardly and downwardly along the lengths of said upper support legs and for attaching the platform to each of said legs at locations along their respective lengths, a plurality of elongated, substantially vertical lower support legs respectively mounted in laterally spaced apart relation to each other on said lower support platform structure for vertical movement with respect thereto independently of each other and independently of said upper platform, a buoyancy tank on the lower end of each of said lower support legs for rendering the same at least partially buoyant, winch and cable means operable from said upper platform and including removable pulley means mounted substantially adjacent to the tops of said upper support legs for raising and lowering said lower support legs with respect to said lower support platform structure, and means for attaching each of said lower support legs to said lower support platform structure at locations along their respective lengths, said upper and lower support legs and said lower support platform having substantially wave-transparent construction, and said lateral spaced apart relation of said lower support legs being wider than that of said upper support legs.

29. Jack-up type offshore platform apparatus comprising a floatable upper platform, a plurality of elongated support legs in laterally spaced apart relation to each other and respectively engaging said upper platform for vertical slidable movement with respect thereto, each of said support legs being at least 250 feet long and having an upper length portion and a lower length portion, said lower length portion of each leg being formed by a pair of substantially empty upper and lower cylinders arranged in telescoping slidable relation with each other, said upper cylinder of each leg being at least 40 feet long and having a closed upper end and an open lower end, and said lower cylinder of each leg being at least 40 feet long and having an open upper end and a buoyancy tank on and closing its lower end, means on each said support leg for introducing fluid under presSure into, and for discharging the same from the interior of its said cylinders for inducing said telescoping slidable movement relative to each other and independently of such movement of said cylinders on any other of said support legs, means on each of said lower cylinders for admitting and discharging sea water into and from the interior thereof, and means for locking together each of said pairs of upper and lower cylinders, respectively, at locations along the lengths of their said relative movement, a horizontal lower support platform structure attached to and extending between said lower ends of all of said upper cylinders whereby said support legs project upwardly a uniform height therefrom, and means for attaching said upper platform to said upper length portions of said support legs.

30. Jack-up type offshore platform apparatus according to claim 29 wherein said lower support platform structure and said upper length portions of said support legs have wave-transparent construction, and which further comprises jack means on said upper platform for jacking of the platform upwardly and downwardly along the lengths of said support leg upper length portions.