US2907172A

US2907172A - Method and apparatus for constructing offshore drilling platforms

Info

Publication number: US2907172A
Application number: US534932A
Authority: US
Inventors: Wilfred S Crake
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1955-09-19
Filing date: 1955-09-19
Publication date: 1959-10-06
Anticipated expiration: 1976-10-06

Description

Oct; 6, 1959 Filed Sept. 19. 1955 W. S. METHOD AND APPARATUS FOR CONSTRUCTING OFFSHORE DRILLING PLATFORMS 6 Sheets-Sheet 1 76 7s 76 I @111 A V 1% 74 \i/m E x E x

X

32 I ,23 ,22 33 X l2 I3 :2 .ZTIJEEILZZZZZZZZII::iiiijjji lmf F i i FIG 2 FIG I INVENTOR W. S. CRAKE BY M HIS AGENT Oct. 6, 1959 W. S. CRAKE Filed Sept. 19. 1955 6 Sheets-Sheet 2 l2 X X x 3| ,I4 22 33 ;I3 o J O M:

I? m 9- w FIG 3 77 7,6 76 77 u fifi FIG 4 INVENTOR w;s. CRAKE .Mwf HIS GENT Oct. 6, 1959 w. s. CRAKE 2,907,172

METHOD AND APPARATUS FOR CONSTRUCTING OFFSHORE DRILLING PLATFORMS Filed Sept. 19. 1955 6 Sheets-Sheet 3 m mas-2 E 2 I2 73 72 73 i 72 39 3| BO-"' 8O l6 I6 32 36 we FIG 5 37 j. 54

FIG IO FIG l2 V/38 FIG l3 FIG ll INVENTOR W. S. CRAKE HIS AGENT Oct. 6, 1959 w. s. CRAKE 2,907,172

METHOD AND APPARATUS FOR CONSTRUCTING OFFSHORE DRILLING PLATFORMS Filed Sept. 19. 1955 6 Sheets-Sheet 4 FIG.6

l6 87 x j W5 1 75 8| 5 FIG 7 a 73 so Y S INVENTOR 8| W. S. ORAKE FIG. 8 BY w HIS GENT Oct. 6, 1959 w. s. CRAKE METHOD AND APPARATUS FOR CONSTRUCTING OFFSHORE DRILLING PLATFORMS 6 Sheets-Sheet 5 Filed Sept 19. 1955 INVENTOR W. S. GRAKE BY $M J HIS AGENT I Oct. 6, 1959 w. s. CRAKE ,9 7,

METHOD AND APPARATUS FOR CONSTRUCTING OFFSHORE DRILLING PLATFORMS Filed Sept. 19. 1955 6 Sheets-Sheet 6 N co X m E H] w w INVENTOR w. s. 'CRAKE BY dbl?! HIS AGENT United States Patent IMETHOD AND APPARATUS FOR CONSTRUCTING OFFSHORE DRILLING PLATFORMS Wilfred S. Crake, Houston, Tex., assignor to Shell Development Company, New York, N.Y., a corporation of Delaware Application September 19, 1955, Serial No. 534,932

Claims. (Cl. 61-465) This invention relates to marine foundation structures and pertains more particularly to offshore platforms for drilling oil and gas wells and to methods for constructing said platforms.

At present, one type of stationary platform commonly used for offshore drilling is erected at an offshore location by driving a number of piles into the ocean floor and then constructing a complete platform on top of the piles above the level of the wave action. Piles used in this type of ofishore platform may be of wood or cement but are generally elongated tubular steel members.

Instead of employing a plurality of individual piles as a substructure for the platform, it is also a common practice to use a substructure which is constructed in the form of a large template, preferably composed of a single section comprising a group of spaced hollow steel columns rigidly held together by structural crossbracing. Piles are then driven through the hollow template legs to the depth required for foundation support purposes. The piles are then affixed to the template and cut-off at predetermined levels. The columns are normally made of a predetermined length of pipe or casing so as to extend from the ocean floor at the offshore drilling location to a point above the average wave level.

Alternative type of substructure for an offshore drilling platform is formed by a plurality of detachable pier sections which are secured together at the drilling site and sunk to the ocean floor. Each pier section is an elongated open work steel structure which may be generally rectangular in cross section and composed of a plurality of tubular columns suitably braced together by means of conventional structural girders and cross members to form a strong load-carrying structure having a high degree of rigidity. Piles are then driven through the hollow legs.

Mounted upon the selected substructure (that is, upon piles, fabricated template, or pier sections) is a large platform from which drilling operations are conducted. Placement of a drilling platform upon a substructure at an offshore location is both diflieult and dangerous. One type of platform is constructed on the substructure at the drilling site by connecting together the necessary girders or other structural elements and then covering them with suitable flooring. Alternatively, the platform may be fully fabricated on shore and then transported to the offshore drilling location upon a barge. The platform is generally constructed of a plurality of parallel structural trusses extending longitudinally and transversely of the area of the platform and intersecting each other at a plurality of points to form a generally rectangular box-like open work structure having a surface area of requisite dimensions for its intended use as a working platform. This structural framework of the platform is then covered by suitable flooring material upon which a conventional drilling derrick and suitable drilling equipment may be mounted.

The most diflicult operation in constructing an offshore ice drilling structure is to mount the platform upon the substructure. When a platform is floated into position above an offshore substructure, the barge or barges carrying the platform are floated through, or on either side of, the substructure and are subsequently partially flooded until the platform rests on the top of the substructure. The lifting barges .or pontoons are then towed away.

It is also a common practice, at times, to employ a large barge-mounted crane to hoist a platform from its transporting pontoons onto the top of the piles or substructure.

Due to the tremendous weight of the platform being transferred to the substructure, it will be appreciated that this operation can only be carried out at a time when the ocean is very still, that is, when the wave action is very small. When even a moderate wave action exists, the pontoons carrying the platform, or the barge upon which the crane is mounted, are caused to rise and fall in such a manner with respect to the stationary substructure that platform cannot be readily lowered onto the top of the substructure without being smashed or greatly damaged. Thus, it may be seen that the time available for transferring a platform onto a substructure and offshore drilling location is considerably limited and it is not uncommon to have to wait two or three days before the seas subside to a point where this operation can be carried out safely.

Although hydraulic means have been commonly used to lift or gradually let down heavy loads, it must be particularly stressed here that such systems are not satisfactory to accomplish the purposes of this invention for the reason that hydraulic liquids, being incompressible, are not quite capable of fully absorbing and neutralizing the jarring shocks which are bound to occur when handling extremely heavy loads under average offshore weather and Wave conditions.

It is therefore the main object of this invention to provide for this purpose a combined hydraulic and pneumatic control system wherein the main lifting efiort is exerted by hydraulic means capable of eflectively handling a load of any desired weight, and wherein pneumatic means are used in auxiliary cooperation with said hydraulic means to provide an additional cushioning effect against critical impacts, the fluid used in said pneumatic means being, of course, of a compressible nature.

Another object of this invention is to provide a method and apparatus for transferring heavy loads at sea from a floating vessel, barge or pontoon to a stationary structure.

A further object of this invention is to provide a hydraulic and pneumatic system for mounting a drilling or producing platform on the top of a plurality of piles or other suitable substructure fixedly positioned on the ocean floor.

Another object of the present invention is to provide an improved method whereby a drilling or producing platform may be erected in any water depths commonly encountered at an offshore location with a minimum of difliculty and expense.

These and other objects of this invention will be understood from the following description taken with reference to the drawing, wherein:

Figures 1 and 2 are front and side elevations showing the barge structure of the present invention with a drilling or producing platform mounted thereon while being transported to the offshore drilling location.

Figure 3 side and Figure 4 end views are partially in cross-section illustrating the transporting barge of the present invention with a drilling platform mounted thereon in position above a suitable substructure at an offshore location prior to the lowering of the platform onto the substructure.

Figure 5 is an end view, partially in cross-section, illustrating the positions of the transporting barge, drilling platform and substructure at a time when the platform has been lowered onto the substructure.

Figures 6, 7 and 8 are enlarged detailed views in crossse'ction of the hold-down device carried 'by the drilling platform to establish contact with the piles or tubular members of the substructure, said figures illustrating various stages in the operation of lowering the drilling platform onto the substructure.

Figure 9 is an end view in partial cross-section of the barge of the present invention showing shock-absorbers mounted on the walls of the barge to contact the substructure.

Figure 10 is a view in cross-section of a hoisting and shock-absorber cylinder carried by the barge of the present invention.

Figure 11 is an enlarged cross-sectional view illustrat ing the connection between the top of the hoisting cylinder of Figure 10 and the platform.

Figure 12 is a plan View of the hoisting cylinders of Figure 10 positioned in its support tower.

Figure 13 is a side view, partly in cross-section, of the structure of Figure 12.

Figure 14 is a cross-sectional side View of another embodiment of the hoisting and shock-absorbing device illustr'ated in Figure 10.

Figure 15 and 16 are cross-sectional 'sideviews showing two positions of auxiliary shock absorbers carried by the platform.

Figure 17 is a flow diagram of a hydro-pneumatic control system of the present invention.

Referring to Figure 1 of the drawing, an operating platform 11 adapted to be mounted on an offshore structure is positioned on a plurality of towers 12 mounted on the top of a barge 13 for transpotirng the operating platform 11 to a drilling location. The barge 13 is provided with a slot 14 in one end thereof, said slot 14 being of such Width that portions of the barge 13 may extend on either side of a substructure 15 (Figure 5 which is firmly erected on the ocean floor. The vertical members 16 of the substructure 15 are preferably tubular and extend a suitable distance above the surface of the water so that the tops thereof are above the wave action. If desired, the vertical members 16 of the substructure 15 may be reinforced by suitable cross-bracing 17.

Instead of employing a barge 13 having a slot 14 therein, the barge may, alternatively, comprise two-or more Pontoons rigidly secured together in such a man- 'ner as to transport an operating platform to the drilling site said pontoons bracketing the substructure while being unloaded. As shown in Figures 1 and 2, and in greater detail in Figure 9, the barge 13 is preferably equipped with shock absorbers and centering means which are mounted on the sides of the pontoon forming the slot and in the wall of the pontoon forming the closed end of the slot.

The shock absorbers and centering means may be of any suitable type comprising, for example,

horizontal bars

21, 22 and 23 secured to

piston rods

24, 25 and 26, each of which is attached to a piston such as shown at 27mounted for sliding movement inside a cylinder 28 positioned inside the hull of the barge 13. In their retracted position the

horizontal bars

21, 22 and 23 are substantially flush with the hull of the barge 13 along the walls of the slot 14 thereof, and are extensible therefrom by pneumatic or hydraulic pressure means so as to contact the vertical members 16 of the substructure 15.

Each of the towers 12 (Figures 1, 2 and 4) of the barge 13 is provided with hydro-pneumatic lift means 31, 32, 33, and 34 for lifting the operating platform off the tops of the towers 12 and raising it to a height greater than the top of the substructure on which the platform is to be positioned. As shown in Figure 10, each of the hydro-pneumatic hoists 31, 32, 3 3 and 3d comprises a 1 cylinder 35 containing a piston 36 therein mounted for vertical sliding movement, said piston 36 being equipped with packers 37. The piston rod 38 is tubular and enters the cylinder 35 through a head 39 secured thereto. An inlet port 40 is provided near the outward end of the hollow piston rod 38, whereby air pressure can be introduced through a hose 41, port 41!, and piston rod 38 into the cylinder 35. The air is suplpied through hose 41 from a compressed air supply source (not shown) of conventional type.

The lower end of the cylinder 35 is provided with port means 42 to which a hose 43 is connected for introducing liquid under pressure from a hydraulic pump (not shown) into the cylinder 35 below the piston 36. The top of the piston rod 38 and the bottom of the cylinder 35 are preferably provided with universal joint or spherical alignment means 44 and 45 which allow limited self-alignment of the movement of the loads, such as the operating platform 11 on the barge 13.

As shown in Figure 11, the operating platform 11 may be secured to the top of the piston 38 of the hydropneumatic hoist, by means such as an extension rod 48 fixedly attached to the top of the piston 38 and extending through the opening 49 in the operating platform 11, which opening is preferably tapered to allow a limited change in position of the extension rod 48 during alignment of the load on the hydro-pneumatic hoists. The operating platform 11 may be secured to the extension rod 48, as by means of a large wing nut 50. If desired, shock absorbing pads 51 may be provided around the extension rod 48, said pads 51 being mounted between the wing nut and a plate member 52 which is slidably mounted on the upper surface of the operating platform 11. As shown in Figures 12 and 13 the cylinder 35 of the hydro-pneumatic hoist is provided with a plurality of shock absorbing pads 54 mounted between the casing cylinder 35 and the tower 12.

The essential feature of the structure of the hydropneurnatic hoist shown in Figure 10 is that, by filling a portion of the cylinder 35 with a hydraulic fluid pumped in through conduit 43, and the other portion of said cylinder and hollow piston rod 38 with compressed air pumped in through conduit 41, a hydraulic hoist provided with an air cushion is made available for hoisting loads off the barge while at the same time compensating for and softening any violent shocks due to vertical movement of the barge caused by wave action. I

Another form of a hydro-pneumatic hoist contemplated for use with the present invention is shown in Figure 14 as comprising a pair of

vertical cylinders

57 and 58, wherein cylinder 57 is provided with a hollow piston rod 59 and solid piston 60 equipped with packing 61, movement-limiting ring 62, and spherical alignment means 63 and 64, which are substantially identical in construction with those shown in Figure 10. Cylinder 57 is provided near the bottom thereof with an inlet port 65 and hose 66 through which liquid can be introduced into the bottom of cylinder 57. A port or conduit 67, connecting the bottoms of

cylinders

57 and 58, allows the passage of hydraulic pressure liquid between the cylinders. Cylinder 58 is provided near the top thereof with an inlet port 68 and hose 69 for introducing compressed air. The two

cylinders

57 and 58 may be mechanically coupled together by any desired means.

In the event that it is not desired to Secure rigidly the top of the piston rod 38 (Figure 11) to the operating platform 11, the bottom of said platform (Figure 3) may be provided with a recessed portion. 71 directly above each of the hydro-pneumatic hoists 31, 32, 33, etc. into which the top of the piston rod 38 would fit, thus preventing movement of the operating platform 11 relative to the barge 13 in a horizontal plane. While similar recesses could be provided in the bottom of the operating platform 11 into which the tops of each of the vertical 5 members 16 of the substructure wean fit, platform 11 is preferably provided with a plurality of downwardly extending mounting tubes or feet 72. These feet 72 may extend a short distance below the bottom of the operating platform 11 or may be mounted a substantial distance therebelow as illustrated in Figures 1 to 5 of the drawing. Preferably, at least four of these mounting tubes 72 are provided and it is often advantageous to provide at least one mounting tube 72 for each vertical member 16 of the substructure 15. The spacing of the feet 72 is equal to that of the vertical members 16 of the substructure 15 so that, when the operating platform 11 is lowered into position, one of the mounting tubes 72 is aligned with each of the vertical tubular members 16. To facilitate the accurate setting of the mounting tubes 72 on the upper ends of the vertical tubular members 16 of the substructure, either the tops of the vertical members 16 or the bottoms of the feet 72 may be provided with cone-shaped alignment means 73 or other suitable alignment means.

As illustrated in Figure 3 of the drawing, each mounting tube 72 is supported a short distance below the operating platform 11 in a rigid manner, as by being welded to steel support plates 74. The support plates 74 are in turn welded to the bottom of the operating platform 11 and are so positioned that a cable 75 may run from cable winch means such as a winch or hoist 76, driven by a prime mover such as a motor 77, down through a hole 78 in the operating floor 11 and down into the mounting tube 72, where it is connected to a hold-down device 80. Alternatively, the winches 76 may be mounted on the underside of the operating platform.

The hold-down device 80 of Figure 3 is shown in enlarged detail in Figures 6, 7 and 8 as comprising a heavy metallic weight member 81 which is preferably tapered to facilitate its entry into the alignment collar 73 and into the vertical member 16 of the substructure. The upper portion of the weight member 81 is constructed in the form of a tapered cone 82 and has slidably mounted thereon suitable slips or toothed elements 83 which are fixedly secured to a ring member 84 which is in turn slidably mounted on a shaft 85. The teeth on the slips 83 are formed so that the hold-down device can drop downwardly but cannot be raised upwardly by cable 75. When the hold-down device 80 is lowered into the top of the tubular members 16 of the substructure 15, as shown at Figure 7, the teeth of the slips 83 contact the inner wall of the tubular member 16 and, by pulling upward on the cable 75, are set against the walls. Each hold-down device 80 is provided with a yoke 86 against which the slips 83 seat when tension is released on cable 75 and an upward pull is applied to bridle pull lines 87 After the slips 83 are disengaged from the inner wall of the tubular member 16, the entire hold-down device 80 may be removed upwardly by pulling both the cable 75 and bridle lines 87 together.

If desired, the mounting tubes or feet 72 (Figure 3) may be provided with auxiliary shock absorbing devices such as those illustrated in Figures 15 and 16. In this embodiment, the mounting tubes 89 form the hollow rod of a piston 90 slidably mounted for vertical movement in a cylinder 91 which is welded in a fluidtight manner to the bottom of the operating platform 11. Conduit means 92 pass through the operating platform 11 and communicate with the interior of the cylinder 91 whereby compressed air pressure may be applied to the cylinder 91.

The piston 90 is also secured to a hollow rod 93 which passes in a fluidtight manner through the operating platform and is threaded at its upper end, whereby a locking nut 94 can be turned down so as to hold the piston One form of a hydro-pneumatic control system for use with the present invention is shown in Figure 17 as comprising an air compressor 95, an air receiver 96, a hydraulic .pump 97, a fluid sump 98, and a plurality of hydraulic accumulator cylinders 106. The hydropneumatic hoists which are mounted on the barge of the present invention are diagrammatically represented in Figure 17. by cylinders having conduits from the bottom thereof manifolded through valves 99,while the cont'uits 41 from the top of said cylinders 35 are manifolded through control valves 100. All of the

valves

99 and 100 are power-actuated valves of any well known type which may bev operated electrically, pneumatically, hydraulically or mechanically. The controllines from all the valves are preferably run to a remote central control station 101. This remote control station 101 also operates a hydraulic fill valve 102, a hydraulic drain valve 103, a compressed air fill valve 104 and an air discharge valve 105. If desired, all of the hoist motors 77 (Figure 5) may also be controlled from this remote control point.

In constructing an offshore installation in accordance With the present invention, a series of piles, pier sections or a template 15 (Figure 3) comprising a plurality of vertical members 16 are installed on the ocean floor at the drilling site. The pilings or vertical members 16 are preferably tubular and hence adapted to receive the holddown devices 80, previously described. In the event that solid piles are used, the holddown devices may comprise clamp means which fit on the outside of the piles and are attached to cables which would run outside the mounting elements or feet.

After the substructure 15 (Figure 3) is in place, the drilling platform 11 is transferred from a dock (not shown) to the towers 12 of the barge 13 (Figure 2) with the hydro-

pneumatic hoists

32 and 33 in their retracted position. The platform is preferably secured to the tops of the hydropneumatic hoists 32 and 33 contained in towers 12 in any suitable manner, as by wing nut 50 as shown in Figure 11.

The barge 13 carrying the operating platform 11 is then floated or towed to the drilling site. Prior to bringing the barge in position with regard to the substructure 15, the cylinders 35 and pistons 38 (Figures 3 and 10) are filled with compressed air pumped in through conduit 41. The compressed air is admitted to the cylinders until the pressure being applied to the pistons 36- (Figure 10) is substantially equal to that necessary to just raise the load or platform 11 clear of the tops of the towers 12. Hydraulic fluid is then pumped into the cylinders 35 through conduits 43 and the operating platform 11 is raised to the extended position of the pistons 38 of the hydropneumatic hoists 32 and 33, as shown in Figures 3 and 4.

The barge is then positioned so that the substructure 15 .is within the slot 14 of the barge 13 (Figures 3, 4 and 5). In the event that the slot 14 in the barge 13 is wider than the outermost dimension of the substructure 15, the

horizontal bars

21, 22 and 23 of the shock absorbers or centering means are expanded (Figure 9) until they contact the outer walls of the substructure 15 and prevent any substantial horizontal movement of the barge 13 with relation to the substructure 15. Centering of the sub-- structure 15 within the slot 14 of the barge 13 in this manner aligns the tubular mounting elements 72 on the bottom of the operating platform 11 with the tops of the vertical members 16 of the substructure 15.

With the feet 72 of the operating platform positioned over the vertical members 16 of the substructure 15, cable 75 is unwound from all of the hoists 76 so as to lower the pulldown devices through the feet 72 and into the vertical tubular members 16 of the substructure 15.

With the hold-down devices inside the legs of the substructure 15 (Figures 4 and 7),'the slips 83 are set against the inner walls of the tubular legs 16 upon the application of slight upward pull on the cable 75. At

this point the operating platform 11 and the substructure 15 are rigidly held together -by cables 75 against vertical movement withfelation to each other. Thus, any rise or fall of the barge '13 due to wave action on the barge is absorbed in the hydro-pneumatic hoists 31 to 34 thereof by the compressing and decompressing of the air in the cylinders 35. v

As more power is applied to the hoists 76, more or the cable 75 is reeled in and the operating platform 11 is slowly pulled downwardly against the hydro pneurnatic pressure of the hoists 31 to 34. Asthe operating platform 11 is slowly pulled downwardly by cable 75, the valves 99 and 103 (Figure 17) in the hydraulic line from the hydro-pneumatic hoist chambers 35, are manually opened so that the hydraulic fluid in the cylinders 35 is slowly bled to the sump 98. The hydraulic relief valve 103 also is capable of opening in an emergency to prevent excessive increase in pressure in cylinders 35 due to the action of hoists 76. The hydraulic fluid is bled from the cylinders 35 at a rate such that the pneumatic absorbing pressure in the cylinders remains about constant.

Since a rigid tie by cables 75 is maintained between the operating platform 11 and the substructure 15 and since wave action on the barge 13 is compensated for by the alternate compression and de-compression'of the air in the cylinders 35 of the hydro-pneumatic hoists 31 to 34, a gradual and controlled contact is made between the feet 72 on the bottoms of the operating platform 11 and the legs 16 of the substructure 15 (Figures and 8) by continued action of the hoists 76 An important aspect of this invention is of the compression ratios of the air and fluid within the cylinder 35 of the hydropn'eumatic hoists 31 to 34 may be varied depending upon the heights of the waves to minimize and substantially eliminate the rapid movement of the barge due to wave action. The compression ratios within the cylinders 35 'may be changed either by changing the pressure of the air introduced thereto or by changing the height of the air column within the cylinder as the hydraulic fluid is withdrawn therefrom. In most operations it is preferred to maintian the air pressure within the cylinders 35 at a substantially constant value while removing the hydraulic fluid beneath the air cushion as the load is'pulled down onto the substructure 15.

With the platform 11 positioned on the substructure 15 as shown in Figure 5, the hydraulic fluid in the cylinders of the hydro-pneumatic hoists 31 to 34 is withdrawn and subsequently the air in said cylinders is released. The fastenings 5t (Figure ll) are then disconnected and the pistons 38 of the hydro-pneumatic hoists 31 to 34 are retracted. The barge 13 is then free to be removed. The hoists 76, through cables 75 and hold-down devices 80, continue to anchor the operating platform to the top of the substructure 15. If desired, however, the feet 72 may be welded or temporarily bolted or otherwise secured to the tops of the vertical members 16 of the substructure, in any well known manner.

The removal of the platform 11 from the substructure 15 is accomplished by reversing the above-described operations. The'barge 13 is first placed in position near the substructure 15, air pressure is applied to the hydropneumatic hoists 31 to 34 to raise the pistons 33 thereof in position against the bottom of the operating platform 11, fastenings (Figure '11) are connected to secure the pistons to the bottom of the operating platform ll, air pressure in the hoists is increased until it is sufficient to support the weight of the platform 11, and excess hydraulic pressure is then applied to the hoists 31 to 34 as tension is relaxed slowly on the cable 75 by the hoists 76 to allow the hydraulicpress'ure to raise the operating platform 11 to thefull extension of'the pistons 38 of the hydro-pneumatic hoists'3l to 34. The hold-down devices 80are'thendisengaged from the inner walls of the legs of thesubstructure 15 and'are'withdrawn upwardly. The

8 barge carrying the drilling platform 11 and any drilling equipment mounted thereon are now free to be transferred to another drilling location.

I claim as my invention:

1. In a method for erecting an oifshore structure on piling sunk in the ocean floor and-extending to a level above that of wave action, the steps of supporting a platform on floating means, raising said platform to a level higher than said piling by the hydraulic pressure of an incom'ressible fluid and the pneumatic pressure of a comp- :ole fluid, positioning said platform above said piling by straddling'said piling by said floating means, the points of support of said platform being on the opposite sides of said piling, and pulling said platform down on the tops of said piling against the cushioning pressure of at least one of said fluids.

2. The method of erecting an ofishore well-drilling structure which comprises vertically positioning a plurality of piles at an olfshoe location to form a stationary substructure wherein the upper ends of the piles extend above the wave action level of the water, transporting to the offshore location an operating platform on barge means, said barge'means having a slot formed therein, said slot being wider than the stationary substructure and being open at least at one end, raising the platform by incompressible hydraulic and compressible pneumatic pressure fluids to a height greater than the upper ends of the piles, positioning'said barge means adjacent'and astraddle said substructure with said platform'suspended thereabove, securing said platform to said substructure against vertical movement while permitting the barge means to rise and fall with wave action, pulling said platform down into contact with said substructure against'the cushioning pressure of the hydraulic and pneumatic pressure fluids of said hoist means thereby transferring the load of said platform from said barge means to said substructure, and subsequently withdrawing said barge means from a position adjacent said substructure and from under said platform.

3. Apparatus for erecting an offshore structure on piling extending to a level above that of wave action, comprising floating means, a platform, a plurality of lifting means, adapted to support said platform on said floating means, each of saidlifting means comprising cylinder and piston elements, one of said elements being fixedly connected to said floating means and the other to said platform, a supply of incompressible hydraulic fluid, a supply of compressible'pneumatic fluid, means for applying said fluids to said cylinder and piston elements, whereby said platform is lifted above said piling, the spacing between said lifting means being suflicient to straddle the'piling therebetween andmeans for lowering said platform onsaid piling against the cushioning pressure of at least one of saidfluids.

4. Apparatus for transferring'heavy loads 'at' sea from floating barge means to astationary'structure fixedly anchored to the ocean floor, said apparatus comprising barge means adapted to be positioned adjacent said stationary structure, said barge means having a slot formed therein, said slot being wider than the stationary structure and being open at least at one end, hydro-pneumatic lift means carried by said barge means for supporting a load to be transferred to said stationary structure, said hydro-pneumatic lift means being adapted to raise said load above said stationary structure, cable Winch means carried by said load and adapted to extend therebelow to said stationary structure, connecting means carried by said'cable winch means for fixedly connecting saidwinch means'to said stationary structure to prevent any downward vertical movement due to wave action betwee'n'said load and said stationary structure, a source of compressed air and a source of hydraulic pressure'fluid for said hydro-pneumatic lift means, and pr'irne-'mover= means'for actuating said winch means to pull said load 'down'to said station- 9 ary structure against the forces exerted by said hydropneumatic lift means wherein said compressed air compensates for rise and fall of said barge means due to wave action.

5. Apparatus for transferring heavy loads at sea from floating barge means to a stationary structure having a plurality of vertical tubular columns fixedly anchored to the ocean floor, said apparatus comprising barge means adapted to be positioned adjacent said stationary structure, said barge means having a slot formed therein, said slot being winder than the stationary structure and being open at least at one end, at least four hydro-pneumatic lift means carried by said barge means for supporting at four points a load to be transferred to said stationary structure, said hydro-pneumatic lift means being adapted to raise said load above said stationary structure, cable winch means carried by said load and adapted to extend therebelow to said stationary structure a cable partially wound on each of said cable winch means, slip-type connecting means carried at the end of each cable and 20 adapted to enter and be anchored within a tubular column of said stationary structure to prevent any down ward vertical movement due to wave action between said load and said stationary structure, a source of compressed air and a source of hydraulic pressure fluid for said hydropneumatic lift means, and prime mover means for actuating said winch means to pull said load down to said stationary structure against the forces exerted by said hydropneumatic lift means wherein said compressed air compensates for rise and fall of said barge means due to wave action.

References Cited in the file of this patent UNITED STATES PATENTS 1,873,807 Arnold Aug. 23, 1932 2,210,408 Henry Aug. 16, 1940 2,364,865 Mattingly Dec. 12, 1944 2,475,933 Woolslayer et a1. July 12, 1949 2,736,172 McChesney Feb. 28, 1956 2,771,747 Rechtin Nov. 27, 1956 2,817,212 Stubbs Dec. 24, 1957