US3094847A - Offshore platform structure - Google Patents

Description

June 25, 1963 1. c. POGONOWSKI 3,094,847

\ OFFSHORE PLATFORM STRUCTURE Fi led Oct. 19, 1960 2 Sheets-Sheet 1 hzl INVENTOR l. C. POGONOWSKI BY Q-J-(I'M HIS AGENT June 25, 1963 1. c. POGONOWSKI 3,

OFFSHORE PLATFORM STRUCTURE Filed 001,. 19, 1960 2 Sheets-Sheet 2 FIG. 4

A i I FIG. 5 FIG. 6 FIG. 7

FIG. IO

INVENTOR l. C. POGONOWSKI HIS AGENT 3,094,847 OFFSHGRE PLATFORM STRUCTURE Ivo C. Pogonowski, New Orleans, La., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Oct. 19, 1960, Ser. No. 63,616 4 Claims. (Cl. 61-46) This invention relates to marine foundation structures and pertains more particularly to oifshore platforms for drillingoil and gas wells and to methods for constructing platforms of this type.

At present, one type of a stationary platform structure commonly used for offshore drilling or producing of wells makes use of 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 cross-bracing. Piles are then driven through the hollow template legs or columns to the depth required for foundation support purposes The piles are then fixedly secured to the template, preferably by welding and then cut off at predetermined levels. The columns of the template 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.

Mounted upon the substructure formed by the template and piles is a large platform on which drilling or producing operations are con-ducted. 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 required 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 or producing equipment may be mounted. It is common for the platform to have a plurality of legs extending downwardly therefrom which are so constructed that they are in alignment with and seat within the tops of a plurality of legs or columns of the template or in the piles installed therein.

Offshore platform structures of the above-described type utilizing a unitary template through which piles are driven and on which a platform is mounted have been used for several years in drilling and producing locations on the Continental Shelf along the coasts of Louisiana and Texas. The well locations are generally several miles from shore. These templates are of enormous weight and as the selected drilling locations have been in deeper and deeper water it has been found to be impossible at some water depths to transport and install an offshore platform structure of the template type because of the great size and weight of the template. Merely to divide the template into a number of sections that were installed separately and connected above sea level at the drilling location did not prove efiicient as it was difiicult and almost impossible to align exactly the various segments of the structure. Deck sections consequently did not have the proper stress carrying capacity because of misalignment of the load carrying trusses. Also there is no under water continuity of a sectionalized structure of this type thus reducing its ability to withstand forces 3,094,847 Patented June 25, 1963 due to wind and wave action and reducing the load carrying capacity.

It is therefore a primary object of the present invention to provide an offshore platform structure consisting of a plurality of structural segments adapted to be aligned exactly with each other both above and below the surface of the water.

A further object of the present invention is to provide a structure for an offshore platform on which a platform or deck section can be readily and accurately aligned.

Another object of the present invention is to provide a method and apparatus for constructing an offshore platform structure possessing rigid continuity of structure below the water line to give it additional strength.

Still another object of the present invention is to provide an offshore platform structure composed of a plurality of sections whose weight and size are that which could be handled by presently available construction equipment at ofishore locations.

Another object of the present invention is to provide a sectionalized oifshore platform structure wherein each section is provided with means for aligning and guiding it into place with the adjacent sections.

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

FIGURE 1 is an isometric view of one of the sub structure sections of the present oifshore platform structure positioned on the ocean door with the ends of all of the legs extending into the ocean floor somewhat, while the tops of the long legs extend to a point above the surfaceof the water;

FIGURE 2 is an isometric view of a mating section of the substructure of the present platform prior to it being raised and moved into position so that its short upper legs can be lowered down over the guide piles drive through the short lower legs of the substructure section of FIG- FIGURE 3 is a view in enlarged detail of a line or conduit positioned along one of the legs of the substructure section of FIGURE 1. The line is to be used to cement underwater the annulus between the leg and the guide pile;

FIGURE 4 is a diagrammatic view illustrating a tug towing a barge with a substructure section of the present invention to a position where the crane barge may engage FIGURE 5 is a schematic view showing a substructure section in place on the ocean floor while a crane barge lowers a second substructure section into place using guide piles as a homing device;

FIGURE 6 is a schematic View illustrating the substructure of the present platform structure in place on the ocean floor at the time the deck section is being lowered into place;

FIGURE 7 is a schematic View illustrating the completely assembled offshore platform structure of the present invention;

FIGURE 8 is -a view taken in enlarged cross-sectional detail of auxiliary guide means which may be employed to connect close to sea bottom, two sections of the substructure of the present platform in addition to guide piles which are cemented underwater to one section and welded above water to the other;

FIGURE 9 is a schematic plan view of the completed 7 structure of FIGURE 6 after the center pile has been installed through field installed bracing placed above water surface; and,

FIGURE is an exploded diagrammatic view of block-like elements which would fit together to form one type of an offshore platform in accordance with the present invention as illustrated in plan view in FIGURE 9; the two upper blocks of FIGURE 10 representing the substructure sections shown in isometric view in FIG- URES 1 and 2.

Referring to FIGURE 1 of the drawing, a substructure section in accordance with the present invention is shown as comprising a plurality of long vertical tubular legs 11, 12, 13 and 14 in spaced relationship with each other and interconnected by cross-bracing members 15 arranged in any suitable configuration, preferably in a manner to provide the greatest rigidity to the structure. Positioned in spaced relationship with the long legs 11, 12, 13 and 14 and in planes parallel thereto and at right angles to each other are a plurality of short, lower, tubular vertical legs 16, 17, 18 and 19 which are connected together and to the long legs by suitable bracing members 20. Additionally, diagonal braces 21 are provided between the long legs or columns 11, :12, 13 and 14 and the short legs or columns 16, 17, 18 and 13, if desired. Preferably, the lower ends of the diagonal braces 21 are in open communication with the interior of the short legs 16, 17, 18 and 19 through the walls thereof so as to serve as conduit means for conducting a cement slurry to the short lower legs 16, 17, 18 and 19. As shown in FIG- URE 3, a small-diameter vertical conduit or cement pipe 22 may run down the outside of the vertical column .11, the lower end of the cement pipe being in open communication with the upper end of the diagonal brace 21 through the wall thereof so that cement slurry may be injected into the diagonal brace 21 or through a smaller separate conduit and hence pumped down into the annulus of the short leg 16 and guide pile 35. Similar cement pipes would be provided for injecting cement slurry into the other short legs 17, 18 and 19.

In the event that the present offshore structure is to be positioned on a soft ocean bottom, it is preferred that vertical stabilizing steel plates or other suitable material be secured to the outside of the legs as at 23 and 24. These plate skirts 23 and 24 are illustrated in FIGURE 1 as being positioned entirely below the bottom 25 of the body of water while the long legs 11, 12, 13 and 14 extend upward-1y a distance at least above the surface of the water 26. The section of FIGURE 1 is illustrated with piles 30, 31, 32 and 33 which extend through the long legs 11, 12, 13 and 14 and deep into the ocean floor. Extending outwardly from the long legs 11, 12, 13 and 14 are bracing members 34 which are adapted to be secured in any suitable manner, as by welding or bolting, to guide piles 35, 36, 37 and 38, after the guide piles have been driven into place through the lower short legs 16, 17, 18 and 19 of the substructure section. For ease of illustration, the guide piles 35, 36, 37 and 38 have been shown in broken lines rather than solid lines. If desired, guide keyways 40 may be secured, as by welding, outwardly on the lower short legs 16, 17, 18 and 19 and extend substantially the length thereof. As shown in greater detail in FIGURE 8, the longitudinal keyway 40 is designed to receive a key 41 carriedon a downward extension from an upper short leg of an adjacent section. The lower short legs 16, :17, 18 and 19, while being illustrated as being about half the length of the long legs 11, 12, 13 and 14, may be of any length desired but preferably extend at least above the ocean floor 25. The lower short legs .16, 17, 18 and 19 preferably include rubber packers properly arranged to exclude soil from leg and guide pile annulus for effective cemented connection.

'In FIGURE 2, a substructure section in accordance with the present invention is shown which would be installed adjacent the section shown in FIGURE 1. The substructure section of FIGURE 2 is provided with a pair of short upper legs 42 and 43 which are short tubular members of a length and diameter to slide down over the guide piles 37 and 38 of FIGURE 1 and form with the short lower legs 18 and 19 of FIGURE 1, a complete leg having a length equal to the long legs 11, 12, 13 and 14 of FIGURE 1, and the similar vertical tubular legs 44, '45, 46 and 47 of FIGURE 2. The legs are interconnected with suitable braces 48 and the lower ends of the legs are provided with stabilizing skirts 49 and 50. In addition, the sbustructure section of FIGURE 2 is provided with two short lower legs 52 and 53 extending outwardly from the long legs of the section at right angles to the direction taken by the upper short legs 42 and 43. The lower short legs 52 and 53 are provided with keyways 40 as described above, while the upper short legs 42 and 43 have downwardly extending vertical support members 54 and 55 to which are attached keys 41 as shown in FIGURE 8.

For ease of illustration, block-like segments A, B, C and D of FIGURE 10 are shown in exploded view. Two of the parts A and B represent the sections shown in detail in FIGURES 1 and 2, respectively. It will be apparent from studying FIGURE 10 that section C is identical with section B when turned at in a clockwise direction. Likewise, section D is identical to section A if section A were turned upside down and rotated 90. When two pairs of substructure sections as shown in FIGURES 1 and 2 are put together in a manner illustrated in exploded view of FIGURE 10', the resultant substructure of the offshore platform has a plan view as shown in FIGURE 9 of the drawing, with the central pile 56 being added later. While the offshore platform structure of the present invention has been described with regard to having components which are rectangular in shape which are adapted to be assembled together to make a rectangular substructure and platform as shown in FIGURE 9, it is to be understood that triangular or other configurations of the individual substructure sections may be employed, the essential feature being that adjacent legs of any two sections be shorter than the other legs and be adapted to pass over or contain within their entire length a guide pile adapted to be secured to the short legs by welding above water or cementing underwater or in any other suitable manner to form a leg equal in length to the other vertical support members of the substructure.

In erecting an offshore platform structure of the present invention, the substructure sections and deck section are prefabricated on shore. In FIGURE 4 of the drawing, a tug 60 is shown as towing a barge 61 containing the first section A (FIGURE 10) to the desired location where a crane barge 62 is located. The crane picks up the section A and lowers it to the ocean floor as shown in FIGURE 1 of the drawing. Files are then driven through legs 11, 12, '13 and 14 through the full length thereof and deep into the ocean floor. The legs or columns 11, 12, 13 and 14 may be sections of 33-inch diameter pipe while the piles driven therethrough are of pipe of a slightly smaller diameter (usually 30-inch diiameter piles). The piles 3t}, 31, 32 and 33 are then welded to the tops of the long legs 11, 12, 13 and 14 and if necessary cut off so that they are all even. Piles 35, 36, 37 and 38 (FIGURE 1) are then driven through the short lower legs .16, 17, 18 and 19, which legs may be 36-inch diameter pipe. By using the same size piles in the slightly larger diameter short lower leg, it is possible to subsequently pump cement into the short lower legs as will be described hereinbelow. After being driven, the piles 35, 36, 37 and 38 extend above the surface of the water.

As shown in FIGURE 5, the crane barge 62 then picks up section B of FIGURE 10 or the section shown in FIGURE 2 and stabs the short upper sleeves 42 and 43 (FIGURE 2) over the top of the guide piles 37 and 38 (FIGURE 1) at which time the keys 41 (FIGURE 8) carried on support members 54- and 55 (FIGURE 2) will pass downwardly into keyways 40 on the lower legs 18 and 19 (FIGURE 1) when the substructure B (FIGURE 5) is lowered by the crane barge 62 down through the water to .a level with that of section A. With the two sections A and B (FIGURE 5) assembled together, piles would then be driven down through legs 44, 45, 46 and 47 (FIGURE 9). Guide piles would thereafter be driven through the short lower underwater legs 52 and 53 (FIG- URE 2) and section C (FIGURE 10) would be stabbed over these guide piles and lowered into place. Subsequently, piles would be driven through the long legs of sectionC and guide piles through the short legs. It is apparent that the last section D would be stabbed down over the guide piles extending upwardly from sections A and C (FIGURE 10). After driving piles through all the long legs of section D, all of the piles extending above the water line would be welded or otherwise suitably connected to the legs through which they extended. This applies to the guide piles as well as the piles extending through the long legs of the various sections. At the same time all lateral braces such as the braces 34 of FIGURE 1 would be welded to short upper legs containing the guide piles.

Although not necessary in some installations, it is preferred that a central pile 56 (FIGURE 9) be driven into the ocean floor and connected by suitable lateral bracing to the adjacent legs. If desired a guide collar may be installed in the center of the open square before driving pile 56. After the erection of the substructure has been completed the deck 70 provided with downwardly extending leg 71 is lifted by the crane barge and lowered into place with the legs '71 aligning with and seating to a short distance within some of the piles of the substructure. Due to the size of many of these offshore installations it is necessary that the deck section be constructed in several mating sections which are later connected in the field. With the deck section in place, suitable equipment is moved on the deck to connect hoses to the cement pipes 22 (FIGURE 3) running down the legs of the substructure section and into the cross-bracing members 21 which terminate in the underwater short legs of the substructure. Cement is then pumped down into the annulus between the piles and the underwater short legs of the substructure to obtain underwater continuity of the structure.

I claim as my invention:

1. An offshore platform structure comprising a framework-type substructure made up of a plurality of prefabricated tubular-legged substructure sections adapted to be positioned on the floor of a body of water one at a time, each of said substructure sections having a plurality of long vertical legs of a length greater than the water depth when normally extending to the water bottom and a plurality of short vertical legs, cross-bracing members securing the long and short legs together to form a framework, at least one of said substructure sections having at least two short legs arranged in the lower portion of the section on one side thereof, a guide pile extending through each short leg and into the floor, said short leg guide piles extending upwardly at least above the water level, a pile extending through each of at least some of said long legs and into the floor, .and at least another of said framework substructure sections having at least two Short legs arranged on the upper portion of said section, said upper short legs being of a spacing and diameter sufficient to pass downwardly over the guide piles in the lower short legs of said other substructure section, the combined length of said upper and lower short legs being no greater than the length of said long legs.

2. An offshore platform structure comprising a framework-type substructure made up of a plurality of prefabricated tubular-legged substructure sections adapted to be positioned on the floor of a body of water one at a time, each of said substructure sections having a plurality of long vertical legs of a length greater than the water depth when normally extending to the water bottom, and

a plurality of short vertical legs, cross-bracing members securing the long and short legs together to form a framework, at least one of said substructure sections having at least two short legs arranged in the lower portion of the section on one side thereof so that the bottoms of the short legs extend to the floor of the body of water, a guide pile extend-ing through each short leg and into the floor, said short leg guide piles being secured to the short legs and extending upwardly at least above the water level, a pile extending through each of a plurality of said long legs and into the floor, and at least another of said framework substructure sections having at least two short legs arranged on the upper portion of said section, said upper short legs being of a Spacing and diameter suflicient to pass downwardly over the guide piles in the lower short legs of said other substructure section, said upper and lower short legs being arranged in coaxially displaced relationship on said guide piles and being fixedly secured thereto to form a leg equal in length to the long legs of said substructure sections, .a horizontally-disposed deck section supported on said substructure.

3. An offshore platform structure comprising a framework-type substructure made up of a plurality of prefabricated tubula-r-legged substructure sections adapted to be positioned on the floor of a body of water one at a time, each of said substructure sections having a plurality of long vertical legs of a length greater than the water depth and a plurality of short vertical legs of a length less than the water depth, cross-bracing members securing the long and short legs to form a framework, at least one of said substructure sections having at least two short legs arranged in the lower portion of the section on one side thereof so that the bottoms of the short legs extend to the floor of the body of water, a guide pile extending through each short leg and into the floor, said short leg guide piles being secured to the short legs and extending upwardly at least to the height of the long legs, a pile extending through each of a plurality of said long legs and into the floor, at least another of said framework substructure sections having at least two short legs arranged on the upper portion of said section, said upper short legs being of a spacing and diameter suflicient to pass downwardly over the guide piles in the lower short legs of said other substructure section, said upper and lower short legs being arranged in coaxially displaced relationship on said guide piles and being fixedly secured thereto to form a leg equal in length to the long legs of said substructure sections, and a horizontally-disposed deck section mounted on and secured to the tops of a plurality of the legs of said joined substructure sections.

4. An offshore platform structure comprising a framework-type substructure made up of a plurality of prefabricated tubular-legged substructure sections adapted to be positioned on the floor of a body of water one at a time, each of said substructure sections having a plurality of long vertical legs of a length greater than the water depth and a plurality of short vertical legs of a length less than the water depth, cross-bracing members securing the long and short legs to form a framework, outlining a geometrical figure having a closed perimeter, at least one of said substructure sections having at least two short legs arranged in the lower portion of the section on one side thereof so that the bottoms of the short legs extend to the floor of the body of water, a guide pile extending through each short leg and into the floor, said short leg guide piles being cemented in the short legs and extending upwardly at least to the height of the long legs, a pile extending through each of a plurality of said long legs and into the floor, at least another of said framework substructure sections having at least two short legs arranged on the upper portion of said section, said upper short legs being of a spacing and diameter sufficient to pass downwardly over the guide piles in the lower short legs of said other substructure section, said upper and lower short legs being arranged in coaxially displaced References Cited in the file of this patent UNITED STATES PATENTS Quet June 7, 1921 Boschen Nov. 6, 1951 FOREIGN PATENTS Germany Dec. 7, 1950

Claims (1)

1. AN OFFSHORE PLATFORM STRUCTURE COMPRISING A FRAMEWORK-TYPE SUBSTRUCTURE MADE UP OF A PLURALITY OF PREFABRICATED TUBULAR-LEGGED SUBSTRUCTURE SECTIONS ADAPTED TO BE POSITIONED ON THE FLOOR OF A BODY OF WATER ONE AT A TIME, EACH OF SAID SUBSTRUCTURE SECTIONS HAVING A PLURALITY OF LONG VERTICAL LEGS OF A LENGTH GREATER THAN THE WATER DEPTH WHEN NORMALLY EXTENDING TO THE WATER BOTTOM AND A PLURALITY OF SHORT VERTICAL LEGS, CROSS-BRACING MEMBERS SECURING THE LONG AND SHORT LEGS TOGETHER TO FORM A FRAMEWORK, AT LEAST ONE OF SAID SUBSTRUCTURE SECTIONS HAVING AT LEAST TWO SHORT LEGS ARRANGED IN THE LOWER PORTION OF THE SECTION ON ONE SIDE THEREOF, A GUIDE PILE EXTENDING THROUGH

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