Offshore platform structures

April 26, 1960

2,933,898

Μ. M. UPSON

OFFSHORE PLATFORM STRUCTURES

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April 26, 1960 m. _M. upson 2,933,898

OFFSHORE PLATFORM STRUCTURES

Filed Nov. 16, 1955 ’ 3 Sheets-Sheet 2

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ATTORNEYS.

2,933,898

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April 26, 1960

Filed Nov. 16, 1955

Μ. M. UPSON

OFFSHORE PLATFORM STRUCTURES

Sheets-Sheet 3

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United States Patent Office „ 233339s

Patented Apr. 26, 1960

2,933,898

OFFSHORE FLATFORM STRUCTURES

Maxwell M. Upson, Englewood, NX, assignor to Raymond International Inc., a corporation of New Jersey

Application November 16,1955, Serial No. 547,076

Claims. (CI. 61—46)

This invention pertains to offshore marine platforms of the type which find particular utility, among other possibilities, in offshore oil well drilling arid producing operations.

Due to the extensive oil well drilling activity now in progress in the waters along the continental shelf of this 20 country, there has developed a distinct need for offshore structures of a type suitable to support oil well drilling and producing facilities. Offshore construction problems are both unique and multifold. In the first place, it is highly desirable to provide an operating platform of such 25 design that it may be prefabricated on land and shipped in relatively few pieces to the offshore construction location. Such prefabrication in large units on shore is a prerequisite to economical operation, for offshore construction costs are extremely high, both due to the fact ³⁰that the same is carried out oftentimes many miles at sea and far removed from the main operational base, with barges or floats being the only suitable means for transporting and assembling the material and because any such offshore construction program can be delayed for lengthy ³⁵periods due to stormy weather, thereby causing serious losses. Another basic problem in such offshore construction lies in the fact that the ultimate structure Or platform must be able to withstand the force of wave action, always variable and oftentimes of great intensity. But ⁴⁰perhaps the most difficult offshore construction problem lies in the fact that generally speaking poor foundation material prevails over much of the desirable oil drilling grounds. It is more the rule than the exception to find greatly variable foundation capacity on the sea bottom at closely adjacent spots in the proposed erection loca- ⁴⁶tion. For example, actual past history of one company engaged in such operations reveals that a 24-inch diameter tubular pile must be driven to penetrations varying from 145 to 240 feet to obtain identical load carrying capacity. Such greatly varying penetration depths have been a prime obstacle to the Use of composite bearing piles in such offshore structures for a reason which will be described in more detail hereinafter.

A large variety of different types of offshore structures ₆₅have been designed in an effort to overcome the aforesaid ° problems. Many have been of the jacket type disclosed in U.S. Patent No. 2,429,952 issued October 28, 1947, to Μ. B. Willey. Such jacket type structures consist basically of three integral parts, each of which is pre- _eofabricated on shore in relatively very large size, the exact ° dimensions being limited only by the available erection equipment. In order of installation, the first structural unit in this type of platform is a jacket comprised of a plurality of upstanding tubular columns rigidly interconnected by transverse and diagonal pipe braces. Such a jacket is first lowered into position on the ocean floor and then bearing piles having a diameter slightly less than the jacket columns are inserted in said columns and driven to the desired penetration in the sea bottom. The upper ends of these bearing piles then serve to support the third part of the structure, namely, the working deck unit or operating superstructure. It should be understood that the height of the jacket columns will depend upon the depth of water at the particular drilling location, while the jacket’s size, column and brace spacing 5 will depend in large part upon local operating conditions, such as wave exposure, etc. Such jacket type structures are highly desirable, since the jacket portion can be completely prefabricated on shore, thereby assuring that the i n columns th® same may be made to close tolerances ¹⁰ and since the bearing piles and likewise can be prefabricated to close tolerances, such a structure insures proper fitting of the piles within the jacket and, therefore, substantially vertical alignment of the individual piles can be accomplished without extensive offshore pulling and ¹⁵ pushing techniques. Furthermore, the use of such a jacket provides a strong underwater cross bracing system.

Heretofore such jackets have been fabricated of steel, but because of the use of such metallic construction, they have been subject to certain inherent disadvantages. One of the greatest disadvantages involved in the use of steel in water it is susceptibility to deterioration by electrolytic and chemical corrosion. Such corrosion takes place in the steel both above and below the water level, _2g but is most prevalent in what is known as the splash zone, which js alternately wet and dry due to wave action. Such corrosive action on steel jackets is most deleterious and to date no effective method of preventing the same has been developed except for that portion of the steel ₃θ structure which is entirely and continuously submerged beneath the surface of the water. This corrosion problem of necessity presents a high cost factor involved in the maintenance of steel jackets of this type.

The present invention provides a way of overcoming ₃₅ these and other disadvantages of presently known types of offshore platforms by providing a platform structure of the composite type which utilizes a prefabricated, partially concrete and partially metal jacket and prefabricated, partially concrete and partially metal bearing piles. ₄₀ Concrete is a very poor conductor of electricity and, therefore, is not subject to electrolytic corrosion. This invention therefore utilizes concrete to form the upper or above-water portions of the jacket and bearing piles while a metal such as steel is utilized in the lower or totally submerged portions of these elements. A primary 45 source of generation of the electrical currents which create the electrical potential necessary to institute the damaging electrolytic corrosion of a steel jacket is the various electrical equipment which operates on the platform, as well as the currents set up by relative movement 50 between dissimilar materials on the operating deck of the platform from which heretofore all -metal supporting members have extended into the water. According to the instant invention, by providing a concrete portion extending from this platform deck structure down to a 55 level which is beneath the low water mark, an insulating zone is established between these deck developed currents and the steel portions which are totally submerged in the water.' This concrete insulating zone then serves to prevent these currents from being transferred to the steel ⁶⁰ portions in the water and hence prevents a substantial amount of damaging electrolytic corrosion.

Of course, in utilizing composite concrete-steel bearing piles in those offshore locations where as mentioned above the foundation soil gives rise to varying penetration depths, an additional problem must be faced; namely, if both the concrete sections of the piles as well as the metal sections thereof are to be totally prefabricated on shore, provision must be made to compensate for varying penetration depths of each pile in order that the upper end of the concrete sections of each pile will terminate in the same horizontal· plane so as to provide for a level

2,933,808 with its timber mat 17 resting tion as shown in Fig. 1 on the ocean floor 12.

These jacket columns lower metal portions as portions 22, 22'. i—

13, 14 may be comprised of at 21, 21' and upper concrete -L, ·. As will be best seen in Fig. 4, the concrete portions 22, 22' of these jacket columns consist of relatively large diameter prestressed concrete cylinders which may be constructed and pretensioned in accordance with the method disclosed in my U.S. Patent No. 2,706,498, issued April 19, 1955. The lower metal portions 21 of the jacket columns, on the other hand, consist of the conventional steel pipe which has been heretofore used in jacket structures as described above. For securing portions 22 and 21 of the jacket columns together, the lower end of the concrete portion 22 of each column is provided with a circumferential band 23 which grips the outer surface thereof in close hugging relationship. To the lower ends of these circumferential bands 23 are welded annular plates 24, while to the upper ends of each of the portions 21 of the jacket column are welded annular rings 25 with the abutting surfaces of said plates 24 and rings 25 being then welded together so as to provide an integrally joined composite column such as 13 having its upper portion 22 formed of concrete and its lower portion 21 formed of steel. In the particular embodiment illustrated in the drawings the diameter of the steel portions 21 of the jacket columns is in relative size less than the diameter of the concrete portions 22, but it will be, of course, understood that the relative proportioning of the diameters of these respective portions could be reversed or they could be similar in size. It should be understood that the length of these jacket columns 13 and 14 is by design dependent upon the depth of water in which it is intended to position the offshore platform.

surface for supporting the working deck unit. The instant invention accomplishes this result by providing a novel joint construction for securing the concrete and metal sections of each pile. Thus the relative elevation of the top of the steel section of a bearing pile as driven and the lower portion of the concrete section of that pile need not have any definite predetermined relationship. The invention accomplishes this result by utilizing grout, cement or mortar to join the concrete section to the metal section via the tubular jacket columns.

Other and more specific objects, features and advantages of the invention will appear from the detailed description given below taken in connection with the accompanying drawings which form a part of this specification and illustrate by way of example the presently preferred embodiment of the invention.

In the drawings:

Fig. 1 is a schematic side elevational view partly in section of a composite offshore marine platform according to the invention and showing the same fully erected in its offshore location;

Fig. 2 is a schematic side elevational view showing the platform with its jacket portion positioned on the ocean floor and with the metal sections of its bearing piles driven into the subsurface soil, while the concrete sections of said bearing piles and attached deck structure are being lowered into position in the jacket;

Fig. 3 is an enlarged vertical side elevation partly in section showing the grout line connections adapted for use in joining together the composite sections of a bearing pile;

Fig. 4 is an enlarged fragmentary vertical sectional view showing the composite bearing pile joint construction of the invention; and ---------,— * . ,. -,,

Fig. 5 is an enlarged fragmentary vertical sectional 35 For example, platforms of a size as mentioned herei view of the pile joint construction of the mvention, showing the concrete section and steel section of a bearing pile in different relative positions than seen in Fig. 4.

Referring now in more detail to the drawings and par- ---- ~ , .,, , , ., ticularly to Fig. 1 thereof, there is shown a composite ⁴³ shown, the upper ends of those columns wifl be above the marine platform 10 according to the invention having a jacket structure 11, designed to be positioned on the ocean floor 12 at the particular offshore location desired. This jacket structure 11 may be generally rectangular in shape and is of the composite, concrete-metal type, com- 45 prising a plurality of upstanding tubular columns such as 13 and 14 which are rigidly interconnected by a series of transverse and diagonal pipe braces such as 15 and 16. Those of the braces 15, 16 which by design will be above the water surface when the jacket is in operative 60 position on the sea floor, may at the time of prefabricating said jacket be coated with a protective, non-conducting, adhesive coating which may comprise a mixture of sand, cement and water, such as for example the coating above are contemplated for use in water depths up to several hundred feet and in such instances the length of jacket columns 13 and 14 will exceed this depth in order that when the jacket is resting on the ocean floor as high-water mark. Similarly, by design the relative lengths of the concrete and steel portions 22, 21 of these jacket columns will be such as to insure that the upper end of the steel portion is always entirely submerged beneath the water surface. Thus for any given location the length of the metal portions 21 of the jacket structure will be designed so as to be of less magnitude than the distance between the ocean floor and the low water level, thereby insuring total submersion of the steel portion of the jacket during all tidal conditions. The concrete portions 22 will of course be designed of a length suitable to make the over-all column height extend well above the high water mark. As has been stated above, the entire fabrication ______ of this jacket structure may be completed at the shore of that type which is known under the trade name of 55 installation orcompleted in sections, andjhe^same trans“Gunite.” A timber mat 17 is secured near the lower ^{1 v}'’ * ends of the tubular jacket columns and may cover as much as desired of the lower area of the jacket so as to provide a level supporting base for said jacket structure ported only after assembly to the desired offshore location.

Once this jacket 11 has been positioned at the desired _r___________________₌___________,_____________ location on the ocean floor as shown in Fig. 2, the steel when the latter is lowered to the sea floor. The tubular 60 sections 26 and 27 of the bearing piles 18 and 19 are incolumns 13 and 14, etc., of the jacket 11 are open ended ’ so as to permit reception of bearing piles such as 18 and 19, which latter server to support the working deck unit 20 of the marine platform assembly. It should be understood that the marine platforms contemplated by this qq driving apparatus, invention are generally of massive construction, for example, the working deck 20 may extend over several thousands of square feet and weigh in the order of 200 tons and with the jacket structure 11 being comparatively serted by conventional hoisting cranes in the respective columns of the jacket and then these steel sections are driven down through the lower ends of the jackets columns into the ocean floor by means of conventional pile . As mentioned above, it is not uncommon for the foundation capacity of underwater soil to vary greatly at closely adjacent spots, thereby resulting in different penetration depths of the individual piles in _______________________________{_}________ . order that the same may all possess the same load-carrysized with a height of 80 to 100 feet and weighing in the 70 ing capacity. Thus as shown in Fig. 1, the steel sections order of 350 tons. The deck unit 20, the jacket 11 and ~~ ^r - >--the bearing piles 18 and 19 may be prefabricated in large sections on shore and transported to the desired offshore drilling location by barges or other available transportation means. ' of bearing pile 19 had to be driven only to a relatively shallow depth, and the upper end 28 of this section 27 was still positioned within the hollow interior of the concrete portion 22 of its jacket column. To obtain the same The jacket 11 is then lowered into posi- 75 load-carrying capacity, steel section 26 of bearing column

2,983,898 had to be driven to a much greater depth, thereby resulting in its upper end 29 being positioned completely out of contact with the upper concrete portion 22' of its jacket column 13 and well down into the steel portion 21'. As shown, the steel section of other bearing piles in this jacket structure may well have to be driven to quite different penetration depths to obtain the same load carrying capacity and as a result, the final position of the upper ends Of these metal pile sections will vary greatly and not be in any way predetermined relative to one another.

Ordinarily, under such conditions using heretofore known methods of connecting concrete pile sections to these already driven steel pile sections would pose a problem, since it is desirable to have the upper ends of all concrete pile sections terminate in the same horizontal plane so as to provide a level base of support for a working deck structure. The instant invention accomplishes this objective in the following manner. After the jacket structure has been thus positioned on the ocean floor and the steel sections of the bearing piles have been driven through the jacket columns, the working deck unit 20 is lowered into position by conventional crane means. This working deck unit may be formed for example of cast concrete and to its undersurface are suitably or integrally joined the concrete sections such as 30 and 31 of the bearing piles. These concrete sections 30 and 31 are of the prestressed concrete cylinder type and may be constructed and pretensioned in accordance with the method discussed in the above mentioned U. S. Patent. 2,706.498. Each of these concrete pile sections is designed of equal length, with that length being determined by the height to which it is desired to maintain the working deck 20 above , the jacket structure 11.. It should be understood that this working deck unit 20 with the concrete sections 21, 21' secured to the underside thereof may be fully prefabricated as an integral unit on shore.

As shown in Fig. 2, the deck unit 20 with its concrete pile sections attached thereto is lowered down into position so that each of said concrete pile sections 30, 31 slides down into the respective upper concrete portions 22, 22' of the jacket columns 13 and 14, the outer diameter of these pile sections being by design, of course, less than the inner diameter of the concrete portions 22 of the jacket, columns. As shown in Fig. 4, this downward travel of the deck unit 20 will come to a halt when, for example, the lower end of concrete pile section 30 comes to rest on the upper end of metal portion 21 of the jacket column indicated at 32. It should, of course, be understood that since all of these concrete pile sections as at 31 are of equal length and that similarly all of the concrete jacket sections as at 22, 22' are all of equal length, that all concrete pile sections will simultaneously come to rest on the upper ends of the metal portions 21 of their respective jacket columns. Thus, the lower steel portions 21 of the jacket columns support the vertical load of the upper concrete sections of the bearing piles and the attached working deck unit 20. According to the invention, these upper concrete sections as at 30, 31 of the bearing piles are then secured through their respective jacket columns to the lower steel sections of said bearing piles by means of grout or cement or other suitable adhesive mixture, as will now be explained.

After the platform has been assembled as described above with its steel pile sections driven and with its concrete pile sections telescopically received within the respective concrete portions of the jacket columns, grout or cement under pressure is forced as from a nozzle 33 (Fig. 3) into the spaces which exist between the inner surface of the concrete jacket column portions and the outer surface of the concrete pile sections. Considering bearing pile 14 (Figs. 1, 4) for the moment, as more and more grout is forced in, the same travels downwardly along the sides of the concrete portion of the bearing pile until it reaches the lower end thereof, wherein radially extending apertures as at 36, if desired, may be provided so as to permit the grout to pass down into the space 37 existing between the inner wall of the steel portion of the jacket columns and the outer wall of the steel section of the bearing pile. This group under pressure may also be forced after passing through the holes 36 upwardly into the annular space 38 which exists between the inner wall of the concrete section 30 of the bearing pile and the outer wall of the steel section of the bearing pile. Thus with the steel and concrete bearing pile sections relatively positioned as shown in Fig. 4, the grout thus inserted upon setting will effect a secure bond between the inner wall of the concrete jacket portion and the outer wall of the concrete pile section, the inner wall of the concrete pile Section and the outer wall of the steel pile section, also of the inner wall and the steel portion of the jacket column and the outer wall of the steel section of the bearing pile. Upon setting, such grout connection will allow transfer of stresses from the bearing pile to the jacket column. In order to insure that sufficient grout is introduced to effect the lowermost of the aforesaid connections, a grout line 39 may be run from a barge 40 down to a nipple 41 provided at the lower end of each of the steel sections of the jacket columns and grout under pressure forced downwardly through the line 39 and nipple 41 into the space between the lower end of the metal portion 21 of the jacket column and metal sections of the bearing piles. The grout thus introduced will be forced upwardly in this space, if necessary, until it meets with the grout being forced downwardly from conduit 34 and passages 36.

As has been pointed out above, such a grout bond between metal and concrete sections of the bearing piles is quite independent of the respective positioning of the upper end of the steel section of the pile relative to the lower end of the concrete section of the bearing pile. By design the lower ends of each of the concrete pile sections will terminate at the level of the upper ends of the steel, sections of the jacket structure while, on the other hand, the upper ends of the steel sections of the bearing piles may' assume any one of several locations such as shown in Fig. 1 at 28, 29, 51, and 52, it only being necessary that the upper end of the steel section of each bearing pile terminate at an elevation no lower than about 10 to 20 feet above the lower end of the jacket columns in order to provide the necessary strength and rigidity for the over-all structure.

In the case of a steel bearing pile section such as 26 whose upper end is positioned as at 29 beneath the lower end of the concrete section of its concrete jacket portion 22', grout will be introduced in similar fashion into the space between the concrete portions of the jacket column and the concrete section of the bearing pile as at 42 (Fig. 5), thereby uniting those two members together, while grout will also be introduced through a connection similar to nipple 41 provided at the lower end of jacket column 21' into the space between the said steel portion of the jacket column and the steel section of the bearing pile as shown at 43, thereby effecting a union of those two members. With the parts in this relative position, vertical loads from the deck structure will be transmitted downwardly through the concrete section 38 of the bearing pile and thence by direct end bearing as at 44 to the steel portion 21' of the jacket and thence via the grout connection as at 43 to the steel section of the bearing pile 26. It should be understood that in some instances depending upon local operating conditions, it may be desirable to use a composite jacket type platform of the type herein described having bearing piles whose sections are directly connected together rather than joined together by the grout bonding means hereinabove described. In such instances this may be particularly true in those offshore locations where depth penetrations are running uniform. In such instances the jacket structure will remain the same as described above and bearing piles will similarly be of the composite concrete-metal

3,033,898 type with their concrete sections being joined to their metal sections in the manner described in the copending U.S. application of Myers Van Buren, Serial No. 547,148, filed Nov. 16, 1955 and now abandoned. (Designated Case RCP-137.)

While, as shown in Figs. 1 and 2, the jacket structures are indicated as confined substantially to one plane, it should be understood that in practice such jacket structures will usually include several parallel or adjacent rows of jacket columns all secured together by horizontal and diagonal bracing. It should be further understood that while the jacket structures and piles have been disclosed as having upper concrete portions and lower metal portions, insofar as the utility in practice of the grout bond joint between sections of a pile is concerned, the entire jacket as well as upper and lower pile sections could comprise either all concrete or all metal or any combination thereof, it being only desirable that if the upper or out of water portions of both jacket and piles are formed of metal, the same be provided with a corrosion-resistant coating. Furthermore, it should be understood that the piles need not be vertically disposed, since some or all could be batter piles such as disclosed in copending Maxwell M. Upson application, Serial No. 536,202 filed September 23, 1955, and now Patent 2,927,435 dated March 8, 1960.

Although certain particular embodiments of the invention are herein disclosed for purposes of explanation, various further modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.