US 3824943 A
A floating platform for drilling after natural deposits beneath the floor of the sea. The platform has a reduced cross section at the sea surface, a service deck above the sea surface, and a substructure extending downwardly below the sea surface. The platform is monolithic and comprises a plurality of vertical cells of concrete. A bottom deck closes the bottom of the vertical cells and is adapted to be positioned deep below the sea surface and above the floor of the sea. The vertical cells are arranged such that at least one but not all of the cells extend from the bottom deck to the top deck and the center of gravity of the platform is below its center of buoyancy.
Description (OCR text may contain errors)
United States'Patent 11 1 1111" 3,824,943
M0 g 1451 July 23,1974
1 1 DRILLING PLATFORM 3,572,043 3 1971 Clara ..61 46 3,681,923 8/1972 Hyde  Inventor- Gmnsundvelen 3,708,987 1 1973 Roulet (it al. 61 46 Nesbru, Norway  Filed: Mar. 13, 1972 OTHER PUBLICATIONS The 011 and Gas Journal of Sept. 14, 1970, pages 60,
 Appl. No.: 233,879 1  Foreign Application Priority Data Primary Examiner-Jacob Shapiro Mar. 16, 1971 Norway 1008/71 Attorney Agent Taylor and Hinds  US. Cl. 114/.5 D, 114/.5 T, 61/465, ABSTRACT 175/7 A floating platform for drilling after natural deposits beneath the floor of the ea The platform has a re- Field of Search 61/465, T, duced cross section at the sea surface, a service deck 114/5 D; 9/8; 175/7 above the sea surface, and a substructure extending downwardly below the sea surface. The platform is  References Cited monolithic and comprises a plurality of vertical cells UNITED STATES PATENTS of concrete. A bottom deck closes the bottom of the 2,940,266 6 1960 Smith 61/465 vertical cells and is adapted to be Positioned p 55 4 below the sea surface and above the floor of the sea. 61/465 X The vertical cells are arranged such that at least one 6 /465 but not all of the cells extend from the bottom deck to 2,972,973 2 1961 Thearle 3,154,039 10/1964 Knapp 3,273,526 9 1966 016m rh d g 11415 T the top deck and the center of gravity of the platform anning H4 .5 T v is below its center of buo anc 3,510,892 5/1970 Monnereau et al 9/8 7 y y 3,535,884 10/1970 Chaney 61/465 7 Claims, 2 Drawing Figures ,II'III' rIIII'II DRILLING PLATFORM The invention relates to a floating drilling platform for drilling after and production of natural deposits under the sea.
The new and characteristic which form the basis for the present invention, is the thought that a platform of that type which has a reduced cross-section at the floating line, e.g. semi-submersible state, can be made monolithic of concrete as one or more vertical cells, preferably tube shaped, with a bottom. This very simple construction will, as showed below, offer many advantages compared with the conventional floating platforms.
For a better understanding of the invention it will be described further by means of an example.
FIG. 1 shows a vertical section B B through the platform and FIG. 2 shows a horizontal section A A.
1 is a cell which is terminated under the water surface, 2 is a cell which is terminated above the water surface and 3 is a cell without a bottom which the drill 4 passes through. 5 is the workingor service deck of the platform and 6 is the drilling tower.
The tubes may have varying wall thickness and diameter. It is, however, an advantage if the variations are small, since the platform in that case can be made by means of slip forms.
It will immediately appear from the figure that it is easy to achieve the center of gravity to be below the center of buoyancy and there are thus no problems at tached to the stability.
The cells may during the drilling be filled withair,
sand or water. There must always be some air present for buoyancy, while sand is an excellent ballast material. Other solid ballast material, of course, can be used. Water will be the natural medium for trimming.
The cells may also be used for tanks, e.g. for oil storage or as a dumping place for polluted materials.
A series of advantages are achieved in that the drilling takes place through a tube. The work will not be hindered by waves or ice. Such a solution means a big advantage, especially for the divers, since their work often becomes restricted due to the difficulties in getting up and down through the wave area. The tube will also beable to collect spill of oil, and prevent the oil from spreading in the sea.
As it appears from the figure, the platform will extend downwards much deeper than other floating platforms. The figure shows a platform which has a sub structure nearly double the height of the drilling tower,
e.g. a sub structure of 70 80 metres. This is 3 4 times the normal depth of a sub structure of a semisubmersible platform. At these depths the sea is practically calm irrespective of the waves on the surfaceThe large weight of the concrete, the reduced cross-section of the platform at the floating line and possibly ballast of sand all adds to the stability, and the result is a platform whichv lies far more steady in the sea than other floating platforms. In contrast to the existing platforms, a platform according to the invention will thus not need to interrupt the work due to bad weather. This is of large importance in so called wild-cat"-drilling, and absolutely of vital improtance for production. None of the existing floating platforms may be used for production, namely because production must go on continously irrespective of the weather. The weight and stability of the platform is also necessary, if it is to be provided with industrial plants, fishplate arrangements etc. The service deck can thus be provided with industrial equipment, quay installations, and the like.
The large sub structure of the platform is also advantageous for conventional anchoring, since the anchors may be fastened far down and thus obtain a greater effect since the chain or the wire remains lying more horizontally. Dynamic anchoring may be employed.
The cell formed concrete structure is in itself particularly favourable. The construction can take up very large pressure-forces, since buckling problems practically do not exist. This is of importance with regard to the large water pressures in question, and with more occasional local stresses, e.g. from ice.
A platform according to the invention offers no production difficulties, since the production can be performed exclusively by means of simple method and modest aids. A natural way is to cast the bottom and a bit of the walls in a dry-dock, tow this out to a deep sea area and thereafter erect the walls by means of slip forms, while the platform gradually sinks down in the water. Alternatively, the platform may be provided with its own propulsion equipment.
Compared with a conventional semi-submersible platform, the platform according to the invention has the following advantages:
a. a simpler manufacture, b. a more robust construction,
c. substantially better stability,
d. no corrosion, i.e., little maintenance,
e. protection for the drilling work,
f. possibilities for collecting spill of oil,
g. cheap storage or oil etc.,
h. probably more favourable with regard to price and building time, i. conventional anchoring becomes more efficient. 'The platform is more difficult to move than other floating platforms. This plays less importance if it operates within a limited geographical area, and is completely without inportance for a production platform.
It will immediately be understood that the design of the invention which is shown on the drawing and described above, is only meant to illustrate the inventive thought, and that this may be varied in a series of ways within the idea of the invention.
1. In a floating platform for drilling after natural deposits beneath the floor of the sea having a reduced cross section at the sea surface, a service deck above the sea surface and a sub structure extending downwardly below the sea surface, the improvement wherein said platform is monolithic and mobile, and comprises a plurality of contiguous vertical cells of concrete at least one of the cells lengthened to above sea level to form a support for a service deck, a service deck permanently fixed to said platform, the nonlengthened cells located a substantial distance below the deck section so that the top of said non-lengthened cell or cells is at a substantial depth below the surface of the sea, a drilling structure on said service deck, a bottom deck closing the bottom of said vertical cells and adapted to be positioned deep below the sea sur- 7 face and above the floor of the sea, the whole structure being constructed and arranged such that the center of gravity of said platform is below the center of buoyancy thereof.
2. An improved platform according to claim 1 further including a drill extending from said service deck down through one of said verticle cells to the sea floor.
3. An improved platform according to claim 1 wherein said sub structure extends at least 70 meters below the surface of the sea.
4. An improved platform according to claim 1 wherein said platform includes a first group of adjacent vertical concrete cells extending from said service deck to said bottom deck and a second group of vertical concrete cells in surrounding adjacency with said first group and extending from said bottom deck upwards to ballast material.