US3456448A - Leg for supporting a marine structure - Google Patents

Description

July 22, 1969 R. F. LUQUE 3,45

LEG FOB. SUPPORTING A MARINE STRUCTURE Filed July 21, 1967 a auzww v INVENTORI v RAFAEL FERNANDEZ LUQUE 5. wwqlaz HIS AGENT United States Patent US. Cl. 6146.5 3 Claims ABSTRACT OF THE DISCLOSURE A leg for supporting at least part of a marine structure on the floor of a body of water including a generally flat plate surrounding the leg and resting on the water floor to prevent sea currents from causing the leg to sink into the floor. The plate is movable along at least a part of the lenght of the leg so that it will freely slide along the leg and into contact with the floor of the body of water. In addition to a unitary plate, several interconnected plates may be employed which are connected by flexible elements to permit limited angular displacement between the plates to accommodate irregularities in the water floor.

Background of the invention The present invention relates to marine structures and more particularly to leg means suitable for supporting a marine structure. Such a structure may be formed by a pontoon or a platform which may carry equipment, for example, for drilling boreholes in the floor of a body of water (hereinafter to be indicated by sea bottom) or for handling oil or gas being produced via a well penetrating the formations below the sea bottom. Dolphins, bridges, jetties and wharfs are mentioned as other examples of marine structure to which the present invention is applicable.

The present invention deals in particular with marine structures which are carried by legs being suitable to be placed on, or extend over a relatively small distance into a non-cohesive, permeable sea bottom such as sand.

The effect of water currents acting on the legs of existing marine structures often produces a serious affect on the load bearing capacity of the leg, The water currents tend to scour away the sea bottom in the vicinity of the leg thus causing the leg to sink resulting in an uneven structure and possible structural damage to the leg or platform being supported. In addition, eddy currents are formed which may cause the flow of fluids in the underlying formation due to the lower pressure created by the eddies which in turn can convert a permeable sea bottom into quicksand, again causing the leg to sink.

It is noted that the application of the invention is not restricted to a certain number of legs on which a marine structure is being supported. Although most of the marine structures are supported by more than three legs, monoleg structures do also exist. The supporting means for the marine structures may, in addition to the expression legs, also be indicated by the expression columns, spuds or piles.

Summary The primary object of the present invention is to provide a leg for a marine structure supported by a noncohesive permeable sea bottom which will maintain its position without any decrease in its load-carrying capacity, even if strong water currents are passing therealong.

According to the invention, a leg for supporting a marine structure is provided with a substantially flat element or plate means having an opening through which "ice the leg passes, said element being displaceable along the leg over at least part of the length thereof.

The opening in the flat element may have a configuration equal to the configuration of the cross-section of the leg taken in a plane perpendicular to the central axis of the leg, and be of a slightly greater area than the area of this cross-section. It is advantageous to use a flat element of which the upper side has an area '(exclusive the area of the opening provided therein) which is at least 3 times the area of the cross-section of the leg.

When applying a fiat element of circular configuration, good results will be obtained when choosing the diameter thereof at least two times the greatest dimension of the cross-section of the leg taken in a plane perpendicular to the central axis of the leg.

The lower side of the fiat element may be provided with means suitable to induce eddy currents in fluid passing along this lower side. In addition, the fiat element may consist of more than one section, the sections being interconnected by means allowing at least an angular displacement betwen the sections.

Description of the drawings The invention will now be described in more detail with reference to the accompanying drawings in which:

FIGURE 1 is an elevational view of a marine structure carried by legs according to the invention;

FIGURE 2 is an enlarged detail view of one of the legs of the structure shown in FIGURE 1 showing one modification of the invention;

FIGURE 3 is a cross-sectional view of another modified flat element;

FIGURE 4 is a plan view of the embodiment shown in FIGURE 3 looking from the bottom;

FIGURE 5 is a plan view of a fiat element of still another configuration; and,

FIGURE 6 is a cross-section of the flat element according to FIGURE 5 taken along the line 5-5.

Description of the preferred embodiments The marine structure as shown in FIGURE 1 consists of a platform 1 carrying a drilling derrick 2 and other means (not shown) required for carrying out drilling operations by means of the derrick 2. Legs 3, of which only two are shown, support the structure, and are connected thereto by means 4 which are equipped with power means (not shown) allowing a relative movement between the platform 1 and the legs 3 for raising and lowering the platform when these legs are supported by the floor of a body of water or sea bottom 5, or for raising and lowering the legs 3 with respect to the platform 1 when this platform is riding on water surface 6 either by its own bouyancy or by means of pontoons. The means 4 are further equipped with suitable locking mechanisms (not shown) for locking the legs 3 to the platform 1, when the platform is at a desired level above the sea surface 6 for carrying out drilling operations or well servicing operations. Since the means 4 are known per se in a great number of various constructions, they are not described here in detail.

As can be seen from FIGURE 1, the lower parts of the legs 3 are partially buried in the sea bottom 5 so that they penetrate over some length thereof into the formation 7 underlying the sea bottom 5.

The legs 3 may be partly driven into the sea bottom 5 by lowering the legs 3 from the platform II to a position wherein the legs touch the sea bottom 5, whereafter by action of the means 4 the legs are pressed to the formation 7 at the same time lifting the platform 1 out of the water.

To prevent the legs 3 from being non-uniformly loaded by the action of sea currents which may result in damage of the legs and the platform, each leg is provided with a substantially flat element 9 encircling this leg and being movable along the length thereof.

The element 9 consists of a substantially flat plate which is provided with a central opening 10 through which the leg 3 passes and is preferably made of metal. In the position shown, the element 9 cuts off the communication between the pore space of that part of the formation 7 supporting the leg 3 and the sea current (see arrow 11) flowing around the leg 3 and thus prevents the lower pressure zone of the disturbed flow pattern of the liquid passing along the leg 3 from communicating with this pore space. A reduction in pressure in this pore space tends to create a flow of formation fluid, which might render the formation part on which the leg 3 rests into quicksand, thereby reducing the bearing capacity of this part of the formation 7. When the capacity for load carrying of the formation falls below the value of the loads exerted on the leg resting thereon, the leg will sink deeper into the formation 7, which may cause the platform to settle ununiforrnly. Under extreme conditions, the marine structure and the leg may even be damaged.

Since the flat element 9 is slidable along the length of the leg 3, it can, during the positioning of the leg on the sea bottom, be held around the leg at a level relative to the sea bottom where it does not interfere with the positioning operation. Although the element 9 may be placed on the sea bottom before the leg has reached its final position, it is preferred to postpone the placing of the element until the leg has been set. Since no fixed connection exists between the leg 3 and the element 9, this element will remain on the sea bottom 5 in its protective position even if the relative position between the sea bottom 5 and the leg 3 is subject to small changes.

The element 9 need not be absolutely fiat. It may be of slightly conical shape, as shown in FIGURE 2, having side walls 9 which enclose an angle of less than with the plane passing through the lower edges of the walls 9'.

An alternative form of a substantially flat protection element or plate means is shown in FIGURES 3 and 4. The element as shown comprises a circular plate 12 and is used in combination with a leg having a circular crosssection over the interval at which the element may slide. A circular opening 13 is arranged in plate 12 and is of an area which is approximately 10% greater than the area of the cross-section of the leg. The border of the opening 13 may be provided with a rim 14 acting as a guide for guiding the element along the leg. Radially arranged reinforcement ribs '15 are located at the lower side of the plate 12 and connected thereto and to the rim 14 in a suitable manner.

The plate 12 may be provided with nozzles which are arranged to remove the sand at the surface of the sea bottom at the location where the protective element is to be placed. One such nozzle 16 is shown in FIGURES 3 and 4. The nozzle is connected via a tube 17 with a pressure source (not shown) so that a liquid flow can be issued in the direction of arrow 18 which blows, when the protective element is placed on the sea bottom, the sand or silt out of the segment-shaped space bounded by reinforcement ribs and 15 and the guide ring 14. By providing nozzles similar to nozzle 16 in the other segment-shaped spaces, and connecting these nozzles to a suitable pressure source, the sand or silt below the protective plate 12 can be removed by the liquid jets issuing from the nozzles when the plate is placed on the sea bottom. As a result, the protective plate will sink a small distance into the formation, thereby being unaffected by slight changes in the sea bottom 5 which invariably occur due to changing sea currents. If desired, further nozzles (not shown) may be arranged so as to terminate in the annular space between the rim 14 and the leg passing therethrough. Further means such as pumps may be provided for draining the fluid from below the plate 112 so as to improve the compaction of the soil just below the plate.

In FIGURE 5 a top view of a flat protective element is shown which is of a flexible nature within rather narrow limits. The element is of a quadrangular shape and consists of eight quadrangular plates 19 which enclose quadrangular opening 20 to accommodate a marine structure leg. The plates 19 are interconnected by flexible strips 22 (see also FIGURE 6) which may be of rubber or other suitable elastomeric material and glued to the plates 19. Nails or spikes 23 are, in one embodiment of the invention as shown in FIGURE 6, connected to the lower side of the plates 19. When placed on the sea bottom 5 in the position as shown in FIGURE 6, these nails or spikes partly sink into the formation 7. Sea currents flowing below the plates 19, however, create eddy currents at the spikes and nails 23, thereby loosening the surface of the sea bottom 7 by the formation of quicksand, so that the nails and spikes and even the protective element itself will sink over a small distance below the level of the sea bottom 5.

The flexibility of the element as shown in FIGURES 5 and 6 is of particular advantage when placing the ele ment on a sea bottom which is not of a flat nature since the element will tend to conform to any irregularities in the sea bottom.

It will be appreciated that although only a circular and quadrangular-shaped protective element or plate means have been shown in the drawings, it is anticipated that protective elements having still another configuration may be employed. The same applies for the cross-section of the leg on which the protective element is being used. These legs may have a closed side wall, or may be of an open construction or framework but having a closed side wall over the portion facing the protective element when the y element is situated on the sea bottom.

It will further be appreciated that the platform 1 with derrick 2 in FIGURE 1 is only being shown as an example of a marine structure which can be used in combination with legs according to the invention. The term platform is intended to cover any form of generally horizontal structure adapted to be positioned above the surface of a body of water.

Further, it is noted that the invention is not limited to legs which are connected to the marine structure by means of mechanisms 4. The legs according to the invention may be connected immovably to a marine structure or they may be first set in place at a desired location and a marine structure subsequently added.

I claim as my invention:

1. A marine structure supported by the floor of a body of water including apparatus for preventing said structure from sinking into said floor, said structure comprismg:

elongated leg means partially buried in the floor of said body of water and extending above the water surface;

generally horizontal platform means carried by said leg means and adapted to be positioned above the water surface; a series of adjoining rectangular plates surrounding and substantially normal to said leg means; and

flexible means interconnecting said plates to permit limited angular displacement between said plates, said plates being displaceable along at least a part of the length of said leg means and adapted to be moved along said leg means into contact with the floor of said body of water.

2. A structure as defined in claim 1 including eddyinducing means attached to the lower surface of said rectangular plates.

3. A structure as defined in claim 2 wherein said eddyinducing means comprise spaced depending spikes.

(References on following page) 5 6 References Cited 2,954,676 10/1960 Guy et a1. 61-465 UNITED STATES PATENTS 3,315,473 4/1967 Hauber 6t a1. 6146.5

219,618 9/1879 Carley et a1. 61-53 JACOB SHAPIRO, Primary Examiner 2,352,370 6/1944 Carruthers 6146.5 2,600,761 6/1952 Halliburton 61-465 5 2,892,314 6/1959 Hornsby et a1. 61-465 37-73; 52-720; 61-48, 53

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