US3745777A - Configurations for ice resistant platforms - Google Patents

Abstract

This concerns a deck or platform supported by piles above a body of water. The deck is supported by slanted or battered piles which converge to a small apex area at about the water line elevation. The slanted piles permit the horizontal transfer of load into the soil by means of axial loading on the piles.

Description

nited States Patent 1 1 Blenkarn [4 1 July 17, 1973 1 CONFIGURATIONS FOR ICE-RESISTANT PLATFORMS [75] lnventor: Kenneth A. Blenkarn, Tulsa, Okla.

[73] Assignee: Amoco Production Company, Tulsa,

Okla.

[22] Filed: June 18, 1970 [21] Appl. No.: 47,403

[52] US. Cl. 61/46, 52/648 [51] Int. Cl E021) 17/00 [58] Field of Search 61/465, 46, 50,

[56] References Cited UNITED STATES PATENTS 3,645,104 2/1972 Hogan 61/465 2,775,095 12/1956 Harris 61/46 2,592,448 4/1952 McMcnimcn 61/465 3,429,133 2/1969 Hauber 61/465 1,637,259 7/1927 Malone 52/653 OTHER PUBLICATIONS Oil and Gas Journal, Apr. 27, 1970, p. 44

Primary ExaminerJacob Shapiro Attorney--Paul F. Hawley and John D. Gassett [57] ABSTRACT This concerns a deck or platform supported by piles above a body of water. The deck is supported by slanted or battered piles which converge to a small apex area at about the water line elevation. The slanted piles pennit the horizontal transfer of load into the soil by means of axial loading on the piles.

8 Claims, 7 Drawing Figures PAIENIEB J 7 3.745. 7 7 T smu 2 0r 4 #QY/Q/Q/Q/Q/Q/W/QW FIG. 4

KENNETH A. BLENKARN INVENTOR.

ATTORNEY PAIENIEU Jul 1 7 SHEU 3 (IF 4 KENNETH A. BLENKARN INVENTOR.

AT TORNE Y PATENTEB Jul 7 SHEEI '4 0f 4 KENNETH ABLENKARN INVENTOR.

BY y, g M

ATTORNEY CONFIGURATIONS FOR ICE-RESISTANT PLATFORMS I BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a platform or deck supported above a body of water. It relates especially to a particular arrangement of piles for supporting the deck in which each of the piles is slanted in a particular manner to aid in the transfer of horizontal load by axial pile loading.

2. Setting of the Invention During the last years or so, there has been a tremendous increase in the amount of exploration for, and production of, oil in water-covered areas. In a large part of such exploration and production, decks are supported above the bodyof water by piles which are set in the bottom. The working deck, piles, etc., are frequently referred to collectively as an offshore platform. Then wells are drilled from drilling equipment supported on the offshore platforms in a manner quite similar to dry land operations. The design of the platforms is usually a difficult problem. If the platform is underdesigned there is danger of failure endangering both human life and property. On the other hand, if the platform is over-designed there is an economic loss and loss of valuable materials in over-building the structure. Thus, there has been a tremendous amount of study and effort put into research in the proper design of such platforms. This research involves the study of currents, waves, hurricane forces, ice floes, etc. One of the most difficult areas is the Arctic North where there are ice floes. There the ice forces will be even greater than those experienced in any other area, even those experiencedin the Cook Inlet of Alaska. These ice forces create a tremendous horizontal force on the structure. One of the major problems involved in the design of structures for the high loads to be expected in the Arctic, is the transfer of horizontal loads into the soil. For conventional offshore structures, and for the present Cook Inlet structures, the horizontal transfer of load into the soil is through bending of vertical piles. For the higher loads, to be expected in the Arctic, transfer of horizontal loads in the conventional manner would propose very difficult design problems, especially if the soils are very soft as sometimes encountered in offshore areas. Thus it is seen that there is a need for a new design to lessen this problem. The present invention provides such a radically different design.

BRIEF DESCRIPTION OF THE INVENTION This invention concerns an embodiment of an offshore platform in which the horizontal as well as vertical loads are transferred essentially by means of axial load on piles. A plurality of piles supports a deck above the body of water. The piles are all slanted inwardly and converge at a small apex area at or near the water line elevation. This configuration makes a small area for the ice floes to attack and also provides for the horizontal transfer of load to the soil by means of axial load on the slanted piles.

DESCRIPTION OF THE DRAWINGS Various objectives and a better understanding of the invention can be had from the following description taken in conjunction with the drawings.

FIG. 1 is a side elevation view of one embodiment of an offshore platform according to my invention.

FIG. 2 is a view taken along the line 2-2 of FIG. 1.

FIG. 3 is a view of a segment of another embodiment of the invention taken between lines 3-3 and 3'--3' along the line 3-3 of FIG. 1.

FIG. 4 illustrates a modification of the embodiment of FIG. 1 in which the configuration of the piles of FIG. 1 has been enclosed by a sheet of metal.

FIG. 5 shows another arrangement of piles supporting a platform according to my invention.

FIG. 6 is a section view taken along the line 66 of FIG. 5.

FIG. 7 is a view taken along the line 7--7 of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION Attention is directed to FIG. 1 that shows a deck 10 supported above the surface 12 of the body of water 14. This support is by battered or slanted piles 16 which extend deep into the bottom 18 of water 14.

As mentioned above it is important that these piles have a configuration which has two main features: (I) that they be slanting so that the transfer of horizontal loads can be by axial load on the piles and (2) that near the water line the piles converge to a small area so that the area of the ice to which the piles may be subjected is minimized. It is preferred that the smallest area to which the piles converge be slightly above the normal air-water interface so that the ice floes will break as they ride up the sloping piles. A vertical line 20 is drawn to intersect the upper end of pile 16A so as to define an angle 0. Angle 0 should be sufficiently great so that the slope of the composite structure causes significant vertical force component to be exerted upon an ice sheet bearing against the structure. Typically, this minimum angle can be about 20. Typically, the maximum angle can be about 45. Ordinarily, drilling operations will be conducted down through piles 16. The present technology includes slant drilling rigs capable of drilling wells from platforms at an angle of up to 30 from the vertical, but equipment to drill at greater angles could be developed.

As mentioned above it is important to bring the piles to a small water line area so that the ice loads on the platform are generally reduced. This is accomplished in the embodiment shown in FIG. l as it can be seen that the piles converge in a small area at about the water line 12. This is obtained by having each of the piles slant inwardly at about the same angle 0. The direction of the piles with respect to the deck are all inwardly. Perhaps this can better be seen in FIG. 2 which shows piles 16A through 16H. The top of these piles defines a polygon of eight sides. They also all lie on a circle defined by the top of such piles. Each of these piles is directed inwardly at the same angle p with the sides of a polygon illustrated by dotted line 22. By proper selection of the angle p the pile 16 can be made to converge at a relatively small area at about the water line 12.

The piles in FIG. I between deck 10 and the bottom of water 18 approach an hour-glass figure having a minimized area at or near the water line. As can be seen each of the piles constitutes an element of a hyperboloid of one sheet. These piles can, if desired, be enclosed by skin or sheath such as sheet metal 24. This makes a structure such as shown in FIG. 4. If desired, the void exterior of piles and interior of skin or sheath 24 can be filled with gravel 26 as illustrated in the cutaway portion of 24 to give added stability to the platform.

Production tubing 28 is provided inside piles 16 and extends down to the producing zone. Casing is set and cemented in the well in connection with piles 16 in the usual manner and is therefore not shown here. Wells drilled through these piles 16 are directionally drilled under control conditions to complete them at the desired lateral positions. The drilling equipment and producing equipment used is supported by deck 10; however, such equipment has not been shown as such equipment is well known.

The embodiment of FIG. 1 may be modified in various manners. For example, for reasons of symmetry one may choose to make designs in which there are two sets of piles. One set of piles would be similar to that shown in FIGS. 1 and 2. The interior circle or set of piles would have a battered direction opposite to that of the external set of piles. This is shown in FIG. 3 which shows a portion of the modification between the line 3-3 and line 3'--3 of FIG. 1. The outer set of piles 30 is set on an outer circle 32 and each has the same angle p with a tangential plane 34. An inner group of piles 36 is placed about an inner circle 38. These each have the same angle p with a tangent 40. p in each case is the same for the inner circle and outer circle except that the direction of holes in one set is reversed with respect to those of the other.

Attention is next directed to FIG. 5 which shows another modification of the invention. Shown there is a deck 42 supported above a body of water 44 which has a bottom 46. The air-water line is indicated by reference 48. Four structural members or legs 50, 52, 54 and 56 support the deck. These legs, like piles of FIG. 1, are slanted inwardly with respect to the center of platform 42 and make an angle 0 with the vertical. FIG. 6 illustrates the small apex area at the water line 48 where the four legs converge. These legs are tied together at the area of convergence. As shown in FIG. 6, a steel plate 58 is welded or otherwise secured to each of the four legs. Thus, the composite structure is a rigid frame structure.

FIG. 7 shows the direction of the legs which they have along the line 7-7 of FIG. 5. Each of these legs can contain several individual piles 51 which are placed deep into the ocean bottom. Drilling and production operations are conducted through these piles 51. The massive cylindrical legs are typically 10 to 20 feet in diameter and usually do not penetrate the bottom very deeply, ordinarily not over about 10 feet, for example.

The inner piles within the massive cylindrical legs are typically 24 to 42 inches in diameter and penetrate the bottom 46 as deep as necessary to develop design holding capacity.

While the above embodiments of the invention have been described in considerable detail it is to be understood that various modifications of the system can be made without departing from the spirit or scope of the invention.

I claim:

I. An offshore structure for use in a water-covered area subjected to ice floes which comprises:

a deck;

a first set of a plurality of battered legs for supporting said deck from the bottom of said water-covered area, the points of contact between said legs and said deck defining a polygon, each of said legs forming an angle with the vertical, the direction of said legs being such that each leg enters the water at a point within the vertical projection of said polygon to form a small apex area at about the water line elevation, there being no bracing exterior of said legs between said deck and said bottom of said water-covered area.

2. A structure as defined in claim 1 in which the vertical angle of each said leg is between about 20 and about 45.

3. A structure as defined in claim 1 in which the legs are arranged such that each leg constitutes an element of a hyperboloid of one sheet.

4. A structure as defined in claim 2 in which the legs are arranged such that they compose a set of osculating surfaces at about the water-air interface.

5. A structure as defined in claim 4 in which the legs are rigidly tied together at about the level of the waterair interface.

6. A structure as defined in claim 4 in which the osculating surface is just above the water-air interface so that ice floes can ride up the sloping legs, thus causing such ice floes to break.

7. A structure as defined in claim 2 in which the top of the legs are arranged to define a circle, each leg making the same vertical angle with a vertical plane which is tangential to said circle at such leg.

8. A structure as defined in claim 7 in which a second set of battered legs are arranged inside said first set and having a battered direction opposite to that of said first set of battered legs.

Claims (8)

1. An offshore structure for use in a water-covered area subjected to ice floes which comprises: a deck; a first set of a plurality of battered legs for supporting said deck from the bottom of said water-covered area, the points of contact between said legs and said deck defining a polygon, each of said legs forming an angle with the vertical, the direction of said legs being such that each leg enters the water at a point within the vertical projection of said polygon to form a small apex area at about the water line elevation, there being no bracing exterior of said legs between said deck and said bottom of said water-covered area.

2. A structure as defined in claim 1 in which the vertical angle of each said leg is between about 20* and about 45*.

3. A structure as defined in claim 1 in which the legs are arranged such that each leg constitutes an element of a hyperboloid of one sheet.

4. A structure as defined in claim 2 in which the legs are arranged such that they compose a set of osculating surfaces at about the water-air interface.

5. A structure as defined in claim 4 in which the legs are rigidly tied togetHer at about the level of the water-air interface.

6. A structure as defined in claim 4 in which the osculating surface is just above the water-air interface so that ice floes can ride up the sloping legs, thus causing such ice floes to break.

7. A structure as defined in claim 2 in which the top of the legs are arranged to define a circle, each leg making the same vertical angle with a vertical plane which is tangential to said circle at such leg.

8. A structure as defined in claim 7 in which a second set of battered legs are arranged inside said first set and having a battered direction opposite to that of said first set of battered legs.

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