US3849993A

US3849993A - Method for constructing sea ice islands in cold regions

Info

Publication number: US3849993A
Application number: US382006A
Authority: US
Inventors: J Robinson; Durning
Original assignee: Union Oil Company of California
Current assignee: Union Oil Company of California
Priority date: 1973-07-23
Filing date: 1973-07-23
Publication date: 1974-11-26
Anticipated expiration: 1991-11-26

Abstract

A method for constructing sea ice islands in cold regions in which a water impervious membrane is placed on the surface of a floating sheet of natural ice and sea water is thereafter deposited on the membrane and allowed to freeze to form an ice body having a mass such that its draft is greater than the water depth, whereby the ice island is permanently grounded. Brine is drained from the ice body through wells penetrating the upper portion of the ice body above the membrane. Alternatively, sea water can be frozen directly on the surface of the natural ice until the ice sheet is thickened sufficiently that the bottom of the ice is just above the marine floor. The ice body is cured at ambient conditions to allow brine to drain from the bottom of the body. Next, a water impervious membrane is applied to the surface of the ice body and additional sea water frozen thereon to thicken the ice body sufficiently to ground it on the marine floor and to raise the surface of the body above the surrounding floating ice. Brine is drained from the upper portion of the ice body above the impermeable membrane through wells penetrating this portion of the body.

Description

United States Patent 1 Robinson et al.

[ 1 Nov. 26, 1974 METHOD FOR CONSTRUCTING SEA ICE ISLANDS IN CDLD REGIONS [75] Inventors: Joel P. Robinson, Los Angeles; Paul .1. Burning, La Habra, both of Calif.

[73] Assignee: Union Oil Company of California,

Los Angeles, Calif.

[22] Filed: July 23, 1973 [21] Appl. No.: 382,006

[52] US. Cl 61/46, 61/1, 61/36 A, 62/1, 62/260 [51] Int. Cl. E021) 17/00, F25c 1/02 [58] Field of Search .1 61/46, 50, 1, 58, 46.5, 61/36 A; 62/1, 260, 58

[56] References Cited UNITED STATES PATENTS 3,660,983 5/1972 Gill 61/1 3,750,412 8/1973 Fitch et a1 61/46 Primary Examiner-Jacob Shapiro Attorney, Agent, or Firm-Dean Sandford; Richard C. Hartman [57] ABSTRACT A method for constructing sea ice islands in cold regions in which a water impervious membrane is placed on the surface of a floating sheet of natural ice and sea water is thereafter deposited on the membrane and allowed to freeze to form an ice body having a mass such that its draft is greater than the water depth, whereby the ice island is permanently grounded. Brine is drained from the ice body through wells penetrating the upper portion of the ice body above the membrane. Alternatively, sea water can be frozen directly on the surface of the natural ice until the ice sheet is thickened sufficiently that the bottom of the ice is just above the marine floor. The ice body is cured at ambient conditions to allow brine to drain from the bottom of the body. Next, a water impervious membrane is applied to the surface of the ice body and additional sea water frozen thereon to thicken the ice body sufficiently to ground it on the marine floor and to raise the surface of the body above the surrounding floating ice. Brine is drained from the upper portion of the ice body above the impermeable membrane through wells penetrating this portion of the body.

10 Claims, 4 Drawing Figures METHOD FOR CONSTRUCTING SEA ICE ISLANDS IN COLD REGIONS This invention relates to the construction of sea ice islands, and more particularly to a method for forming artificial sea ice islands to serve as a base for operations.

Because of the increased activity in cold areas such as the polar regions, and especially in the Arctic, and the lack of land masses in much of the area, need exists for suitable bases from which exploratory drilling, petroleum recovery, supply, tanker berthing and scientific operations can be conducted. Some of these operations have been successfully carried out from floating pack ice or from fast ice along the shore. The ice pack, which accounts for almost all of the ice cover in the Arctic ocean, is a conglomeration of very young ice and ice several years old. However, because of the low strength of the relatively thin, e.g., 2 to 4-foot thick sheet ice, and the vigorous forces and pressures that exist within the pack ice that tend to keep it in a continual state of fracture, the pack ice is highly unreliable as an operational site. The use of fast ice along the shore as a base for operations is also often unsatisfactory since the desired operational site may not be frozen over, and often operations must be deferred until late in the season to obtain ice of sufficient thickness to support the intended operations.

Natural ice islands, formed by a calving from a land ice mass, are occasionally found adrift in the ice pack. Because of their substantial size and thickness, these floating blocks are found to be excellent platforms from which certain operations can be conducted. However, often these natural ice islands can not be found at the desired location, and because they are usually adrift, they cannot be employed in a fixed location, unless the island happens to be grounded. Furthermore, even ifa natural ice island is found grounded at the desired location, experience has shown that changes in the wind, currents, or forces exerted by surrounding pack ice can cause the ice island to break up or to be set adrift.

Attempts have been made to thicken sheets of natural sea ice by placing sea water on the surface of the ice and allowing the water to freeze. ln this manner the sheet ice is thickened to provide additional strength. While these attempts have been somewhat successful in providing a base for certain light operations, at least on an experimental basis, because of the relatively low strength and mobile nature of the sheet ice, the technique does not provide a suitable base for heavy duty operations in a fixed location.

Oftentimes, sea water is the only available water for ice island construction. However, a major problem encountered in constructing artificial sea ice islands is that, upon freezing, the salts contained in the sea water concentrate in small pockets of highly concentrated brine which weaken the ice. In natural, or floating sea ice, these brine pockets slowly migrate to the bottom of the ice and drain into the sea water beneath the ice. However, if the sea ice rests on the marine floor, there is no escape for this concentrated brine, and it builds up in the bottom layers of ice, greatly weakening them. Thus, need exists for a method for constructing artificial sea ice islands to provide'both temporary and permanent fixed bases from which various operations can be conducted.

Accordingly, it is a principal object of this invention to provide a method for constructing relatively high strength, fixed location, sea ice islands.

Another object of the invention is to provide a method for constructing a relatively high strength sea ice island in a fixed location from which various operations can be conducted.

Still another object of the invention is to provide a method for constructing an artificial sea ice island useful as an offshore drilling platform.

A still further object of the invention is to provide a method for thickening natural sheet ice to provide a bottom-supported, fixed location, sea ice island.

Other objects and advantages of the invention will be apparent from the following description and accompanying drawings, in which:

FIG. 1 is a cross-sectional view schematically illus trating a typical sheet of natural sea ice floating on a marine body;

FIG. 2 is a cross-sectional view schematically illustrating the completed sea ice island;

FIG. 3 is a cross-sectional view schematically illus trating a sea ice island during construction by an alternative method and prior to bottoming on the marine floor; and

FIG. 4 is a cross-sectional view schematically illustrating the completed sea ice island constructed by the alternative method.

Briefly, the invention contemplates a method for constructing sea ice islands in cold regions in which a water impervious membrane is placed on the surface of a floating sheet of natural ice and sea water is thereafter placed on the membrane and allowed to freeze 'to form an ice body having a mass such that its draft is greater than the water depth, whereby the ice island is permanently grounded. Brine is drained from the ice body through wells penetrating the upper portion of the ice body above the membrane. Alternatively, sea water can be frozen directly on the surface of the natural ice until the ice sheet is thickened sufficiently that the bottom of the ice is just above the marine floor. The ice body is cured at ambient conditions to allow brine to drain from the bottom of the body. Next, a water impervious membrane is applied to the surface of the ice body and additional sea water frozen thereon to thicken the ice body sufficiently to ground it on the marine floor and to raise the surface of the body above the level of the surrounding ice. Brine can be drained from the upper portion of the ice body above the impermeable membrane through wells penetrating this portion of the body.

Artificial sea ice islands can be constructed by the method of this invention in any geographic region having average ambient temperatures during the construction period sufficiently low to freeze sea water. As a practical matter, it is preferred that the method be practiced in a region exhibiting average daily ambient temperatures below about 25 F. during the construction period, and most preferably below about 10 F. Average daily ambient temperatures within these ranges are encountered in both the Arctic and Antarctic during a substantial portion of the year.

HO. 1 illustrates a typical floating ice sheet wherein a substantially uniform sheet of ice 10 is floating on a marine body 12 overlying a marine floor 14. Ice sheet 10 can be part of the polar ice pack or can be fast ice attached to the shore. Marine body 12 can be an ocean,

sea, bay, or like salt water body. Preferably, the construction site is selected at a location and construction commenced at a season of the year during which the construction site is covered with a layer of sea ice of substantially uniform thickness and having a relatively fracture-free, smooth surface. Although the sheet of sea ice need only have sufficient thickness to support the weight of the men and equipment employed in the construction operation, and may have an initial thickness of one foot, or less, thicker initial ice coverage is preferred. Oftentimes, the initial ice sheet will be up to 6 feet in thickness, with coverages of 2 to 3 feet being typically encountered.

Construction of the ice island is commenced by placing water-impervious membrane 16 directly on the surface of the ice sheet 10 at the desired location of the ice island, or at a preselected location such that drift during the construction. operation will place the island over the desired location at the time of grounding. This membrane can be constructed of any material that can be applied under the ambient conditions encountered at the construction site and which remains water impervious at the ice temperatures encountered. Suitable materials include water impervious plastic sheets, such as polyethylene, polyvinyl chloride, polyurathane, elastomer, and expanded polystyrene foam sheeting; impregnated fabrics; impregnated paper such as asphalt impregnated paper; metal foils such as aluminized paper; road oil; cutback asphalt, vinyl and the like, or a combination of those materials. Sea water is deposited upon water impermeable membrane 16 either by flooding with sea water pumped onto the surface of the membrane, or by spraying sea water onto its surface. Either confined flooding or free-flooding can be employed. In the confined flooding technique, a system of dikes having the desired shape are formed to contain the sea water during the freezing operation. In the free flooding technique, the sea water is placed on the surface and allowed to disperse in all directions from the point of discharge. The water is discharged onto the membrane 16 covering the surface of the natural ice at the center of the point to be thickened, and an oval or circular pattern having its thickest portion at the middle and tapering outwardly t the edges is usually obtained. The size and shape of the ice island will depend on the initial thickness of ice sheet 10, the water discharge rate and application technique, and the air temperature. If a large ice island is to be formed, water can be discharged at several points. The location of the discharge points relative to each other will affect the shape of the resulting ice island. With either the confined or free-flooding techniques, it is usually not necessary to remove snow from the surface ofthe ice or to otherwise prepare the surface. However, the show can be leveled to knock down the drifts, which will also pack the snowand produce better spreading of the initial floodings.

The sea water can be applied to the surface of the natural sheet ice continuously at a rate such that freezing prevents accumulation of excessive depths of water or, alternatively, the ice can be flooded intermittently to a shallow depth and allowed to freeze to form successive layers of ice. The depth of each layer should be about 2 to 6 inches, measured at its deepest part, the optimum depth for individual flooded layers being about 4 inches. The depth of the water and the ultimate thickness of each layer is thickest at the center of the body, and less towards the edges to produce the tapering thickness.

As schematically illustrated in FIG. 2, the weight of the added layers of ice 18 applied by free-flooding causes relaxation or plastic deformation of the natural ice sheet 10 until a new point of buoyancy equilibrium is established, resulting in a buildup ofa convexo-plane shape with the convex surface laying at the interface of the original ice surface. Of course, the pattern obtained by confined flooding will be different since the ice buildup will conform to the shape of the dike. This less tapered configuration often causes more severe stresses in the ice sheet 10 at the edge of and adjacent to the ice buildup. The elevation of the surface of ice 18 will be somewhat higher than the surrounding sheet ice since the larger ice mass will float higher in the water than the thinner sheet ice.

The application of sea water to the surface of ice body 18 is continued until the mass of the ice body is such that its draft is greater than the depth of marine body 12, whereupon the ice body becomes grounded and anchored in place. As illustrated in FIG. 2, ice layers applied to the surface subsequent to grounding can no longer cause the body to sink to a lower point of buoyancy equilibrium, thus the ice builds up above the surface of the surrounding ice as additional layers are applied. Flooding is continued until the mass of the ice island is sufficient to securely anchor the island to the marine bottom, and to obtain an elevated working platform. It is preferred that additional ice layers be applied until the surface of ice body 18 is at least about 3 feet above its maximum free-floating elevation to assure permanent grounding. Ice islands having surface elevations up to about 40 feet higher than the surrounding sheet ice can be constructed, and surface elevations as much as 10 to 30 feet above the surrounding sheet ice are readily attainable.

Brine drainage of ice 18 is accomplished by providing a series of wells or bore holes 20 which penetrate ice 18 to a point adjacent to impervious membrane 16. It is important that membrane 16 is not punctured or perforated, otherwise the brine could drain into natural ice sheet 10 below impervious membrane 16. Wells 20 can be provided by positioning a vertical conduit at the desired location of each well prior to placement and freezing of the sea water. Upon completion of the flooding and freezing operation the conduits can be perforated to provide drainage, or the conduits can be removed to provide the formed well in ice 18. Also, wells 20 can be provided by drilling a series of boreholes through ice 18 to a point immediately above impervious membrane 16. In either case, brine will drain from ice 18 and accumulate in wells 20, from where it can be removed by pumping. Wells 20 are spaced throughout ice mass 18 so as to provide for brine drainage from the ice mass, and are preferably spaced at intervals of about 20 to feet.

In an alternative mode of practicing the invention illustrated in FIGS. 3 and 4, construction of the ice island is commenced by depositing sea water directly on the surface ofice sheet 10 to form a body of ice 22. The application of water to the surface of ice body 22 is continued until the mass of the ice body is such that its draft approaches the water depth of marine body 12, but is not sufficient to ground the ice body. The alternate flooding and freezing operation is then discontinued and the ice mass cured for a sufficient period of time to allow drainage of concentrated brine from the bottom of the ice mass. The time required for the brine to migrate through the ice to drain from the bottom of the ice mass will depend in part upon the thickness of the ice and the ambient air temperatures. However, curing of the ice prior to grounding for a period of one to 6 months is usually adequate to obtain drainage of the concentrated brine from the ice mass.

After the ice mass has been cured, water impervious membrane 16 is placed on the surface of ice mass 22. After impervious membrane 16 is installed, the application of water to the surface of the ice body is resumed to form ice body 24 until the mass of the combined ice is such that the draft of the ice body is greater than the water depth of marine body 12, whereupon the ice body becomes grounded and anchored in place. As illustrated in FIG. 3, ice layers applied to the surface subsequent to grounding can no longer cause the body to sink to a lower point of buoyancy equilibrium, thus ice 24 builds up above the surface of the surrounding ice as additional layers are applied. Flooding is contin ued until the mass of the ice island is sufficient to securely anchor the island to the marine bottom, and to obtain an elevated working platform. The system of wells 26 is provided in the previously described manner to provide brine drainage from ice body 24.

The method of this invention can be used to construct ice islands in waters having depths of less than about 50 feet, and is especially suited for construction of ice islands in water up to about 30 feet in depth, and particularly in relatively shallow water having a depth of feet or less.

If desired, the ice island can be constructed in a plurality of layers separated by a like plurality of water impervious membranes 16.

Also, if desired, piles or other supportive members can be frozen into the ice during the construction process to provide an integral support system for a drilling rig or other equipment to be placed upon the artificial ice island.

This invention is further illustrated by the following examples which are illustrative of specific modes of practicing the invention and are not intended as limiting the scope of the invention as defined by the appended claims.

EXAMPLE I This example illustrates the practice of the invention in a cold region. The ice island is constructed in a marine body having a depth of about 8 feet at mean low tide. The construction site is covered by a sheet of floating natural ice that is relatively smooth and free of fractures. Snow drifts are leveled and the loose snow compacted. The site to be flooded is covered with polyvinyl chloride sheeting placed directly upon the compacted snow. The joints between adjacent sheets are overlapped and sealed to provide a water impervious membrane. A pump is set and sea water pumped onto the surface of the ice sheet covered by the membrane. The surface is flooded to a shallow depth of between about 2 and 6 inches at its deepest portion and the water allowed to freeze. This alternate pumping and freezing operation is continued until the resulting ice body has a draft greater than the water depth so that 6 pleted ice island has an elevation at its highest point about 10 feet above the surrounding floating ice, and a contour that tapers from the center to the edges. A system of bore holes spaced about 30 feet apart are drilled through the ice body so as to terminate immediately above the membrane, and the brine that drains into the bore holes is removed by pumping.

EXAMPLE 2 This example illustrates an alternative method for constructing sea ice islands in a cold region. The ice island is constructed in a marine body having a depth of about 15 feet at mean low tide. The construction site is covered by a sheet of floating natural ice that is relatively smooth and free of fractures. Snow drifts are leveled and the loose snow cover compacted. Pumps are set and sea water pumped onto the surface of the ice sheet through a single discharge hose to a depth of about 4 inches. Pumping is discontinued and the water allowed to freeze. This alternate pumping an freezing operation is continued until the resulting ice body has a draft such that the bottom of the ice mass is about 1 foot above the marine floor at low tide. The alternate flooding and freezing operation is discontinued and the ice mass allowed to cure for a 2 month period to permit brine drainage into the sea beneath the ice mass. Next, the surface of the formed ice mass is covered with a water impervious layer of 15 pound roofing felt and cutback asphalt is applied to the roofing felt. The alternate pumping and freezing operation is resumed and continued until the surface of the ice island has an elevation at its highest point about 5 feet above the surrounding floating ice, and a contour that tapers from the center to the edges. A system of bore holes spaced about 25 feet apart are drilled through the ice body so as to terminate immediately above the membrane, and the brine that drains into the bore holes is removed by pumping.

Various embodiments and modifications of this invention have been described in the foregoing description and examples, and further modifications will be apparent to those skilled in the art. Such modifications are included within the scope of this invention as defined by the following claims.

Having now described the invention, we claim:

11. A method for constructing an artificial sea ice island in a marine body covered by a floating sheet of ice, which comprises:

placing a water impervious membrane on the surface of said floating sheet of ice; thereafter placing sea water on said sheet of ice covered by said water impervious membrane under ambient conditions such that the water is frozen to form an ice body having a mass sufficiently large that the draft of the ice body exceeds the depth of the marine body whereby the ice island is permanently grounded and the surface of the island raised above that of the surrounding floating ice;

establishing a plurality of wells in the ice body above said impervious membrane for the drainage of brine from the ice body; and

removing accumulated brine from said wells.

2. The method defined in claim 1 wherein said sea water is intermittently placed on the surface of said sheet of ice covered by said water impervious membrane and allowed to freeze between placements.

3. The method defined in claim 2 wherein said sea water is intermittently placed on said ice to a depth of about 2 to 6 inches at each placement.

4. The method defined in claim 1 wherein said sea water placed on said sheet of ice covered by said water impervious membrane freely floods said surface.

5. The method defined in claim 1 wherein said marine body has a depth of less than about 50 feet.

6. The method defined in claim 1 wherein the elevation of said ice island is at least about 3 feet above its maximum free-floating elevation.

7. The method defined in claim 1 wherein prior to placement of said water impervious membrane, sea

water is placed on the surface of said floating sheet of ice and frozen to form an ice body having a mass sufficiently large that the bottom of the ice body is just above the marine floor, and including the step of curing said ice under ambient conditions for a period of time sufficient to allow brine to drain from the ice body.

8. A method for constructing an artificial sea ice island in a marine body covered by a floating sheet of ice, which comprises:

placing a water impervious membrane on the surface of said floating sheet of ice; placing sea water on the surface of said floating sheet of ice covered by said water impervious membrane to freely flood said surface to a maximum depth of about 2 to 6 inches under ambient condition below the freezing point of said sea water; allowing the sea water placed on said ice to freeze; repeating the alternate flooding and freezing steps to form an ice body having a mass sufficiently large that the draft of the ice body exceeds the depth of the marine body whereby the ice body is permanently grounded and the elevation of the ice body is at least about 3 feet above its maximum freefloating elevation; establishing a plurality of wells in the ice body above said impervious membrane spaced about to 50 feet apart for the drainage of brine from the ice body; and removing accumulated brine from said wells. 9. The method defined in claim 8 wherein prior to placement of said water impervious membrane, sea water is placed on the surface of said floating sheet of ice and frozen to form an ice body having a mass sufficiently large that the bottom of the ice body is just above the marine floor, and including the step of curing said ice under ambient conditions for a period of time sufficient to allow brine to drain from the ice body.

10. A method for constructing an artificial sea ice island in a marine body covered by a floating sheet of ice, which comprises:

placing sea water on the surface of said floating sheet of ice to freely flood the surface to a maximum depth of about 2 to 6 inches under ambient conditions below the freezing point of water; allowing the sea water placed on said ice to freeze; repeating the alternate flooding and freezing steps to form an ice body having a mass sufficiently large that the bottom of the ice body is just above the marine floor; curing the ice under ambient conditions for a period of time sufficient to allow brine to drain from the ice body; placing a water impervious membrane on the surface of the ice body; thereafter placing additional sea water on the surface of said ice body covered by said impervious membrane to freely flood said surface to a depth of 2 to 6 inches under ambient conditions below the freezing point of water; allowing the sea water placed on said ice to freeze; repeating the alternate flooding and freezing steps to form an ice body having a mass sufficiently large that the draft of the ice body exceeds the depth of the marine body whereby the ice body is permanently grounded; continuing the alternate flooding and freezing steps until the elevation of the ice body is at least about 3 feet above its maximum free-floating elevation; establishing a plurality of wells in the ice body above said impervious membrane spaced about 20 to 50 feet apart; and

removing accumulated brine from said wells.

Claims

1. A method for constructing an artificial sea ice island in a marine body covered by a floating sheet of ice, which comprises: placing a water impervious membrane on the surface of said floating sheet of ice; thereafter placing sea water on said sheet of ice covered by said water impervious membrane under ambient conditions such that the water is frozen to form an ice body having a mass sufficiently large that the draft of the ice body exceeds the depth of the marine body whereby the ice island is permanently grounded and the surface of the island raised above that of the surrounding floating ice; establishing a plurality of wells in the ice body above said impervious membrane for the drainage of brine from the ice body; and removing accumulated brine from said wells.

7. The method defined in claim 1 wherein prior to placement of said water impervious membrane, sea water is placed on the surface of said floating sheet of ice and frozen to form an ice body having a mass sufficiently large that the bottom of the ice body is just above the marine floor, and including the step of curing said ice under ambient conditions for a period of time sufficient to allow brine to drain from the ice body.

8. A method for constructing an artificial sea ice island in a marine body covered by a floating sheet of ice, which comprises: placing a water impervious membrane on the surface of said floating sheet of ice; placing sea water on the surface of said floating sheet of ice covered by said water impervious membrane to freely flood said surface to a maximum depth of about 2 to 6 inches under ambient conditions below the freezing point of said sea water; allowing the sea water placed on said ice to freeze; repeating the alternate flooding and fReezing steps to form an ice body having a mass sufficiently large that the draft of the ice body exceeds the depth of the marine body whereby the ice body is permanently grounded and the elevation of the ice body is at least about 3 feet above its maximum free-floating elevation; establishing a plurality of wells in the ice body above said impervious membrane spaced about 20 to 50 feet apart for the drainage of brine from the ice body; and removing accumulated brine from said wells.

9. The method defined in claim 8 wherein prior to placement of said water impervious membrane, sea water is placed on the surface of said floating sheet of ice and frozen to form an ice body having a mass sufficiently large that the bottom of the ice body is just above the marine floor, and including the step of curing said ice under ambient conditions for a period of time sufficient to allow brine to drain from the ice body.

10. A method for constructing an artificial sea ice island in a marine body covered by a floating sheet of ice, which comprises: placing sea water on the surface of said floating sheet of ice to freely flood the surface to a maximum depth of about 2 to 6 inches under ambient conditions below the freezing point of water; allowing the sea water placed on said ice to freeze; repeating the alternate flooding and freezing steps to form an ice body having a mass sufficiently large that the bottom of the ice body is just above the marine floor; curing the ice under ambient conditions for a period of time sufficient to allow brine to drain from the ice body; placing a water impervious membrane on the surface of the ice body; thereafter placing additional sea water on the surface of said ice body covered by said impervious membrane to freely flood said surface to a depth of 2 to 6 inches under ambient conditions below the freezing point of water; allowing the sea water placed on said ice to freeze; repeating the alternate flooding and freezing steps to form an ice body having a mass sufficiently large that the draft of the ice body exceeds the depth of the marine body whereby the ice body is permanently grounded; continuing the alternate flooding and freezing steps until the elevation of the ice body is at least about 3 feet above its maximum free-floating elevation; establishing a plurality of wells in the ice body above said impervious membrane spaced about 20 to 50 feet apart; and removing accumulated brine from said wells.