JPS5921811A - Prevention of growth of ice thickness - Google Patents

Abstract

PURPOSE:To greatly delay the speed of water freezing by covering the surface of water or ice surrounding an artificially made islet with a heat insulator having a coefficient of thermal conductivity smaller than that of ice. CONSTITUTION:An oil-well drilling apparatus 3 is set on an artificial islet 1 surrounded by a side wall 2, and frozen sea area 4 surrounding the artificial islet 1 is covered with a circular heat insulator 6 (e.g., expanded polystyrene, etc.) having a smaller heat conductivity than that of ice. The conductivity of low temperature heat from external area in the sea water or ice below the heat insulator 6 becomes difficult, and the conduction of low temperature heat to the area below the ice becomes interrupted. The speed of ice growth or water freezing can thus be greatly reduced or delayed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing the growth of ice thickness, particularly around water-sea structures.

Currently, it is estimated that about one-third of the earth's oil resources are located in icy waters, and in recent years, oil drilling has begun to be carried out by installing structures in icy waters. By the way, ice in frozen areas usually moves under the influence of wind power, tidal currents, etc., and the amount of movement ranges from several meters to several hundred kilometers per year.

When an offshore structure is installed in an icy area, the movement of the ice applies a large force to the structure.

Generally, the compressive strength of ice is around 30 K4/cd, so offshore structures need to maintain a strength higher than this.
Furthermore, since horizontal displacement of bottom-mounted structures, drills and pipes used when excavating on artificial islands is not allowed, they must be able to withstand large horizontal forces.

For this reason, water and sea structures have to be heavy structures in terms of strength, and artificial islands have to be built to counter horizontal forces.
The drawback is that oil drilling requires the construction of pile-driven caissons or caissons with increased self-weight, as well as ice protection dykes.

Therefore, the present invention has been made in order to eliminate such conventional drawbacks, and is particularly effective in preventing the growth of ice thickness in areas where the amount of ice movement is approximately several meters per year, and is intended to effectively prevent the growth of ice thickness in areas where the amount of ice movement is approximately several meters per year. By minimizing the hydraulic force applied to the water/sea structure, it eliminates the need to make the water/sea structure excessively heavy or to construct an ice break.

That is, the method for preventing ice thickness growth of the present invention is characterized by covering the water surface or the water surface with a heat insulating material having a thermal conductivity lower than that of ice.

The present invention will be described below based on embodiments shown in the drawings.

FIG. 1 shows a first embodiment of the present invention, in which an oil drilling rig 6 is installed on an artificial island 1 having a side wall 2 around it.
The surrounding sea area 4 is frozen 5, and the water surface around the artificial island 1 is covered with a circular heat insulating material 6.

The heat insulating material 6 may be placed floating on the sea surface before the sea water freezes, or may be placed on the ice after a thin layer of ice has formed.

Here, the heat insulating material 6 used in the present invention may be of any material as long as its thermal conductivity is lower than that of ice, and specifically, synthetic resin foam such as foamed polystyrene, foamed polyethylene, and foamed polyurethane. , natural rubber foam and synthetic resin sheets, preferably synthetic resin foam and natural rubber foam.

Since these foams have a cellular structure, in addition to the effect of reducing heat transfer due to the low thermal conductivity of the foam material itself, it is possible to expect a heat insulating effect due to the cellular structure. Furthermore, since it has a bubble structure, its apparent specific gravity is lower than the specific gravity of seawater, which is 1.025, and it can be floated on the water surface before it freezes or on the sea surface, and it is easy to transport and cut. Note that there are two types of cell structure: closed cell and open cell, and the closed cell type is particularly excellent in the above characteristics. The thickness of such a heat insulating material can be appropriately determined by taking into consideration the growth rate of ice depending on the outside temperature, as described later, and the position covered by the heat insulating material can also be determined, for example, in a water-sea structure, as shown in the examples described below. It can be selected as appropriate, such as covering the ice surface around the pillar material or covering it at a distance from the pillar material.

Further, the shape of the heat insulating material may be any one such as a disk, a flat plate, a sphere, a sheet, a granule, a box, and a bag, and it may be not only solid but also liquid. Furthermore, it is preferable to color it in a color that absorbs the red IA rays of the sun. By covering the sea surface or water surface with such a heat insulating material 6, (3) the sea water or ice on the bottom surface of the heat insulating material 6 becomes difficult to conduct cold heat from the outside, as if the thickness of the ice increases and the cold heat is conducted below the water surface. As a result,
It can significantly slow down the rate of ice formation and ice thickness growth.

Note that the range covered by the heat insulating material 6 may be made larger than the annual amount of ice movement in the area. Further, although FIG. 1 has been explained using an example of an icy area, the present invention is not limited thereto, and can of course be used to prevent ice thickness in freshwater areas.

Next, the principle of the present invention will be explained.

Generally, since the freezing temperature of seawater is about -2°C, the growth rate of ice in an icy area depends on the outside temperature of -2°C or lower, its duration, and the thermal conductivity of ice. Depending on the temperature difference between the outside air temperature and the freezing temperature, the ice floating on the sea surface grows and increases in ice thickness as the seawater in contact with the sub-ice surface freezes one after another. The latent heat required for this freezing is gradually cooled and removed as the upper surface of the ice is cooled by the outside air and heat conduction occurs from the lower surface of the ice to the upper surface. (4) Therefore, as ice grows, the ice itself begins to act as an insulator, blocking heat transfer, and the rate of ice growth gradually slows down.

Now, assuming that the outside temperature is constant and considering heat conduction only in the thickness direction of the ice, as shown in Figure 2, if the vertical axis is the ice thickness h and the horizontal axis is time t, the ice thickness is h =, tV"' (curve A
).

However, k is a coefficient including the thermal conductivity of ice, the latent heat of ice, etc.

Also, the ice growth rate V is dh k becomes.

Now, if we further take V on the vertical axis in Figure 2, the relationship between the growth rate and time is represented by curve B, and by drawing a horizontal line C from an arbitrary ice thickness on the vertical axis, it is If you draw a perpendicular line from the intersection and find the intersection with curve B, you can find out the ice growth rate. Therefore, it can be understood that in order to make the ice growth rate slower than that of natural ice, it is necessary to increase the thickness of the ice, that is, to artificially place an additional insulating material on top of the ice. Moreover, the smaller the thermal conductivity of this insulating material is than that of the ice itself, the more effective it is. For example, 3
If we consider ice with a thickness of 0 m and cover the water surface with an insulating material that is 10 times smaller than the thermal conductivity of the ice, this insulating material is equivalent to a thickness of 100 m of ice from the perspective of thermal conductivity, so the growth rate of the ice is is equal to that for an ice thickness of 130 m, and (0,56
o*/day), and from Figure 2, the growth rate of 30 cm ice thickness (2
, 43 crn/day). Specifically, the thermal conductivity (0,000064 J/sec, deg, m ) of foamed polyurethane sheets is about 1/46th that of ice, and if a 10 m thick sheet is used, the initial ice thickness + 460 cm Growth rate of thick ice, ′・
In other words, the growth rate is extremely low and the ice thickness actually hardly increases.

Figure 3 shows the relationship between the maximum thickness of ice that grows in some parts of the Arctic Ocean and the thickness of polyurethane foam laid on top of the ice.

According to this FIG. 3, the point where the slope of the song IJE becomes small,
That is, the thickness of polyurethane foam is approximately 150 to 20
It can be seen that a thickness of cm or more is extremely effective in preventing ice thickness growth.

FIG. 4 shows a second embodiment of the present invention, and is an example in which the icy sea surface around the monopot type bottomed structure 7 is covered with a heat insulating material 6 in a circular manner.

Construction of artificial islands becomes difficult as the water depth increases, so bottom-mounted structures are suitable. Conventionally, in this type of bottom-mounted structure, the shape of the side facing the sea surface was made conical to reduce hydraulic power, and the cross-sectional area was made as small as possible.
If the present invention is adopted, the hydraulic force is reduced, so the shape of the side facing the sea surface can be appropriately selected such as cylindrical or square.
There is no need to reduce the cross-sectional area as much as in the conventional case. Furthermore, since the hydraulic force applied in the horizontal direction is small, there is an advantage that there is no need to drive piles to secure the structure, or the number of piles can be reduced.

FIG. 5 shows a third embodiment of the present invention, in which the ice surface around each pillar 9 of a bottom-mounted (7) multi-pillar structure 8 is covered with a heat insulating material 6 independently in a circular shape.

Conventionally, multi-column structures could not be installed in areas with large ice thickness due to the large hydraulic force, but by installing insulation material around each column, the hydraulic force can be weakened, making it possible to install multi-column structures.

FIG. 6 shows a fourth embodiment of the invention, in which a 70-ring type structure 10 is secured by an anchor 11. In this case, the drill pipe 12 is displaced by about 5% of the water depth, but it is impossible to lock the drill pipe 12 with the chain 16 and the anchor 11 in a sea area with large hydraulic power and large ice thickness.

However, if the water surface around the structure 10 is covered with the heat insulating material 6, the hydraulic force will be reduced, and anchorage and anchor mooring will become possible.

FIG. 7 shows a fifth embodiment of the present invention, in which a half-submerged wooden structure 1
4 is moored by Cheno 16.

If the water surface is covered with the heat insulating material 6, the hydraulic force will be reduced, making mooring possible during freezing.

FIG. 8 shows a sixth embodiment of the present invention, in which the columns 9 of a multi-column (8) structure are not independent, but the entire surrounding water surface is covered with a heat insulating material 6.

9A and 9B show a seventh embodiment of the present invention, in which a ring-shaped insulating material 6 is placed around the pillar 9 of the structure at intervals.
This is an example covered with

In this case, the ice part 5A not covered by the insulation material 6 becomes thick, but as shown in FIG. 9B, when the ice moves, the water breaks at the thin ice part 5B covered by the insulation material 6. This has the same effect as covering the entire circumference of the column 9 with the heat insulating material 6.

FIG. 10 shows an eighth embodiment, in which a pillar 9 is surrounded by a gear-shaped heat insulating material 6.

FIGS. 11A and 11B show a ninth embodiment, in which a pillar 9 is partially covered with a heat insulating material 6 having a cutout shape.

These 8th and 9th embodiments can not only be expected to have the same effects as the 7th embodiment, but also require transportation of supplies on ice by trucks on ice when ice forms on artificial islands.
Access 15 with large ice thickness can be used. Furthermore, even if the ice thickness in the notch increases, it has little effect on the overall hydraulic power.

12A and 12B show the tenth embodiment, and FIG. 12A shows the case where the spherical heat insulating material 6 is laid around the pillar 9, and FIG. 12B
1 and 2 respectively show the case where a small plate-shaped heat insulating material 6 is installed.

As described above, since the present invention covers the water surface or the water surface with a heat insulating material having a thermal conductivity lower than that of ice, this heat insulating material prevents the infiltration of cold heat and delays the freezing period.
After freezing, it is possible to prevent the ice from growing thicker. In particular, the smaller the thermal conductivity of the insulation material is than that of ice, the more
The effect of preventing ice thickness growth will be greater. Another advantage of the insulation material is that you can choose the thickness, shape, method of laying it on the ice surface, etc. as you like.

Therefore, the present invention prevents the growth of ice thickness around oil drilling structures in ice-cold areas and reduces the hydraulic force exerted on these structures. This eliminates the need for construction, allowing for more economical construction.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional schematic diagram showing the first embodiment of the present invention, and FIG.
The figures show the relationship between ice thickness and time and the ice growth rate and time, Figure 3 shows the relationship between maximum ice thickness and polyurethane foam thickness, and Figure 4 shows a second embodiment of the present invention. FIG. 5 is a vertical cross-sectional schematic diagram showing the third embodiment of the present invention, FIG. 6 is a longitudinal cross-sectional schematic diagram showing the fourth embodiment of the present invention, and FIG. 7 is a vertical cross-sectional schematic diagram showing the fourth embodiment of the present invention. A vertical cross-sectional schematic diagram showing the fifth embodiment,
FIG. 8 is a cross-sectional schematic diagram showing a sixth embodiment of the present invention, and FIG.
Figure A is a schematic cross-sectional view showing the seventh embodiment of the present invention, Figure 9B is an explanatory longitudinal cross-sectional view thereof, Figure 10 is a schematic cross-sectional view showing the eighth embodiment of the present invention, and Figure 11A is , B are schematic cross-sectional views showing a ninth embodiment of the present invention, and FIGS. 12A and 12B are schematic cross-sectional views showing a tenth embodiment of the present invention, respectively. 6...Insulation material. Figure 4 JP-A-59-21811 (8) Figure 7 Figure 8 7〈Go-=〉, [i-cho

Claims (1)

[Claims] A method for preventing ice thickness growth, which comprises covering a water surface or a water surface with a heat insulating material having a lower thermal conductivity than ice.