US3670813A

US3670813A - Pontoon structures in man-made lake for arctic operations

Info

Publication number: US3670813A
Application number: US59402A
Authority: US
Inventors: Floyd R Duncan
Original assignee: Pan American Petroleum Corp
Current assignee: Pan American Petroleum Corp
Priority date: 1970-07-30
Filing date: 1970-07-30
Publication date: 1972-06-20
Anticipated expiration: 1989-06-20

Abstract

The surface of the ground in the Arctic is unstable due to settling of the permafrost during thawing periods and to uneven heaving when extreme temperature changes occur within the permafrost zone. Extraction of hot fluids from deep subsurface wells drilled through the permafrost and other sources of heat emission such as from surface installations aggravate and add to the permafrost instability. This causes problems with foundations for surface installations. These problems are relieved by the use of a man-made lake to buoyantly support a surface installation such as a drilling rig, oil treating facilities, etc. The barge supporting the surface installation must be water-tight during periods of thaw and must be of sufficient strength to withstand ice forces in the winter.

Description

United States Patent Duncan [451 June 20, 1972 [72] Inventor: Floyd R. Duncan, Tulsa, Okla.

[73] Assignee: Pan American Petroleum Corporation,

Tulsa, Okla.

221 Filed: July 30,1970

[21] Appl.No.: 59,402

Hendrick ..6l/.5 X

26 TO GATHERING FACILITIES TREATING FACILITIES OTHER PUBLICATIONS Muller, Permafrost or Permanently Frozen Ground and Related Engineering Problems, J. W. Edwards, 1nc. Ann Arbor, Michigan, 1947, pp. 130, 176, 177.

Primary Examiner-David .I. Williamowsky Assistant Examiner-David H. Corbin Attorney-Paul F. Hawley and John D. Gassett ABSTRACT The surface of the ground in the Arctic is unstable due to settling of the pennafrost during thawing periods and to uneven heaving when extreme temperature changes occur within the pennafrost zone. Extraction of hot fluids from deep subsurface wells drilled through the permafrost and other sources of heat emission such as from surface installations aggravate and add to the permafrost instability. This causes problems with foundations for surface installations. These problems are relieved by the use of a man-made lake to buoyantly support a surface installation such as a drilling rig, oil treating facilities, etc. The barge supporting the surface installation must be water-tight during periods of thaw and must be of sufficient strength to withstand ice forces in the winter.

12 Claims, 2 Drawing Figures l8 WATER SUPPLY OR WITHDRAWAL PIITENTEDmzo I972 3.670.813"

' SHEET 2 or 2 PERMAFROST WATER SUPPLY OR WITHDRAWAL FIG.2

TREATING FACILITIES TO GATHERING FACILITIES INVENTOR- FLOYD R. DUNCAN A TTORNE Y PONTOON STRUCTURES'IN MAN-MADE LAKE FOR ARCTIC OPERATIONS BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to a system for supporting surface installations or equipment on top of a permafrost zone in the Arctic. It relates especially to a system utilizing a man-made lake to support such surface installations.

2. Setting of the Invention The search for oil and gas has led man to all comers of the earth. One of the recent such far comers is the Arctic North and especially the North Slope of Alaska. One of the biggest problems facing operation in areas covered by permafrost is the obtaining of a stable foundation upon which to place various surface facilities. The surface of permafrost is subject to widely changing states of conditions within a yearly period. For example, in the summer, it is common for the upper 4 or 5 feet to melt; this leaves the surface in more or less a marsh or swampy condition. Thus facilities that were set on the surface when the permafrost was rigidly frozen would ordinarily sink deep into the permafrost during seasons of thawing or even in winter if there is a substantial emission of heat attendant to surface or subsurface installations. The surface is also subjected to uneven heaving during extreme cold periods in the winter. Thus whenever equipment of any size, e.g., drilling derricks, installation facilities, warehouses, living quarters, etc., is to be used in the Arctic North there must be special means provided to support them in a stable fashion. At the present time such special means usually consists of using gravel pads or piles or combinations of these where piles are placed deep in the permafrost so that at the time of maximum thawing there is adequate piling penetration in the unthawed or unaltered permafrost to provide continuing support. The present invention discloses another manner of supporting surface installations and which in some cases may be superior and useable when more conventional means of support would fail or be more costly to install and maintain.

BRIEF DESCRIPTION OF THE INVENTION A man-made lake, usually of water, is created at the location at which it is desired to support a surface installation. A barge is placed on the lake, with optional access by means of a pontoon bridge. This barge is of sufficient size to support any installation or facility selected to be placed on it. Further, the barge is made sufficiently strong so that it' can withstand the ice forces in winter. The lake is'made so that the water depth is sufficient to buoyantly support the barge during periods of thaw and to hydraulically dampen any upward or downward heaving action of the permafrost beneath the lake itself. Water is added to or taken from the lake to maintain a desired level therein, and thereby maintain a prescribed absolute elevation for the surface installation where such a feature is important to the installation.

BRIEF DESCRIPTION OF THE DRAWINGS v Various objectives and a better understanding can be had of the invention by the following description of the drawings.

FIG. 1 illustrates a view, partly in cross-section, of a manmade lake carved out of the permafrost and on which is shown a barge carrying a derrick, a casing and other facilities.

FIG. 2 is similar to FIG. 1 except that the lake is made by dikes above the surface.

DETAILED DESCRIPTION OF THE INVENTION Attention is first directed to FIG. 1 which shows a barge supported by a body of water 12 which is made by excavating a cavity in permafrost zone 14. The area of the body of water 12 is sufficient to accommodate a barge 10 of selected size. The size of the barge l0 depends upon the services it is to perform. The depth of the body of water 12 is sufficient to maintain the barge 10 in a floating position during periods of thaw and also is sufficiently deep to minimize and dampen any upward or downward heaving action of the permafrost beneath the created lake. A typical thickness or depth of water is about 6 to 10 feet. The depth should be slightly more than the depth of the normal thaw line of the permafrost, but of course being deep enough to support the barge to be placed thereon.

In addition to barge 10 being of sufficient size to provide proper buoyancy for its load, it must also be built strong enough to withstand the forces of ice when the lake freezes in the winter.

It is ordinarily desired to maintain the level of water 12 fairly constant, particularly where several subsurface wells and associated well head facilities are supported and served by the barge facility. Thus a pump 16 is provided for pumping water from a source not shown into the lake through pipe l8 to offset surface subsidence. If the level in the lake rises too much, water can be pumped out through line 18 so as to main tain the proper level. I

Barge 10 is shown in a position above a well bore 20. This well bore has casing 22 mounted therein. The upper end of casing 22 is shown supported from dezrrick 24 by constant tensioning means 26 which are not usually essential but would be helpful in some situations such as if the level of water in the lake should vary. The derrick 24 can be used for drilling a well but is ordinarily removed after the well is completed; although it may be desirable to leave the derrick there for future workover operations.

. The barge facility can also be useful for producing operations. For example, a producing string 28 can be mounted inside casing 22 in a conventional manner. The upper end of tubing 28 is connected to a treating facility 30. The outlet of treating facility 30 is to a discharge line 32 which goes to a gathering facility not shown. The barge 10 can also be used to support any other facility such as living quarters with or without borehole 20 and its accompanying producing facilities.

When using the barge to support a casing it is important that the barge be maintained in a more or less fixed position. Thus anchors 36 are connected to winches 38 on the barge by anchor lines 40.

I shall now discuss briefly one method of creating the lake and placing a barge thereon. I prefer to create a lake by excavating permafrost in its frozen state in the winter. I make the excavation deep enough with sufficient area to accommodate the barge which is to be placed on the lake to be created. While the ground is frozen, I slide the barge into the excavation and let it come to rest on the bottom thereof. The barge will preferably be on skids. When the thaw comes the excavated lake will normally fill with water naturally from the surrounding thawing permafrost. As the lake fills, the barge will eventually be buoyantly supported by the water. The surface of the lake will seek the level of the surrounding ground water in the thawed permafrost. The barge is then anchored as described above.

As stated above it is normally desirable that the lake be created by excavation as this is usually more economical and the maintenance of the proper amount of water is easier. However in some instances it may be desirable to build the manmade lake with leveesrln some cases it may even be desirable to build the lake by a combination of excavations and levees. A levee-type lake is shown in FIG. 12. There the lake 42 is shown as being held by levees or dams 44. If the dams or levees or the bottom of the lake are exceptionally permeable it may be necessary to place an impermeable barrier over these areas. Such an impermeable area may be an impermeable asphalt sheet designated in the drawing as reference numeral 46. There are many ingenious ways in which the seepage of water through any artificial restraining walls and their resulting deterioration can be minimized by usage of impermeable barriers such as by relatively low-cost pliable thin films, membranes, natural clays, bentonitic materials as would appear justifiable by the physical circumstances encountered. However, it is to be understood that some movement of waters into and out of the lake can be tolerated without incun-ing excessive corrective costs. This movement of water might occasionally be a problem in the embodiment of H6. 2 but will probably seldom if ever be a problem in the embodiment of FIG. 1.

Barge l placed in a lake as shown in FIG. 2 would function quite similarly as a barge in the embodiment of FIG. 1. in either type lake, access to the barge can be by pontoon bridge 48 as illustrated in FIG. 2.

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

I claim:

1. A method of supporting an installation at a selected location in the permafrost area which comprises:

constructing a lake-retaining means at the selected location in said pennafrost area;

filling said lake-retaining means with a liquid to form a body of said liquid, the depth and volume of said liquid being sufficient to buoyantly support a barge and to dampen any upward or downward heaving action of the permafrost beneath said body of said liquid;

placing a floating barge on said body of liquid;

placing the installation to be supported on said barge;

maintaining said barge in a relatively fixed position.

2. A method as defined in claim 1 wherein said lake retaining means is made by excavating permafrost.

3. A method as defined in claim 1 in which said lake retaining means is made by building a retaining wall above the natural surface of the permafrost.

4. A method as defined in claim 1 including the additional steps of:

drilling a well from said barge;

placing casing in said well bore.

5. A method as defined in claim 1 in which said lake retaining means is made by a combination of digging an excavation and building a levee around such excavation.

6. A method as defined in claim 5 including the steps of placing an oil treating facility on said barge and then treating said produced oil on said oil treating facility.

7. A method as defined in claim 1 in which said liquid is water and including the steps of maintaining a selected level of said liquid by adding liquid thereto or removing liquid as required.

8. A method as defined in claim 1 including the step of making the lake a minimum depth of about 6 feet to minimize thawing of the permafrost immediately below the lake.

9. A method of supporting a barge at a selected location in an area of permafrost which comprises:

constructing a lake at the selected location by excavating a cavity in said pemiafrost when frozen;

sliding a barge onto the bottom of the resulting cavity while the exposed permafrost is still frozen;

leaving the barge in the cavity while allowing the surrounding permafrost to thaw and provide a body of liquid in the cavity, the depth and volume of said liquid being sufficient to buoyantly support said barge;

then maintaining said barge in a relatively fixed position.

10. A method as defined in claim 9 including the additional steps of:

drilling a well from said barge;

placing casing in said well.

11. A method as defined in claim 9 including the steps of placing an oil treating facility on said barge and then treating said produced oil on said oil treating facility.

12. A method as defined in claim 9 which includes the steps of maintaining a selected level of said body of liquid by adding liquid thereto or removing liquid as required.

Claims

1. A method of supporting an installation at a selected location in the permafrost area which comprises: constructing a lake-retaining means at the selected location in said permafrost area; filling said lake-retaining means with a liquid to form a body of said liquid, the depth and volume of said liquid being sufficient to buoyantly support a barge and to dampen any upward or downward heaving action of the permafrost beneath said body of said liquid; placing a floating barge on said body of liquid; placing the installation to be supported on said barge; maintaining said barge in a relatively fixed position.

4. A method as defined in claim 1 including the additional steps of: drilling a well from said barge; placing casing in said well bore.

9. A method of supporting a barge at a selected location in an area of permafrost which comprises: constructing a lake at the selected location by excavating a cavity in said permafrost when frozen; sliding a barge onto the bottom of the resulting cavity while the exposed permafrost is still frozen; leaving the barge in the cavity while allowing the surrounding permafrost to thaw and provide a body of liquid in the cavity, the depth and volume of said liquid being sufficient to buoyantly support said barge; then maintaining said barge in a relatively fixed position.

10. A method as defined in claim 9 including the additional steps of: drilling a well from said barge; placing casing in said well.