US3703929A

US3703929A - Well for transporting hot fluids through a permafrost zone

Info

Publication number: US3703929A
Application number: US87449A
Authority: US
Inventors: Robert W Rardin
Original assignee: Union Oil Company of California
Current assignee: Union Oil Company of California
Priority date: 1970-11-06
Filing date: 1970-11-06
Publication date: 1972-11-28
Anticipated expiration: 1989-11-28

Abstract

A well adapted to transport hot fluids through a permafrost zone comprising a surface conductor, a short section of refrigerated casing adapted to support the upper section of the well without melting of the surrounding permafrost, a surface casing extending through the permafrost, production casing and production tubing. All casing strings are supported in the well so that the upper sections are in compression. Pressure integrity between casing strings is maintained by packing glands in the well head. Also, a short section of casing can be provided in the annulus exterior of the surface casing to provide a separately enclosed refrigeration reservoir, or to provide for circulation of refrigerant.

Description

[ Nov. 28, 1972 United States Patent Rardin [5 WELL FOR TRANSPORTING HOT OTHER PUBLICATIONS FLUIDS THROUGH A PERMAFROST ZONE Alaskan Completions will be Complicated, World Oil, January 1970, Page 85.

m5 5 ..D me m mu 0 mm A we 3 2w... mm mm? m m m n v. m M @C W w. Rm Um m m m [22] Filed: Nov. 6, 1970 ABSTRACT 21 A 1. N 87 9 PP ,44 A well adapted to transport hot fluids throu gh a permafrost zone comprising a surface conductor, a short section of refrigerated casing adapted to su [52] U.S. Cl............ ......166/302, 166/D1G. l, 166/57 pport the [51] Int. Cl. 43/24 upper section of the well without melting of the sur- [58] Field of Search....................166/302, 57, DIG. 1 r n ing p f surface ing en ing rrnaf through the pe rost, production casing and production tubing. All casing strings are supported in pper sections are in compression.

[56] References Cited the well so that the u UNITED STATES PATENTS Pressure integrity between casing strings is maintained 2,772,737 12/1956 Bond et a1. ..................l66/57 Yj t g' i 8 3,142,336 66/57 g pl'OVl e in e annu us ex erior 3,160,208 166/57 3,405,763 166/208 3,498,381 3,561,531

parately enclosed geration reservoir, or to provide for circulation of refrigerant.

of the surface casing to provide a se refri 15 Claims, 2 Drawing Figures 7/1964 Doscher 12/1964 Jorda........................... 10/1968 Pitts et 3/1970 Earlougher, Jr.............166/57 2/1971 Miller...................l66/DIG. 1

Z a M7. m A

WELL FOR TRANSPORTING HOT FLUIDS THROUGH A PERMAFROST ZONE This invention relates to wells for recovering earth fluids, and more particularly to wells penetrating a permafrost zone and to a method for completing such wells.

Permafrost is perennially frozen ground found in the Artic regions. The permafrost zone contains some layers of gravel free of ice known as dry permafrost, but the bulk of the zone is composed of rocks or of unconsolidated aggregates of sand, silt. and gravel in which the interstitial water is frozen to ice. Permafrost is formed by the spreading downward of the low temperatures found at the surface in the Artic winters, particularly in regions of low snowfall. There is seasonal thawing and freezing at the surface, but thawing rarely penetrates more than 18 inches where the permafrost is protected bytundra or vegetation. The downward spread of freezing temperatures to form permafrost continues until an equilibrium is reached with the heat flow from the earths interior. The thickness of the permafrost zone varies with latitude and with particular geographic location. Permafrost is not believed to exist under most deep large Artic lakes or under the Artic Ocean.

Permafrost generally has sufficient strength to support oil exploration and recovery operations, so long as it remains frozen. However, when melted, the permafrost shrinks and subsides, causing a downdrag force on a well casing in the permafrost zone. Drilling operations can generally be conducted without causing any substantial melting of the permafrost. However, melting of the permafrost is experienced around wells conducting hot fluids through the permafrost zone. While various methods of completing wells in the permafrost to permit production of hot oil from lower zones have been proposed, none of these techniques have been completely satisfactory. Thus, need exists for a method of completing wells in the permafrost that will permit the production of hot oil or injection of hot fluids without damage to the well from subsidence or failure of the supporting earth around the well.

Accordingly, a primary object of this invention is to provide a technique for completing a well in a permafrost zone. Another object of the invention is to provide a well for transporting hot fluids through a permafrost zone that remains structurally supported by the permafrost. Yet another object of the invention is to provide a method for completing a well in a permafrost zone.

The manner of accomplishing the foregoing objects as well as further objects and advantages of the invention will be apparent from the following description taken in conjunction with the drawings, wherein like numerals refer to corresponding parts, and in which:

FIG. I. is a schematic vertical sectional view illustrating the well assembly of this invention installed in a percomprised of surface conductor 14 cemented in the upper strata of permafrost zone 10 with cement 16. The drilling rig is often conveniently set on piling prefrozen in the permafrost at a depth of about 20 feet. Surface conductor 14 is run to eliminate the possibility of a wash out or severe melting around the piling and cellar area directly adjacent to the well bore. Setting the surface conductor at a depth below the bottom of the piling eliminates the possibility of melting or wash out around the piling and loss of adequate rig support. Typically, surface conductor 14 is comprised of a length of relatively large diameter pipe, such as 30-inch diameter casing, 20 to feet in length, and preferably about 40 feet in length.

Casing 20 is the main support string for the balance of casing strings and provides initial blowout control protection until casing is installed through the permafrost. Fluted subsea hanger 22 is run at the bottom of casing 20 and provides the point at which the surface casing string is landed. Casing 20 is cemented in place by means of cement 24. Casing 20 extends into the permafrost zone sufiiciently to provide support for itself and the other casing strings, the permafrost surrounding this section of casing being maintained permanently frozen over substantially its entire length to provide the necessary support for the well. In a typical installation, casing 20 extends to a depth of 350 feet and the permafrost is maintained frozen to a depth of at least 300 feet by means refrigeration. Maintaining the permafrost frozen to a depth of 300 feet should provide adequate support for the well, and any thawing below this point is considered harmless.

Casing 20 serves as the outer wall of the refrigeration reservoir for the phase change refrigeration system, with casing 30 serving as the inner wall. Annulus 26 between casing 20 and casing 30 is sealed with packing in the well head and by hookwall packer 28 run at the bottom of casing 30, the packer providing support for casing 30 and sealing the bottom of annulus 26. When filled with refrigerant this annulus will serve as the heat sink or evaporator side of the cooling system. Casing 30 should remain at a substantially constant temperature created by the refrigerant, and will be standing in compression supported by the hookwall packer, with packing only being installed in the surface casing head. Refrigerant is added to annulus 26 through a small diameter conduit 32 strapped on the exterior of casing 30.

Surface casing 40 is the primary pressure protection string, and is run deep enough for protection from possible shallow zones and deep enough to cover the entire permafrost section. The lower section of casing 40 and subsea type packoff and re-entry assembly 22 is run on the casing along with a sub-sea landing mandrel. The landing mandrel typically has an outside diameter larger than casing 30 and, therefore, the lower section of casing 40 with the sub-sea hanger is run on drill pipe,

hung from the shoe and cemented with cement 44 prior to installation of casing 30. The top section of casing 40 with the re-entry assembly is run following installation of casing string 30. The use of the packoff and reentry assembly also allows a means for displacing mud and cement from the well bore with diesel oil. Displace ment of mud from all well annuli adjacent permafrost zones is necessary to prevent freezing of the mud which may fracture the well casing.

Casing 50 is run as the production string and will be subjected to direct zone pressure. It will be suspended from subsea type hanger and mandrel assembly 52 at the bottom of casing 40, or alternatively from a point adjacent hanger 22. Casing 50 will be provided with a DV cementer 54, or other means for change over to diesel in the subsea hanger, at a point above the bottom of casing 40, and a DV cementer at such other locations as required for proper zone separation and cement coverage. Change over from mud and cement to diesel oil above subsea hanger 52 will prevent freezing of fluids in

casings

40 and 50 opposite the permafrost. As in the case of casing 40, the upper section of casing 50 above hanger 52 will be supported in compression, with a packing gland installed around the casing at the surface and flanged to casing 40. This will allow differential expansion and contraction between casing 40 and casing 50 without creating excessive stress.

The well is completed in conventional manner by extending casing 50 through h the productive zones and perforating at selected intervals, or by terminating the casing above the productive zones and hanging a liner in these zones that is pre-slotted or perforated. Production tubing 60 handles production flow from the producingzones to the surface, or flow from the surface to the producing zones if the well is to be used as an injector. A packer, not shown, will be run in and set on tubing 60 above the perforations, and the tubing will be landed on subsea type hanger and mandrel assembly 62 located adjacent hanger and mandrel assembly 52. Diesel oil is circulated as the packer fluid in the annulus between the production tubing and casing 50. Tubing 60 is provided with insulation 64 extending through the permafrost zone to reduce the transfer of heat into the permafrost and to minimize the refrigeration load. Any convenient means of insulating tubing 60 can be employed, such as strapping half cylinders of 2-inch thick polyurethane on the tubing in the permafrost zone.

Centralizers, such as the centralizers 34, should be provided to maintain

casings

30, 40 and 50 centered in the permafrost zone. Also, centralizers can be provided for tubing 60 to protect insulation 64.

The well of this invention is. completed with a well head assembly that permits independent vertical expansion and contraction of the various casing strings without creating excessive stress and provides pressure integrity between casing strings. Referring more specifically to FIG. 2, casing 20 is fitted with a slip and packing seal type well head 70 having an inner landing and seal assembly 92 to accommodate casing 30. Casing 30 is packed off in the well head, but the slips are not used. Casing pack-off flange 72 having a steamtype packing assembly 94 is installed around casing 40. The stub of casing 40 projecting above pack-off assembly 72 is fitted with a slip and packing assembly type well head 74 having an inner packing seal 96. Casing pack-off flange 76 having a steam-type packing assembly 98 is installed around casing 50 and slip and packing type tubing head 80 is installed on the upwardly projecting stub of casing 50. Tubing 60 is landed in a donut type hanger in the tubing head and block-type Christmas-tree 82 is mounted on tubing head 80. The landing slips in well head 74 and tubing head 80 are not utilized.

Conduit 84 connects the wing valve of well head 70 to the suction of compressor 86. The discharge of compressor 86 is connected to condenser 88 and to well head by conduit 90, which in turn is connected to conduit 32 internally in well head 70. Condenser 88 is preferably air cooled to avoid freezing problems associated with water coolers during the winter months. In operation, hot fluids are withdrawn from the lower productive strata or are injected into these strata through tubing 60. While the flow of heat from the hot fluid into the permafrost zone is minimized by insulation 64, nevertheless suflicient heat is transferred to the permafrost below the refrigerated section of casing 20 to cause melting of the permafrost in the region 18 surrounding the well bore. Melting of the permafrost in the region 18 and the resulting subsidence and settling is not considered a problem since the upper section-of the well is firmly supported by the permanently frozen permafrost above this region. In this manner, it is not necessary to refrigerate the well through the entire permafrost zone, but only a sufficient length of the well need be refrigerated to provide the necessary support.

With the aforedescribed well casing system, all casing and tubing strings are supported internally within the well and the upper section of each casing and tubing string above its respective landing shoe is standing free. Excepting for casing 30, the upper section of each casing string is free to move independently of support string 20, thus avoiding excessive tensile and compressive forces created by expansion and contraction caused by temperature changes. Pressure integrity of each casing string is provided by the steam-type packing glands installed around each individual casing string and flanged to the casing head installed on the next outer casing string. Casing 30, which is not a support or protective string, is at substantially the same temperature as casing 20 and will thermally expand at about the same rate as casing 20. Therefore, it is not necessary to provide for any significant differential expansion between casing 30 and casing 20.

While any suitable refrigeration system can be employed to maintain the permafrost surrounding casing 20 frozen, a phase change system employing the vaporization of a refrigerant for heat removal is preferred. For example, a liquid refrigerant such as propane, butane, or other hydrocarbon, or a halogenated hydrocarbon refrigerant, or ammonia is introduced into annulus 26 by means of conduit 32. A reservoir of the refrigerant is maintained in the annulus and, as heat is absorbed, the refrigerant is vaporized. The vapors pass upwardly in the annulus and are withdrawn through conduit 84, compressed, condensed and returned to the annulus.

In another embodiment of the invention, packer 28 at the bottom of casing 30 is deleted, or other means of communication provided between the annulus 26 and the annulus on the interior of casing 30. Refrigerant is then circulated downwardly through annulus 26 between casing 20 and casing 30 and upwardly through the annulus between casing 30 and surface casing 40. Also, in a non-preferred embodiment of the invention, casing 30 can be omitted and the annulus between casing 20 and surface casing 40 used as the refrigeration reservoir.

While it is to be recognized that considerable latitude and flexibility is available in the design of the various casing strings to meet the particular circumstances and conditions encountered, the following casing schedule represents a suitable design for a completion encountered in many permafrost regions.

Diameter, Pipe Weight, Depth, Casing Inches Pounds/Foot Feet Surface conductor 30 l 19 40 Support string 20 94 350 Intermediate string 16 75 300 Surface string 13% 61 2500 Production string 9% 44.3 10,000:

Also, it is to be recognized that additional casing strings can be run below the surface strings where required by local conditions. These additional casing strings would be landed in the well and packed off in the well head in similar manner to provide free expansion at the top of the well.

A well in accordance with this invention can be drilled employing generally conventional Artic drilling practices modified in the manner hereinafter described so as to provide the desired installation.

The well is spudded in by drilling a large diameter hole with an auger-type drill to a depth below the support piles of the drilling rig, e.g., to a depth of 20 to 60 feet. Surface conductor 14 is run into the hole and stood on the bottom and cement l6 placed around the conductor.

Next, a smaller diameter hole is drilled to a sufficient depth to provide support for the well, e.g., to about 350 feet, and casing 20 is run into the hole and cemented in the proper location. Well head 70 is installed on casing 20.

Next, an even smaller diameter hole is drilled to a point below the permafrost zone. The lower part of casing 40 is set in the hole on drill pipe and hung from hanger 22 at the bottom of casing 20. Casing 40 is cemented in the hole with cement 44. Casing 30 is run into the hole and packer 28 set at the desired depth. This casing is packed off in well head 70 and refrigeration conduit 32 connected to an outlet in the casing head. The upper section of casing 40 is run into the hole and connected to the lower section of casing 40 previously placed in the hole. Casing packoff flange 72 having a steam-type packing assembly is installed on casing 40 and made up to well head 70. Well head 74 is installed on casing 40.

The. hole is then drilled to the final depth and production casing 50 is run in and hung from hanger 52 at the bottom of casing 40. Casing 50 is cemented above the bottom of casing 40 with cement 56. Casing packoff flange 76 having a steam-type packing assembly is installed on casing 50 and made up to casing head 74. Tubing head 80 is installed on casing 50. The well is perforated or otherwise completed for production or injection service and tubing 60 having insulation in the permafrost zone is run into the well and hung from hanger 62. Christmas-tre 82 is mounted on tubing head 80 and the refrigeration system installed and placed in service. The well is now placed on production or injection started, depending on the service in which the well is to be used.

It is preferred that all cementing in the permafrost zone be done with high alumina cements of the socalled fondu type such as that marketed under the trademark Ciment Fondu, or with 50/50 mixtures of ash and fondu cement. Also, cement and mud should be circulated out of all casing in the permafrost zone with diesel oil to prevent freezing and possible rupture of the casing.

This invention is further illustrated by the following example which is illustrative of a specific mode of practicing the invention and is not intended as limiting the scope of the invention as defined by the appended claims.

The well is spudded in by drilling a 36-inch hole to 40 feet with an auger type drill. 40 feet of 30-inch casing is run into the hole and stood on the bottom. Fondu cement is poured around the casing to ground level.

Next, 26-inch hole is drilled to 350 feet with a conventional rotary bit using refrigerated mud to prevent thawing of the permafrost. 20-inch, 94-pound casing is fitted on the bottom with a drill pipe stab-in shoe, and a 20-inch X 13-%-inch subsea fluted casing hanger is installed at the first joint above the shoe. The casing is run and hung in the rotary table so that the shoe is at the proper depth. Drill pipe is then run and stabbed into the shoe. Fondu cement is pumped down the drill pipe and returned to the surface up the annulus on the exterior of the 20-inch casing. The drill pipe is pulled and a 20-inch slip and packing seal type of well head fitted with an inner landing to accommodate 16-inch casing is installed. A 20-inch pack-off type of blowout preventer and well head flange is then installed.

Next, l7- /z-inch hole is drilled to approximately 2,500 feet 13-%-inch, 61 pound casing is fitted with a 20-inch X l3-%-inch landing mandrel to suspend the l3-%-inch casing from the previously installed 20-inch X l3-%-inch fluted hanger. A subsea packoff and reentry assembly is installed on top of the hanger mandrel and the inner top sleeve of the packoff and re-entry assembly is subbed to a drill pipe. A conventional float shoe and a l3-%-inch X 9-%-inch landing mandrel is installed on the bottom joint of l3-%-inch casing and a float collar on the first joint above the float shoe. A liner type plug is suspended in the l3-%-inch casing on the bottom of the drill pipe running in sub. The casing is then lowered on drill pipe and landed in the 20-inch l3-%-inch hanger and cemented to the hanger with fondu/ash 50/50 cement followed by fondu cement. The floats are tested for positive check and immediately thereafter the drill pipe is released from the subsea packoff and re-entry assembly and any cement around the mandrel and hanger is circulated out to the surface. The drilling mud is displaced with diesel oil and the drill pipe sub and top sleeve of the packoff and re-entry assembly is pulled, out of the hole.

Approximately 300 feet of l6-inch, pound casing having a l6-inch 20-inch mechanical set packer on the bottom and a l-inch circulating string strapped to the exterior is run and hung in the 20-inch well head. The packer is set, tested and the l6-inch casing packed off in the well head. The slip assembly in the 20-inch well head is not used. The l-inch circulating string is connected to the outlet of the casing head.

The balance (approximately 305 feet) of 13-%-inch casing with a subsea top packoff and re-entry sleeve on the bottom joint is run into the well and stabbed into and secured to the subsea packoff and re-entry assembly installed at the top of the previously run 13-% inch casing. The casing string is tested for leaks, the 20- inch blowout preventer removed and a 20-inch, 2000 pound X l3-%-inch, 2000 pound-casing packoff flange having a steam-type packing assembly installed around the 13-%-inch casing. The l3-%-inch casing is cut off one foot above the packing gland and a 12-inch, 3000 pound slip and packing seal type well head is installed on the l3-%-inch stub. A 12-inch blowout preventor is installed and tested.

Next, l2-V4-inch hole is drilled 10,000 feet and 9-%- inch casing run. The casing has a cement float shoe on the bottom, a float collar two joints above the bottom and DV cementers at intervals. The top DV cementer is installed at 2100 feet (just below the bottom of the permafrost). A l3-%-inch X 9-%-inch subsea hanger is installed just below the top DV cementer to land the casing. Alternatively, means for circulating the well can be provided in the subsea hanger and the top DV cementer deleted. The 9-%-inch casing is cemented so that the top of thecement is brought high enough for definite tie-in to the l3-%-inch casing. The top DV cementer is then opened and the cement circulated out of the 9-%-inch annulus above the l3-%-inch X 9-%-inch landing mandrel with mud. The cement is allowed to harden for about 10 hours, then the mud is circulated out the top DV cementer with diesel oil and the DV cementer is closed. The blowout preventer is removed and a casing packoff flange with steam-type packing assembly is then installed around the 9-%-inch casing and the casing is cut off one foot above the packing gland. A 10-inch, 5000 pound slip and packing type tubing head is installed on the 9-%-inch casing stub.

A blowout preventer and test connections are installed on the 10-inch tubing head. The well is perforated and prepared for production. 3-%-inch tubing insulated in the permafrost zone is run on a single hydroset packer and landed on the l3-%-inch X 9-%- inchsubsea hanger. A packing gland is provided in the tubing head to seal the tubing. A Christmas-tree is mounted on the tubing head and the refrigeration equipment installed and connected to the -inch by 16-inch annulus.

Diesel oil is pumped down the annulus and out the tubing to-displace the mud. The hydroset packer is set. The wing valve in the well head between the 16 and 20- inch casing strings is opened. Liquid butane is pumped down the l-inch stinger and up the annulus to displace the diesel and prepare the refrigeration system for operation. The well is placed on production and the refrigeration system is placed in service and adjusted to maintain the permafrost zone at a constant temperature of about 14F.

Various embodiments and modifications of this invention have been described in the foregoing description and drawings, 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 our invention, we claim:

1. A well for conducting hot fluids through a permafrost zone, which comprises:

a surface conductor cemented in the permafrost;

a first casing placed concentrically within said surface conductor and cemented therein, said casing extending sufficiently into the permafrost to provide support for the upper section of the well;

a surface casing placed concentrically Within said first casing and extending downwardly through the permafrost zone, said surface casing being sup ported from the bottom of said first casing and said casing being cemented below the bottom of said first casing;

means to refrigerate the annulus between said first casing and said surface casing;

a production casing placed concentrically within said surface casing and extending downwardly to the producing strata, said casing being supported from said surface casing at a point within the well; and

production tubing to convey fluids between the producing strata and the surface or vice versa, said tubing being insulated through the permafrost zone and said tubing being supported from the production casing within said well.

2. The apparatus defined in claim 1 including a second concentric intermediate casing placed between said first casing and said surface casing and terminating above the bottom of said first casing, said second casing being supported from said first casing at a point near its bottom.

3. The apparatus defined in claim 2 wherein the annulus between said first and said second casings is closed at its bottom by a packer and including a small diameter conduit fastened to said second casing and extending substantially its length to introduce refrigerant into said annulus, and means to withdraw vaporized refrigerant from the top of said annulus.

4. The apparatus defined in claim 2 ,wherein the annulus between said first and said second casings is open at the bottom and wherein refrigerant is circulated down the annulus between said first and said second casings and up the annulus between said second casing and said production casing.

5. The apparatus defined in claim 2 including a well head comprising means to seal the annulus between said first and said second casings, a packing gland to seal the annulus between said second casing and said surface casing, a packing gland to seal the annulus between said surface casing-and said production casing, a tubing head and a Christmas-tree.

6. A well for conducting hot fluids through a permafrost zone, which comprises:

a large-diameter surface conductor cemented in the permafrost;

a first casing placed concentrically within said surface conductor and cemented therein, said casing extending sufficiently into the permafrost to provide support for the well in the permafrost zone;

a second casing placed concentrically within said first casing and tenninating above the bottom of said first casing, said second casing being supported from said first casing at a point near its bottom; I

a surface casing placed concentrically within said second casing and extending downwardly through the permafrost zone, said surface casing being sup ported from the bottom of said first casing and said surface casing being cemented below the bottom of said first casing;

a production casing placed concentrically within said surface casing and extending downwardly to the producing strata, said casing being supported from said surface casing at a point within the well and said casing being cemented below said surface casing;

production tubing to convey fluids from the producing strata to the surface or vice versa, said tubing being insulated through the permafrost zone and said tubing being supported from the production casing within said well; and

means for refrigerating the interior of said first casing.

7. The apparatus defined in claim 6 wherein the annulus between said first and said second casings is closed at its bottom by a packer and wherein said means to refrigerate said first casing includes a small diameter conduit fastened to said second casing and extending substantially its length to introduce refrigerant into said annulus, and means to withdraw vaporized refrigerant from the top of said annulus.

8. The apparatus defined in claim 6 wherein the annulus between said first and said second casings is open at the bottom and wherein said means for refrigerating said first casing includes means for circulating refrigerant down the annulus between said first and said second casings and up the annulus between said second casing and said surface casing.

9. The apparatus defined in claim 6 wherein said first casing extends into said permafrost to a depth of about 350 feet.

10. The apparatus defined in claim 6 including a casing head on said first casing, means to seal the annulus between said first and said second casings, a packing gland to seal the annulus between said second casing and said surface casing, a casing head on said surface casing, a packing gland to seal the annulus between said surface casing and said production casing, a tubing head on said production casing, and a Christmas-tree mounted on said tubing head.

11. A well for conducting hot fluids through a permafrost zone, which comprises:

a large-diameter surface conductor cemented in the permafrost;

a first casing placed concentrically within said surface conductor and cemented therein, said casing extending sufficiently into the permafrost to provide support for the well in the permafrost zone; second casing placed concentrically within said first casing and terminating above the bottom of said first casing, said second casing being -supported from said first casing at a point near its bottom;

a casing head on said first casing including means to seal the annulus between said first casing and said second casing; surface casing placed concentrically within said second casing and extending downwardly through the permafrost zone, said surface casing being supported from the bottom of said first casing and said surface casing being cemented below the bottom of said first casing; a packing gland to seal the annulus between said second casing and said surface casing;

a casing head installed at the top of said surface casa production casing placed concentrically within said surface casing and extending downwardly to the said tubing being supported from the production I casing within said well;

a Christmas-tree mounted on said tubing head; and

means for refrigerating the interior of said first cas- 12. The apparatus defined in claim 6 wherein the annulus between said first and said second casings is closed at its bottom by a packer and wherein said means to refrigerate said first casing includes a small diameter conduit fastened to said second casing and extending substantially its length to introduce refrigerant into said annulus, and means to withdraw vaporized refrigerant from the top of said annulus.

13. The apparatus defined in claim 6 wherein the annulus between said first and said second casings is open at the bottom and wherein said means for refrigerating said first casing includes means for circulating refrigerant down the annulus between said first and said second casings and up the annulus between said second casing and said surface casing.

14. The apparatus defined in claim 11 wherein said first casing extends into said permafrost to a depth of about 350 feet.

15. A method for drilling a well through a permafrost zone, which comprises:

drilling a large diameter hole into said permafrost to a depth below the bottom of the piles supporting the drilling rig;

placing a surface conductor pipe in said hole and cementing said conductor therein;

drilling a smaller diameter hole in said permafrost to a depth sufficient to support the well in the permafrost;

placing a first casing in said hole and cementing said first casing to the surface; drilling an even smaller diameter hole to a depth below the bottom of the permafrost;

placing the lower section of a surface casing in said hole, supporting said surface casing from the bottom of said first casing, and cementing said surface casing above the bottom of said first casing; placing a second casing in said first casing and supporting said second casing from said first casing; placing the upper section of said surface casing in said well;

drilling an even smaller diameter hole through the producing zones;

placing a production casing in said well and supporting said production casing from said surface casrefrigerating the annulus between said first and said second casings; and placing said well in service.

Claims

1. A well for conducting hot fluids through a permafrost zone, which comprises: a surface conductor cemented in the permafrost; a first casing placed concentrically within said surface conductor and cemented therein, said casing extending sufficiently into the permafrost to provide support for the upper section of the well; a surface casing placed concentrically within said first casing and extending downwardly through the permafrost zone, said surface casing being supported from the bottom of said first casing and said casing being cemented below the bottom of said first casing; means to refrigerate the annulus between said first casing and said surface casing; a production casing placed concentrically within said surface casing and extending downwardly to the producing strata, said casing being supported from said surface casing at a point within the well; and production tubing to convey fluids between the producing strata and the surface or vice versa, said tubing being insulated through the permafrost zone and said tubing being supported from the production casing within said well.

4. The apparatus defined in claim 2 wherein the annulus between said first and said second casings is open at the bottom and wherein refrigerant is circulated down the annulus between said first and said second casings and up the annulus between said second casing and said production casing.

5. The apparatus defined in claim 2 including a well head comprising means to seal the annulus between said first and said second casings, a packing gland to seal the annulus between said second casing and said surface casing, a packing gland to seal the annulus between said surface casing and said production casing, a tubing head and a Christmas-tree.

6. A well for conducting hot fluids through a perma-frost zone, which comprises: a large-diameter surface conductor cemented in the permafrost; a first casing placed concentrically within said surface conductor and cemented therein, said casing extending sufficiently into the permafrost to provide support for the well in the permafrost zone; a second casing placed concentrically within said first casing and terminating above the bottom of said first casing, said second casing being supported from said first casing at a point near its bottom; a surface casing placed concentrically within said second casing and extending downwardly through the permafrost zone, said surface casing being supported from the bottom of said first casing and said surface casing being cemented below the bottom of said first casing; a production casing placed concentrically within said surface casing and extending downwardly to the producing strata, said casing being supported from said surface casing at a point within the well and said casing being cemented below said surface casing; production tubing to convey fluids from the producing strata to the surface or vice versa, said tubing being insulated through the permafrost zone and said tubing being supported from the production casing within said well; and means for refrigerating the interior of said first casing.

11. A well for conducting hot fluids through a permafrost zone, which comprises: a large-diameter surface conductor cemented in the permafrost; a first casing placed concentrically within said surface conductor and cemented therein, said casing extending sufficiently into the permafrost to provide support for the well in the permafrost zone; a second casing placed concentrically within said first casing and terminating above the bottom of said first casing, said second casing being supported from said first casing at a point near its bottom; a casing head on said first casing including means to seal the annulus between said first casing and said second casing; a surface casing placed concentrically within said second casing and extending downwardly through the permafrost zone, said surface casing being supported from the bottom of said first casing and said surface casing being cemented below the bottom of said first casing; a packing gland to seal the annulus between said second casing and said surface casing; a casing head installed at the top of said surface casing; a production casing placed concentrically within said surface casing and extEnding downwardly to the producing strata, said casing being supported from said surface casing at a point within the well and said production casing being cemented below said surface casing; a packing gland to seal the annulus between said surface casing and said production casing; a tubing head at the top of said production casing; production tubing to convey fluids from the producing strata to the surface or vice versa, said tubing being insulated through the permafrost zone and said tubing being supported from the production casing within said well; a Christmas-tree mounted on said tubing head; and means for refrigerating the interior of said first casing.

12. The apparatus defined in claim 6 wherein the annulus between said first and said second casings is closed at its bottom by a packer and wherein said means to refrigerate said first casing includes a small diameter conduit fastened to said second casing and extending substantially its length to introduce refrigerant into said annulus, and means to withdraw vaporized refrigerant from the top of said annulus.

15. A method for drilling a well through a permafrost zone, which comprises: drilling a large diameter hole into said permafrost to a depth below the bottom of the piles supporting the drilling rig; placing a surface conductor pipe in said hole and cementing said conductor therein; drilling a smaller diameter hole in said permafrost to a depth sufficient to support the well in the permafrost; placing a first casing in said hole and cementing said first casing to the surface; drilling an even smaller diameter hole to a depth below the bottom of the permafrost; placing the lower section of a surface casing in said hole, supporting said surface casing from the bottom of said first casing, and cementing said surface casing above the bottom of said first casing; placing a second casing in said first casing and supporting said second casing from said first casing; placing the upper section of said surface casing in said well; drilling an even smaller diameter hole through the producing zones; placing a production casing in said well and supporting said production casing from said surface casing; cementing said production casing above the bottom of said surface casing; placing a production tubing in said well; refrigerating the annulus between said first and said second casings; and placing said well in service.