US3627047A

US3627047A - Gas producing method

Info

Publication number: US3627047A
Application number: US38755A
Authority: US
Inventors: Leland E Wilson; Jerry M Trickey
Original assignee: Atlantic Richfield Co
Current assignee: Atlantic Richfield Co
Priority date: 1970-05-19
Filing date: 1970-05-19
Publication date: 1971-12-14
Anticipated expiration: 1988-12-14
Also published as: CA926300A

Abstract

A method and apparatus for producing a gas well wherein gas is produced through a well bore and the well bore passes through a permafrost zone. The method and apparatus prevent solid hydrate from forming in the gas while passing through the permafrost zone toward the earth''s surface.

Description

United States Patent 72] Inventors Leland E. Wilson;

Jerry M. Trlckey, both of Anchorage, Alaska May 19, 1970 Dec. 14, 1971 Atlantic Rlchfield Company New York, N.Y.

[21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] GAS PRODUCING METHOD 9 Claims, 1 Drawlng Fig.

[52] U.S. Cl 166/302, 166/314, l66/D1G. 1

[51] Int. Cl EZlb 43/24 [50] Field of Search 166/302-304, 310, 57, 61, D16. 1, 314

[56] References Cited UNITED STATES PATENTS 3,207,219 9/1965 Mitchell 1,012,777 12/1911 Wigle 166/61 735,449 8/1903 Berger 166/57 UX 2,614,635 10/1952 Williams et a1. 166/303 X 2,914,124 11/1959 Ripley 4 166/57 3,348,614 10/1967 Sinclair eta1.. 166/310 3,393,733 7/1968 Kuo et a1. 166/303 X 3,103,973 9/1963 Mullen 166/D1G. 1 OTHER REFERENCES Frlck, Thos. C. Petroleum Production Handbook, Vol. 11, NY. McGraw-Hill, 1962 page 30- 32.

Primary Examiner-Stephen .l. Novosad A t!0rney.l Blucher S. Tharp and Roderick W. MacDonald ABSTRACT: A method and apparatus for producing a gas well wherein gas is produced through a well bore and the well bore passes through a permafrost zone. The method and apparatus prevent solid hydrate from forming in the gas while passing through the permafrost zone toward the earth's surface.

Patented Dec. 14, 1971 AT IORNFY GAS PRODUCING METHOD BACKGROUND OF THE INVENTION Heretofore in the drilling of wells in the North Country where either continuous or discontinuous permafrost existed, it was thought that the portion of the well bore which passed through the permafrost zone would have to be insulated, refrigerated, and the like.

This is generally true in the case of oil wells where thawing of the permafrost is to be avoided, but it has now been found not to be as applicable to gas wells.

SUMMARY OF THE INVENTION It has been found that natural gas or other hydrocarboncontaining gas being produced through a well bore which passes through a permafrost zone can be sufficiently cooled while passing through the permafrost zone to cause the formation of a hydrate which is a solid icelike material containing both water and hydrocarbon which can form at temperatures substantially above 32 F.

It has been found that this hydrate can be formed in the produced gas in such quantity that plugging of the tubing through which the gas is produced and/or pipes for carrying the gas over the earth's surface can occur. The plugging is particularly troublesome wherever the flow path of the gas has to change directions such as when passing through valves, Ts, and L's in the pipe system.

According to this invention there is provided a method for producing a gas well through a permafrost zone and avoiding the problem of plugging due to hydrate formation in the produced gas by producing the gas through the well bore in a first conducting zone, heating the gas in the first conducting zone during at least part of the length of the well bore, and controlling the heating step so that the gas is not cooled sufficiently while passing through the permafrost zone to cause the formation of substantial amounts of hydrate.

There is also provided according to this invention apparatus for producing gas from a well in an area of permafrost utilizing a first conduit means in the well bore for transmitting gas through the well bore to the earth's surface, heater means for heating at least part of the first conduit means, and means for supplying energy to the heater means.

It is unusual to apply heat to a well bore which passes through a permafrost zone, but in the situation wherein a hydrocarbon-containing gas which also contains water is produced through a permafrost zone, controlled heating of that gas is generally necessary to prevent substantial hydrate formation and to prevent hydrate plugging of the production tubing and/or surface piping associated with the well.

Accordingly, it is an object of this invention to provide a new and improved method for producing a gas well in permafrost areas. it is another object to provide a new and improved method for preventing the formation of solid hydrate when producing gas through a permafrost zone. It is another object to provide new and improved apparatus for gas well production in a permafrost area. It is another object to provide new and improved apparatus for the prevention of hydrate formation while producing a gas through a permafrost zone.

Other aspects, objects, and advantages of this invention will be apparent to those skilled in the art from this disclosure and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION The drawing shows one apparatus setup employing this invention,

More particularly, the drawing shows a well bore 1 which can be lined with conventional casing or not, as desired, and which is drilled in the earth 2 in a permafrost area so that well bore 1 penetrates a zone of surface tundra 3 which overlies a much thicker zone of permafrost 4. Under the permafrost layer is unfrozen rock and the like from which gas is produced in a conventional manner from formation 9. The well contains a surface wellhead 5 which contains a first conduit (first con ducting zone) 6, a second conduit (second conducting zone) 7, and a return conduit or zone 8.

A gas, such as natural gas, other hydrocarbon-containing gas, carbon dioxide, and the like, is produced from gas producing formation 9 into the bottom 6 of conduit 6 up the well bore through permafrost zone 41 into'the earths surface for further processing, use, and the like.

The gas passing from conduit 6 at the earth's surface normally passes through a piping system for further processing such as dehydration, sulfur and sulfur compound removal, and the like. Because of this, the gas passes through a large number of pipes and changes direction by way of pipe T5 and L's a large number of times shortly after it leaves conduit 6.

Conduit 7 terminates in the well bore at a position above end 6' of conduit 6 and preferably terminates in or near permafrost zone 4. Ends 6' and 7 of

conduits

6 and 7 are physically isolated from one another by a conventional single completion packer l0.

Conduit 8 has a conventional valve means 12 therein for regulating the flow of fluid from well bore 1 above packer l0 and into conventional heater 13.

Heater 13 heats a fluid received from conduit 8 and passes the heated fluid into conduit 14 by way of pump 15. From pump 15 the heated fluid passes into conduit 7 and back down well bore 1.

In the apparatus of the drawing, at least part of the length of conduit 6 in the permafrost zone 4 can be heated to above the temperature at which hydrate would form in the gas passing through conduit 6. The heating is accomplished by way of a heated fluid emitting from end 7' of conduit 7. The heated fluid contacts at least part of conduit 6 as it rises toward the earths surface for removal from well bore 1 by way of conduit 8.

The length of conduit 7 can vary widely so that end 7 can emit the heated fluid therefrom at a point below the lowest level of permafrost zone 4, at about the lowest level of permafrost zone 4, above the lowest level of permafrost zone 4, and any desired combination thereof so long as the gas passing through conduit 6 is sufficiently heated so that hydrate does not form in the gas as it passes through permafrost zone 4.

Conduit 7 can also be employed concentrically with respect to conduit 6 or either the interior or exterior or both of conduit 6. Thus, the heated fluid flows downwardly in inner and/or outer concentric contact with conduit 6 and the fluid emitted from end 7' rises in the annulus of the well bore to the earths surface for removal through conduit 8.

The heating fluid employed could be gaseous or liquid but is preferably liquid because of a liquids normally higher thermal capacity and conductivity. Any liquid used should be of an antifreeze typeso that it will not freeze when exposed to the permafrost nor freeze in conduits 8 and 14 should the system be shut down and exposed to ambient freezing conditions for prolonged periods. For example, alcohol, particularly glycols such as ethylene glycol, can be used alone or in any combination with each other or with water (fresh or salt water).

The antifreeze material preferably has a freezing point of at least 60 F. The antifreeze can be composed of from about 10 to about volume percent water with the remainder being essentially one or more alcohols, and the like. Of course,

heated air or any other readily available heated gas can be employed if desired although better heat transfer results are achieved using a liquid heat exchange medium.

Well bore 1 is preferably lined with casing and the casing should be adapted to either prevent thawing of the permafrost in those areas of the well bore which are: heated by way of conduit 7, e.g., by insulating the casing and/or refrigerating the casing, or to accept some subsidence of the permafrost such as r by the use of slip joints spaced periodically along the length of the casing in at least part of the permafrost zone.

Other heating means can be employed such as by the use of electric downhole heaters and the like, so long as the gas passing through conduit 6 is heated sufficiently that it is not cooled by exposure to permafrost zone: 4 to the point where substantial amounts of hydrate will form. Thus, substantially any heater means for heating at least part of conduit 6 over at least part of its length in the well bore can be employed in combination with means for supplying energy to that heater means.

According to the method of this invention the gas containing hydrate forming water and hydrocarbon is initially above the temperature and pressure at which substantial amounts of hydrate form. By initially" it is meant that gas as produced from formation 9 into the lower portion of well bore 1 adjacent end 6.

According to this method the substantially hydrate free gas is produced through well bore 1 in a first conducting zone 6 and the gas is heated in the first conducting zone during at least a part of the length of well bore 1 in a controlled manner so that the gas in conducting zone 6 is not cooled sufficiently while passing through permafrost zone 4 to cause substantial hydrate formation.

The hydrate itself is a complex combination of hydrocarbons and water. The chemical composition of the hydrate is presently unknown. The hydrate is formed through the mechanism of water vapor in the gas condensing and freezing in a manner which ties hydrocarbon molecules in with the frozen water. The hydrate is solid like ice but has a substantial hydrocarbon content. The hydrate forms at temperatures above 32 F. and can form at temperatures up to about 80 F. and higher in some situations.

Any water present in the gas produced is a potential hydrate former so that there is substantially no minimum amount of water in a hydrocarbon containing gas below which the hydrate formation potential is nonexistent. Normally, the gas produced from a formation is saturated with water so that there normally is a very substantial potential for the formation of large amounts of hydrate.

The formation of a hydrate and its pipe plugging propensities are significant in the production of gas wells through a permafrost zone. The problem of hydrate formation is not presently considered significant in the production of oil wells. This is so because there is a smaller amount of gas associated with the liquid oil and the liquid oil flowing through the conduits and pipes carries the hydrate out rather than allowing the hydrate to build up in the piping as was discovered to be the case with gas wells.

In an exemplary situation, the gas is, as initially produced, above about 80- F. and above about 100 p.s.i.g. In this situation the hydrate normally forms in the gas at less than 80 F. and less than 10,000 p.s.i.g. In this situation the gas in conduit 6 is heated to maintain a temperature of that gas greater than 80 F. while in permafrost zone 4. Of course, pressure plays some role in the determination at which temperature hydrate formation will occur. Generally. however, there is a temperature such as 80 F. for most natural gases, above which substantially no hydrate will form at any practical pressure, i.e., less than about 10,000 p.s.i.g.

The heating of the gas in conducting zone 6 can be carried out in any part of well bore 1 but is preferably carried out in at least part of the length of permafrost zone 4.

in the method of this invention the heating can be carried out in any manner disclosed hereinabove with respect to the apparatus and therefore includes, inter alia, passing a heated fluid down the well bore in a second conducting zone such as conduit 7, contacting the first conducting zone 6 with the heated fluid, and raising the heated fluid at least part way to the earth's surface while in contact with the first conducting zone. The heated liquid is preferably raised while in concentric contact with the interior or exterior or both of the first conducting zone.

The heating can also be carried out by passing the heated liquid down the well bore in the second conducting zone 7, the second conducting zone being substantially concentric with the interior and/or exterior of the first conducting zone 6 so that the heated liquid passes down the well bore in contact with the first conducting zone 6 and is removed from the first conducting zone at the lower end of the second conducting zone for retrieval upward in the well bore to conduit 8.

EXAMPLE A natural gas well in northern Alaska was produced using substantially the apparatus shown in the drawing. The permafrost zone 4 was about 1,800 feet thick and the natural gas produced at the bottom of the production conduit 6 was at a temperature of about 175 F. and a pressure of about 4,000 p.s.i.g. This gas contained about 170 pounds of water per million cubic feet of gas. The average temperature of well bore 1 in permafrost zone 4 was l0 F. and hydrate formation started in the gas when cooled to a temperature in the range of 75 to F.

Without employing the heating concept of this invention the natural gas removed from conduit 6 at the earth 's surface was less than 75 F. and about 3,000 p.s.i.g. at a flow rate of about 3 million cubic feet per day and contained sufficient solid hydrate that the three-inch inside diameter piping employed for carrying the natural gas to and through additional processing steps was readily plugged in a plurality of places by a buildup of hydrate.

Employing the heating concept of this invention, a direct fired heater 13 having a capacity of 4,000,000 B.t.u. per hour was utilized to heat a mixture composed of 60 volume percent ethylene glycol and 40 volume percent water to about l80 F. The heated glycol-water mixture was then pumped downwardly through conduit 7 at a maximum rate of 75 gallons per minute, the interior casing diameter for the well bore in permafrost zone 4 being 20 inches. By following this procedure the natural gas in conduit 6 was maintained at a temperature greater than 80 F. as it passed through permafrost zone 4 and no hydrate plugging problems were encountered in piping the thus heated natural gas over the surface of the earth through various subsequent processing plants.

Reasonable variations and modifications are possible within the scope of this disclosure without departing from the spirit and scope of this invention.

We claim:

1. In a method of producing a gas well wherein gas is produced through a well bore which passes through a permafrost zone, said gas containing hydrate forming water and hydrocarbons but initially being at a temperature sufficiently elevated so that hydrate is not present, the improvement comprising producing said gas through said well bore in a first conducting zone, heating said gas while in said permafrost zone, said heating being conducted so that said gas'is not cooled sufficiently while passing through the permafrost zone of said well bore to cause the formation of substantial amounts of hydrate in said gas while in said first conducting zone and so that thawing of the permafrost due to said heating is substantially prevented.

2. A method according to claim 1 wherein said gas is saturated with water as it enters said first conducting zone.

3. A method according to claim 1 wherein said gas is natural gas and is initially above about 80 F. and p.s.i.g. hydrate forms in said gas at less than 80 F. and 10,000 p.s.i.g. and said gas is heated to maintain a temperature greater than 80 F. while in the permafrost zone of said well bore.

4. A method according to claim 1 wherein said heating is carried out by passing a heated liquid down said well bore in a second conducting zone, contacting said first conducting zone with said heated liquid, and raising said heated liquid at least part way to the earth's surface while in contact with said first conducting zone.

5. A method according to claim 4 wherein said heated liquid is raised while in concentric contact with at least one of the interior and exterior of said first conducting zone.

6. A method according to claim 1 wherein said heating is carried out by contacting at least a portion of said first conducting zone in at least part of the length of said permafrost zone with a heated liquid antifreeze.

7. A method according to claim 6 wherein said antifreeze has a freezing point of at least 60 F.

8. A method according to claim 6 wherein said antifreeze is composed of from abut 10 to about 90 volume percent water, the remainder being essentially ethylene glycol.

9. A method for producing a gas well wherein natural gas is produced through a well bore which passes through a permafrost zone, said gas containing hydrate forming water and hydrocarbons, said hydrate forming in said gas at less than 80 F. and 10,000 p.s.i.g., said gas initially being above about 80 F. and 100 p.s.i.g., the steps comprising producing said gas through said well bore in a first conducting zone, passing a heated fluid down said well bore in a second conducting zone, contacting said first conducting zone with said heated fluid near the bottom of said permafrost zone, raising said heated fluid at least part way to the earth's surface while in contact with said first conducting zone, controlling said heated fluid so that said gas is maintained at a temperature greater than F. while in said permafrost zone, and preventing substantial thawing of the permafrost during passage of said heated fluid through said conducting zones.

*3 l! l t 141

Claims

1. In a method for producing a gas well wherein gas is produced through a well bore which passes through a permafrost zone, said gas containing hydrate forming water and hydrocarbons but initially being at a temperature Sufficiently elevated so that hydrate is not present, the improvement comprising producing said gas through said well bore in a first conducting zone, heating said gas while in said permafrost zone, said heating being conducted so that said gas is not cooled sufficiently while passing through the permafrost zone of said well bore to cause the formation of substantial amounts of hydrate in said gas while in said first conducting zone and so that thawing of the permafrost due to said heating is substantially prevented.

3. A method according to claim 1 wherein said gas is natural gas and is initially above about 80* F. and 100 p.s.i.g. hydrate forms in said gas at less than 80* F. and 10,000 p.s.i.g. and said gas is heated to maintain a temperature greater than 80* F. while in the permafrost zone of said well bore.

4. A method according to claim 1 wherein said heating is carried out by passing a heated liquid down said well bore in a second conducting zone, contacting said first conducting zone with said heated liquid, and raising said heated liquid at least part way to the earth''s surface while in contact with said first conducting zone.

7. A method according to claim 6 wherein said antifreeze has a freezing point of at least -60* F.

8. A method according to claim 6 wherein said antifreeze is composed of from about 10 to about 90 volume percent water, the remainder being essentially ethylene glycol.

9. A method for producing a gas well wherein natural gas is produced through a well bore which passes through a permafrost zone, said gas containing hydrate forming water and hydrocarbons, said hydrate forming in said gas at less than 80* F. and 10,000 p.s.i.g., said gas initially being above about 80* F. and 100 p.s.i.g., the steps comprising producing said gas through said well bore in a first conducting zone, passing a heated fluid down said well bore in a second conducting zone, contacting said first conducting zone with said heated fluid near the bottom of said permafrost zone, raising said heated fluid at least part way to the earth''s surface while in contact with said first conducting zone, controlling said heated fluid so that said gas is maintained at a temperature greater than 80* F. while in said permafrost zone, and preventing substantial thawing of the permafrost during passage of said heated fluid through said conducting zones.