US3680636A

US3680636A - Method and apparatus for ignition and heating of earth formations

Info

Publication number: US3680636A
Application number: US889061A
Authority: US
Inventors: Holland J Berry; William C Hardy; Dale W Zadow
Original assignee: Sun Oil Co
Current assignee: Sunoco Inc
Priority date: 1969-12-30
Filing date: 1969-12-30
Publication date: 1972-08-01
Anticipated expiration: 1989-08-01

Abstract

A heater for stimulating wells which include a heat shield with openings for air in the heat shield side walls, an air inlet upstream of a burner to premix the fuel and air, and a burner made up of a bundle of tubes of varying lengths to vertically spread the flame. Alternatively, to vertically spread the flame, a burner is provided in tubular form with perforations extending the length of the tube. Wireline run ignitors, using energy from batteries are used to ignite the burners. Also, a wireline run catalytic material combined with an injected hydrogen mixture can be used for ignition.

Description

[ 51 Aug. 1, 1972 United States Patent Berry et al.

X99X9 55 5 5mw5w 6116] m mm m mm m u m W @MHTH 68890 66667 99999 mmmmm uuumm 5mm 33333 mn m "M R "mm RA C.C 0E m FF ms; so 0 mo 6 v. m m m K nu J w DWS m N H M O mm N w m m Em 0 V MwF .m M m Tex.

[73] Assignee: Sun Oil Company, Dallas, Tex.

Primary Examiner-Stephen J. Novosad Attorney-George L. Church, Donald R. Johnson, Wilmer E. McCoiquodale, Jr. and John E. Holder [22] Filed: Dec. 30, 1969 [21] App]. No.: 889,061

ABSTRACT A heater for stimulating wells which include a heat shield with openings for air in the heat shield side s21 U.S. CL.....................................166/302, 166/59 511 int. Cl. 43/24 walls, an air inlet upstream of a to premix the 581 ma 6: Search.... ..166/59, 5s, 60, 63, 256, 260,

fuel and air, and a burner made up of a bundle of tubes of varying lengths to vertically spread the flame.

Alternatively, to vertically spread the flame, a burner m Cited is provided in tubular form with perforations extend- UNITED STATES PATENTS ing the length of the tube. Wireline run ignitors, using 3,113,623 12/1963 Krueger........................

energy from batteries are used to ignite the burners.

"166/59 Also, a wireline run catalytic material combined with an injected hydrogen mixture can be used for ignition. 2,927,641 3/1960 Buck ........................166/65 2,985,240 5/1961 Emery 35 Claims, 8 Drawing Figures 1,678,592 7/1928 Garner et PATENTEDMIB 1 I972 3.680.636-

SHEEI 1 or 3 INVENTOR DALE W. ZADOW HOLLAND J. BERRY J ILLIAM c. HgRDY El 1 3 41 I 1 'l l I "I /I II /I I ATTORNEY PATENTEDMIB 1 I912 I 3.680.636

SHEET 2 0F 3 {r1 BATTERY T T /T PACK i z 1 I T WEIGHT 5 ACTUATED SWITCH v I 1 OSCILLATOR 8 E v I I 5 /22 HIGH VOLTAGE A "2O STEP-UP I r TRANSFORMER v v r I 44 4 l 62 ELECTRODES l8 ii I I I E T 52 26 I v FIG. 3A A 5o\w.. T I8 7o 1 w u g G I i a I E WA;

' BATTERY 70 I I PACK FIG. 4

W 72 OSCILLATOR we HIGH VOLTAGE STEP-UP r96 74 TRANSFORMER A I INVENTOR DALE w. ZADOW ELECTRODES HOLLAND J. BERRY 62 ATTORNEY W7ILLIAM 0. HA Y 82 I 5% FIG. 5 FIG. 5A

PATENTEHMIB H912 3.680.636

SHEET 3 OF 3 F IG 6 INVENTOR DALE w. ZADOW HOLLAND J. BERRY ILLIAM C. HARZY ATTORNEY METHOD AND APPARATUS FOR IGNITION AND HEATING OF EARTH FORMATIONS BACKGROUND OF THE INVENTION This invention relates to a burner device for heating oil well formations and is related to two co-pending applications filed of even date herewith and entitled METHOD AND APPARATUS FOR IGNITING WELL HEATERS, Ser. No; 88906.0, and METHOD AND APPARATUS FOR CATALYTIC IG- NITION OF EARTH FORMATIONS Ser. No. 889,059, now abandoned and the continuation-in-part of that application entitled Method and Apparatus for Catalytically Heating Wellbores Ser. No. 92,836. In the stimulation of oil wells, several methods have been utilized to apply heat to the formations This heat may be provided for several purposes. One purpose is to supply enough heat to lower the viscosity of the petroleum, or to melt paraffin which is in the vicinity of the wellbore. Another purpose is to ignite the oil in the formation, which ignition is termed in situ combustion. Essentially, an in situ combustion process involves igniting the formation so that the heat from the combustion lowers the viscosity of the oil in front of it and also gasifies lighter hydrocarbons providing pressure to drive the oil in the direction of a producing well. The in situ combustion process involves several steps. First, air is injected into the oil bearing formation through an injection well. The injection pressure is sufficient to cause air to flow through the formation from the injection well to one or more producing wells, and it is injected at a sufiicient rate to support a combustion reaction of a fraction of the oil in the formation. Additionally, the air pressure forces the oil away from the casing of the injection well so that the well is relatively free of liquids. In order to initiate a combustion reaction in most oil bearing formations, it is necessary to inject heat along with the air. The heat is carried by the air into the reservoir where it contacts the formation oil. By flowing a sufficient volume of hot air into the reservoir, the crude oil in the vicinity of the injection well is heated to its ignition temperature and commences to burn.

Several popular methods of igniting the oil in the formation are by downhole electrical heaters, downhole gas burners, and natural spontaneous combustion reactions occurring when unheated air is injected into the formation. There are limitations to the methods now being employed. The downhole electrical heater requires an electrical cable from the surface to the heater. High voltages are required for the electrical heater, since the cable operates as a resistance. Because of voltage dissipation due to cable resistance, it may be difficult to maintain sufficient voltage at the heater if the cable length exceeds about 3,000 ft.

The formations that ignite by natural spontaneous combustion reactions depend upon a set of circumstances that do not readily occur in all reservoirs. Most napthenic crudes spontaneously ignite while paraffinic crudes do not. Therefore, downhole gas burners have been used mostly in deep paraffinic wells. There however have been problems related to downhole well pipe damage due to the intense heat generated by gas burners.

Ordinarily, in downhole gas burners an orifice or nozzle surrounded by a cylindrical heat shield is run on standard oil field tubing to the vicinity of the top of the formation which is to be heated. Gas is. flowed down the tubing through the noule and into the heat shield. Air is flowed down the annular spaced between the tubing and the casing to the bottom of the hole where part of the air enters the heat shield and mixes with the gas entering from the tubing, while the balance'of the air enters the formation being heated. When the burner is ignited, heat from the burner is. transferred to the balance of air entering the formation. This heated air raises the temperature in the formation surrounding the wellbore until the formation oil is ignited. Upon formation ignition, fuel gas is no longerinjected, and air is pumped to the formation to support combustion of the formation oil.

To ignite this gas-air mixture within the heat shield, pyrophoric chemicals are introduced, which are highly combustible in air at standard conditions. Therefore, special precautions must be taken, such as purging the lubricator and tubing of air with nitrogen so that the pyrophoric chemical does not react with air before reaching the burner. This method of ignition is not often successful, since the fuel mixture and pyrophoric material must be present in the right proportions to initiate combustion of the fuel gas. If the fuel-air mixture is too rich when the pyrophoric chemical ignites, an explosion will occur which can cause serious damage to the heat shield, tubing, and casing. The rich mixture is usually caused by poor mixing, creating areas which are predominantly fuel gas or air. Poor mixing is not uncommon, and-the explosions resulting therefrom can cause such extensive damage that the well can no longer be used.

When the burner is successfully ignited, other problems arise with the burners 'now being used. Damage to the well pipe canresult from having a single flame area at the nozzle which concentrates the heat so that it acts on only a small area of the heat shield, causing the shield to burn through, thus exposing the casing to high temperature oxidation and resultant damage.

If the fuel-gas velocities are too high, the flame stand-off distance between flame and nozzle becomes excessive and the flame can jump to the end of the heat shield. When the flame is transferred to the end of the heat shield, the casing is left totally unprotected. If this happens for any length of time, the casing will be damaged, since the heatof combustion of natural gas can run in the neighborhood of 4,000 F.

Because of the problems created by current formation heating practices, it is an object of the present invention to provide new and improved downhole gas burners and related ignitors.

SUMMARY OF THE INVENTION With this and other objects in view, the present invention includes a burner which is in tubular form with perforations extending along-the length of the tube. This effectively vertically spreads the flame to eliminate concentration of the flame in one area, and thereby reduces the chances of damage to downhole equipment. An opening is provided upstream of the gas burner to allow air to enter and mix with the fuel gas prior to reaching the burner, so that the flame does not stand off from the burner tip. A heat shield surrounding the burner has air inlets withadjacent baffles to admit Y 3 turbulent air to the burner area, thereby substantially eliminating extremely lean and rich'mixtures.

Additionally, an alternate burner is provided consisting of a bundle of varying length tUbCSIO vertically spread out-theflame areato avoid concentration of the heat'ofcornbustion. A

\, Ignit'ors are provided for use with the burners, which can bef run on wireline" and are battery operated,

eliminating the heed for pyrophoric materials. Also, the burners be ignited by contacting a catalytic material,"run to the heaterarea by wireline, with an injected hydrogen mixture. n

. Acomplete" underst'andinglof this invention may be had by reference-to the following description, when read in conjunction with the accompanying drawings illustrating embodiments thereof. nm pssc m s [or TI-IEJDRAWINGS ..FIG..l is .a crossrsectionof a multiple length tubular burner in position in a well;

lets 18. Baflles are located below the uppermost air in;

lets 18 whichare adjacent the attachment members 20. These baffles are illustrated in FIG. '2, and indicated :as

32. The premix air inlet l6 aflo'rds the fuel gas and air an opportunityjto beforereaching the burner tube ports, thereby preventing the flame'from standing off from burner tube If stand-ofiwereallowedto f FIG. 2 is a cross-sectional view ofthe multiple length tubular bumerin the wellbore surrounded by'the heat shield takenalong lines 2-2 of FIG. 1;

-FIG S .'3' and 3A are aside view and schematic respectively, of a burner ignitor for use in the multiple tubeburner shownin FIGS. 1 and 2;

- FIG. 4 is a cross-section of a perforated tubular burner in position inawell; A

"FIGS. Sand 5A area side view and schematic respectively, of an ignitor used to ignite the burner of FIG. 4; and v .FIG. 6 is a catalytic ignitor which is run on a wireline.

' DESCRIPTION OFTHEPREFERRED EMBODIMENTS.

happen, damage to casing 12 located below the heat shield couldoccur.

tion of intense heat. when the; oil formation has, been heated or ignited, fuel gas is no longer and the burner can be retrievedby wireline.

In lieu of making the burner wireline retrievable, it

can be welded to the end of the tubing or to the inside of the heat shield 26. In that event, shoulders 34 and 42,

would not be needed. Making the burnerretrievable by use of a wireline retrieving tool which engages the flange 36 is desirous in order to allow the burner to be easily pulledfor repairs or inspection, or upon occur Y rence of ignition.

Referring first to FIG. 1, there is seen a heat shield 26 I comprising-a burner. These multiple length burner tubes 24have burner tube ports28. Located upstream from thebumer is a premixair inletl6. The heat shield has airscoops '18 for admitting air to the interior of the A heat shield and to the vicinity of the burner tube ports 28. Tubing 14 has a seating nipple 22 located at its lower extremity. The seating nipple 22 is used to sup port a shoulder 34 located at the top of burner 52. The

7 burner 52 also has an inside shoulder 42 making the burner wireline retrievable.

In the operation of the apparatus shown in FIG. 1,

the multiple length burner tubes are seated on seating nipple 22, and are located just above perforations 30 inside the heat shield 26. Airis pumped down the annulus between casing 12 and tubing 14. This air operates to force reservoir fluids away from the wellbore and support combustionat the burner. Fuel gas is pumped down the inside of tubing 14 to the burner area. As the air proceeds down the annulus, some air enters the tubing through premix air inlet 16 to allow the air to mix with-the fuel gas before reaching the burner tubes 24. After this fuel gas and air has been ignited, preferably by the ignitor'shown in FIGS. 3 and 3A, a flame caps the burner ports 28. Additional air is supplied to the burner tube ports 28 and heat shield interior by air in- FIG. 2 illustratesa cross-sectional plan .view of the burner as arranged in FIG. 1. There thetubes are shown at 24 inside of tubing 14 which is located in casing 12. The heat shield 26 isattached to the tubing by attachment members 20. Baffles '32 are located adjacent the attachment members 20 to give the air tur'- bulence as it enters the bumer-area.- Additional air is. provided to the interior of the heat shield 26by air in, lets 18 to supplyair to the burner area." Once the .forrna-., tion is heated, or in situ combustionhas commenced, the fuel gas will beterminated, andin the case of in situ combustion, theair will be supplied continuously to the formation to support combustion, or both air and fuel gas will be shut off and burner equipment removed from the wellbore if the formation isano longer to be heated.

FIGS. 3 and 3A depict an ignitor for use with the burner of FIG. 1. The ignitor.72 is suspended from wireline 76. The ignitor hasa series of batteries mounted above a pressure switch 80. An electrode probe 74 is located below the switch and terminates with electrodes 82 formed into a spark gap 86. An adjustable stop 88 is located on the electrodeprobe 74.

When the ignitor 72 is run into the tubing 14, the stop 88 contacts the top of the burner 52 of FIG. 1. This allows the weight of the batteries 70 to compress the spring 90 whereupon the

contacts

92 and 94 touch together. Sufficient electrical energy is then available by operation of the equipment shown in FIG. '3A. The electrical energy provided by battery pack 70 is converted to alternating current by oscillator '78, and boosted byhigh voltage step-up transformer 96. From the transformer 96, the energy proceeds to electrodes 82 and generates a spark across spark gap 86 of FIG. 3.

The stop 88 can be adjusted so that the spark generated will be located at the burner tube ports 28 of FIG. 1.

FIG. 4 is illustrative of a burner which is a perforated tubular member with a spark gap built therein. Tubing 14 is located inside a casing 12. Attached to the lower portion of tubing 14 is a burner 52 consisting of a tubular member with perforations 44 extending along its length. The heat shield 26 surrounds the burner 52 and is attached by members 20. Air inlets 18 are located in the side walls of heat shield 26. Premix air inlet 16 allows air to enter the tubing prior to reaching the burner 52. A seating nipple 22 is provided which allows use of a wireline retrievable burner. Therefore, at the top of burner 52 is located a shoulder 34 for engaging the seating nipple 22. There is also an inside shoulder 42 opposite shoulder 34, for engaging the wireline pulling tool.

In the operation of the apparatus of FIG. 4, fuel gas is flowed down the tubing into and through the burner 52. Air is flowed down the annulus between the tubing 14 and the casing 12, and a portion enters the premix air inlet 16 and air inlets 18, with the remainder exiting perforations 30 located in the casing wall. Adjacent the upper air inlets 18 are baffles similar to those shown at 32 in FIG. 2, for imparting turbulence to the air entering the heat shield 26. The air entering premix air inlet 16 mixes with the fuel gas so that upon ignition of the fuel, the flame caps the burner perforations 44 on the burner 52, since a proper air-fuel mixture is available at the perforations 44 to support combustion. The multiplicity of perforations 44 spreads the flame so that the flame is not concentrated in one area which could cause damage to the heat shield 26, tubing 14, and the casing 12.

Ignition of the burner of FIG. 4 may be initiated by use of the ignitor shown in FIGS. 5 and 5A. The electrode probe 74 of the ignitor 72 is lowered by wireline 76 of FIG. 5 into the electrode probe socket 50 and properly seated by guide 58. Energy emanating from the batteries 70 surges across the spark gap 56 to ignite the fuel mixture flowing down the annulus of the tubing when the fuel reaches the burner 52. The heat from burner 52 is transmitted to the air stream flowing to perforations 30 on its way to the formation. Upon ignition of the formation in an in situ combustion operation, the fuel gas flowing down the tubing is terminated and the air flowing down the annulus supports the in situ" combustion in the formation.

Electrical energy sufficient to generate a spark across spark gap 56 is provided by the apparatus illustrated in FIG. 5A. There the energy provided by battery pack 70 is converted to alternating current by oscillator 78 and boosted by transformer 96 connected to electrodes 82 which make up part of the spark gap 56 of FIG. 4 when the ignitor is properly positioned by guide 58. Upon ignition of the burner the ignitor can be removed by wireline.

FIG. 6 illustrates a catalytic ignitor for use in the burner of FIG. 4 with or without the electrode probe socket located at its bottom. Proper spacing of the ignitor would allow its use in the burner having an electrode probe socket, however it is shown in a burner without a spark gap in FIG. 6. The ignitor 38, preferably having platinum supported on asbestos, asbestos-burlap, or ceramic material, is run by cable 40 to the interior of the burner 52 having perforations 44. The ignitor 38 is supported by seating nipple 22 which is in contact with a no-go landing flange 46. The ignitor exterior is sealed from the tubing 14 by O-rings 48. The burner 52 is surrounded by heat shield 26 which protects casing 12 fromexcessive heat. The casing 12 has perforations 30 located below the heat shield 26. The heat shield 26 is attached to the lower end of the tubing 14 by attachment members and has air inlets 18. Baflles are located next to the uppermost air inlets l8 and are similar to those shown at 32 in FIG. 2. The tubing 14 has centralizers 60 for keeping the heat shield 26 out of contact with the casing 12. A stand-off section 62 insures that the catalytic surface is not close enough to damage the seating area of the ignitor.

A thermocouple 64 is located on the skin of the cata- I lytic surface of the ignitor 38 and is connected to the cable 40 which is adapted to transmit temperature indications to the surface. The thermocouple 64 allows surface personnel to be able to determine when ignition of the burner occurs so that theignitor can be withdrawn. Gas inlet ports 68 allow fuel gas flowing down the tubing 14 to enter the interior of the ignitor pipe 66 so that it will flow through the catalytic surface of ignitor 38 to the interior of the heat shield 26.

In the operation of the catalytic ignitor 38, air is injected into the annulus between casing 12 and tubing 14 and a mixture of natural gas and hydrogen is injected into the tubing. The hydrogen-natural gas fuel mixture enters ports 68 and flows down pipe interior 66. The fuel then exits through the catalytic surface where it reacts spontaneously with air which has entered heat shield 26 and burner perforations 44 through air inlets 18. Once a reaction has commenced between the hydrogen-natural gas mixture and air and the temperature is raised sufficiently to support a reaction of natural gas and air alone, the hydrogen is no longer injected. Natural gas will react with air at approximately 250 F. if a catalyst is present and hydrogen will react at approximately 20 F. so no additional energy source is required. Accordingly, the hydrogen reaction will raise the temperature sufficiently to react the natural gas and air which in turn will go to flame to ignite the burner 52. When ignition is indicated by thermocouple 64, the ignitor 38 is removed to the surface. The catalytic ignitor 38 is easily and inexpensively fabricated and the thermocouple 64 allows knowledgeable control of the ignition process. For these reasons it appears superior to the prior art ignitors.

Not shown but contemplated herein are sealing elements between the wireline retrievable burners of FIGS. 1 and 4 and the seating nipples. The sealing elements could be O-rings-similar to those shown at 48 in FIG. 6. Also, in lieu of having wireline retrievable burners, the burners of FIGS. 1 and 4 can be welded in place at the end of the tubing or attached to the heat shield.

Additionally, thermocouples could be employed in all the burners while being ignited and/or after ignition. Automatic controls and alarms might then be connected to the thermocouple indicator so that excessive or deficient temperatures could be avoided.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. Apparatus for heating an underground formation penetrated by a wellbore, comprising: well pipe located in the wellbore; a heat shield open at the bottom and attached to the lower end of the well pipe; and a burner located inside the heat shield, said burner having a plurality of burner ports which are radially and vertically spaced on the burner and which provide individual flame points.

2. The apparatus of claim 1 wherein the burner comprises a tubular member having a multiplicity of perforations extending through the burner wall.

3. Apparatus for supplying heat in a wellbore comprising: well pipe located in the wellbore; and a burner attached to the lower end of the well pipe, said burner comprising a plurality of varying length burner tubes.

4. The apparatus of claim 3 including premix air admission means located upstream of the burner, and air inlet means located in the side wall of the heat shield.

' 5. The apparatus of claim 4 including means for attaching the heat shield to the well pipe, wherein the air inlet means includes spaces between members of said attachment means and baffles located adjacent the spaces between attachment means members.

6. Apparatus for heating an underground formation penetrated by awellbore comprising: well pipe extending from the surface to the vicinity of the underground formation; a burner attached to the lower end of the well pipe having vertically and radially spaced burner ports providing individual flame points; a heat shield open at the bottom and encircling said burner; and premix air inlet means located upstream of the burner and communicating with the interior of the burner.

7. The apparatus of Claim 6 including means for admitting air to the interior of the heat shield and exterior of the burner and means for imparting turbulence to air entering the heat shield.

8. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending from the surface to a point adjacent and above the underground formation to be heated; a tubular burner attached to said well pipe and having an interior communicating with the interior of the well pipe, said burner having a multiplicity of burner ports which are vertically and radially spaced on the burner and extend through the wall of the tubular burner, said ports providing individual flame points; means for insulating the burner from the wall of the wellbore; and premix air admission means located above the burner and communicating with the interior of the burner.

9. The apparatus of claim 8 including means for admitting air between the insulator means and the burner, and means for bafiling the air entering the air admission means, said bafi'ling means located adjacent the air admission means.

10. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending from the surface to a pointabove and adjacent the formation to be heated; a burner having a multiplicity of burner ports spaced vertically and radially on the burner, wherein the interior of the burner commu-. I

nicates with the interior of the well pipe and the exterior of the burner communicates with the space between the well pipe and the wellbore wall; a heat shield open at the bottom and encircling the burner; and air inlet means located in the side wall of the heat shield,: wherein the air inlet means is a tortuous channel through the heat shield side wall.

11. The apparatus of claim 10 including premix air admission means located above said burner and baffles located adjacent said air inlet mean in the heat shield.

12. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending from the surface to the vicinity of the formation; a wireline retrievable burner comprising a plurality of varying length tubes wherein the tube interiors communicate with the well pipe interior; a heat shield open at the bottom and encircling said burner; and premix air admission means located above the burner and communicating with the interior of the; varying length tubes.

13. The apparatus of claim 12 including means for admitting air to the interior of the heat shield and baffle means located adjacent the air admission means.

14. Apparatus for heating an underground formation penetrated by a wellbore having casing and tubing pathway to the interior of the heat shield; and premix air admission means located above the burner.

15. The apparatus of claim 14 including means for baffling the air entering the heat shield so as to impart turbulence to the entering air stream.

16. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending between the surface and a point adjacent the formation being heated; a burner attached to the lower end of the well pipe, said burner having a plurality of burner ports vertically and radially spaced; a heat shield open at the bottom and encircling said burner, said heat shield being secured to the lower end of the well pipe by attachment means having connection members; and air inlet means located in the heat shield side walls and adjacent the connection members.

17. The apparatus of claim 16 including baffle means located adjacent the air inlet means located between the connection members of the attachment means.

18. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending from the surface to a point adjacent the formation to be heated; a burner attached to the lower end of the a well pipe and having a plurality of radially and vertically spaced ports which provide individual flame points; means for insulating the wall of the wellbore from the burner; and means for igniting the burner;

19. The apparatus of claim 18 wherein the burner ignition means is a self contained electrical energy source located adjacent the burner.

20. The apparatus of claim 18 wherein the burner ignition means is a catalytic material located adjacent the burner.

21. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending from the surface to a point adjacent the formation to be heated; a burner having a plurality of varying length burner tubes attached to the lower end of the well pipe; ignitor means located adjacent the burner comprising a shelf contained electrical energy source, means for increasing the intensity of the electrical energy flowing from the electrical energy source and means for flowing the electrical energy between spaced electrical contacts at spaced intervals of time; and means for insulating the burner from the wall of the wellbore.

22. Apparatus for heating an underground formation penetrated by a wellbore comprising: a tubular burner having a multiplicity of burner ports extending through the wall of the tubular burner arranged such that the ports are vertically and radially spaced and provide individual flame points; means for supplying a fuel mixture to the burner; means for insulating the wall of the wellbore from the burner; means for igniting the burner located adjacent the burner comprising an independent source of electrical energy, and means for increasing the voltage of the electrical energy; and means for converting the electrical energy to an electric arc.

23. The apparatus of claim 22 wherein the electrical are means is a pair of spaced electrical contacts separated by air which contacts are located in the interior of the burner and arranged to receive the electrical energy from the ignitor means.

24. Apparatus for heating an underground formation penetrated by a wellbore comprising: a tubular burner having a multiplicity of burner ports spread vertically and radially on the surface of the burner; means for insulating the wall of the wellbore from the burner; means for introducing a gaseous fuel to the burner; means for introducing air to the exterior of the burner; and means to ignite the burner comprising a catalytic material located adjacent the burner and communicating with the interior and exterior of the burner.

25. The apparatus of claim 24 wherein the ignition means comprises a tubular member having a permeable inner wall, a permeable retaining means constituting an outer wall, baffle means located between the inner and outer walls, and wherein the catalytic material is located adjacent the retaining means.

26. Apparatus for heating an underground formation I material adjacent the retaining means.

27. The apparatus of claim 26 wherein the gas burner includes a tubular member with the ports being perforations in the sidewall of the tubular member and wherein the ignition means is of smaller diameter than the burner, and the ignition means is located inside the fiqfi process for supplying heat in a wellbore having well pipe therein including the steps of: attaching a burner; to the lower end of the well pipe, flowing air down the annulus between the well pipe and the wellbore so that air contacts the exterior of the burner; flowing a fuel gas down the interior of the well pipe and into the burner; dispersing the fuel so as to vertically and radially spread the fuel on the burner surface; insulating the wellbore from the burner; admitting an air stream between the insulation and burner and creating turbulence in the air stream by use of a baffle; and igniting the burner.

29. The process of claim 28 including the step of admitting premix air into the interior of the burner.

30. The process of claim 28 wherein ignition of the burner is effected by generating a spark gap in the presence of a combustible mixture with stepped up electrical energy derived from an energy source located in the wellbore.

31. The process of claim 28 wherein spontaneous ignition of the burner is effected by contacting a catalytic surface, located adjacent the burner, with a hydrogen containing fuel gas.

32. A process of heating an underground formation penetrated by a wellbore having well pipe extending from the surface to a point near the top of the formation, comprising: attaching a burner to the lower end of the well pipe so that the burner interior communicates with the interior of the well pipe; insulating the burner from the wall of the wellbore; flowing fuel gas through the well pipe and into and through the burner so that fuel gas is radially and vertically distributed on the outside surface of the burner; flowing air down the annular space between the well pipe and wellbore wall to the formation; passing a portion of the air flowing down the annulus between the insulation and burner so as to contact the outside surface of the burner; and igniting the fuel gas and air mixture present at the burner surface.

33. The process of claim 32 including admitting premix air into the fuel gas flow at a point immediately prior to the burner.

34. The process of claim 32 wherein ignition of the burner is accomplished by creating a spark gap at the burner by using stepped up electrical energy provided by a self contained energy source located adjacent the burner.

35. The process of claim 32 wherein ignition of the burner is accomplished by catalytically reacting hydrogen and air at the burner by injecting hydrogen into the fuel gas flow so that it contacts a catalytic material located adjacent the burner.

Claims

5. The apparatus of claim 4 including means for attaching the heat shield to the well pipe, wherein the air inlet means includes spaces between members of said attachment means and baffles located adjacent the spaces between attachment means members.

6. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending from the surface to the vicinity of the underground formation; a burner attached to the lower end of the well pipe having vertically and radially spaced burner ports providing individual flame points; a heat shield open at the bottom and encircling said burner; and premix air inlet means located upstream of the burner and communicating with the interior of the burner.

9. The apparatus of claim 8 including means for admitting air between the insulator means and the burner, and means for baffling the air entering the air admission means, said baffling means located adjacent the air admission means.

10. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending from the surface to a point above and adjacent the formation to be heated; a burner having a multiplicity of burner ports spaced vertically and radially on the burner, wherein the interior of the burner communicates with the interior of the well pipe and the exterior of the burner communicates with the space between the well pipe and the wellbore wall; a heat shield open at the bottom and encircling the burner; and air inlet means located in the side wall of the heat shield, wherein the air inlet means is a tortuous channel through the heat shield side wall.

11. The apparatus of claim 10 including premix air admission means located above said burner and baffles located adjacent said air inlet means in the heat shield.

12. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending from the surface to the vicinity of the formation; a wireline retrievable burner comprising a plurality of varying length tubes wherein the tube interiors communicate with the well pipe interior; a heat shield open at the bottom and encircling said burner; and premix air admission means located above the burner and communicating with the interior of the varying length tubes.

14. Apparatus for heating an underground formation penetrated by a wellbore having casing and tubing located therein, comprising: a tubular burner connected to the lower portion of the tubing and located adjacent the formation, said tubular burner having vertically and radially spaced perforations extending through the wall of the tubular burner defining burner ports; a heat shield open at the bottom and encircling said burner, interposed between the burner and casing, said heat shield having openings for air admission which are arranged so that the air travels a tortuous pathway to the interior of the heat shield; and premix air admission means located above the burner.

18. Apparatus for heating an underground formation penetrated by a wellbore comprising: well pipe extending from the surface to a point adjacent the formation to be heated; a burner attached to the lower end of the well pipe and having a pluralIty of radially and vertically spaced ports which provide individual flame points; means for insulating the wall of the wellbore from the burner; and means for igniting the burner;

23. The apparatus of claim 22 wherein the electrical arc means is a pair of spaced electrical contacts separated by air which contacts are located in the interior of the burner and arranged to receive the electrical energy from the ignitor means.

26. Apparatus for heating an underground formation penetrated by a wellbore comprising: a gas burner having a plurality of radially and vertically spaced ports on the burner surface; a heat shield open at the bottom and encircling said burner; means for introducing a fuel mixture to the burner surface; and means for igniting the burner comprising a tubular member located adjacent the burner, said member having a permeable inner wall communicating with the well pipe, permeable retaining means, baffle means located between the retaining means and the inner wall, and catalytic material adjacent the retaining means.

27. The apparatus of claim 26 wherein the gas burner includes a tubular member with the ports being perforations in the sidewall of the tubular member and wherein the ignition means is of smaller diameter than the burner, and the ignition means is located inside the burner.

28. A process for supplying heat in a wellbore having well pipe therein including the steps of: attaching a burner; to the lower end of the well pipe, flowing air down the annulus between the well pipe and the wellbore so that air contacts the exterior of the burner; flowing a fuel gas down the interior of the welL pipe and into the burner; dispersing the fuel so as to vertically and radially spread the fuel on the burner surface; insulating the wellbore from the burner; admitting an air stream between the insulation and burner and creating turbulence in the air stream by use of a baffle; and igniting the burner.