US 3804163 A
A catalytic wellbore heater, capable of being suspended from the lower end of well fire, utilizes a tubular member having a wall which is permeable to gas flow. A catalytic material may be coated directly on the tubular member or on a matrix material covering the tubular member.
Claims available in
Description (OCR text may contain errors)
United States Patent Bradley et a1.
CATALYTIC WELLBORE HEATER Inventors: William S. Bradley; William C.
Hardy, both of Richardson, Tex.
Related US. Application Data Continuation-impart of Ser. No. 263,724, June 8, 1972, abandoned.
US. Cl. 166/59, 431/328 Int. Cl E21b 43/24 Field of Search 431/328, 329, 268;
References Cited UNITED STATES PATENTS 10/1963 Kehn 166/59 Apr. 16, 1974 12/1963 Krueger 166/59 3,119,439 1/1964 Weiss 431/328 3,191,659 6/1965 Weiss 431/268 X 3,223,166 12/1965 Hunt et al 166/59 X 3,244,231 4/1966 Grekel et a1. 166/59 X 3,425,675 2/1969 Twine 431/328 X 3,498,381 3/1970 Earlougher 166/57 X 3,712,375 1/1973 Berry et a1. 166/251 3,713,482 l/1973 Lichte et a1 166/59 Primary Examiner-David H. Brown Attorney, Agent, or Firm-George L. Church; Donald R. Johnson; John E. Holder  ABSTRACT A catalytic wellbore heater, capable of being suspended from the lower end of well fire, utilizes a tubular member having a wall which is permeable to gas flow. A catalytic material may be coated directly on the tubular member or on a matrix material covering the tubular member.
19 Claims, 3 Drawing Figures PATENTEDAPR as \974 CATALYTIC WELLBORE HEATER This application is a continuation-in-part application of Ser. No. 263,724 filed June 8, 1972, now abandoned, entitled CATALYTIC WELLBORE HEATER.
BACKGROUND OF THE INVENTION This invention relates to a catalytic wellbore heater which is an improvement over that described in Number US. Pat. No. 3,712,375, entitled METHOD AND APPARATUS FOR CATALYTICALLY HEATING WELLBORE filed Nov. 25, 1970.
Wellbore heaters are used for various purposes such as wellbore and perforation clean out, reduction of viscosity of produced fluids, sand consolidation, in-situ combustion, etc. Various methods and apparatus have been used for supplying downhole heat. The more successful methods and apparatus utilize electrical heaters, gas burners, and recently catalytic reactors.
There are, however, significant draw backs to the various known methods.
Electrical heaters are limited to shallow wells because of difficulty with supplying adequate electrical power at depths in excess of 3,000 feet. Below such depths resistance in the conductor cable builds up to a point where excessively high voltages are needed to supply sufficient electrical power to the heater. In addition, the electrical heaters have a tendency to short out due to a liquid invading the connections to the heater.
Gas burners are ordinarily used in wells in excess of 3,000 feet where electrical heaters cannot be economically used. Damage, however, frequently occurs to well pipe as well as the adjacent formation since the combustion temperature of natural gas can approximate 4,000 F. Heat shields are used to protect the casing from such high temperatures, however, damage can still result, especially if the flame'stands off from the nozzle where the fuel gas exits.
Ignition of the gas burners is also extremely difficult. The current ignition procedure utilizes pyrophoric chemicals. When igniting with pyrophoric chemicals the well tubing must be purged with nitrogen to eliminate the presence of air in the tubing. This is necessary because the pyrophoric chemicals will ignite spontaneously in the presence of air at standard conditions. Once the tubing has been purged with nitrogen, a fuel gas is used to displace the nitrogen. At that time the flow rate is cut down to have only a small amount of fuel gas exiting the lower end of the tubing. Air is pumped down the annular space between the tubing and the casing so that a fuel mixture is present adjacent the lower end of the tubing. The pyrophoric chemical is then lowered down the tubing until it reaches the lower end of the tubing whereupon such chemical ignites upon contacting the air in the annular space adjacent the lower end of the tubing. Unfortunately, an explosive mixture of fuel gas and air is present in the space below the tubing and an explosion occurs upon this mixture being triggered by the pyrophoric chemical. If poor mixture of the fuel gas and air occurs and the result of the mixture is too lean, such mixture will not ignite when the pyrophoric chemical is contacted by air. If the mixture is too rich a heavy explosion occurs. Although in-situ combustion of a formation can be initiated with gas burners, well damage normally results which necessitates expensive well workover.
A heater which may be used at depths in excess of 3,000 feet which runs little risk of well damage, is a catalytic heater. Catalytic heaters have not been widely used due to various troublesome problems. One of the problems is the initiation of the catalytic reaction. One method of initiating the catalytic reaction involves preheating the fuel gas so that it reacts when it reaches the catalytic surface. For example, if a propane-air fuel mixture is used, preheating to 600 F is necessary for reacting the propane and air at the catalytic surface. A methanol-air fuel mixture requires pre-heating to some 200 F to initiate a catalytic reaction.
Besides ignition problems, most of the catalytic heaters involve extremely expensive equipment and in addition the systems are designed in a manner which results in poor heat exchange to the surrounding environment. Most of the heaters are either totally enclosed systems or are vented to allow exhausting the reaction products.
One system that obviates most of the problems normally found in catalytic heaters is the subject of Number U.S. Pat. No. 3,712,375, entitled METHOD AND APPARATUS FOR CATALYTICALLY HEATING WELLBORES. In the system described therein the catalytic reaction is completely exposed to the wellbore and adjacent formation thereby allowing flow rates of fuel gas through the heater sufficient to permit efficient heating of carrier gas transmitting the heat to the formation.
A problem with one of the systems described in U.S. Pat. No. 3,712,375 is that the system includes various components which must be assembled by hand and very carefully tested to insure proper flow through the heater. There is included in the system a distribution pipe having a multiplicity of holes in the side wall thereof. This distribution pipe is surrounded by a fiberized silica material on the exterior of which is wrapped a burlap material coated with a catalytic material. These components when assembled are arranged in a tubular configuration which is protected by a heavy wire screen. The fiberized silica material serves to randomly distribute the fuel gas that enters the catalytic area through the tubing by way of the distribution pipe.
An additional problem with the system described above relates to a permeability breakdown of the formation after heating has taken place sufficiently long to melt paraffin and lower the viscosity of accumulated heavy hydrocarbons located adjacent the wellbore. When this occurs gas in the tubing is pulled through the heater at high rates causing overly rich mixtures resulting in the fuel mixture going to flame and subsequent break down of the uniformity of the fiberized silica. When this occurs a cutting torch effect is created at each point of channeling due to the breakdown in uniformity since the fuel gas channels through the breakdown points. In order to obviate the complexity of fabrication and to provide for consistent flow characteristics of a catalytic heater, it is an object of the present invention to provide an improved downhole catalytic heater.
SUMMARY OF THE INVENTION which includes a tubular member having a wall which is permeable to gas flow. Catalytic material may be coated directly on the exterior of the permeable tubular member or on a matrix covering the permeable tubular member.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevational view shown partially in crosssection of a catalytic heater located in a downhole position in a wellbore.
FIG. 2 is a cross-sectional view of the catalytic heater taken along lines 22 of FIG. 1; and
FIG. 3 is a cross-sectional view of an alternative embodiment of the catalytic section of the heater.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1 of the drawings there is shown a wire line suspended catalytic heater located in a wellbore. Since wellbore heaters are ordinarily used to initiate in-situ combustion of the formation, FIG. 1 describes a system which would be used in such a process. In such cases, the wellbore is lined with casing which has perforations 14 located adjacent the formation 54. Tubing 12 located inside casing 10 extends from the surface to a point slightly above the perforations 14 in casing 10. A more complete system is shown in schematic form in US. Pat. No. 3,712,375 referred to previously and includes means at the surface for supplying fluids under pressure to the downhole components location in the tubing and below the tubing inside the casing The present system includes apparatus as shown therein, such as means at the surface for introducing air under pressure into the casing and tubing annulus and means for introducing fuel gases such as natural gas and hydrogen into the tubing 12 at the surface. The tubing 12 is maintained in a central position in the casing 10 by centralizers 18. The centralizers 18 do not obstruct gas or liquid flow through the annular space between casing 10 and tubing 12. Located at the lower end of tubing 12 is pump seating nipple 16 which has an annular flange for seating wellbore tools. A catalytic heater assembly is shown in the lower end of the interior of tubing 12 and extends below such tubing to a point a short distance above the perforations 14. The catalytic heater assembly 20 is attached to thermocouple cable 32 which is armored to provide the necessary strength for supporting the catalytic heater assembly when it is lowered into or retrieved from the wellbore. The thermocouple cable 32 is made up of thermocouple leads covered with high temperature resistance insulation which is protected by double armoring. The armor provides both resistance to abrasion as well as high tensile strength.
A hanger assembly and fishing neck 34 connects the armored thermocouple cable 32 to the catalytic heater assembly 20 and is also the upper portion of the catalytic heater assembly 20. Directly below the hanger assembly 34 is upper stand-off member 42 which is a blank pipe section to facilitate fishing operations in the event the cable is parted for any reason. Located below the upper stand-off member 42 is a pipe shown in cross section which has upwardly directed perforations 36. Such perforations are drilled through the pipe wall in this manner to prevent sold materials from entering the interior of the catalytic heater assembly 20.
Shown below this perforated pipe and positioned atop pump seating nipple 16 is an assembly having a no-go flange 38 and an O-ring section 40 which is sized so that the flange 38 contacts the annular shoulder of the pump seating nipple 16. Additionally, the O- ring assembly 40 is sized to provide a seal between that portion of the catalytic heater assembly and the interior Wall of the pump seating nipple 16. Lower stand-off member 44 separates the catalytic portion of the heater from the lower end of the tubing. The lower stand-off member 44 is a blank pipe section and is sized to prevent excessive heat from reaching the seal made between the heater assembly 20 and the pump seating nipple 16.
The catalytic section of the heater is positioned directly below the lower stand off member 44 and is shown in partial cross-section. The catalytic section includes a porous metal pipe 22 which has a multiplicity of pores sized to permit gas flow therethrough. Porous metal pipe is presently made available by several companies such as Union Carbide Corporation or l-Iuyck Metals Company. The porous metal is preferably made of a high heat resistance metal such as INCONEL. Since the porous metal can be made available having porosities from approximately 10-90%, the pipe can be tailored to meet any wellbore heating requirements. The porous metal pipe 22 is encircled by a fiberized silica material 24 such as FIBERGLASS or CERAFELT. A catalytic material 46 which preferebly is a platinum group oxidation catalytic can be coated on the fiberized silica material or on burlap type material which may be wrapped around the CERAFELT and is used as a matrix on which the catalyst is formed. A wire screen 26 shown both in cross-section and in normal elevation surrounds the catalytic materials 46 so as to protect it from being damaged by striking well pipe or foreign objects therein. Located below the catalytic section is a thermocouple sub 28 having a thermocouple 30 positioned therein which is exposed to the environment directly below the catalytic section of the heater. The thermocouple should have the capability to transmit accurate information from ambient to l,200 F. The entire catalytic heater assembly is ordinarily located directly above the perforations l4 and the adjacent for-- mation 54 which is to be heated.
In the operation of the catalytic heater some preparation is ordinarily required to insure proper conditions for utilizing the heater in the wellbore. Typical preparations would involve either the use of new tubing or cleaning of the old tubing to prevent debris from plugging the perforations 36 or from entering the interior of the heater itself. In addition, the proper size pump seating nipple 16 and centralizers 18 are attached to the lower joint of tubing 12. The tubing 12 is then purged ordinarily with the fuel gas fed from a fuel gas supply at the surface to be utilized in the normal heating operation. This purging of the tubing is to eliminate any air present therein to prevent having a combustible mixture present in the tubing. This ensures that detonation of an explosive mixture will not occur due to pipe friction, etc.
The catalytic heater assembly is then lowered by thermocouple cable 32 into the tubing until flange 38 contacts the annular shoulder of pump seating nipple 16. When the pressure required for fuel gas injection increases it is indicative that the fuel gas is no longer able to exit through the lower end of the tubing but section of the heater assembly 20, since this portion of the heater is suspended below the lower end of the tubing 12. When the catalytic heater assembly 20 is seated in position, a fuel mixture is available to the heater since fuel gas exits the tubing through the catalytic section of the heater and air is located adjacent the exterior of the catalytic section. The air which descends down the annular space between casing and tubing 12 is present at the exterior of the catalytic section of the heater in sufficient quantity to supply fuel mixture requirements and to act as a carrier gas for transferring the heat of the reaction to the formation 54.
In order to initiate the catalytic reaction it is necessary to raise the temperature to the reaction temperature of natural gas and air. This can be done in various ways such as preheating the gases being pumped from the surface to the heater, by providing some type of electrical heat, or preferably by injecting hydrogen gas into the tubing at the surface either alone or with normal fuel gas. The hydrogen reacts spontaneously with air in the presence of a platinum group catalyst at temperatures in excess of F. It may be preferable to continuously inject hydrogen in the fuel gas being pumped down the tubing 12. This has the advantage of immediate re-ignition of the heater if the temperature of the heater drops below the reaction temperature of the fuel mixture. The temperature may fall below this critical level for various reasons such as an interruption in fuel supply or an insufficient amount of one of the fuel components.
Additionally, if hydrogen alone is utilized a flow rate of only 6 SCF/hour/square foot of catalyst can be used whereas with a mixture of hydrogen and natural gas the flow rates can be increased to 20-25 SCF/hour/square foot of catalyst. Upon the seating of the catalytic heater assembly 20 a catalytic reaction of the hydrogen contained in the fuel gas and the air adjacent the exterior of the heater will occur. Once the hydrogen-air reaction elevates the heater temperature to some 250 F a catalytic reaction of the natural gas and air will occur. When the wellbore and adjacent formation are heated sufficiently to ensure that the heater will not have to be re-ignited, the hydrogen injection can be terminated which permits an increase in flow rates to some 45 SCF/hour/square foot of catalyst.
The heat resulting from the reaction of the fuel gas (usually natural gas) and air is carried into the formation 54 by injecting air in excess of that required for the catalytic reaction. Such excess air acts as a carrier gas to transfer heat to the formation 54 through the perforations 14. The temperature of the catalytic reaction may be monitored by observing the information transmitted by the thermocouple 30 located directly below the catalytic section of the heater. By controlling the injection rates of the fuel gas and air in response to information transmitted by the thermocouple 30, the reaction temperature of the heater can be controlled. Additional thermocouples can be employed at various downhole locations so that the various reactions and their effect can be more accurately monitored. The fuel mixture is fed to the catalytic heater until such time as in-situ combustion commences in formation 54. Such combustion in the formation can be ascertained by monitoring gases produced from adjacent wells. When, for example, carbon dioxide markedly increases it is indicative of initiation of in-situ combustion.
In the early stages of flowing the heated air into the formation 54 permeability breakdown often occurred, sometimes resulting in serious damage to the catalytic heater. Normally located adjacent the perforations 14 there are such things as paraffin deposits and permeability reducing heavy hydrocarbons. When these materials are heated their viscosity is reduced and upon such reduction there is a sudden increase in permeability. Additionally, dehydration of formation rock as well as burning of coke and rock expansion causes an increase in permeability. When this permeability breakdown occurs, there is less restriction to flow into the formation and a lower bottom hole pressure. The fuel gas therefore discharges out the tubing at an unacceptable rate causing an enriched fuel mixture at the catalyst surface. When this enriched fuel mixture reacts the temperature quickly reaches the flame temperature of the fuel mixture. Since flame temperatures can approach the range of 4,000 F the heater will fail due to the temperature being in excess of what the heater will withstand. The high flow rate and turbulence of combustion also tends to breakdown the fiberized silica material and createlarge flow channel therethrough. The fuel gas preferentially passes through these less restrictive passages and these locations then act like cutting torches to further damage the heater and adjacent well pipe. The heater breaks down in this manner because of the structure of the catalytic section of the heater. As the heater was previously structured the pressure drop through the catalytic section of the heater occurred where the catalytic material was deposited. Since this area of the heater comprising either burlap or a fiberized silica material has very little strength, failure would often occur upon having a breakdown in formation permeability. If the catalyst is coated on burlap and an area of the burlap has broken down, the pressure drop then took place through the adjacent fiberized silica material, which also possesses little structural strength. By this process a hole is blown through the heater wall and channeling of the fuel gas results thereby creating a small area of enriched fuel mixture which goes to flame.
Porous metal pipe obviates the problems caused by a sudden change in formation permeability since its pore size is such that the pressure drop will occur as it passes through the pipe wall which has greater strength and therefore will not be damaged. No appreciable pressure change will occur at the surface where the catalytic material is coated since the major pressure drop is at the porous metal pipe. The diffusing material 24 also acts to reduce any channeling of the fuel gas to a particular area of the catalytic surface.
It is contemplated that besides porous metal pipe there could be utilized a pipe section having very small holes drilled therein. Such a pipe section would serve to restrict the gas flow to an extent that the primary pressure drop through the heater occurs when the gas passes through these drilled holes. In addition, these drilled holes should be sized and spaced to distribute the. gas along the length and periphery of the catalytic section of the heater. A further diffusing medium formed on the exterior of the drilled pipe may serve also as a surface on which to coat a catalyst. Since the diffusing medium by design has a great many tortuous pathways therethrough only a slight pressure drop occurs as the gas passes therethrough.
It is contemplated that in lieu of having a porous metal pipe surrounded by a fiberized silica material on which is coated on oxidation catalyst, that porous metal pipe along with catalyst coated thereon be used. The porous metal pipe would serve not only to provide strength but also to distribute and disperse the fuel gas. Catalyst coated directly on the porous metal pipe would have a greater permeability than the pipe so that the pressure drop of the fuel gas occurs as it passes through the pipe. This configuration would serve to greatly facilitate fabrication of the heater.
A better understanding of the makeup of the catalyst section of the heater can be seen by looking at a crosssection of the heater taken along lines 2-2 which has been illustrated in FIG. 2. The porous metal pipe 22 having pores 48 therein is formed into a hollow cylinder. The porous metal pipe is also the interior wall of the catalytic section of the heater. Arranged around the exterior surface of the porous metal pipe 22 is fiberized silica material 24. This fiberized silica material 24 is arranged to provide a multiplicity of tortuous pathways from the exterior surface of the porous metal pipe 22 to the exterior surface of the fiberized silica material 24. Impregnated or coated on the outside surface of the fiberized silica material 24 or on burlap wrapped around such silica materaial is catalytic material 46. Providing protection and strength to the catalytic section of the heater is a wire screen 26 arranged to act as the exterior surface of the catalytic section of the heater. This wire screen 26 is normally constructed of a heat resistant metallic material such as stainless steel, MONEL INCONEL. In addition to their high heat resistance, these materials also have high strength characteristics for protection of the remainder of the catalytic section of the heater.
When the heater is in operation, fuel gas is flowed down the tubing and into the interior of the catalytic heater. The fuel gas then travels through the wall of the catalytic section of the heater by passing through the porous metal pipe 22 by way of pore spaces 48. Upon passing through the porous metal pipe 22 by way of pore spaces 48 the gas is diffused by the fiberized silica material 24. There is a minimal pressure drop as the gas diffuses through the fiberized silica material 24 since the primary pressure drop through the catalytic section of the heater occurs as the gas passes through the porous metal pipe 22. After the gas has been diffused it then comes in contact with the catalytic material 46. Since air is flowing down the annular space between tubing 12 and casing 10 there is air present at the surface of the catalytic material 46. A fuel mixture is thus present at the catalyst surface for providing a catalytic reaction. Excess air flowing down the annular space between tubing 12 and casing 10 carries the heat of the catalytic reaction into the formation 54 by way of perforations 14. In the event that a permeability breakdown occurs it can be seen from FIG. 2 that the pressure drop will occur as the fuel gas passes through the porous metal pipe 22, thereby protecting the silica material 24 and catalyst 46 from excessive flow rates and resultant structural damage.
An alternative embodiment of the catalytic section of the heater has been shown in FIG. 3. In this configuration a distribution pipe 50 is shown as the interior surface of the catalytic section of the heater. Drilled holes 52 extend through the wall of the distribution pipe 50. These drilled holes 52 are arranged to distribute the fuel gas along the entire length and around the entire circumference of the catalytic section of the heater. Shown surrounding the distribution pipe 50 is a porous metal pipe 22 having pore spaces therein. Coated upon the exterior wall of the porous metal pipe 22 is catalytic material 46 which is preferably vacuum deposited thereon.
This particular configuration of the catalytic section of the heater eliminates the need for using the fiberized silica material, the wire screen and the burlap if it is used as a base on which to deposit the catalyst. The distribution pipe 50 functions both as a means to distribute evenly the fuel gas which eventually contacts the catalytic material 46 but also serves to provide strength for the catalytic section of the heater. The porous metal pipe 22 acts both as a mechanism to diffuse the fuel gas and as a surface upon which to deposit the catalytic material 46. This particular configuration requires much less fabrication time and thus reduces the cost of the equipment. The use of porous metal pipe therefore reduces equipment, cost and additionally solves the problem of damage to the heater and well pipe due to permeability break down in the formation.
It is also contemplated that the distribution pipe 50 could be eliminated and only the porous metal pipe 22 used as a base for the catalyst and as a diffusing medium. If greater strength is needed or protection from impingement is necessary, an interior or exterior reinforcing ribs or a protective screen such as the screen 26 shown in FIG. 2 could be used.
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. In a catalytic heater for use in a wellbore having well pipe therein the improvement comprising: a porous metal cylinder having an open upper end, a closed lower end; an oxidation catalyst coated on the cylinder; and means for suspending the cylinder from the well pipe.
2. The catalytic heater of claim 1 including a perforated distribution pipe located within and co-extensive with the porous metal cylinder.
3. The catalytic heater of claim 1 wherein the porous metallic cylinder is sized and arranged to allow the interior of the cylinder to communicate with the interior of standard well tubing and wherein the catalyst is coated on the exterior surface of the cylinder.
4. Apparatus for use in providing heat to a wellbore having well pipe therein comprising: a porous metal cylinder closed at its lower end and open at its upper end and which has a catalytic material coated on the exterior surface of the cylinder, wherein the open upper end of the cylinder communicates with the interior of the well pipe.
5. The apparatus of claim 4 including a distribution tube having a multiplicity of holes through the wall of the tube, which holes are radially and vertically spaced on the tube.
6. Apparatus for use in providing heat to a wellbore having well pipe therein comprising: a permeable tubular member capable of being suspended from the lower end of the well pipe and having an open upper end and a closed lower end; a catalytic material deposited on the exterior surface of the permeable tubular member; a distribution pipe having a porous metal pipe wall which is positioned adjacent the interior surface of the permeable tubular member and which is less permeable than the permeable tubular member, said distribution pipe being co-extensive with the permeable tubular member.
7. The apparatus of claim 6 including thermocouples positioned on the catalyst surface and adapted to be connected with surface recording instruments.
8. The apparatus of claim 6 wherein the catalytic material is uniformly deposited on the exterior surface of the tubular member and has a generally uniform permeability to gas flow passing through the tubular member.
9. Apparatus for use in providing heat to a wellbore having well pipe therein comprising: a tubular member having a wall permeable to gas flow; catalytic material uniformly distributed on the exterior surface of the tubular member and having a greater permeability to gas flow than the tubular member; and means at the upper end of the tubular member for engaging the lower end of the well pipe, and wherein the tubular member is arranged so that gas flowing down the well pipe will enter the interior of the tubular member.
10. The apparatus of claim 9 wherein a substantial portion of the tubular member extends below the well pipe thereby exposing the catalytic material distributed on the tubular member to any gases flowing down the annular space between the well pipe and the wellbore.
11. The apparatus of claim 9 including a distribution pipe inside of and co-extensive with the tubular member and having perforations through the pipe wall and spaced longitudinally and radially on the distribution p1pe.
12. The apparatus of claim 9 wherein the tubular member has an open end which communicates with the interior of the well pipe and wherein the tubular member has a closed lower end.
13. A system for use in providing heat to a wellbore having a casing lining the wellbore and tubing located inside the casing, comprising: a pump seating nipple located at the lower end of the tubing; a porous metal tubular member permeable to gas flow and having an open upper end communicating with the interior of the tubing and a closed lower end communicating with the interior of the tubing and a closed lower end, said tubular member also having means located at its upper end for engaging the pump seating nipple; and catalytic material uniformly distributed on said tubular member, such tubular member, seating nipple, tubing and easing being arranged so as to provide a conduit means for flowing a first gas down the tubing, into the tubular member, through the permeable wall of the tubular member and into contact with the catalytic material, and a separate conduit means for flowing a second gas down the annular space between the casing and the tubing and into contact with the catalytic material.
14. The apparatus of claim 13 wherein the permeability of said porous metal tubular member is less than the permeability of the catalytic material and its permeability is sufficient to allow the passage of at least 20 standard cubic feet of a hydrocarbon natural gas per hour per square foot of porous metal tubular member with a pressure drop from 5-10 psi.
15. Apparatus for supplying heat in a wellbore having well pipe therein comprising: a porous metal pipe having an open upper end and a closed lower end, wherein the upper end is adapted for suspension from the well pipe; a matrix attached to the outside surface of the porous metal pipe having a permeability to gas flow greater than that of the porous metal pipe; and an oxidation catalyst uniformly distributed on the matrix.
16. The apparatus of claim 15 wherein the open upper end of the metal pipe communicates with the interior of the well pipe.
17. The apparatus of claim 15 wherein the matrix covers substantially all the exterior surface area of the porous metal pipe and the catalytic material covers substantially all the exterior surface areas of the matrix.
18. The apparatus of claim 15 wherein the matrix is formed to provide a multiplicity of tortuous pathways between the porous metal pipe and the catalytic material.
19. In a downhole catalytic wellbore heater, the improvement comprising: a rigid cylindrical member having an open upper end, a closed lower end and side walls, which side walls have permeability to gas flow;
through than the permeability of the diffusing means.