US3091225A - Initiating and controlling underground combustion - Google Patents

Description

May 28, 1963 T. w. LEGATSKI 3,091,225

INITIATING AND CONTROLLING UNDERGROUND comsuswrcm 2 Shae Filed Dec. 29. 1958 mm 2 20 m w 52 mom owximmm ENTOR. T. W. L EGATSK I W W? 9 TEE NM M A TTORNEKS May 28, 1963 T. w. LEGATSKI INITIATING AND CONTROLLING UNDERGROUND COMBUSTION Filed Dec.

INVENTOR. TW. LEGATSKI ATTORNEYS United States Patent 3,091,225 INITIATING AND CONTROLLING UNDER- GROUND COMBUSTION Theodore W. Legatslri, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Dec- 29, 1958, Ser. No. 783,447 7 Claims. (Cl. fill-156) This invention relates to apparatus for initiating and controlling combustion in a subterranean formation containing carbonaceous matter from a borehole penetrating the formation.

In situ combustion in the recovery of a diflicultly flowable hydrocarbon from underground strata containing such hydrocarbons or carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move through the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial proportion of the remaining hydrocarbon material. By the term remaining hydrocarbon material is meant that hydrocarbon material recovered and which is not consumed in the combustion.

The ignition of carbonaceous material in a stratum around a borehole, followed by injection of air through the ignition borehole and recovery of product hydrocarbon in combustion gas through another borehole in the stratum, is a direct air drive process for clfecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation, the stratum usually plugs in front of the combustion zone because a heavy viscous fluid bank collects in the stratum in advance of the combustion zone and prevents movement of air to the combustion process. To overcome this ditficulty and permit the continued progress of the combustion zone through the stratum, inverse air injection has been resorted to. By this latter technique, a combustion zone is established around an ignition borehole by any suit able means and air is fed through the stratum to the combustion zone from one or more other boreholes.

In operating with either direct or indirect air injection to produce hydrocarbons from a carbonaceous stratum by in situ combustion, it is necessary to ignite first the carbonaceous material in the stratum around. a borehole. Various methods of igniting this carbonaceous material have been devised. Also, many burners have been devised for downhole use, such as gas fired burners and electric heaters. One difi'iculty in the use of any of these types of burners in such downholc operation is that the formation tends to become overheated in the immediate vicinity of the burner and the remaining portion of the borehole through the formation may not. be heated sufficiently to initiate combustion. Thus, there is overheating at one point and underheating at another point.

Accordingly, it is an object of this invention to provide a downhole heater of such construction that heat is uniformly transferred to the face of the borehole in the carbonaceous material containing formation. Another object of this invention is to provide a heater for heating the formation containing carbonaceous material which distributes heat of sufficient intensity for ignition or the carbonaceous matter at all levels of the formation face exposed in the borehole. A further object of this invention is to provide a downhole heating apparatus which does not overheat at one level and underheat at another level. Other objects and advantages of my invention will be realized by those skilled in the art upon consideration of the accompanying disclosure.

3,091,225 Patented May 28, 1963 In a copending application, Serial No. 741,329, filed June 11, 1958, now Patent No. 3,035,638, is a full and complete description of a method for initiating and maintaining inverse in situ combustion in a subterranean carbonaceous material containing formation. In this application. it is stated that one important point of said onpcnding application in solving the problem of maintaining in situ combustion by inverse air flow is to mix a small percentage by volume of a combustible gaseous material with air and inject this mixture into an input well or borehole in such a manner that this mixture of fuel and air flows through the carbonaceous matter containing formation toward the ignition well. The ignition well as considered herein is the borehole extending from the surface of the ground into the carbonaceous material containing formation from which the formation is ignited in the combustion operation. The injection well or borehole is the borehole into which the mixture of air or air and fuel gas is injected into the formation for maintaining this combustion. In said copending application, a mixture of air and fuel gas suitable for maintaining continuous combustion within the carbonaceous material containing formation contained from about one to five percent by volume and more desirably from about two to four percent of fuel gas by volume. Propane was disclosed as being a preferred fuel gas but other fuel gases than propane, for example, ethane or even methane, that is either pure methane or in the form of natural gas is sometimes used. It is preferred that the B.t.u. con tent of the fuel gas used in such an operation be relatively high and, for this reason, the use of propane is preferred.

In the drawing, FIGURE 1 is a longitudinal view, partly in section, of a preferred embodiment of my invention. FlGURE 2 is a longitudinal view, partly in section, of another embodiment of heating apparatus of my invention. FIGURE 3 illustrates still another embodiment of heater of my invention. FIGURE 4 is a longitudinal view, partly in section, of still another embodiment of my invention. FIGURE 5 illustrates, in digrammatic form, a sectional view through a carbonaceous material bearing formation and overlying strata illustrating a method of initiating combustion within a carbonaceous material bearing formation. FIGURE 6 illus trates one method for recovering carbonaceous material from a carbonaceous material containing zone being produced by underground combustion.

Referring to the drawing and specifically to FIGURE 1, this embodiment of formation heater involves a, tubular outer shell 12 in which is disposed a tubular shell 13 of smaller diameter than shell 12. These two tubular shell members are disposed substantially concentrically with respect to one another and at a spaced distance so as to provide an annulus 23 therebetween. The upper end of annulus 23 is closed by a closure 27 as illustrated. The bottom ends of shells 12 and 13 are closed as illustrated by substantially semispherical closures 14 and 14a, respectively. Disposed within annulus 23 and the lower portion between closures 14 and 14a is an easily meltable and boilable metal 20. An upper closure member or cover 22 is disposed as illustrated for confining combustion gases and directing same to a vent pipe 24.

Disposed within the inner shell 13 is a burner, that is, a fuel gas burner which comprises a burner tip 25 surrounded by a burner shield 15. Connected with burner tip 25 are pipes 16 and 17 through which air and fuel gas, respectively, are passed from the surface of the ground. The burner is lit or in other words the fuel gas is ignited as by a sparltplug 19 energized by an electric current passed through wires 18 from above ground. As is well known in such art, a high voltage low amperage current is required to operate such an ignitor.

A burner or heat transfer apparatus of this type operates in the following manner. Fuel gas and air are passed downward through pipes 16 and 17, respectively, and then electric current is passed through wires 18 to form a spark at spark plug 19 which in turn ignites the gas. When the gas has been ignited and flame issues from within burner shield 15, the apparatus then starts to become heated. The metal 20 in the bottom portion of this heater is such a metal as sodium, potassium, lithium, rubidium, caesium, or a mixture of any two or more of these metals. Of these metals, caesium boils at a temperature of 1238 F. and lithium boils at a temperature of about 2437 F., these two temperatures representing the extreme limits of boiling points of these several metals. It is preferred to use metallic sodium in this apparatus because it is less expensive to purchase. Metalic sodium boils at a temperature of 1615 F. Thus, upon ignition of the gas at burner 25, the shield directs the flame downward against the lower portion of the inner shell 13 and at closure member 14a so that the fiame will be directed substantially toward the metal 20. Upon continued heating, the metal is gradually raised to a temperature approaching its boiling point. When the metal begins to boil, vapor rises upward in annulus 23 and heats the walls of the inner and outer shells 12 and 13, respectively. The wall of the inner shell 13, is, of course, quite hot because it is exposed to the temperature of the combustion gas. The wall of shell 12, being adjacent the carbonaceous material bearing formation is materially cooler than shell 13. As the vapor of the metal rises in annulus 23, it condenses mainly on the surface of shell 12. As the metal shell becomes heated by condensation of the vapor, the vapor rises higher up the annulus until finally the entire inner surface 21 of shell 12 is in contact with condensing metal vapor and is thus heated to a sufficiently high temperature. It is realized by those skilled in the art that such a means of distributing heat all the way up and down the heater is particularly adapted to heating uniformly an object to be heated. Thus, by the construction of this apparatus of such length that it extends in the borehole across the entire face of the carbonaceous material containing formation, the entire surface of the formation becomes heated to a desired temperature. When this surface of the carbonaceous material containing formation exposed to the borehole becomes sufficiently hot then upon arrival of air from an adjacent air input well conditions are right for ignition to begin. As mentioned hereinbefore and as fully disclosed in said copending application, by mixing a small percentage of a combustible gas with the air being injected into an adjacent air input well upon ignition of the surface of the carbonaceous material bearing formation exposed to the heater a combustion front travels slowly and radially outwardly from the borehole into the formation.

On reference to FIGURE 5, reference numeral 11 identifies such a heat transfer assembly as illustrated in FIGURE 1 disposed in a borehole 63 within a carbonaceous material containing subterranean formation 61. Pipes 16 and 17 pass air and fuel gas, respectively, to the burner of the heat transfer assembly and upon igniting spark plug 19 (FIGURE 1) by passage of a high voltage current down leads 18 the burner within the heat transfer assembly 11 is lit and heating begins. After the heat transfer assembly 11 becomes well heated and heating is continued, the surface of the well bore is raised to a combustion temperature and upon passage of air or air and a fuel gas down a tube 70 in an air input well 72 and through formation 61 combustion progresses from borehole 63 in a direction toward borehole 72. Reference numeral 62 identifies the leading surface of a combustion zone as propagated in the manner just disclosed. Borehole 63 is in terms of this art frequently referred to as an ignition well. Such ignition wells are ordinarily provided with casing, as for example, a casing 64, which is provided with a head or casing cover 65 at the head of the well. In FIGURE 5 air for passage to pipe 16 to the burner in the heat transfer assembly is illustrated as being provided from the atmosphere by a pump 69 which transfers the air through a pipe 88 to tubing or pipe 16. A fuel gas from a source, not shown, for firing the heater is provided through a pipe by a pump 67 and through a pipe 86 and a pipe 89 with valves in these pipes being open, to tubing or pipe 17 for passage down the well to the burner.

The heater is operated in this manner until such time that it is certain that the combustion in the formation had been well started and is progressing satisfactorily. Progression of the combustion zone may be observed by providing a small diameter well bore 74 which may be cased by a casing 75, as desired, and which is provided with one or more thermocouples 76. These thermocouples communicate to electrical apparatus above ground through a cable 77 to conventional electrical apparatus for converting electrical impulse to degrees F., for example. Such electrical equipment is well known in the art. At such a time that thermocouples 76 indicate that the combustion zone has progressed a substantial distance from the heat input well then the valves in pipes 86 and 89 and in pipe 88 may be closed to shut off the flow of gas and air to the burner in the heat transfer assembly. When these valves are closed and the flame in the heat transfer assembly is extinguished, the heat transfer assembly is pulled from the well by unbolting casing cover 65 and pulling the tubes or pipes and the heater in a conventional manner.

While the heat transfer apparatus is being withdrawn from well bore 63, air with a small content of fuel gas is passed through tubing 70 into the air input well 72 for maintenance of combustion within the formation. In this passage of the air and gas mixture down tubing 70, the gas is passed under the influence of pump 67 through pipe 85 and pipe 68 with the valve in that pipe being open and air from pump 69 is passed through pipe 87 with the valve in this pipe being open and the mixture then enters the air inlet pipe 70 for passage down the well.

After the heat transfer assembly 11 has been withdrawn from the ignition well 63, a production tubing is run into the well and is attached to the casing by means of a casing cover similar to casing cover 65. In FIG- URE 6 is illustrated the well 63 provided with such a production tubing 66 attached to the well casing by a casing cover 65a. After this tubing 66 is run into the well and attached to the casing by the cover 65a, combustion gases and vaporous hydrocarbon material which leave the formation and enter well 63 at the borehole surface 73 enter tubing 66 and are conducted up the well. This produced material leaves the well head, passes through a pipe 78 into a separator 79 in which produced liquids separate from produced gas. If desired, all or a portion of the produced hydrocarbon material from production tubing 66 is by-passed from pipe 78 and passed through a by-pass line containing a condenser for condensation of condensable material. This condenser can be a large surface atmospheric condenser, or a liquid condenser in which the coolant is a cooling water or the condenser may even be a refrigerated condenser. Whatever type of condenser is used, condensed and uncondensed materials pass on into separtor tank 79 in which gases are separated from liquid. Liquid is passed from separator 79 through a pipe 80 into a storage tank 81 for such disposal as desired. Gases sepa rated in separator 79 are withdrawn through a pipe 82 and, if desired, a small portion of this produced gas is passed through a pipe 84 into pipe 86 of FIGURE 5 and further passed through pipe 68 for use in producing the air-fuel gas mixture for injection into the air input well. Gas separated in separator 79 and passed through pipe 82 not required for such combustion maintenance is withdrawn from the system through a pipe 83 for such disposal as desired.

In FIGURE 2. is illustrated another embodiment of heater apparatus involving the principles of my invention. A difference between this heater and the one illustrated in FIGURE 1 is in the actual fuel gas burner arrangement. The burner illustrated in FIGURE 2 is intended to utilize a premix air and fuel mixture in place of separate fuel gas and air. A premixed mixture of fuel gas and air is passed from the surface of the ground down the heat input well or ignition well through a pipe 33 to the heating apparatus. Since the premixed air and fuel is obviously an explosive mixture, a flame arrestor 34 is provided in pipe 33 at a point adjacent the heating apparatus. After passing through the flame arrestor 34 the mixture enters the actual heating apparatus and flame then passes through a flame tube 36 provided with openings 32 only at and near the lower end of the flame tube 36. Flame is needed only in the general vicinity of the liquid metal 20 in the bottom portion of the heater. Heat issuing through the openings 32 in this lower portion of flame tube 36 heats the metal to a boiling temperature and upon boiling the vapor rises up the annulus 23 and condenses mainly on the walls of the outer shell 12 for imparting heat to the formation to be ignited. The combustible mixture of gas and air is ignited by spark plug 19 energized by high voltage current through leads 18 as mentioned hereinbefore. The vent pipe 24 is provided for passage of burned gases up the well bore to the surface of the ground for disposal.

In FIGURE 3 is illustrated an embodiment of heater of my invention which is heated by electrical means in place of a fuel gas. The main heating portion of the apparatus that is the inner and outer shells 13 and 12, respectively, forming an annulus in the bottom of which is a quantity of boilable metal, is all similar to that illustrated in FIGURES 1 and 2. For heating the metal in this embodiment, a heating coil 40 is wound around the inner wall of the inner shell 13 and is held in place by a refractory cementing material 41, such as Kaocast, high alumina, castable, hydraulically setting refractory. The electrical heating element may be maintained or held in close contact with the inner wall of shell 13 in any other suitable manner, if desired. Lead wires 42 conduct electric current from the surface of the ground down the well bore to the resistance element 40. As the metal 20 is heated to its boiling point vapor than passes upward in the annulus 23 to heat the Walls of the outer shell 12 for bringing to combustion temperature carbonaceous matter on the borehole walls of the formation. A cover 91 is provided at the top of this apparatus to provide support for wires 42. Cover 91 is provided with a vent 90 for inlet and outlet of gases of expansion formed during heating and cooling of this apparatus.

In FIGURE 4 is still another embodiment of my invention. In this embodiment, heat is again supplied by combustion of a fuel gas with air. However, in place of having to provide one or more tubes or pipes for passage of premixed air and fuel or air and fuel separately from the surface of the ground down to the heating apparatus I provide bottles of fuel gas and air under pressure with the apparatus. As illustrated in this figure a case 45 is attached to the lower portion of the outer shell 12. Case 45 houses a burner ring 52 which is connected by tubes 56 and 57, respectively, to a fuel gas bottle 47 and to an air bottle 46. Tube 56 is provided with a solenoid valve 51 while tube 57 is provided with a solenoid valve 50. These solenoid valves are operated from the surface of the ground by passage of electrical impulse through electrical cable 54. Additional wires are provided in cable 54 for transmission of high voltage current to a spark plug 53. In the aboveground operation, apparatus is so provided that upon closing of a circuit to solenoid valve 59 and 51 high voltage current is simultaneously passed to spark plug 53 so that upon passage of air and fuel gas through tubes 57 and 56, respectively, to burner ring 52 the spark plug becomes activated and ignites the fuel gas. Upon ignition of the gas the metal 20 becomes heated and finally boils. The operation from this point on is similar to that described relative to the heating apparatus of FIGURES l, 2 and 3. The construction of the heater apparatus is slightly different in this modification of FIGURE 4 than in the other modification. This difference is that an opening 58 is provided in the bottom of the heating apparatus for accommodation of the electrical wiring. If the electrical wiring cable 54 were on the outside of the heat transfer assembly 11 upon lowering this apparatus down the Well bore the cable might easily be injured so that the electrical portion of this apparatus would not function properly. After ignition of gas in burner ring 52, it is immaterial whether the wiring at this point is destroyed or not because it has fulfilled its purpose. Furthermore, burned gases from the flame issuing from burner 52 pass upward through opening 58 and impart additional heat to the inner wall of the inner shell 13 and these burned gases finally exit up the well through vent pipe 55 for such disposal as desired.

Materials of construction for use in building the heating apparatus of my invention may be selected from among those commerically available taking into consideration the particular metal 20 heated to boiling within the apparatus and further taking into consideration temperatures involved. Some stainless steels withstand temperatures in the vicinity of 2600 to 2700" F. Such materials might be expected to withstand temperatures within the ignition wells maintained for the length of time required to start combusion in the formation.

Referring again to FIGURE 4 the air containing bottle 46 is fixed to case 45 by support 48 while the fuel gas bottle 47 is attached by member 49 to case 45.

In FIGURE 2, cover 35 is provided for confining combustion gases from burner tube 36 so as to direct them up the vent pipe 24.

In each case or type of heater described herein it is necessary and important that the length of the actual heat transfer portion of the apparatus be at least equal to the length of the borehole in the carbonaceous material hearing formation. In other words, the length of the heater should be at least equal to the thickness of the carbonaceous material containing formation for uniform heating to combustion temperatures of the material in the formation. By so providing this heater and with its unusually uniform distribution of heat throughout its length hot spots and spots heated to too low a temperature are not involved. As is well known, portions of formations which are overheated frequently become sintered and more or less imprevious to the passage of fluid. Furthermore, spalling and caving due to excessive temperatures or partial fusing are not involved.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. Apparatus for heating a subterranean formation containing carbonaceous matter from a bore hole penetrating said formation comprising, in combination, a first tubular member having the lower end thereof closed, a second tubular member having the lower end thereof closed disposed within and along the axis of said first tubular member, said second member being disposed at a spaced distance from said first member thereby providing an annulus therebetween having completely closed ends, a body of metal having a boiling point between about l200 and 2450 F. disposed in and partially filling said annulus at a lower end thereof, said body of metal being present in an amount suificient upon boiling to substantially vaporize and fill said annulus with condensing metal vapor, a closure member closing the end of said second tubular member at an upper end of said annulus, means supported by said closure member for heating said metal which is so adapted as to provide a combustion area in a position adjacent to the lower end of said annulus and said body of metal so as to effect vaporization of same, and a vent in said closure member and in communication with said combustion area.

2. The apparatus of claim 1 wherein said metal is selected from the group consisting of sodium, potassium, lithium, rubidium, cesium, and mixtures of two and more of these metals.

3. The apparatus of claim 1 wherein said means for heating said metal is a gas fueled burner.

4. The apparatus of claim 3 wherein said gas fueled burner for heating said metal is disposed within the inner of said first and second tubular members, and said burner being so positioned as to direct flame downward.

5. The apparatus of claim 3 wherein said axis is vertically disposed and said closure member is at about the top of the apparatus and wherein said gas fueled burner is disposed outside the outer tubular member of the first and second tubular members and below the lower closure means of said separate closure means, a separate vent in said lower closure means and in said closure member, first and second bottles for fuel gas and a combustion supporting gas, respectively, supported by and below said burner, separate conduit means communicating said first and second bottles with said burner, separate valves in each conduit means for opening said valves and means for igniting fuel gas in said burner.

6. Apparatus for heating a subterranean formation containing carbonaceous matter from a bore hole penetrating said formation comprising, in combination, a first tubular member, a second tubular member disposed within and along the axis of said first tubular member, said second member being disposed at a spaced distance from said first member thereby providing a completely closed annulus thcrebetween, a body of metal having a boiling point between about 1200 and 2450 F. disposed in and partially filling said annulus at one end thereof, said body of metal being present in an amount sufiicient upon boiling to substantially vaporize and fill said annulus with condensing metal vapor, and means for heating said metal by an upper portion of said tubular member so as to effect vaporization of said body of metal, said means for heating being external said annulus and adjacent said body of metal in same.

7. In the apparatus of claim 6, wherein said means for heating said metal is a gas fueled burner disposed within said second tubular member, a conduit communicating with said burner and extending through said closure member for passage of premixed fuel gas and gaseous oxygen to said burner, a flame arrestor in said conduit, and means to ignite fuel gas in said burner.

References Cited in the file of this patent UNITED STATES PATENTS 1,146,310 Colby July 13, 1915 1,639,114 Smith Aug. 16, 1927 1,840,588 Knox Jan. 12, 1932 1,983,386 Mikeska Dec. 4, 1934 2,163,599 Houdry June 27, 1939 2,556,984 Smith June 12, 1951 2,584,606 Merriam et al. Feb. 5, 1952 2,669,661 Riddiford et a1. Feb. 16, 1954 2,717,580 Maher et al. Sept. 13, 1955 2,820,134 Kobayaski Jan. 14, 1958 2,865,827 Dwyer Dec. 23, 1958 2,893,701 Bell July 7, 1959 2,902,270 Salomonsson et a1 Sept. 1, 1959 2,932,352 Stegemeier Apr. 12, 1960 FOREIGN PATENTS 808,316 France Nov. 14, 1936 902,703 France Dec. 22, 1944

Claims (1)

1. APPARATUS FOR HEATING A SUBTERRANEAN FORMATION CONTAINING CARBONACEOUS MATTER FROM A BORE HOLE PENETRATING SAID FORMATION COMPRISING, IN COMBINATION, A FIRST TUBULAR MEMBER HAVING THE LOWER END THEREOF CLOSED, A SECOND TUBULAR MEMBER HAVING THE LOWER END THEREOF CLOSED DISPOSED WITHIN AND ALONG THE AXIS OF SAID FIRST TUBULAR MEMBER, SAID SECOND MEMBER BEING DISPOSED AT A SPACED DISTANCE FROM SAID FIRST MEMBER THEREBY PROVIDING AN ANNULUS THEREBETWEEN HAVING COMPLETELY CLOSED ENDS, A BODY OF METAL HAVING A BOILING POINT BETWEEN ABOUT 1200* AND 2450*F. DISPOSED IN AND PARTIALLY FILLING SAID ANNULUS AT A LOWER END THEREOF, SAID BODY OF METAL BEING PRESENT IN AN AMOUNT SUFFICIENT UPON BOILING TO SUBSTAN-

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