US3044551A - Heater - Google Patents

Description

R. C. PRYOR HEATER Filed Dec. 29, 1958 July 17, 1962 INVENTOR. R.C. PRYOR A TTORNEYS g on 1 I mm 8 vm 1| v 893 96805 om United States 3,044,551 HEATER Robert C. Pryor, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Dec. 29, 1958, Ser. No. 783,500

. 9 Claims. (Cl. 166-59) This invention relates to gas fired heaters for heating a well bore.

In situ combustion in the recovery of hydrocarbons from underground strata containing 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 comlbustion zone is caused to move thru 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.

The ignition of carbonaceous material in a stratum around a borehole therein, followed by injection of air thru the ignition borehole and recovery of product bydrocarbons and combustion gas thru another borehole in the stratum, is a direct air drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum frequently plugs in front of the combustion zone because a heavy viscous fluid bank collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this difiiculty and permit the continued progress of the combustion zone thru the stratum, inverse an injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is ied thru the stratum to the combustion zone from one or more surrounding 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 first ignite the carbonaceous material in the stratum around a borehole therein. One method of ignition utilizes a downhole heater either of the electric or gas fired type. Electric heaters have been found difficult to design to withstand the downhole heat and have also been rather slow in heating the formation up to combustion supporting temperature. 7

In a carbonaceous stratum of substantial thickness, such as 25 or 30 feet and more, it has been found difiicult to ignite the entire thickness of stratum with available gas heaters. The copending application of A. S. Rogers et 221., SN. 719,890, filed, March 7, 1958, discloses a gas fired heater which avoids a number of the disadvantages of prior art heaters and is adapted to heat relatively thick strata for ignition purposes. The present invention is concerned with an improvement in the heater disclosed in the aforesaid application.

Accordingly, it is an object of the invention to provide a downhole heater of such construction that the adjacent borehole can be adequately heated to combustion supporting temperature without contacting the Wall of the borehole with combustion gas from the heater and without overheating the conduit on which the heater is suspended. Another object is to provide a downhole heater which effects better gas turbulence and heat distribution in the exhaust conduit leading from the heater. It is also an object of the invention to provide a downhole heater which is effective in heating a stratum upwards of 25 or 30 feet in thickness. Another object of the invention is to provide a downhole heater of high efliciency for initiating in situ combustion in a carbonaceousstratum. A further object is to provide downhole heating R 3,644,551 Patented July 17, 1962 apparatus which prevents overheating of the apparatus. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

The heater of the invention is an improvement in the heater of the above-identified application in providing a constriction in the burner between the combustion chamber and the exhaust conduit whereby the combustion gases are given a jetting action to increase the turbulence in the exhaust conduit of the heater with better heat distribution and more uniform heating of the conduit. This improvement makes it possible to utilize a longer exhaust conduit on the heater between the constricted area and the turn at the bottom of the heater for heating a longer section of stratum.

In a second embodiment of the heater of the. invention the heater per se is constructed in a similar manner but the lower end of the exhaust conduit is open to the bore hole so that the hot combustion gases pass upwardly thru the annulus between the heater and the boreholewall and are vented thru the Well head. 7 In either embodiment the jetting of the exhaust gases into the tail pipe of the heater (exhaust conduit) provides more uniform heating than can be obtained without the jetting cited and also permits the use of a longer tail pipe, thereby adapting the heater to use in the heating of thicker strata than without this feature of the invention.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing of which FIGURE 1 is an elevation of one embodiment of the downhole heater of the invention positioned in a borehole adjacent a carbonaceous stratum with the auxiliary apparatus for initiating combustion in a carbonaceous stratum; FIGURE 2 is an elevation, partly in section, of one embodiment of the burner of the invention; and FIGURE 3 is an elevation showing another embodiment of a downhole heater in a borehole with auxiliary equipment.

Referring to FIGURE 1, a carbonaceous stratum 10 is penetrated by a borehole 12 in which is positioned a casing 314 closed at the top by well head 16. Conduits 18 and 29 are provided for introducing combustion air and for withdrawing produced gases, respectively, from the casing. Heater 22 is suspended in borehole 12 within stratum 10 and is of a length substantially corresponding to the thickness of the stratum. The heater is suspended by means of conduits 24 and 26. Conduit 24 contains a concentric inner conduit or burner feed line 28 which is supplied with a combustible mixture of fuel gas and air by means of lines 3i} and 32, respectively, which connect with a mixing valve 34. A coolant supply line 36 connects with the annulus between conduit 24 and feed line 28.

Referring to FIGURE 2, the heater 22 includes a burner comprising a metal shell 42 in the form of a cylinder or tube, an elongated tubular refractory liner converging toward each end from an intermediate cylindrical section 41 by means of frusto- conical sections 43 and 45. The space between the liner and the shell is filled with a ceramic material 44. The liner forms a downwardly flared combustion zone 46. Insulating material 44 may comprise any suitable highly refractory ceramic material such as Babcock Wilcox Companys Kaokast or Johns-Manvilles 3X Firecrete. These materials are'mixed with water to form a plastic mud or mortar which is introduced into shell 42 on which it is held by stainless steel rods 43 welded to the shell at the outer ends. Rods 43 may be omitted if desired as shown in FIGURE 3. The upper end of burner 42 is closed by plate 50 thru which feed line 28 passes into the inlet end of theburner.

A flame arrester 52 is positioned in the end of feed line- 2-8 to prevent burning of the combustible mixture therein. An ign-iter comprising a heating coil 54 positioned in a the teed end of the burner is connected by insulated conductors 56 with a suitable electric current source at the surface, such as battery 55, thru switch 57. Section 45 of the liner converges to an outlet conduit 47 which coincides with an opening 49 in lower end plate '51.

An exhaust conduit 26 makes a U-turn or a turn of 180 and connects with the exhaust end of heater 4% by means of conduit 58. A conduit 60 connects the annulus around conduit 28 with exhaust conduit 26 just above the heater to provide flow of coolant therebetween. Conduit 60 has an upturned end to jet coolant into the exhaustgases and enhance their flow out of conduit 26.

FIGURE 3 illustrates an embodiment of the invention wherein burner 22 is open to the borehole thru after burner or tail pipe 58. Line 20 includes a back pressure control valve 70- to regulate the back pressure on the combustion gas being vented thru line 20. Line 18 is provided for injection of air to initiate combustion of the hot stratum after ignition temperature has been reached.

In utilizing the apparatus of FIGURES 1 and 2 in initiating in situ combustion, fuel gas is burned in combustion zone 46 and the hot combustion gases heat the burner shell 42 and conduit 58 adjacent the stratum and the combustion and heating are continued 'until'the temperature of the stratum is raised to the ignition point of the carbonaceous material in the stratum and, at this time, air or other O -containing gas is brought into con tact with the hot stratum so that ignition takes place. When ignition by direct injection is practiced, air is introduced thru line 18 to initiate and sustain the combustion and when the ignition is by inverse air injection, air is injected thru the stratum from a ring of boreholes therein so that it arrives at the hot section of stratum adjacent borehole 12 and initiates and sustains combustion there in. After initiation of combustion by direct air injection and establishment of a substantial combustion area, inyerse air injection is readily instituted by cutting off the flow of direct air thru line 18 and injecting air thru the stratum to the combustion area from air injection boreholes positioned close by. I V a When utilizing either direct or inverse air injection to initiate the combustion of carbonaceous material around borehole 12, the burner is withdrawn from the borehole after combustion is well established. Borehole 12 becomes a production borehole during inverse air injection thru one or more surrounding air injection boreholes and production is removed thru line 20 or thru tubing inserted thru well head 16, by conventional means. During direct injection in situ combustion, borehole 12 serves as an air injection borehole and produced hydrocanbons and combustion gases are removed from surrounding boreholes by conventional means.

When utilizing the burner of FIGURE 3, the combustion gas may be vented thru line 20 under any desired back pressure regulated by adjusting valve 70 or any .portion or all of the hot combustion gas may be driven thru the stratum to one or more boreholes therein closely spaced to the ignition borehole. This manner of operating; may be utilized only in strata where plugging does not readily occur. In strata of this type where plugging does occur hot combustion gases are vented thru line 20.

:In the event hot combustion gases are driven thru the stratum, combustion is initiated when the stratum immediately surrounding borehole 12 reaches ignition temperature by injecting air thru line 18, forcing the combustion-supporting air down the annulus and into contact with the hot stratum. During this phase of the process, combustion in burner 22 may be continued, diminished, or completely terminated, depending upon the temperatureto which the stratum is heated before air injection is commenced.

A burner was constructed substantially as shown in meter and 8 inches long. The frusto-conical section at the exhaust end of the burner was 9 inches long and l inches in diameter at the exhaust outlet. The shell of the burner was a 16 gauge 304 stainless steel tube 22 /2 inches long forming a sleeve around the lower end of the gas injection conduit. The insulating material was poured into the annulus between the shell and the liner without the aid of lugs illustrated in FIGURE 2 and comprising Kaokast. A 10 foot long tail pipe 3 /2 inches in diameter open at the exhaust end was utilized. Tests were run on this burner and on a burner without a constriction in the exhaust line downstream of the combustion zone at an input rate of approximately 300,000 B.t.u. per hour. Thermocouples were positioned at regular spaced intervals along the tail pipe or afterburner of each burner at 6 points numbered from adjacent the burner to the downstream end of the tail pipe. The temperatures obtained in the two runs are set forth in the table below.

constriction in the exhaust line while heater B represents the heater of the invention utilizing a constriction in the burner between the combustion zone proper and the tail pipe. The more uniform heating along the tail pipe of heater B demonstrates the advantage of this type of burner for use in heating thick carbonaceous strata for the purpose of initiating in situ combustion therein.

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

I claim: 1. Apparatus for heating an earth borehole within a carbonaceous stratum to combustion temperature comprising in combination an elongated tubular burner including an intermediate cylindrical section, an upper frusto-conical section converging from said cylindrical section to a gas inlet, a flame arrester in said gas inlet, and a lower trusts-conical section converging from said cylindrical section to an exhaust outlet of substantially lesser diameter than said cylindrical section; a downwardly extending elongated exhaust conduit of substantially larger diameter than said exhaust outlet connected therewith, said exhaust outlet forming a constriction in the gas passageway from said burner into said exhaust conduit to impart jetting action to exhaust gases passing into said conduit and establish turbulence therein; an igniter in said burner; and conduit means connected with said gas inlet for supplying fuel and combustionsupporting gases thereto.

2. The apparatus of claim 1 including a U-turn on the exhaust end of said exhaust conduit and an upwardly extending conduit parallel to and extending above said burner.

3. The apparatus of claim 1 wherein said burner is encased in insulating material.

4. The apparatus of claim 1 wherein said burner is positioned in a well bore adjacent a carbonaceous stratum; said conduit means comprises a tubing string extending thru a well head; and including exhaust means thru said well head.

5. The apparatus of claim 4 including a pipe string concentric with said tubing string providing an annulus therewith for flow of coolant substantially to the upper end of said burner; a crossover conduit from'said pipe string to said exhaust means adjacent said burner, terminating in an upwardly directed end section, said exhaust means comprising a conduit of substantially the diameter of said exhaust conduit and extending from same thru saidwell head.

6. The apparatus of claim 4 wherein said exhaust conduit opens into said well bore at a lower level of said stratum and exhaust gases pass upwardly thru the annulus around said tubing string to the exhaust means thru said well head.

7. A burner for downhole heating comprising an elongated tubular refractory liner of diminishing transverse cross sectional area each direction along its axis from an intermediate section to a combustible gas inlet at one end and to an exhaust gas outlet at the opposite end; a flame arrester in said inlet whereby the upstream section of said liner forms the initial section of the combustion zone of said burner; igniter means for said burner; and an elongated exhaust conduit of substantially larger diameter than said exhaust outlet connected with.

said outlet and coaxial with said tubular liner.

8. The burner of claim 7 including a U-turn conduit on the exhaust end of said exhaust conduit; and an exhaust Igas withdrawal conduit connected with the open end of said U-turn conduit, extending back along said burner.

9. The burner of claim 7 including an insulating ceramic covering encasing said liner.

References Cited in the file of this patent UNITED STATES PATENTS

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