US3379256A - Oil well ignition device - Google Patents

Description

April 1968 J. D. ALEXANDER ETAL 3,379,256

oI'L WELL IGNITION DEVICE 5 She ets-Sheet 1 Original Filed Sept. 28, 1964 INVENTORS BY WILL/AM Lo MA r/k/ ge/V5) April 1968 J. D. ALEXANDER ETAL OIL WELL IGNITION DEVICE Original Filed Sept. 28, 1964 3 Sheets-Sheet 2 ATTOFNE'Y April 23, 1968 J. D. ALEXANDER ETAL OIL WELL IGNITION DEVICE Original Filed Sept. 28, 1964- Jae 3 Sheets-Sheet Z5 F lL'Eu-LD IN VENTORS L/OHN 0. 4 emu/Jae f GENE) United States Patent 3,379,256 OIL WELL IGNITION DEVlCE John D. Alexander and William L. Martin, Ponca City, Okla., assignors to Continental Oil Company, Ponca City, Okla., a corporation of Delaware Continuation of application Ser. No. 399,442, Sept. 28, 1964. This application Feb. 27, 1967, Ser, No. 619,071 14 Claims. (Cl. 166-66) ABSTRACT OF THE DISCLOSURE An oil well ignition device which includes a plurality of elongated, parallel electrical heater elements each having a hot central section and relatively cooler end portions. The heater elements are spaced from each other by spacer rings and by upper and lower headers through which the end portions of the elements pass. A bottom cap is secured to the lower header and encloses and protects the end portions of the elements which project through the lower header. A top cap is secured to the upper header and encloses and protects the end portions of the elements which project through the upper header. A power cable extends into the top cap, is anchored there by a cable clamp, and supplies electrical power to the heater elements. A motion control piston may be included in the assembly by mounting such piston slidably around the power cable above the top cap.

This application is a continuation of Ser. No. 399,442, filed Sept. 28, 1964 and abandoned.

This invention relates to a device for igniting the crude oil adjacent an injection well used in firefiooding and in-situ combustion processes of secondary petroleum recovery. More particularly, the present invention relates to an electrical resistance heater of compact construction which can be lowered into an air injection well for the purpose of igniting crude oil in a petroliferous formation preparatory to propagating a combustion front through the formation.

It is presently well known that residual oil can be produced from oil bearing reservoirs which cannot long-er be economically produced by primary recovery techniques.

One procedure used for accomplishing the secondary recovery of petroleum is in-situ combustion or fireflooding. In the conventional forward combustion process, air is initially forced into an oil reservoir through an injection well to establish a flow path for the movement through the reservoir of combusion gases. The crude oil adjacent r the air injection well is then ignited, and finally, the combustion front is propagated through the oil bearing formation by continued injection of air. The combustion front advances from the injection well in a radial direction so as to move oil to surrounding production wells.

Various types of igniters for igniting the crude oil, and heaters for heating the air injected through the injection well have heretofore been proposed. Of the types of igniters and heaters which have been used, electrical resistance heaters have been most widely employed. One of the problems in utilizing electrical igniters and heaters is that the necessary size of these devices sometimes restricts their use to well bores of relatively large diameter. These devices are also frequently rather complicated in their construction, and their fragility often reduces their effective operating life. Difliculties have also been encountered in lowering electrical heaters and igniters into the well tubing when a very high well pressure exists as such pressures tend to force the heater upwardly in the tubing, and sometimes, upon sudden variations in the well pressure, the devices are completely ejected from the tubing.

The present invention comprises an improved igniter and heater for igniting the crude oil adjacent an air injection well in secondary recovery by in-situ combustion and fireflooding techniques, and for heating the air subsequently injected into the oil bearing formation. Broadly described, the electrical ignition device of the present invention comprises three elongated, parallel, tubular, electrical resistance heater elements each having an upper end and a lower end; means spacing the heater elements from each other and positioning the axes of the elements at the vertices of a triangle in the transverse cross-sectional plane of the heater elements; conductor means connecting the elements to each other at the lower ends thereof; lower cap means enclosing the conductor means in a gas tight enclosure; top cap means having a bore enclosing the upper ends of the elements and a counterbore dimensioned to receive one end of a power cable, the top cap means further having a downwardly facing shoulder formed by the termination of said bore where it communicates with said counterbore; a power cable extending through the counterbore and having one of its ends inside the bore; a cable clamp connected to the power cable and bearing against the downwardly facing shoulder; and means positioned in the bore and electrically interconnecting the electrical conductors of said power cable to each of the heater elements.

More specificallly, in a preferred embodiment of the invention, the three elongated, substantially parallel Zheater elements each comprises a heated central section an unheated upper section and an unheated lower section; and the means spacing the heater elements comprises a first set of spacer rings positioned between said elements with said elements spaced from each other around the exterior periphery of the spacer rings in said first set of spacer rings, and a second set of spacer rings positioned exteriorly around the heater elements and in contact therewith, said spacer rings all being spaced from each other longitudinally along said elements and each spacer ring being secured to an element of said heating elements. The spacing of the heater elements is also maintained by bottom and top headers which receive the ends of the upper and lower unheated sections of the elements. The top header is apertured to permit two thermocouples to be extended therethrough and a thermocouple tube is extended through the bottom header and lower cap means to permit the hot junction of one of the thermocouples to be positioned below the cap means for measuring the well bore temperature at, or slightly below, the heater. The hot junction of the air thermocouple is protectively enclosed in an apertured protective housing which permits free air circulation into contact with the hot junction. The second thermocouple is used to monitor the temperature of the heater elements, and its hot junction is located in a metallic sleeve at the lower end of the hot sections of the heater elements.

In another aspect of the present invention, one embodiment of the novel heater of the invention is especially adapted for use in combination with a motion control piston to facilitate lowering the ignition device into a well bore under conditions in which a high gaseous pressure exists in the well bore. In this combination, the top cap means of the ignition device includes a tubular main body portion surrounding a bore; an elongated neck portion extending upwardly from the main body portion and enclosing the counterbore; and an upwardly facing annular seat at the upper end of the main body portion and extending around the base of the elongated neck portion. The motion control piston which cooperates with the top cap means comprises an elongated, rigid tubular member dimensioned to telescope over the elongated neck portion of the top cap means and abut said upwardly facing annular seat, and at least one resilient, radially expandable member mounted on said elongated, rigid tubular member and adapted to be radially expanded into contact with the walls of the tubing string or well bore by fluid pressure acting downwardly in the well. In a preferred embodiment of the combination, a pair of the resilient, radially expandable members are used and take the form of rubber swab cups mounted in axially spaced relation along the elongated tubular memher.

A major object of the present invention is to provide an improved, highly efficient ignition device for use in an air injection well in secondary petroleum production.

A further object of the present invention is to provide an ignition device for use in secondary petroleum recovery, which device is compact in construction and can be lowered in well tubing strings having an inside diameter as small as 2 /2 inches.

An additional object of the present invention is to provide an ignition device for use in igniting petroleum in a petroleum reservoir in the course or" an in situ combustion recovery procedure, and for heating air injected into the reservoir, which ignition device is especially and novelly adapted for use in combination with a motion control piston to permit the device to be lowered into the well bore in a controlled, uniform manner.

Another object of the present invention is to provide an oil well ignition device which employs heating elements capable of converting 13,000 watts of power into heat and characterized by a watt density which can exceed 30 watts per square inch.

Another object of the present invention is to provide an oil well ignition and heating device which is mechanically rugged in construction, and is characterized by a long and trouble-free operating life.

In addition to the foregoing described objects and advantages of the invention, other objects and advantages will become apparent as the following detailed description of the invention is read in conjunction with the accompanying drawings which illustrate the invention.

In the drawings:

FIGURE 1 is an elevational view showing one embodiment of the oil well ignition device of the invention attached to the lower end of an electrical power cable, and further illustrating a motion control piston adapted for use in combination with the ignition device.

FIGURE 2 is a transverse cross-sectional view through the ignition device taken along line 2-2 of FIGURE 1 showing the details of the low-temperature portion of electric heating elements shown in FIGURE 1.

FIGURE 3 is a transverse cross-sectional view taken along line 33 of FIGURE 1 showing the details of the high-temperature portion of electric heating elements shown in FIGURE 1.

FIGURE 4 is a vertical sectional view taken through the lower end portion of the ignition device.

FIGURE 5 is a transverse cross-sectional view taken along line 55 of FIGURE 4.

FIGURE 6 is a vertical sectional view taken through the center of the upper end portion of the ignition device.

FIGURE 7 is a transverse cross-sectional view taken along line 77 of FIGURE 6.

FIGURE 8 is a vertical cross-sectional view taken through the center of the motion control piston assembly of the present invention.

FIGURE 9 is a longitudinal sectional view through a connecting assembly which can be used to interconnect the cable conductors with the heater elements of the ignition device.

FIGURE 10 is a schematic illustration of the ignition device being lowered in a well bore.

Referring now to the drawings in detail, and particularly, to FIGURE 1, the oil well ignition device of the present invention is designated generally by reference character 10 and is connected to the lower end of a power cable 122 for lowering the device into a well tubing string. A motion control piston assembly 14 is positioned concentrically around the power cable 12 above the ignition device 10, and is movable axially on the cable to a position illustrated in dashed lines in FIGURE 1 for a purpose hereinafter described.

A preferred embodiment of the ignition device 10 comprises three elongated, generally parallel, tubular, electrical resistance heater elements 16, each of which has an upper and a lower end relative to the power cable 12 to which the ignition device is connected at its upper end. The heater elements 16 are maintained in parallel, spaced relation to each other by spacing means which includes a plurality of internal spacer rings 18 positioned interiorly of the heater elements and spaced axially from each other along the heater elements. The heater elements 16 are spaced from each other by an amount of around the outer periphery of the internal spacer rings 18. The spacing means includes a second set of spacer rings 20, hereinafter termed external spacer rings, which are also spaced axially along the heater elements 16, and are each axially aligned with respect to one of the internal spacer rings 18. The external spacer rings 20 are dimensioned to confine the heater elements 16 by engagement with the outer periphery thereof. The arrangement of the internal spacer rings 18, the heater elements 16 and the external spacer rings 20 is best illustrated in FIGURES 2 and 3 of the drawings. Each of the internal spacer rings 18 has circumferentially spaced weld beads 22 around the outer periphery thereof to restrain the heater elements 16 in their evenly spaced circumferential positions and each of the internal and external spacer rings, 18 and 20, respectively, are welded to one of the heater elements 16.

The heater elements 16 are each high watt density elements comprising a tubular outer metallic sheath 30 positioned concentrically around a longitudinally extending coil 32 of wire constructed of a high resistance material, such as Nichrome, which is surrounded and insulated by a magnesium oxide packing 34. This construction is most clearly illustrated in FIGURE 3 of the drawings. The high resistance coil 32 of Nichrome wire extends longitudinally through only the central section of each heating element, and is connected at each of its ends to a low resistance conductor pin 36 preferably constructed of nickel. The low resistance conductor pins 36 are of sufficient length that when the heating elements 16 are operating at rated power, the upper end section of each element containing the low resistance conductor pins constitutes a cold section which does not increase in temperature above the ambient temperature. Preferably, the length of the hot central section of each heater element 16 is approximately 179 inches, the length of the cold section at the top of each element is about 27 inches and the length of the cold section at the bottom of each element is about 6 inches. With the described construction, each heating element can be made to convert approximately 13,000 watts of power into heat and the watt density of the hot sections of the elements can be made as high as 37 Watts per square inch if desired.

The upper and lower ends of the elements 16 are welded into a top header 40 and a bottom header 42, respecpectively, so that the axes of the three elements extend through the vertices of an equilateral triangle lying in a transverse cross-sectional plane through the elements. This geometrical arrangement is also maintained throughout the length of the element by the internal and external spacer rings, 18 and 20, respectively, hereinbefore described. The element spacing, and the selected diameters of the headers 40 and 42 depend upon the size of tubing or pipe into which the ignition device 10 will be run in use.

The bottom header 42 and associated elements of the ignition device 10 are best illustrated in FIGURES 4 and 5 of the drawings. The bottom header 42 is a discshaped block which may be suitably constructed of stainless steel. The three heating elements 16 are extended into the bottom header 42, and the metallic sheath of each of the elements is welded into the bottom header as illustrated. These Welds are :gas tight, preferably up to at least 1000 p.s.i.g. and temperatures up to at least 1000 F. The three nickel conductor pins 36 extending from the cold section at the lower ends of each of the heater elements 16 are bent into convergence and are welded together to form a common electrical connection 47. The conductor pins, however, are not grounded.

A cylindrical bottom cap 46 is welded to the bottom header 42 and extends downwardly therefrom around the junction of the nickel conductor pins 36. The weld between the bottom cap 46 and bottom header 42 is pressure tight and leak proof as in the case of the welds of the heating elements 16 in the header. The bottom closure portion 48 of the bottom cap 46 has a pair of apertures extending therethrough. The first of these apertures, designated by reference character 50, is axially aligned with an identically dimensioned aperture 52 extending through the bottom header 42. The apertures 50 and 52 receive a small tubular member 54 which is welded to the bottom header 42 and the bottom closure portion 48 of the cap 46 with pressure tight welds. The tubular member 54 forms a pass through for an air thermocouple 55. The hot junction of the air thermocouple is positioned in a protector housing 56 which is tack welded to the lower end of the bottom cap 46. The protector housing 56 is provided with a plurality of apertures 58 which permit air to circulate freely through the housing.

The second aperture which is provided through the bottom closure portion 48 of the bottom cap 46 is designated by reference character 60 and is internally threaded. As will be hereinafter explained, a threaded plug is screwed into the aperture 60 after drying and testing the ignition device 10, and is welded in place to maintain the pressure and thermal integrity of the bottom cap 46.

The top header 40 is a disc-shaped block which is preferably formed of stainless steel and which, as illustrated in FIGURES 6 and 7, has five apertures extending t-herethrough. The three apertures 62 of larger diameter receive the upper end portions of the heater elements 16 which are welded to the upper surface of the top header 40. It will be noted in referring to FIGURE 6 that the upper ends of the heater elements 16 extend upwardly past the top header 40 to facilitate connec tion of the heater elements with the conductors 64 of the power cable 12 as hereinafter described.

The two relatively small diameter apertures 66 receive fittings 68 for mounting two metal sheathed thermocouples through the top header 40. One of the thermocouples is the air thermocouple 55, hereinbefore described, used to monitor the temperature of the air in the proximity of or slightly below the ignition device 10, and the second thermocouple 70 is used to monitor the temperature of the heater elements 16. The sheathed thermocouples 55 and 70 are each extended downwardly from their respective fittings 68 through the internal spacer rings 18. The hot junction of the heater element thermocouple 70 is positioned in a stainless steel sleeve 72 disposed at the lower end of the heater elements 16 as shown in FIGURE 1. The hot junction of the air thermocouple 55 is positioned in the protector housing 56 as hereinbefore described.

The top header 40 is provided with a radially outwardly extending circumferential flange 74 and a threaded male body portion 75 to facilitate connection of the top header 40 with a top cap designated generally by reference character 76. The top cap 76 includes an elongated generally cylindrical body portion 78 containing an enlarged bore 80, and also includes an elongated neck portion 82 which contains a relatively small counterbore 84 which communicates with the bore in the body portion 78. The neck portion 82 is welded or otherwise suitably secured to the body portion 76 and forms a downwardly facing shoulder 86 at the junction of the counterbore 84 with the bore 80.

The counterbore 84 is dimensioned to snugly receive the power cable 12 which is retained in the top cap 76 by a cable clamp designated generally by reference character 88. The cable clamp 88 comprises a threesection assembly with each of said sections being annular and having axially extending apertures formed therethrough for receiving threaded tightening bolts 90 used to assemble the clamp. The uppermost annular section is designated by reference character 92, has four apertures 94- extending therethrough, and is provided with an upper surface 96 configured to mate with the downwardly facing shoulder 86. The lower surface 98 of the upper section 92 of the cable clamp 88 is generally convex in configuration and mates with a concave upper surface 100 on the central section 102 of the cable clamp. The central section 102 of the cable clamp has eight circumferentially spaced apertures 104 extended therethrough and is provided with a convex lower surface 106 which mates with a concave upper surface 108 of the lowermost clamp section 110. Four circumferentially spaced apertures 112 are formed through the section 110. The arrangement of the apertures through the sections 92, 102 and 110 is such that the four apertures 112 through the lowermost section 110 are aligned with four of the apertures 104 in the central section 102 when the clamp 88 is assembled, and the other four apertures of the central section are aligned with the four apertures 94 in the upper section 92. In assembling the clamp 88, the upper and central sections 92 and 102, respectively, of the clamp 88 are first bolted together with flared sections 114 of the outer sheathing of the power cable 12 clamped between the sections as illustrated in FIGURE 6. The lower section 110 of the clamp 88 is then bolted to the central section with a more interiorly located portion 116 of the cable sheathing flared outwardly and clamped between these sections of the cable clamp. With the cable clamp 88 secured to the power cable 12 in this manner, the clamp is then secured in abutting contact with the shoulder 86 and against axial movement in the top cap 76 by set screws 118 which extend radially through hte body portion 78 of the top can 76.

The power cable 12 includes the insulated power conductors 64 for transmitting electrical power to the heater elements 16 and also carries the insulated leads for the metal sheathed thermocouples 55 and 70. Before connecting the conductors 64 of the power cable 12 to the nickel conductor pins 36 of the heater elements 16, the outer insulation is stripped away from the insulated conductors 64 at the end of the cable inside the top cap 76 and the cable opening is potted with a potting compound 120 to prevent the entrance of air into the inner cable structure. The instrument leads 122 for the thermocouples are also extended through the potting compound 120 and are connected to the thermocouple Wires through suitable pressure tight connectors 124. In connecting the insulated conductors 64 of the power cable 12 to the nickel conductor pins 36 at the upper ends of the heater elements 16, a sealed pressure tight power connector 126 of the type marketed by the Vector Cable Company can be employed or, alternatively, a power cable to heating element splice of the type illustrated in FIGURE 9 of the drawings can be utilized. In this type of splice connection, the insulated conductor 64 of the power cable 12 is stripped at its end and the wires 129 are electrically connected to the nickel conductor pin 36 by a metallic crimp connector 130 which is threaded to the end of the nickel conductor pin and crimped over the adjoining end of the respective conductor 64 from the power cable 12. A potting compound 132 is used to seal the end of the heater element 16 and protect the end of the nickel conductor pin, and is also extended to cover a portion of the crimp connector 130. Three 7 gum rubber tubes 134, 136 and 138 are positioned around the respective cable power conductor 64, crimp connector 130 and heating element 16 in the manner illustrated in FIGURE 10. Each exposed end of each of the rubber tubes is tied using waxed strings 140.

In preparing the ignition device for use, the heater elements 16 are dried by opening the seals provided by the manufacturer at the top ends of the elements so that moisture in the magnesium oxide insulation 34 can be more easily removed. The upper and lower cold sections of each element are then wrapped with a heating tape and the entire ignition device is evacuated through the aperture 60 formed in the bottom closure portion 48 of the bottom cap 46. Evacuation is also effected through a connection on a test cap (not shown) which is sealingly placed over the top of the heater elements during drying and testing. The drying procedure is carried out by self-heating the elements using 230 volt AC three-phase power and evacuating the elements. Drying continues until the element to ground resistance is greater than 50 megohms, and preferably is infinity as indicated by an ordinary volt-ohm-milliammeter. When the elements are dry, the ignition device is allowed to cool and is pressured with dry helium to about 20 p.s.i.g. A stainless steel plug (not shown) is then screwed into the aperture in the bottom closure portion 48 of the bottom cap 46 and is sealed in place by welding. The ignition device is then again heated and evacuated through the test cap to remove the helium and any moisture that may have entered the magnesium oxide insulation during welding. When the heater elements 16 are dry and the helium has been removed, the ignition device 18 is allowed to cool while continuing to evacuate. The top ends of the three heater elements 16 are sealed against atmospheric moisture by potting with a high temperature potting compound.

The motion control piston 14 used in combination with the ignition device 10 is best illustrated in FIG- URES 1 and 8 of the drawings. The illustrated embodiment of the motion control piston comprises an elongated tubular mandrel 142 which is externally threaded at its lower end 144 and which carries an annular, radially outwardly extending flange 146 spaced downwardly a short distance from its upper end 148. The inside diameter of the tubular mandrel 142 is substantially larger than the diameter of the power cable 12 so that the motion control piston is slidably movable thereon. A compression nut 151) is threaded on the lower end 144 of the tubular mandrel 142 and carries a radiused or beveled seating face 152 on the lower end thereof.

The radiused lower end 152 of the compression nut 150 is dimensioned to mate with an annular groove 154 formed in an upwardly facing annular seat 156 of the elongated neck portion 82 of the top cap 76.

A pair of metallic swab cup thimbles 158 and 160 are slidably mounted around the tubular mandrel 142 and support a pair of swab cups 162 and 164 which can suitably be conventional swab cups of the type used in the oil industry. A spacer sleeve 166 is positioned around the tubular mandrel 142 and extends from the upper thimble 160 to the base portion of the lower swab cup 162. The upper swab cup 164 is restrained against axial movement in an upward direction along the tubular mandrel 142 by the annular flange 146. It will be noted that the swab cups 162, 164 and their respective thimbles 158 and 169 are retained in the illustrated relationship to each other by the compression nut 150 threaded on the lower end of the tubular mandrel 142.

In the operation of the motion control piston 14, a downwardly acting pressure in the well bore into which the ignition device 10 and motion control piston 14 are lowered on the end of the power cable 12 acts to bias the lip portions of the swab cups 162 and 164 outwardly into sealing contact with the walls of the well tubing. The pressure also forces the motion control piston 14 downwardly to the position shown in dashed lines in FIGURE 1. In this position, the radiused lower end 152 of the compression nut mates with the annular groove 154 in the upwardly facing seat 156 of the top cap 76 to form a seal therewith. In this position in which the motion control piston'14 is engaged with the ignition device 10, fluid pressure may be used to force the assembly downwardly in a well bore against an opposing upwardly acting fluid pressure tending to eject the assembly from the well bore.

At a depth in the well bore where the weight of the paid out cable 12 and the ignition device 10 overcomes the upward force caused by the pressure acting upwardly on the cross-sectional area of the cable, the pressure drop across the motion control piston can be reduced by reducing the injection pressure used to force it downwardly in the well. The ignition device 10 will then fall free of the motion control piston 14 under gravitational influence. In some instances, it is desirable to provide some type of radially inwardly projecting protuberance or stop on the well tubing to engage the motion control piston 14 at the depth where the ignition device 10 will fall freely under gravitational influence, This insures that the motion control piston cannot move deeper than desired.

As an example of the use of the ignition device 10 and motion control piston 14, the assembly was placed in a well bore 181) in a tubing 181 as shown in FIGURE 10, in the North Tisdale Field in Wyoming. The motion control piston 14 was detached from the ignition device 10 at a depth of 550 feet by equalizing the pressures above and below the motion control piston and allowing the cable weight to lower the ignition device to its operating level at 848 feet. As shown in FIGURE 10, the permeable, oil bearing sand extended above the top tubing perforation 182 for 14 feet, and 30 feet of the sand is open below the top tubing perforation. In order to obtain the best results and protect the ignition device 10, it was desired to inject the heated air below the top tubing perforation 182 which was located at a depth of 852 feet. To accomplish this, air was injected down the tubingcasing annulus 184 as well as down the tubing 181. The ratio of air injection rates used was the ratio of the feet of hole which was open above the 852 foot depth to that which was open below the 852 foot depth, or

Q easing-tubing annulus l i1 Q tubing 30 The rate of air injection through the tubing 181 was fixed by the desired air discharge temperature, and the heat output of the ignition device 10. The rate of air injection through the tubing-casing annulus 184 was then calculated from the above ratio.

Separate flow meters provided continuous records of both tubing and easing air injection rates. A temperature recorder was used to continuously monitor the ignition device discharge air and element temperatures as measured by the thermocouples 55 and 76. A control system regulated the ignition device power output and provided an automatic power shutdown if the tubing air injection rate fell below a preset minimum, or if the ignition device temperature exceeded a preset maximum. These failsafe devices allowed the ignition device 10 to operate unattended and provided an alarm if the power was shut down because of the low air injection rate, high temperature or blown fuses. Power was automatically restored if the proper injection rate was reattained and the bottom hole temperatures were below the maximum allowable.

The igniter was operated overnight at approximately 250 F. discharge air temperature to check out the controls and to allow the oil used to lubricate the motion control piston 14 to drain from the ignition device 10 and the tubing 181. While operating at full power, the discharge air temperature was then increased to approximately 450 F. and held there for three and a half; days. It was then increased to about 800 F. for one day, rc-

duced to about 400 F. for one-half day and then the ignition device power was turned off. During this time, the maximum air pressure was 755 p.s.i.g., the minimum cold air velocity at the elements was 0.9 feet per second and the temperature of the head at the cable terminals did not exceed 125 F. Air injection continued for another day, after which the ignition device 10 was removed from the tubing 181 by pulling it upwardly until the motion control piston 14 was picked up. Air under pressure was then forced downwardly in the tubing 181 against the upper side of the motion control piston and the tension in the cable 12 controlled to govern the rate of ascent of the engaged assembly in the well bore 180.

From the foregoing description of the invention, it will have become apparent that the present invention provides an improved, compact and mechanically sturdy oil well ignition device which is especially well-adapted for use in combination with a motion control piston. The device is capable of efficiently converting high power inputs to heat, and its thermocouple control system permits it to be operated safely and efiiciently for the purpose of igniting the petroleum bearing formation adjacent air injection wells in in-situ combustion secondary recovery procedures.

Although a preferred embodiment of the invention has been herein described by way of example and in order to inform those skilled in the art of the manner in which the invention is to be practiced, it will be readily apparent that a number of modifications and innovations can be made in the structures and arrangements described without departure from the basic principles underlying the invention. Insofar, therefore, as changes are made in the depicted and described embodiment which are essentially equivalents of the structure thus depicted and described, and which do not entail departures from the basic principles upon which the invention is predicated, it is intended that all such changes shall be circumscribed by the spirit and scope of the invention except as the same may be necessarily limited by the appended claims or reasonable equivalents thereof.

We claim:

1. An improved igniter and heater assembly for igniting the crude oil adjacent an air injection well used in secondary recovery by in-situ combustion, said assembly comprising:

a plurality of elongated electrical resistance heater elements each having an upper end and a lower end; means retaining the heating elements in substantially parallel, equally spaced relation to each other;

a top header positioned around said heater elements adjacent the upper ends thereof;

a bottom header receiving the lower ends of said heating elements;

conductor means connecting the elements to each other at the lower ends thereof;

lower cap means connected to said bottom header and enclosing the conductor means in a gas tight enclosure; 1

top cap means having a main body portion and enclosing the upper ends of said heater elements in a bore in said main body portion, said top cap means further having an elongated neck portion connected to and extending upwardly from said main body portion and have extending therethrough a counterbore smaller than said bore;

a power cable extending through said counterbore and having one of its ends inside the bore in the main body portion of said top cap means;

a cable clamp connected to said power cable and enclosed in the bore of said top cap means;

means positioned in said bore and electrically connecting the electrical conductors of said power cable to each of said heater elements; and

a motion control piston positioned around said power cable and having a bore therethrough of larger diameter than said elongated neck portion, said motion control piston having a lower end portion thereon adapted to sealingly engage said top cap means at the location thereon where said elongated neck portion is connected to said main body portion.

2. The igniter and heater assembly claimed in claim 1 wherein said motion control piston comprises:

a tubular mandrel of larger diameter than said power cable positioned around said power cable; and

at least one annular, resilient, radially expandable sealing member around said mandrel and secured thereto, said sealing member being resiliently responsive to downwardly acting fluid pressure in said air injection well to expand into sealing engagement with the walls of said injection well.

3. The igniter and heater assembly claimed in claim 2 wherein each of said radially expandable sealing members comprises a swab cup and wherein said motion control piston is further characterized to include annular metallic thimbles around said mandrel corresponding in number to the number of said swab cups and each supporting and retaining against downward movement on said mandrel, one of said swab cups.

4. An oil well ignition device comprising:

three elongated, substantially parallel resistance heater elements each having an upper end and a lower end, each of said heater elements comprising;

an elongated tubular metallic sheath;

a wire heating coil extending through said sheath over at least a portion thereof; and

electrically insulating thermally conductive material positioned in said sheath around said coil;

means spacing the heater elements from each other and positioning the axes of the elements at the vertices of a triangle in the transverse cross-sectional plane of the heater elements, said spacing means comprising:

a first set of spacer rings positioned between said elements with said elements spaced from each other about around the exterior periphery of the spacer rings in said first set of spacer rings; and

a second set of spacer rings positioned around the heater elements and in contact therewith;

conductor means connecting the elements to each other at the lower ends thereof;

lower cap means enclosing the conductor means in a gas tight enclosure;

top cap means enclosing the upper ends of the elements and adapted to receive one end of a power cable connected to said elements; and

a cable clamp in said top cap means and adapted for connection to a power cable.

5. An ignition device as claimed in claim 4 and further characterized to include a top header and a bottom header receiving the upper and lower ends, respectively, of said heater elements and connected to said top cap means and said lower cap means, respectively, said top and bottom headers being apertured to facilitate extension of at least one thermocouple therethrough.

6. An ignition device as claimed in claim 5 wherein said bottom header is a disc-shaped block having three apertures therein for receiving the lower ends of said heater elements and wherein said lower cap means has a generally cylindrical side wall sealed at one end to said bottom header and a bottom closure portion integrally formed with said cylindrical side wall and extending parallel to said bottom header, said bottom cap means sealingly enclosing said conductor means and further having a readily scalable aperture in said bottom closure portion to facilitate evacuation of said bottom cap means and said heater elements followed by sealing of said readily scalable aperture. p

7. An ignition device as claimed in claim 6 wherein said ignition device is further characterized to include a second thermocouple extending through an aperture in said top header and through the spacer rings in said first set of spacer rings and having its hot junction positioned adjacent the lower ends of said heating elements and above said bottom header and lower cap means whereby the temperature of said heater elements is sensed by said second thermocouple.

8. An ignition device adapted to be lowered in a wellbore comprising:

three elongated tubular electrical resistance heater elements each having an upper end and a lower end;

means spacing the heater elements from each other and positioning the axes of the elements substantially equidistantly from each other as measured in a crosssectional plane taken transversely through the heater elements;

spacer rings positioned between the heater elements and spacing the elements substantially equidistantly from each other around the periphery of said spacer rings;

conductor means connecting the elements to each other at the lower ends thereof;

lower cap means enclosing the conductor means in a gas tight enclosure;

top cap means having a bore enclosing the upper ends of said elements and a counterbore dimensioned to receive one end of a power cable, the top cap means further having a downwardly facing shoulder formed at the intersection of said bore and counterbore;

a power cable extending through the counterbore and having one of its ends inside the bore;

a cable clamp connected to the power cable and bearing against the downwardly facing shoulder of said top cap means; and

means positioned in the bore and electrically connecting the electrical conductors of said power cable to each of the heater elements.

9. An oil well ignition device comprising:

three elongated, substantially parallel resistance heater elements each having an upper end and a lower end;

means spacing the heater elements from each other and positioning the axes of the elements at the vertices of a triangle in the transverse cross-sectional plane of the heater elements;

conductor means connecting the elements to each other at the lower ends thereof;

lower cap means enclosing the conductor means in a gas tight enclosure;

top cap means enclosing the upper ends of the elements and adapted to receive one end of a power cable connected to said elements, said top cap means comprising:

a main body portion having a bore therein;

an elongated neck portion extending upwardly from the main body portion and enclosing a counterbore communicating with the bore in said main body portion;

a downwardly facing, annular shoulder inside said main body portion and formed by the intersection of said bore and counterbore, said downwardly facing shoulder bearing against the cable clamp, hereafter defined, and restraining said cable clamp against upward movement in said top cap means; and

an upwardly facing annular seat at the upper end of said main body portion and extending around the base of said elongated neck portion for sealingly engaging a generally cylindrical motion control piston telescoped over said elongated neck portion; and

a cable clamp in said top cap means and adapted for connection to a power cable.

10. An ignition device as claimed in claim 9 wherein said ignition device is further characterized to include a first thermocouple extending through an aperture in said top header, through the spacer rings in said first set of spacer rings and through the aperture in said bottom header and an apertured protector housing secured to said lower cap means and housing the hot junction of said thermocouple.

31. An improved igniter and heater assembly for igniting the crude oil adjacent an air injection well used in secondary recovery by in-situ combustion, said assembly comprising:

a plurality of elongated electrical resistance heater elements each having an upper end and a lower end, said heater elements being space-d from, and extending substantially parallel to, each other;

a top header positioned around said heater elements adjacent the upper ends thereof;

a bottom header receiving the lower ends of said heating elements;

conductor means connecting the heater elements to each other at the lower ends thereof;

lower cap means connected to said bottom header and enclosing the conductor means in a gas tight enclosure;

top cap means enclosing the upper ends of the heater elements and adapted to receive one end of a power cable connected to said heater elements;

a power cable extending into said top cap means and connected to said elongated resistance heater ele ments;

a cable clamp in said top cap means and connected to the lower end of said power cable for retaining said power cable in said top cap means;

a motion control piston positioned around said power cable above said top cap means and slidably movable on said power cable.

12. An electrical ignition device for igniting crude oil adjacent an air injection well comprising:

three elongated, parallel, tubular, electrical resistance heater elements each having a heated central section, an unheated upper section, and an unheated lower section;

means spacing the heater elements from each other and positioning the axes of the elements at the vertices of a triangle in the transverse cross-sectional plane of the heater elements;

conductor means connecting the elements to each other at the lower ends thereof;

lower cap means enclosing the conductor means in a gas tight enclosure, and spaced in its entirety from the heated central sections of said heater elements and on the opposite side of said heated central sections from said unheated upper sections thereof;

top cap means having a bore enclosing the upper ends of the heater elements and a counterbore adapter to receive one end of a power cable, said top cap means further having a downwardly facing shoulder formed by the termination of said bore where it communicates with said counterbore, said top cap means being spaced from the heated central sections of said heater elements on the opposite side of said heated central sections from said unheated lower sections;

a power cable extending through the counterbore and having one of its ends inside the bore;

a cable clam-p connected to the power cable and bearing against said downwardly 'facing shoulder, said cable clamp being located entirely within the bore in said top cap means;

means positioned in the bore and electrically interconnecting the electrical conductors of said power cable to each of said heater elements.

13. Heating apparatus comprising:

a power cable;

rigid heating device spacing means including a pair of spaced headers;

a plurality of elongated, heating devices each having first and second ends and extending through each of 13 14 said spaced headers, said heating devices each ina metallic sheath around said heating element and eluding: said conductor, said sheath passing through, and

an elongated resistance heating coil having a first engaged by, each of said headers; and

end and a second end, and located entirely bea quantity of electrical insulating material between tween, and spaced from, said headers; 5 said sheath and the heating element and cona first elongated, unheated electrical conductor ductor.

axially aligned with said elongated resistance 14. Heating apparatus as defined in claim 13 wherein heating element and connected between said said metallic sheath is of uniform wall thickness through- :first end of the elongated resistance heating eleout its length. ment and said power cable, said conductor ex- 10 References Cited tending entirely through one of said spaced headers and being of sufiicient length that its UNITED STATES PATENTS portion connected to said power cable remains 1 457 690 6/1923 Brine :at ambient temperature when aid h at g 1504208 8/1924 Brine 219*27 ment is above ambient mp 15 1 10/1938 W,

a second, elongated, unheated electrical conductor axially aligned with Said el'ongtted reistan9e CHARLES E. OCONNELL, Primary Examiner. heating c011 and connected to sald heating end at the end thereof opposite said first unheated NIL'E C. BYERS, JR., Examiner.

electrical conductor; 20

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