US3114417A

US3114417A - Electric oil well heater apparatus

Info

Publication number: US3114417A
Application number: US134798A
Authority: US
Inventors: Patrick B Mccarthy
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-08-14
Filing date: 1961-08-14
Publication date: 1963-12-17
Anticipated expiration: 1980-12-17

Description

Dec. 17, 1963 P. B. MCCARTHY ELECTRIC OIL WELL HEATER APPARATUS 3 Sheets-Sheet 1 Original Filed March 4, 1958 Patrick 8. McCarthy,

INVENTO/P. By M ATTORI/EX P.B.MCARTHY ELECTRIC OIL WELL HEATER APPARATUS Original Filed March 4, 1958 Dec. 17, 1 963 3 Sheets-Sheet 2 Fig. 2.

A Patrick B. McCqrth INVEN TOR.

ATTORNEX Dec. 17, 1963 P. B. MCCARTHY ELECTRIC OIL WELL HEATER APPARATUS 3 SheetsSheet 3 Original Filed March 4, 1958 h I r G C W c M X B W E .K T N C M W m r w DnWWB 4 United States Patent 3,114,417 ELECTRIC OIL WELL HEATER APPARATUS Patrick E. McCarthy, Van Nuys, Caliil, assignor, by direct and mesne assignments, of twenty percent to Ernest T. Saftig and twenty percent to Burton J. Stansbury, Newport Beach, and twenty percent to Paul F. Lover-ridge, Santa Ana, Calif., and forty percent to Peggy L. McCarthy Continuation of application Ser. No. 719,020, Mar. 4, 1958. This application Aug. 14, 1961, Ser. No. 134,798 16 Claims. (Cl. 166-60) The present invention relates to oil well apparatus, and more particularly to subsurface heaters adapted to be installed in the well bore for the purpose of heating the well production therewithin.

The present application is a continuation of application Serial No. 719,020, filed March 4, 1958, for Electric Oil Well Heater Apparatus, now abandoned.

An object of the present invention is to provide electric heater apparatus for heating the oil within a well bore, to which current is conducted through an appropriate electric cable disposed in the well here, in which the electric cable is not subject to the high temperature at which the heater might be operating, thereby avoiding deterioration or breakdown of the cable insulation and preventing failure of the electric heater circuit.

Another object of the invention is to provide an electric heater for installation in a well bore, which is not susceptible to short circuiting.

A further object of the invention is to provide an electric heater for use in a well bore, which is not susceptible to the deleterious effects of the fluent substances in the well bore, such as acids, salt water, and the like, and which is also not susceptible to electrolytic action in the well bore, such as electrolytic corrosion.

Yet another object of the invention is to provide an electric heater apparatus for use in a well bore to elevate the temperature of the production in the well bore, in which the passage of current to the heater is controlled automatically in response to the Well temperature in the region of the heater.

An additional object of the invention is to provide an electric heater apparatus for use in a well bore, in which the passage of current to the heater is controlled automatically by the temperature in the well bore at the region of the heater, the temperature at which control is effected being readily varied at the top of the well bore. Adjustment of the temperature at which control is eiiected can be made over a wide range from the top of the well bore, at any time.

Still a further object of the invention is to provide an electric heater apparatus to be used in a well bore, which is comparatively simple, economical to manufacture, and of strong and sturdy construction, making the heater easily transportable and not subject to damage while in transit.

Another object of the invention is to provide an electric oil well heater that can be installed at any point in the production string which extends to the top of the Well bore.

Still a further object of the invention is to provide electric oil well heater apparatus in which the passage of current to the well heater is controlled by a resistance element responsive to the heat in the Well bore and through which direct current passes, the direct current making it unnecessary to shield the length of cable in the well bore, which shielding would be required it alternating current were used, to avoid changes in capacitance and inductance in the equipment. The use of alternating current in the control circuit would require extensive and expensive shielding of the cable extending from the top of the well bore to the electric heater there- Within.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

FIGURE 1 is a longitudinal section through a well bore, illustrating diagrammatically one use of the invention therein;

FIGS. 2 and 2a together constitute a longitudinal section, parts being shown in side elevation, through a well heater apparatus, FIG. 2a constituting a lower continuation of FIG. 2;

FIG. 3 is a cross-section on a reduced scale taken generally along the line 33 on FIG. 2a;

FIG. 4 is a top plan view of the end closure plate of the heater;

FIG. 5 is a cross-section on a reduced scale taken along the line 55 on FIG. 2a;

FIG. 6 is a side elevational view of the heater at an intermediate stage of its manufacture;

FIG. 7 is a diagrammatic view of the electrical control circuit for the heater;

FIG. 8 is an enlarged longitudinal section of a portion of the apparatus in the region of connection of one of the electrodes to a power line.

The heater apparatus A disclosed in the drawings is adapted to be disposed at a desired location in a body of oil or other well production B in a well bore C that has a casing D therein extending to the top of the well bore. The heater is secured at the appropriate point to a tubular string E extending to the top of the well bore. In fact, it actually forms part of the tubular string itself. This tubular string may have the usual pump mechanism therein, including a standing valve F and a traveling piston G, which is connected to a string of sucker rods H extending through the production tubing E to the top of the well bore for attachment to reciprocating pump operating apparatus, such as a walking beam (not shown) or a hydraulically operating mechanism (not shown).

The well production elevated by the pump in the tubing string will pass out through the usual outlet pipe I at the top of the hole to a storage tank or pipe line (not shown).

The electric heater includes an inner tubular member 10 having an upper threaded pin 11 for threaded attachment to an upper adjacent section of the tubing E. It may also have a lower threaded pin 12 for threaded attachment to a lower section of tubing 13- that may be perforated to provide an inlet 14 for the well production into the tubing string E, the well production passing upwardly through the inner tubing 10' and through the pump portion thereof F, G- for lifting to the top of the well bore.

Surrounding the inner production tubing 10 is an outer tubing 15 that is spaced from the inner tubing to pro vide an annular chamber 16 therebetween, in which the resistance heating device of the heater is disposed. This resistance heating device includes a resistance wire 17 disposed within a tube 18, preferably made of stainless steel to avoid corrosion and electrolytic action in the well bore. The tube 18 has one portion 19 extending down along one side of the annular chamber 16 from the upper end thereof substantially to its lower end, which merges into an intermediate portion 2% extending arcuately around the inner tube 10, which, in turn, merges into another arm or leg portion 21 that extends upwardly through the chamber 16 to the top thereof substantially diametrically opposite the other leg 18 of the tube. The stainless steel tube 18 is preferably of one piece, with its intermediate portion 21] bent around the inner tubular member 16) substantially 180 degrees, so that the two arms or legs 1?, 21 of the tube are diametrically opposite one another.

The resistance wire 17 extends throughout one leg of the tube 19, through its intermediate portion 20, and throughout the other leg 21 of the tube. An upper end of the wire is suitably secured, as by welding, to a conductor or electrode 22 extending upwardly through an extension 23 of the tube, its other end being secured, as by welding, to a second conductor or electrode 24 extending upwardly through another extension 25 of the tube. Disposed between the resistance wire 17 and the tube 18, and also between the

electrode

22, 24 and the

tubing extensions

23, 25, is electrical insulation material 26, such as magnesium oxide, which may initially be in a powder state and which is highly compacted, to retain the resistance wire 17 and

conductors

22, 24 appropriately spaced from the inner wall of the generally U- shaped tube 18, and to insure the transfer of heat from the resistance wire 17 through the insulation to the stainless steel tubing 18.

The lower end of the annular chamber 16 is closed by a lower end plate 27 which is secured, as by welding material 28, to the lower end of the outer tube 15 and to the periphery of the inner tube 10. Similarly, the chamber 16 is closed by an upper end plate 29 which has a central bore 3G to permit passage therethrough of the inner tube 10, and diametrically opposite smaller bores 31 through which the two

legs

19, 21 of the heater device pass. This upper end plate 29 may also be secured, as by welding material 32, to the upper end of the outer protective tubing 15, to the inner tubing and to the stainless steel

tubular legs

19, 21 themselves.

The heater device between the upper and

lower end plates

29, 27 maybe of any desired length. For example, the length may be about twenty-five feet, providing about fifty feet of resistance wire 17 contained within the stainless steel tube '18. The heater device is appropriately secured to the inner tube '10 by longitudinally spaced bands or straps 33 passing around the

arms

19, 21 of the tube 18 and the inner tubing 10, the ends of each strap being firmly secured to one another in any suitable manner, as through use of a clamp device 34 usually employed in applying straps around packing boxes or cases. After the heater device 18 has been appropriately secured to the inner tube 10 by the straps along the region where the elongate chamber is to be formed (FIG. 6), the outer tube can then be slipped over this assembly and the upper and

lower end plates

29, 27 placed in appropriate relation to the apparatus and welded to the inner and outer tubes 10, 1 5, with the upper end plate 29 also welded to the

arms

19, 21 of the heater device. The extensions 23, '25 above the plate 29 may also be secured to the inner tubing 10 by longitudinally spaced straps or hands 33a.

Current is fed to the heater device through an insulated cable 35 suitably attached to the production tubing E and extending to the top of the well bore. This cable has a total of four conductors or

lines

36, 37, 38, 39 therein, one of which 36 is connected to one of the conductors or electrodes 22, and the other of which 37 is connected to the other conductor or electrode 24. The other two

conductors

38, 39 of the cable 35 may be used in association with a thermally responsive control device or thermistor 40 for determining the application of current to the resistance element 17, which will be described 'hereinbelow.

The

power conductors

36, 37 are not connected to the

electrodes

22, 24 near the resistance wire 17, but are attached to such electrodes at a point remote from the resistance wire, such that the insulation 41 surrounding the power conductor lines is not subjected to the relatively high temperature of the resistance rwire. As disclosed in the drawings, the

tubular arm extensions

23, 25 extend upwardly above the upper end plate 29 and the ends of the resistance element 17 to a substantial extent, which may be of the order of about twenty feet. The

conductors

22, 24 project through the

tubing extensions

23, 24 for its full length, being insulated from the wall of such extensions by the insulating material 26, which may be the same material as surrounds the resistance element 26. The

electrodes

22, 24 may project upwardly beyond the upper ends of the stainless

steel tubing extensions

23, 25, where each

electrode

22 or 24 is suitably spliced to a

companion power conductor

36 or 37.

A cable sheath 43 surrounds the upper portion of each

tubular extension

23, 25, its lower end being suitably secured and sealed, as by solder 44, to the periphery of such extension. The connection 4 5 between each

electrode

22, 24 and the

power conductor

36, 37 may also be soldered together, the cable sheath 43 projecting upwardly around such connection and thereabove to a substantial extent, surrounding the insulated conductor 41 itself. Suitable i-nsulating material 4 6, such as porcelain, may be disposed within each sheath 43 and around the connection 42-5 between each electrode and associated power conductor, this insulating material also extending upwardly to cover the insulation 41 of the cable or

conductor

36, 37 itself. The upper portion of each

insulated cable

36, 37 may also contain a suitable insulating and sealing material 47 capable of being cast into the sheath 43 around the cable.

In the use of the heater, current from a suitable source passes down through one of the power cable lines .36 to one of the electrodes 22, then flowing through the resistance wire 17 along one arm 19 of the heater device, around the intermediate portion of the resistance wire, and up through the resistance wire portion in the other arm 21 of the device to the other electrode 24, which is con nected to the second line 37 of the power cable extending to the source of electrical energy. When the heater apparatus A has been installed at the appropriate location in the well bore, it will heat the oil in the well bore surrounding the outer protective tubing 15 by the transmission of heat from the resistance wire 17 through the electric insulation 26 to the stainless steel tube 18, and from the latter through the outer tubing 15. Heat will also be transmitted through the inner tubing 10 to the oil flowing upwardly therewithin. Thus, the oil in the well bore is subject to the heat emanating from the heater apparatus externally thereof and also internally thereof. The oil passes through the inlet openings 14 of the tubing upwardly through the inner production tubing 10 and through the standing valve F, the pump G then elevating the production through the production tubing E to the top of the well bore in response to reciprocation of the sucker rods H.

The annular chamber 16 may either be sealed against entry of fluid, or it may be provided with upper openings 50 in its upper end and lower openings 51 in its lower end, to permit the well production to pass into the chamber for direct contact with the stainless steel tubing 18 of the heater device. The oil can have no harmful effects on such member since it is preferably made of stainless steel. It cannot adversely afiect the resistance wire 17, since such wire is fully sealed within the stainless steel tube 1 8. The heated oil will probably enter through the lower openings 51 and, as its temperature is increased, will pass out through the upper openings 50, then being drawn downwardly, as the pumping action occurs, around the outer tubing 15 toward the inlet 14, the oil then passing upwardly through the inner tubing '10 where it is subject to i e heat transmitted to the inner tubing from the heater device and the oil in the chamber 16.

If desired, the chamber may be sealed and suitable heat conducting material disposed therein, such as powdered aluminum or steel. The presence of the powdered aluminum or steel completely filling the chamber 16 insures good heat conduction from the stainless steel tube 18 to both the inner production tubing and the outer protective shield or tubing 15.

The

electrodes

22, 24 within the

extensions

23, 25 of the stainless steel tubing 18 have very low resistance and will not be elevated in temperature to any significant extent by the current passing therethrough. Inasmuch as the point at which the splice 45 to each power cable is made is quite remote from the resistance element 17, the splice is not subjected to the high temperature of the latter, which is also true of the

insulation

41, 46. The subjecting of the cable insulation 41 to a comparatively low temperature insures against its breakdown and against its possible short circuiting. It is also to be noted that the stainless steel tubing 18 fully protects the resistance wire 17 and the

electrodes

22, 24 leading therefrom and prevents any short circuiting of these elements. The stainless steel tube 18 contacts the inner and

outer tubing

10, 15, the end plate 29, and other conductive portions of the apparatus, but the resistance element 17 and the

electrodes

22, 24 cannot have such contact in view of their full and complete encompassing by the insulating material 26. The

portions

36, 37 of the power cable and the upper ends of the

electrodes

22, 24 at their interconnections 45 are all fully protected by insulating material, the upper portions being fully sealed against leakage of the oil or other fluids in the well bore into the heater device through the upper shields 43.

The application of heating current to the heater device A is governed by the temperature in the region of the heater device itself. Such temperatures may be varied readily at the top of the well bore. When the preselected temperature is exceeded, the circuit to the heater device is opened. When the temperature drops below a predetermined degree, then the circuit is closed again and current allowed to pass through the resistance heating element 17.

As specifically shown in FIG. 7, current from a main line 60 may pass through a power switch 61, when the latter is closed, to a power relay 62, the power cable leads 36, 37 being connected to such relay and extending down to the oil well heater resistance 17. The relay 62 includes pairs of spaced apart contacts 63 that can be bridged by movable switch or bridge pieces 64 when current passes through the coil 65 of the power relay. Passage of current through such coil is dependent upon the closing of a control relay switch 66, which, in turn, is closed in dependence upon the temperature in the region of the well heater A, which acts upon the thermistor or temperature sensing element 40 incorporated in the heater. When the temperature decreases below a predetermined value, the control relay 66 will close, and when the temperature rises above a predetermined value, the control relay will open.

A contact 67 of the control relay is connected through a suitable lead 68 to one end of the power relay coil 65. The other end of this coil 65 is connected through a suitable lead 69 to one line 70 extending from the secondary coil 71 of a step-down transformer 72, the primary 73 of which is connected across the power line 60 when switch 61 is closed. The other line 74 of this step-down transformer is connected through a suitable lead 75 to the switch arm 76 of the control relay 66. It is evident that when the switch arm 76 engages the control relay contact 67, the circuit through the power relay coil 65 is completed, causing it to close the power relay 62 and complete the circuit through the oil well heater element 17. If desired, a suitable flow switch 76 may be incorporated in one of the lines 68 connected to the power relay coil 65, this flow switch being connected to the prime mover (not shown) operating the deep well pump such that the flow switch is automatically opened when the prime mover ceases operation.

The thermistor 40 is mounted in the annular chamber 16 between the innerand

outer tubing members

10, 15 and consists of a resistance element 80 (FIG. 7) contained within a suitable housing afiixed to a coupling 81 which is threaded in a mounting block 82 suitably attached, as by welding, to the inner tubular member 10. A protective tubing 83, which may be made of stainless steel, is threadedly secured onto the coupling 81, the two leads 38, 39 connected to each end of the resistance element 80 being insulated from one another and also being surrounded by suitable insulation of a two-line cable 84 that extends upwardly through the tubing 83, which extends through a hole 85 in the upper end plate 29. Suitable insulation 86 is preferably provided between the cable 84 and the tubing 83 of the temperature responsive portion of the apparatus. The stainless steel control tube 83 may also be welded to the upper end plate 29, and this control tubing will extend upwardly to the same location as the

arm extensions

23, 25, the two

insulated lines

38, 39 also being encased within the same cable structure 35 and extending along the production tubing E to the top of the Well bore.

An electronic control circuit is employed for determining the passage of current through the control relay 66. Such control circuit may be of any suitable design and has provision for varying the temperature at which current will pass through the control relay coil 90 and be discontinued from passing through such coil.

As disclosed in FIG. 7, the control is elfected by an electronic bridge circuit. The

lines

70, 74 leading from the secondary coil 71 of the step-down transformer 72 are also connected to the primary coil 91 of a controller transformer 92. The voltage is stepped down to a further extent to one secondary coil 93, a lead 94 extending from this coil being grounded. One end of the control relay coil 90 is connected through a suitable line 95 to the plate 96 of an amplifier tube 97, such as a triode, which has a grid 98 and a cathode 99 in its envelope. A heater 100 for the cathode has one end connected to a line 101 running to an end of another secondary coil 102 of the controller transformer 92 which has a relatively low voltage induced therein, the other end of this transformer coil being connected through a line 103 to the other end of the heater 100 and also to the cathode 99.

The grid voltage of the relay amplifier 97 is controlled by a signal amplifier 104, the operation of which is dependent upon the resistance of the thermistor 80, which is related to the temperature of the thermistor. The thermistor is made of a material, such that its resistance decreases as the temperature in the well increases and, conversely, its resistance increases as the temperature in the well decreases. One end of the line 39 from the thermistor is connected through a suitable load resistance 105 to the grid 106 of the double triode 104. One plate 107 of this triode is connected through a suitable resistance 108 to a line 109 running to a rectifier 110 connected to the other end of the secondary coil 93 of the controller transformer 92 and also to the other end of the control relay coil 90. The cathode 111 of the same section of the double triode is connected through a resistance 112 to a temperature controller 113, in the form of a potentiometer, incluing a variable resistance element 114 and an arm 115 shiftable across this resistance element. One end of the temperature controller resistance 114 is connected to one of the lines 103, its other end being connected to ground and also to one of the leads 38 running to the thermistor 80. The other lead 39 extending from the thermistor is connected through a suitable resistance 116 to the line 103 running to the cathode 99 of the relay amplifier 97.

The current from the plate 197 of the double triode passes through a line 117 to a condenser 118 that is con- .nected through another line 11% to the second grid 12% of the double triode tube 164. This line 119 is also connected through a resistance 1 21 to the other cathode 122 of the tube, the resistance 121 being suitably grounded. The other plate 123 of the double triode tube is connected through a resistance 124 to the rectifier 11d, and is also connected through a lead r125 to a condenser 126, another lead 127 from the condenser being connected to the grid 98 of the relay amplifier 97. The relay amplifier circuit also includes a resistance 12? connected to ground and also to the grid 93, as well as a condenser 129 conneoted across this resistance. The cathodes 111, 122 of the signal amplifier 1&4 are energized by heater 130 connected in series, one heater being connected to one of the 'lines 101 and the other heater being connected to the other line M3.

The only portions of the control apparatus, illustrated diagrammatically in FIG. 7, disposed in the well bore are the thermistor '89, 43%} and the two lines 38, '39 connected thereto and running upwardly to the top of the hole. The remainder of the apparatus is above ground.

As the temperature in the well bore changes, so does the temperature of the sensing element 3t) change. As its temperature changes, its resistance also changes. This change of resistance is compared with the preset resistance on the potentiometer 113, which is adjustable by moving the arm 115 over the resistance 114. if the resistance of the sensing element 84 is higher than the preset resistance of the temperature controller, the voltage on the control grid 1% is decreased and more current passes to the plate 107 of the double triode, which, in turn, decreases the voltage on the other grid 12%, allowing a still greater amount of current to pass through the other plate 123 and to the grid 98 of the relay amplifier tube 97. When the grid voltage of the relay amplifier tube reaches the required value, then more current will fiow to the plate 96 and to the coil 96 of the control relay, causing it to beenergized and closing the relay 66. This closing of the control relay 66 completes the circuit of the power relay coil 65, causing the power relay 62 to close and completingthe circuit to the heater element 17.

As the heat in the well increases, the resistance of the thermistor or sensing element 8! decreases. When the heat increases sufficiently, its resistance equals the set resistance of the temperature controller 113. With equality in these resistances, the signal in the signal amplifier tube 1% decreases, which decreases. the current in the relay amplifier tube 97 and the current passing to the relay coil $0, causing the control relay 66 to open and, consequently, effecting opening of the main power relay 62, which discontinues the application of current to the oil well heater element 17.

As the heat in the well then decreases, because of the open circuit to the oil well heater, the resistance of the sensing element or thermistor 88 increases, the signal to the signal amplifier tube 10 4 increasing and thereby in creasing the current in the relay amplifier tube 97. When such current increases sufliciently, the current passing through the control coil 90 will move the switch arm 76 into engagement with the contact 67, closing the relay switch 66 and completing the circuit to the power relay coil 65 once again, which will again cause the power relay switch 62 to close and cause current to again pass to the oil well heater 17.

The foregoing action is repeated intermittently, the heater '17 supplying heat when the temperature drops below a predetermined value and discontinuing the supply of heat when the temperature rises to a predetermined 'value. By changing the pre-set resistance of the temperature controller or potentiometer 113, the temperature at which power will be supplied to the heater l7, and at which the application. of power to the heater will be discontinued, can be varied.

The rectifier ldtl provides direct current in the control circuit including the

conductors

38, 39, which are in the same cable as the

power conductors

35, 37. it alternating current in the electronic control circuit were used, shielding of the

conductors

38, 39 would be necessary to avoid changes in capacitance and inductance in the equipment. Such changes in capacitance and inductance would prevent proper and accurate functioning of the control circuit in determining the passage of current through the electric heater and would prevent maintenance of the temperature in the well bore at the preselected value. The use of direct current, however, makes it unnecessary to shield the cable, and yet results in proper control or" current through the heater and maintenance of the well bore temperature. The lack of need to shield the cable saves considerable cable expense.

The heater apparatus illustrated is of strong and sturdy construction, and is not susceptible to damage while being transported to and from the well location. The heater is easy to install, and it cannot be overheated because of the automatic control of its operating temperature. Its insulated portions are not subjected to inordinately high temperature, and, therefore, are not susceptible to failure, such as short circuiting. in addition, the power cables 3-6, 3'7 running to the top of the well bore are not susceptible to insulation failures, inasmuch as their insulation is relatively remote from the point of application of heat. Since the inner tube ltl is essentially the same as the oil well production tubing itself, the heater can be installed at any desired location in the tubing string E. For that matter, a plurality of heaters can be installed at ditierent points along the tubing string. The operating temperature of the heater is easily varied from the top of the hole, in order that optimum production from the well bore can be secured.

The inventor claims:

1. In well heater apparatus: a tubular member adapted to be connected to production tubing and lowered in a well bore whereby well production can flow through said tubular member and into the productin tubing; an electric heating means adjacent to said tubular member to heat the well production therewithin; an electric circuit connected to said heating means extending to the top of the well bore; thermally responsive resistance means in the well bore adjacent to said tubular member and responsive to the heat in the well bore; and means including a source of current external of the well bore connected to said resistance means and circuit and responsive to change in resistance of said resistance means for selectively opening or closing said circuit.

2. In a well heater apparatus: a tubular member adapted to be connected to production tubing and lowered in a well bore whereby well production can flow through said tubular member and into the production tubing, an electric heating means adjacent to said tubular member to heat the well production therewithin; an electric circuit connected to said heating means extending to the top of the well bore; means for selectively opening and closing said circuit including thermally responsive resistance means in the well bore adjacent to said tubular member and responsive to the heat in the well bore; and means at the top of the well bore including a source of cunrent for said resistance means external of the well bore adapted to be adjusted for varying the effective operating temperature of said thermally responsive means.

3. In well heater apparatus: a tubular member adapted to be connected to production tubing and lowered in a well bore whereby well production can flow through said tubular member and into the production tubing; an electric heating means adjacent to said tubular member to heat the well production therewithin; an electric circuit connected to said heating means extending to the top of the well bore; thermally responsive resistance means in the well bore adjacent to said tubular member and responsive to the heat in the well bore; means including a source of current external of the well bore connected to said resistance means and circuit and responsive to change in resistance of said resistance means for selectively opening or closing said circuit; and means at the top of the well bore for varying the resistance at which said resistance means effects selective opening or closing of said circuit.

4. In a subsurface well heating apparatus: an inner tubular member through which well production is adapted to be conducted; an outer tubular member surrounding said inner member; means mounting said outer member in spaced relation to said inner member; tubing between said members including circumferentially spaced portions extending lengthwise of said members and an intermediate portion disposed arcuately around said inner member and interconnecting said spaced portions; resistance wire in said spaced port-ions and intermediate portion insulated from said tubing; said spaced portions extending upwardly to a point remote from the upper ends of said resistance wire; low resistance electrodes in said spaced portions connected to said resistance wire and insulated from said tubing; said electrodes having means at the upper ends of said spaced portions for connection to adjacent power lines; said point being sufiiciently remote from the upper ends of said resistance wire such that substantial heat from the resistance wire is not transferred to the upper ends of said electrodes and to the adjacent power lines when connected thereto.

5. In a subsurface well heating apparatus: an inner tubular member through which well production is adapted to be conducted; an outer tubular member surrounding said inner member; means mounting said outer member in spaced relation to said inner member; a one-piece tubing between said members including a lower intermediate portion disposed arcuately around said inner member and merging into circumferentially spaced portions extending upwardly therefrom lengthwise of said members; resistance wire in said spaced portions and intermediate portion insulated from said tubing; said spaced portions extending upwardly to a point remote from the upper ends of said resistance wire; low resistance electrodes in said spaced portions connected to said resistance wire and insulated from said tubing; said electrodes having means at their upper ends remote from the upper ends of said resistance wire for connection to adjacent power lines; said point being sufiiciently remote from the upper ends of said resistance wire such that substantial heat from the resistance wire is not transferred to the upper ends of said electrodes and to the adjacent power lines when connected thereto.

6. In a subsurface well heating apparatus: an inner tubular member through which well production is adapted to be conducted; an outer tubular member surrounding said inner member and spaced therefrom; upper and lower closure members around said inner tubular member secured to said tubular members; tubing between said tubular members including a lower intermediate portion disposed arcuately around said inner member above said lower closure member and merging into circumferentially spaced portions extending upwardly therefrom lengthwise of said tubular members and projecting through said upper closure member; resistance wire in said spaced portions and intermediate portion insulated from said tubing; said spaced portions extending upwardly to a point remote from the upper ends of said resistance wire; low resistance electrodes in said spaced portions connected to said resistance wire and insulated from said tubing; said electrodes having means at the upper ends of said spaced portions for connection to adjacent power lines; said point being sufliciently remote from the upper ends of said resistance wire such that substantial heat from the resistance wire is not transferred to the upper ends of said electrodes and to the adjacent power lines when connected thereto 7. In a subsurface well heating apparatus: an inner tubular member through which well production is adapted to be conducted; an outer tubular member surrounding said inner member; means mounting said outer member in spaced relation to said inner member; tubing between said members including circumferentially spaced portions extending lengthwise of said members and an intermediate portion disposed arcuately around said inner member and interconnecting said spaced portions; resistance wire in said spaced portions and intermediate portion insulated from said tubing; electrodes in said spaced portions connected to said resistance wire and insulated from said tubing; said electrodes having means for connection to adjacent power lines; and thermally responsive means in the space between said tubular members, including a control tubing, a thermal sensing element carried by said control tubing, and electric leads connected to said sensing element and extending through said control tubing.

8. In a subsurface well heating apparatus: an inner tubular member through which well production is adapted to be conducted; an outer tubular member surrounding said inner member and spaced therefrom; upper and lower closure members around said inner tubular member secured to said tubular members; tubing between said tubular members including a lower intermediate portion disposed arcuately around said inner member above said lower closure member and merging into circumferentially spaced portions extending upwardly therefrom lengthwise of said tubular members and projecting through said upper closure member; resistance wire in said spaced portions and intermediate portion insulated from said tubing; said spaced portions extending upwardly to a point remote from the upper ends of said resistance wire; low resistance electrodes in said spaced portions connected to said resistance wire and insulated from said tubing; said electrodes having means at the upper ends of said spaced portions for connection to adjacent power lines; said point sufficiently remote from the upper ends of said resistance wire such that substantial heat from resistance wire is not transferred to the upper ends of said electrodes and to the adjacent power lines when connected thereto; and thermally responsive means, including con trol tubing in the space between said tubular members and extending through said upper closure member, a thermal sensing element in said space and carried by said control tubing, and electric leads connected to said sensing element and extending through said control tubing.

9. In a subsurface well heating apparatus: an inner tubular member through which well production is adapted to be conducted; an outer tubular member surrounding said inner member and spaced therefrom; upper and lower closure members around said inner tubular member secured to said tubular members; tubing between said tubular members including a lower intermediate portion disposed arcuately around said inner member above said lower closure member and merging into circumferentially spaced portions extending upwardly therefrom lengthwise of said tubular members and projecting through said upper closure member; resistance wire in said spaced portions and intermediate portion insulated from said tubing; said spaced portions extending upwardly to a point remote from the upper ends of said resistance wire; low resistance electrodes in said spaced portions connected to said resistance wire and insulated from said tubing; said electrodes having means at the upper ends of said spaced portions for connection to adjacent power lines; said point being sufiiciently remote from the upper ends of said resistance wire such that substantial heat from the resistance wire is not transferred to the upper ends of said electrodes and to the adjacent power lines when connected thereto; said outer tubular member having upper and lower openings therethrough to allow ingress and egress of the well production into and from the space between said tubular members.

10. In well heater apparatus: an inner tubular member through which well production is adapted to be conducted; an outer tubular member surrounding said inner member; means mounting said outer member in spaced relation to said inner member; tubing between said members including oircumterentially spaced portions extending lengthwise of said members and an intermediate portion disposed arcuately around said inner member and interconnecting said spaced portions; resistance wire in said spaced portions and intermediate portion insulated from said tubing; electrodes in said spaced portions connected to said resistance wire and insulated from said tubing; an electric circuit for said resistance Wire connected to said electrodes and extending therefrom to the top of the well bore; thermally responsive means in the space between said tubular members, including a control tubing, a thermal sensing element carried by said control tubing, and electric leads connected to said sensing element and extending through said control tubing; and means connected to said leads and electric circuit and responsive to change in temperature of said sensing element for selectively opening or closing said circuit.

11. In well heater apparatus: a tubular member adapted to be connected to production tubing and lowered in a Well bore whereby well production can fiow through said tubular member and into the production tubing; an electric heating means adjacent to said tubular member to heat the well production therewithin; an electric circuit connected to said heating means extending to the top of the well bore; thermally responsive resistance means in the well bore adjacent to said tubular member and responsive to the heat in the well bore; and means including a source of direct current external of the well bore connected to said resistance means and circuit and responsive to change in resistance of said resistance means for selectively opening or closing said circuit.

12. In well heater apparatus: a tubular member adapted to be connected to production tubing and lowered in a well bore whereby Well production can flow through said tubular member and into the production tubing; an electric heating means adjacent to said tubular member to heat the well production therewithin; an electric circuit connected to said heating means extending to the top of the well bore; means for selectively opening and closing said circuit including thermally responsive resistance means in the well bore adjacent to said tublar member and responsive to the heat in the well bore; and means at the top of the well bore including a source of direct current for said resistance means external of the well bore adapted to be adjusted for varying the effective operating temperature of said thermally responsive means.

13. In a well heater apparatus: a tubular member adapted to be connected to production tubing and lowered in a well bore whereby well production can flow through said tubular member and into the production tubing; an electric heating means adjacent to said tubular member to heat the well production therewithin; an electric circuit connected to said heating means extending to the top of the well bore; thermally responsive resistance means in the well bore adjacent to said tubular member and respnsive to the heat in the well bore; means including a source of direct current external of the well bore connected to said resistance means and circuit and responsive to change in resistance of said resistance means for selectively opening or closing said circuit; and means at the top of the well bore for varying the resistance at which said resistance means effects selective opening or closing of said circuit.

14. In Well heater apparatus: a tubular member adapted to be connected to production tubing and lowered in a well bore whereby well production can fiow through said tubular member and into the production tubing; an electric heating means adjacent to said tubular member to heat the well production therewithin; a first electric power circuit connected to said heating means including a power relay at the top of the well here for opening and closing said first circuit; a second control circuit connected to said power relay including a control relay at the top of the well bore for opening and closing said second control circuit; a third circuit including a source of direct current external of the well bore connected to said control relay extending to the top of the well bore; and means for determining the passage of current in said third circuit including thermally responsive means in the well bore adjacent said tubular member responsive to the heat in the well bore.

15. In well heater apparatus: a tubular member adapted to be connected to production tubing and lowered in a well bore whereby well production can fiow through said tubular member and into the production tubing; an electric heating means adjacent to said tubular member to heat the well production therewithin; a first electric power circuit connected to said heating means including a power relay at the top of the Well bore for opening and closing said first circuit; a second control circuit connected to said power relay including a control relay at the top of the well bore for opening and closing said second control circuit; a third circuit for said control relay including a source of direct current external of the well bore, a thermally responsive resistance means adjacent to .said tubular member and responsive to the heat in the well bore, a signal amplifier connected to said resistance means, and a relay amplifier at the top of the well bore connected to said signal amplifier and said control relay.

16. In well heater apparatus: a tubular member adapted to be connected to production tubing and lowered in a well bore whereby well production can flow through said tubular member and into the production tubing; an electric heating means adjacent to said tubular member to heat the well production therewithin; a first electric power circuit connected to said heating means including a power relay at the top of the well bore for opening and closing said first circuit; a second control circuit connected to said power relay including a control relay at the top of the well bore for opening and closing said second control circuit; a third circuit for said control relay including a source of direct current external of the Well bore, a thermally responsive resistance means adjacent to said tubular member and responsive to the heat in the well bore, a signal amplifier connected to said resistance means, a relay amplifier at the top of the well bore connected to said signal amplifier and said control relay, and a temperature adjusting potentiometer at the top of the well bore connected to said resistance means and signal amplifier to vary the temperature to which the resistance means must be subjected for effecting opening and closing of said circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,915,895 Lewis June 27, 1933 2,525,314 Rial Oct. 10, 1950 2,575,113 Lennox Nov. 13, 1951 2,608,256 Matthews Aug. 26, 1952 2,760,046 Rothacker Aug. 21, 1956 2,771,140 Barclay et al. Nov. 20, 1956 2,808,110 Spitz Oct. 1, 1957 2,881,301 Bowman Apr. 7, 1959 2,893,490 Williams et a1. July 7, 1959 2,932,352 Stegemeier Apr. 12, 1960