Wellbore telemetry apparatus

Abstract

An apparatus having coiled conductor stored therein is used in a wellbore telemetry system. The telemetry system permits the monitoring of a subsurface condition as drilling proceeds. The apparatus includes a tubular container, an insulated electric conductor mounted in the container in a configuration which includes left-hand and right-hand coils, and means for dispensing conductor from opposite ends of the container. The apparatus permits the conductor string to be lengthened as the drill string is lengthened.

Description

BACKGROUND OF THE INVENTION

l. Field of the Invention

This invention relates to an improved apparatus for use in well-bore telemetry operations. In one aspect, it relates to an improved cable system for maintaining electric continuity between surface and subsurface locations in a drill string.

2. Description of the Prior Art

In the drilling of oil wells, gas wells, and similar boreholes, it frequently is desirable to transmit electric energy between subsurface and surface locations. One application where electrical transmission has received considerable attention in recent years is found in wellbore telemetry systems designed to sense, transmit, and receive information indicative of a subsurface condition. This operation has become known in the art as "logging while drilling." A major problem associated with wellbore telemetry systems proposed in the past has been that of providing reliable means for transmitting an electric signal between the subsurface and surface locations. This problem can best be appreciated by considering the manner in which rotary drilling operations are normally performed. In rotary drilling, a borehole is advanced by rotating a drill string provided with a bit. Sections of drill pipe, approximately 30 feet in length, are added individually to the drill string as the borehole is advanced. In adapting an electrical telemetry system to rotary drilling equipment, it will thus be appreciated that the means for transmitting an electric signal between subsurface and surface locations must be such as to permit the addition of individual pipe sections to the drill string. An early approach to the problem involved the use of a continuous electrical cable which was adapted to be lowered inside the drill string and to make contact with a subsurface instrument. This technique, however, required withdrawing the cable each time a pipe section was added to the drill string. A more recent approach involves the use of special drill pipe equipped with an electric conductor. Each pipe section is provided with connectors that mate with connectors of an adjacent pipe section and thereby provide an electrical circuit across the joint (U.S. Nos. 3,518,608 and 3,518,609). Disadvantages of this system include the need for special pipe sections and the difficulty of maintaining insulation of the electrical connectors at the pipe section joints.

SUMMARY OF THE INVENTION

The apparatus of the present invention is adapted for use in well drilling operations wherein an electric conductor disposed in a pipe string is employed to transmit electric energy between a subsurface and surface location.

A novel feature of the invention involves the configuration of a conductor within a drill string which permits storage of excess conductor. The invention contemplates the use of a tubular container for maintaining the electric conductor within the drill string in a coiled configuration and for uncoiling the conductor as additional conductor is needed. Thus, as the drill string is lengthened, the electric circuit between the subsurface and surface can be maintained merely by dispensing the coiled portions of the conductor until the excess conductor stored in the container is used up. The coiled conductor is maintained in the container in coiled portions wound in opposite hands, i.e. one portion is provided with left-hand coils and a second with right-hand coils. Means are provided for paying out the conductor from the top and bottom of the container in such a manner that the individual left-hand and right-hand coils are unwound at about the same time or alternatively, thereby preventing twists from forming in the conductor string.

In a preferred embodiment of the invention, the apparatus comprises an elongated open-ended tube capable of being lowered into a pipe string used to drill a well, an electric conductor or cable mounted in the tube having a first portion wound in left-hand coils and a second portion wound in right-hand coils, and means for dispensing the coiled portions from opposite ends of the tube. A preferred form of the dispensing means includes cable brake or clutch which in response to the tension in the conductor string operates to reduce gripping force on the conductor. In one embodiment a cable clutch is provided at each end of the tube for separately gripping cable dispensed from the left-hand coils and from the right-hand coils. One clutch operates in response to movement of the other clutch to enable dispensing of cable from opposite ends at about the same rate. This may be achieved by unwinding the coils at about the same rate or unwinding left-hand and right-hand coils alternatively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is a schematic view of well drilling equipment provided with a telemetry system for monitoring a subsurface condition

FIG. 2 is an enlarged longitudinal sectional view of a container employed in the telemetry system shown in FIG. 1 illustrating the coiled configuration of the conductor stored in the container.

FIG. 3 is a cross-sectional view of the drill pipe shown in FIG. 1, the cutting plane taken along the line 3--3 thereof.

FIG. 4 is a cross-sectional view of the apparatus shown in FIG. 2, with the cutting plane taken along the line 4--4 thereof.

FIG. 5 is a cross-sectional view of the apparatus shown in FIG. 2, the cutting plane taken along line 5--5 thereof.

FIGS. 6, 7, and 8 are schematic views, illustrating sequential steps for adding a section of drill pipe to the drill string.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Conventional rotary drilling equipment, as schematically illustrated in FIG. 1, includes swivel 10, kelly 11, tubular drill string 12, and bit 13. These components, connected in the manner illustrated, are suspended from the drilling derrick 14 by means of rig hoisting equipment. The kelly 11 passes through rotary table 16 and connects to the upper end of the drill string 12. The term "drill string" as used herein refers to the column of tubular pipe 12 between the bit 13 and the kelly 11; and the term "pipe string" refers to the complete pipe column including kelly 11. The major portion of the drill string normally is composed of drill pipe with a lower portion being composed of drill collars. The drill string 12 consists of individual pipe sections connected together in end-ro-end relation by threaded connections. One connection is illustrated at 15 in FIG. 1. In the lower four sections of FIG. 1, the diameters of the borehole and the drill string 12 have been expanded in relation to the upper section to reveal further details.

The borehole 17 is advanced by rotating the drill string 12 and bit 13 while at the same time drilling fluid is pumped through the drill string 12 and up the borehole annulus. The drilling fluid is delivered to swivel 10 through a hose attached to connection 18 and is returned to the surface fluid system through pipe 19. A kelly bushing 20 couples the rotary table 16 to the kelly 11 and provides means for transmitting power from the rotary table 16 to the drill string 12 and bit 13. (The use of a power swivel eliminates the need for the kelly and rotary table. The present invention may be used with either system; for purposes of illustration, however, it will be described in connection with the kelly and rotary table system.)

As mentioned previously, it frequently is desirable to monitor a subsurface drilling condition during drilling operations. This requires measuring a physical condition at the subsurface location, transmitting this data as an electrical signal to the surface, and reducing the signal to useful form. Typical situations where telemetry is applicable in drilling operations include drilling through abnormal pressure zones, drilling through zones where hole deviation is likely to be a problem, directional drilling, exploratory drilling, and the like.

Although the present invention may be employed in most any drilling operation wherein an electric conductor is used in tubular pipe to transmit electric energy between subsurface and surface locations, it finds particularly advantageous application in a wellbore telemetry system such as that illustrated in FIG. 1 comprising an instrument 21, electric conductor 22, and receiver 23.

The instrument 21 capable of measuring a subsurface condition and generating an electric signal indicative of that condition is provided within the drill string 12. A variety of devices capable of sensing a physical condition are available. These include transducers for measuring pressure, temperature, strain and the like; surveying instruments for measuring hole deviation; and logging instruments for measuring resistivity or other properties of subsurface formations. The instrument 21 may be powered by batteries or by energy transmitted through conductor 22. Alternatively, a subsurface generator driven by fluid flowing through the drill string 12 may be used to power instrument 21.

The present invention is concerned primarily with the apparatus for storing portions of the electric conductor 22 is a coiled configuration within the drill string 12. The energy transmitted through the conductor 22 may be a signal generated by the subsurface instrument 21 and transmitted to the receiver 23 at the surface. Alternatively, the energy may be electric power transmitted from the surface to actuate or drive a subsurface instrument or motor, Or, energy may be transmitted down the conductor 22 to power the instrument 21 and simultaneously intelligence may be transmitted up the same conductor.

As applied in telemetry operations, it is preferred that the energy being transmitted be in the form of a pulsating signal. Information can be transmitted by varying the number, amplitude, width or spacing of a train of amplitude of the pulsating signal. More than one transducer or other device may be employed in the instrument 21 if desired, in which case a multiplexer may be used for sending the various signals over a single pair of conductors.

The instrument 21 may be mounted directly in the drill string 12 or, as illustrated in FIG. 1, it may be a separate tool that is lowered into the drill string 12 on the conductor 22.

The conductor 22 extends from the subsurface instrument 21 substantially through the drill string 12, and connects to a suitable conductor 24, provided in the kelly 11 (see FIG. 8). Conductor 24 may be embedded in the kelly 11, in which case the conductor 22 will extend to the upper end of the drill string 12 and connect to conductor 24 at that point. In order to facilitate the addition of pipe sections to the drill string 12, however, it is preferred that conductor 24 be disposed within kelly 11 and extend slightly more than the length of one pipe section below kelly 11. If telemetry operations are to be performed while the kelly 11 and drill string 12 are rotating, the upper end of conductor 24 will be connected to a device 25 capable of transmitting electric energy from a rotating member to a stationary member. Device 25 may be a rotary transformer having a rotor secured to the kelly 11 and a stator secured to the stationary portion of the swivel 10, or it may be a slip ring and brush assembly. Electric conductor 29 interconnects the stationary portion of device 25 and receiver 23 and conductor 39 may be grounded to the pipe string providing a return path for the circuit. If telemetry operations are to be performed at times when the drill string 12 and kelly 11 are stationary, the conductors 29 and 39 may be connected directly to conductor 24 and the pipe string through a suitable connector. In this situation, conductors will be disconnected when the kelly 11 and drill string 12 are rotated. Other means for transmitting the signal to the receiver 23 include a wireless transmitter connected to conductor 22 and located on a rotating member, e.g. kelly 11.

The receiver 23 is an instrument capable of receiving the signal generated by instrument 21 and reducing it to useful form.

In accordance with the present invention, the conductor 22 is arranged within the drill string 12 in a configuration such that the total length of the conductor 22 is substantially longer than the distance between the subsurface instrument 21 and the surface. As described in detail below, the excess length of conductor 22 stored in the drill string 12 permits the conductor 22 to be extended as the drill string 12 is lengthened.

In one aspect, the present invention contemplates storing the excess cable in the form of coils within the drill string 12 in canisters or tubular containers shown generally as 26 in FIG. 1. The containers 26 may be constructed of metal or plastic and have a diameter sufficiently small to permit them to pass internally of the drill string 12. In the preferred form of the invention, several of the containers 26 will be used in the conductor string 22 and each will provide sufficient length of excess cable stored therein to permit the addition of several sections of drill pipe before another container with stored conductor will be required. By coiling the conductor within the tube, substantial lengths of excess cable can be stored therein. For standard A.P.I. drill pipe having an inside diameter of 2.64 inches, a 2.5 inch O.D. container is capable of storing 50 feet of 1/8 inch unarmored cable per foot of container. A 10 ft. container thus is capable of storing approximately 500 feet of conductor. Thus one ten foot container provides sufficient cable to span about 16 sections of 30 foot drill pipe. FIG. 1 illustrates the conductor string 22 as having three containers 26. The lower two containers, as illustrated, have dispensed their stored cable for lengthening the conductor 22 at the point of operations illustrated in FIG. 1.

It should be realized, of course, that the container 26 may be longer than that illustrated in the drawings but for convenience it is preferred that relatively short containers be used. If high strength cable, such as armored cable, is used as the conductor string 22, the containers 26, conductor 22 and connectors can be constructed in a self-supporting fashion. However, if the conductor 22 does not include a reinforcing steel sheath or tension wire, the system may include reinforcing spiders for supporting each container and its conductor section at spaced intervals within the drill string. One spider 30 is illustrated in FIGS. 1 and 3 as being mounted at a joint 15 in the drill string 12 and serving to support the bottom container 26 and its associated cable.

As illustrated in FIG. 2, the container 26 is constructed in two tubular sections 27 and 28 adapted to be joined in end-to-end relation by means of a suitable fastener such as screws. Upper section 27 contains a first portion of coiled cable illustrated as 31 and lower section 28 contains a second portion of coiled cable 32. Coiled cable portions 31 and 32 are wound in opposite hands; that is, portion 31 is arranged in right-hand spiral and portion 32 in a left-hand spiral. The inner ends of coiled portions 31 and 32 are each secured to the inner wall of their respective sections 27 and 28 by bolt and clamp assemblies 33 and 34. The purpose of the clamp assemblies is merely to retain the cable 22 securely to the container 26 after the coiled portions have been paid out. The portions 31 and 32 arranged in opposite hands may be one continuous cable, but in order to facilitate loading the container, it is preferred that they be separate cable sections joined by connectors 35a and 35b. The coiled portions 31 and 32 being wound in opposite hands, upon being dispensed at about the same rate or alternately from their respective compartments, will prevent twists from forming in the conductor string 22.

Means are provided for controlling the dispensing of the coiled portions 31 and 32 of the cable from the container 26. A first cable clutch assembly 36 at the lower end of the container 26 is adapted to grip a straight portion 38 of the cable to retain the coiled portion 32 within lower section 28. Upon being actuated, assembly 36 permits stored cable to be fed out or dispensed from the lower end of container 26. As it unwinds, the cable passes through the clutch assembly 36 and thereby lengthens the conductor string 22.

A second cable clutch assembly 37, positioned in the upper end of container 26 retains coiled cable within section 27. Upon being actuated to a release position, assembly 37 permits cable to unwind and feed out the upper end of container 26. Thus, it is seen that the telemetry conductor is lengthened by cable being unwound from both coiled portions 31 and 32 and being fed out opposite ends of container 26. As noted previously, the portions 31 and 32, being wound in opposite hands, prevent the cable from twisting as individual coils are unwound at the same time or alternately.

As described in more detail below, the upper clutch assembly 37 is movable to its released position in response to actuation of the lower clutch assembly 36. In this embodiment, the lower clutch assembly is actuably responsive to tension in conductor 22. By pulling the conductor 22 upwardly at the surface, clutch assembly 36 releases which in turn causes the upper clutch assembly 37 to release.

As best seen in FIGS. 2 and 5, the lower clutch assembly 36 comprises gripping rollers 40 and 41 arranged within the lower end of container 26 such that the nip of the rollers engages straight portion 38 of the cable. Roller 40 serves as the main clutch and is mounted on bell crank 42. Roller 41 serves as a backup for roller 40 and is mounted on arm 43. Bell crank 42 and arm 43 are pivotally mounted to support member 44 which also supports guide roller 46.

A downwardly extending arm of the bell crank supports, in free-wheeling relationship, roller 40 while the other arm extends outwardly through opening 47 formed in the wall of container 26 and has an outer exposed end 50. The exposed end 50 is connected to rod 48 which interconnects the lower and upper clutch assemblies 36 and 37.

The bell crank 42 is urged inwardly forcing roller 40 to its normal cable engaging position by spring 49. Spring 49 is maintained in position by retainers 51 and 52 which are fastened respectively to the inner wall of container 26 and bell crank 42. Arm 43 supports roller 41 in free-wheeling relationship and is provided with stop 53 which determines the backup position of roller 41. Spring 45 maintains rollers 40 and 41 close together thereby maintaining the cable section properly at the nip thereof. Guide rollers 56 and 57 mounted on support member 58 are provided below the clutch assembly 36.

A brake assembly which forms part of the lower clutch assembly 36 is provided immediately below the coiled cable 32 in section 28 to prevent the coils from unwinding. This assembly comprises a back-up roller 61 eccentrically mounted on support member 62 which in turn is secured to the container 26. A spring loaded, cable engaging member 63 is urged toward the eccentric roller 61 and is also supported by member 62. The cable from coiled portion 32 thus passes downwardly between member 63 and eccentric roller 61, around guide 46, through the nip of rollers 40 and 41, between guide rollers 56, 57 and downwardly out the lower end of container 26. The lower terminal end of the cable is provided with a connector 64 which is adapted to mate with a connector provided in the conductor string 22.

As shown in FIGS. 2 and 4, the upper clutch assembly 37 comprises a cable gripping member 66 pivotally mounted to the upper section 27 as at 67. Member 66 extends through opening 70 of section 27 and has an outer end 75 disposed externally of container 26. Member 66 is adapted to grip an upper straight portion 69 of cable above coils 31 and is adapted to cooperate with back-up member 68 which is secured to the interior of section 27. As illustrated, members 66 and 68 are each provided with a grooved end for gripping cable portion 69. Cable unwound from coiled portion 31 passes through the nip of guide rollers 71 and 72, through the brake assembly 37, through an upper guide 73 which is secured to member 68. The upper end of cable portion 69 terminates in connector 76 which is adapted to mate with a connector of an adjacent cable section.

As mentioned previously, the upper clutch assembly 37 is actuated by the lower clutch assembly 36 through rod 48. Thus, tension in the conductor string above the container 26 caused by the weight of the cable and container or by pulling forces will not release coiled cable from section 27. Rod 48 is secured to the outer exposed ends 50 and 75 of members 42 and 66 and in effect forms a linkage between the two clutch assemblies. Rod guides 79 spaced along the exterior of container 26 maintains the rod in proper position.

In this embodiment the actuation of the lower clutch assembly 36 is by cable tension. In the relaxed position of the conductor string 22, the lower clutch assembly 36 is in the position generally as shown in FIG. 2. In the relaxed position the spring 49 forces roller 40 into gripping engagement with cable portion 38 forcing the cable and back-up assembly to the right stop position as viewed in FIG. 2. This prevents the cable from being pulled from the lower coiled section of the container 26. With roller 40 positioned in its normal gripping position, the brake member 66 of the upper clutch assembly 37 will also occupy the braking position through the linkage comprising bell crank 42 and rod 48. Spring 49 thus not only forces roller 40 into engagement with the cable between the nip of rollers 40 and 41 but also forces member 66 into forceful engagement with conductor portion 69.

An upward pulling force on conductor 22 imparts tension on the cable string which tends to straighten cable portion 38 between guide rollers 56, 57, and guide roller 46. This forces rollers 40 and 41 to the released position. Movement of roller 40 also moves clutch member 66 away from cable portion 69 releasing the upper clutch assembly. Releasing of the upper and lower clutch assemblies 36 and 37, permits cable to be dispensed from opposite ends of the container 26. For each loop of left-hand and right-hand coils dispensed, the container revolves one revolution thereby preventing twists from forming in the cable. The cable is dispensed by coiled portions being unwound and being fed through their respective clutch assemblies. As the cable is dispensed from opposite ends, for every left-handed wound coil a right-handed wound coil is released. Because of the eccentric roller 61, cable is dispensed intermittenly from the lower end. When the lobe of the eccentric roller 61 engages the cable portion 38, the braking forces increase so that the rate of cable being dispensed is reduced. However, once the lobe is forced past the engagement position on the cable, the cable passes through the brake with less resistance thereby increasing the rate at which it can be dispensed. The intermittent action of the brake on cable 38 causes the left-hand and right-hand coils to be unwound and dispensed from the container alternatively.

There are a number of commercially available cables that are sufficiently flexible to permit such cable to be coiled in the manner illustrated in FIG. 2. A particularly suitable cable is a single conductor 12 AWG neoprene jacket conductor sold by Vector Cable Company as B-5025.

In order to facilitate the insertion of the coil conductor within the container 26, it is preferred that the container 26 be constructed in two sections as described previously. The conductor may be installed within each tube section 27 and 28 by winding conductor on a suitable mandrel. The mandrel with the conductor wound thereon is inserted into a tube section as for example through the lower end of section 27. An upper portion of the conductor provided with connector 76 is threaded through the guide rollers 71 and 72, the clutch assembly 37, the guide 73, and finally out the upper end of section 27. A relatively long lead may be provided at this end. With the conductor properly positioned in section 27, the mandrel is turned in the opposite direction of the coils to release the grip of the coiled conductor, permitting the mandrel to be removed from the coils and section 27. The lower end of the coiled cable 31 is clamped to the wall of section 27 leaving connector 35a exposed. The same procedure is used in mounting cable portion 32 within lower section 28 except the coils in this section are wound in opposite hand relative to the coils in section 27. The lower lead extending from coiled portion 32 is threaded through the lower brake and clutch assemblies and may be provided with a relatively long lead extending below the lower end of section 28. As mentioned previously, the lower end of the cable terminates in connector 64. The upper end of the cable within tube section 28 is clamped to the interior wall thereof and the upper connector 35b is mated with the lower connector 35a of cable portion 32. The two tubular sections 27 and 28 are then fastened together and the rod 48 connected to the clutch assemblies 36 and 37.

It should be noted that each cable container is constructed such that there will be very little resistance to the flow of fluids therethrough. During the drilling operations, drilling fluid will be pumped down the drill pipe and will pass around and through the containers 26.

In describing operation of the present invention, it will be assumed that the borehole 17 has been drilled to a certain depth using conventional techniques and at this depth it is desired to commence drilling-while-logging operations. The drill string 12 and bit 13 attached thereto is lowered into the borhole 17 in the usual manner. The instrument 21 is lowered on cable 22 and located at the proper depth within the drill string 12. The upper end of the conductor 22 is provided with a cable clamp and connector 77. The clamp and connector 77 may be located in a spider 78 similar to spider 30 shown in FIG. 3 for supporting the upper end of the cable on the drill string. Since this initial section of cable may extend several thousand feet, it is preferably constructed of armored cable such as a single conductor 3/16-inch armored cable manufactured by the Vector Cable Company and sold as Type I-18P.

With the conductor 22 properly located in the drill string 12, a pipe section 81 provided with a cable container 26 may be added into the system. This may be achieved by the following procedure described with reference to FIGS. 6, 7 and 8.

Pipe section 81 with the cable container 26 therein is elevated by the rig hoisting equipment. The lower connector 64 is mated with connector 77 and pipe section 81 is then screwed into the top section of the drill string 12. The drill string and cable therein is lowered the length of pipe section 81 and again suspended in the rotary table 16 (see FIG. 7). The kelly 11 is then connected to the next pipe section 84 placed in the mouse hole 82 by threading the tail 24 of the kelly conductor into the pipe section 84 and screwing the kelly into the box end of pipe section 84.

This assembly is then elevated above the drill string 12 and the kelly cable 80 is mated with connector 76. The support plate 83 is then removed and the pipe section 84 is screwed into the box end of pipe section 81. It should be noted that because of the excess length of the conductor and the kelly, there will be some slack in the conductor within pipe joint 81. However, this slack will be removed by the addition of the next pipe joint to the drill string 12.

With the drill string 12 and conductor 22 lengthened, drilling may proceed for another length of pipe permitting the monitoring of drilling conditions as desired. The individual sections of drill pipe can be added in the same manner that pipe section 84 was added for each incremental advance of the borehole 17. During the addition of second and subsequent pipe sections, surplus cable is pulled from the coiled portions stored in container 26 permitting the lengthening of the conductor string 22 as the drill pipe 12 is lengthened. Each container 26 will be provided with sufficient amounts of surplus cable in the coiled configuration to accommodate several pipe joints. When the surplus cable is used up, a second container may be inserted into the conductor string 22. If the cable used in the containers does not have sufficient strength to support large loads, a spider may be provided at the upper end of the conductor. This spider may be inserted immediately prior to the addition of the next container and conductor section. The spider may be of the same construction as that illustrated in FIG. 3.

Drilling operations may proceed as described previously using a plurality of the containers 26 in the conductor string 22.

When it becomes necessary to interrupt drilling operations as for example to change bit 13, the conductor 22 which by this time may include several containers 26, may be removed by disconnecting the kelly 11 and kelly conductor 24 in the manner described previously. The cable sections and associated container may be individually retrieved. Each cable section is thus withdrawn from the drill string permitting the removal of the same length of drill pipe before the next cable section is withdrawn.

Although the present invention has been described with reference to specific types of equipment and cable, it should be realized that numerous modifications may be made without departing from the spirit of the invention. For example, the cable within each container 26 may be provided with internal tension members which increase the tensile strength of the material. In this type of construction, the spiders at the upper end of each cable section may not be required.

It should also be mentioned that the present invention may be used with drilling equipment other than that described herein. For example, it may be used in connection with turbodrills in positive displacement hydraulic motors. These devices normally include motor or turbine mounted on the lower end of the drill string and adapted to connect to the drive or bit. The motor or turbine powered by the drilling fluid drives the drill bit while the drill string remains stationary. When this type of subsurface drilling equipment is used in directional drilling operations, the present invention provides a highly useful means for transmitting directional data to the surface.

Claims

I claim:

1. Apparatus for use in an electric system employed in a pipe string to conduct electric signal between a subsurface location and a surface location, which comprises a container adapted to be inserted in said pipe string; an insulated electric conductor mounted in said container and having a first portion wound in left-hand coils and a second portion wound in right-hand coils, said conductor being adapted for connection into the electric system; first conductor gripping means for dispensing conductor from the lower end of said container; and second conductor gripping means for dispensing conductor from the upper end of said container, said first and second conductor gripping means being interconnected so that conductor is dispensed from opposite ends of said container at about the same rate.

2. Apparatus as defined in claim 1 wherein said first conductor gripping means includes a member urged into engagement with said conductor at a point below the coiled portions and wherein said second gripping means includes a member urged into engagement with said conductor at a point above the coiled portions, a linkage interconnecting said members whereby actuation of one member to its released position moves the other member to its released position.

3. Apparatus as defined in claim 2 wherein said member of said first gripping means is moved to the released position by tension in said conductor.

4. Apparatus as defined in claim 1 wherein one of said conductor gripping means is operatively responsive to tension in the conductor dispensed from said container.

5. Apparatus for maintaining electric circuit from a subsurface location to the surface which comprises: a container capable of being lowered into the pipe string, an electric conductor section having two coiled portions wound in opposite hands; one of said coiled portions being mounted in an upper section of said container and the other of said coiled portions being mounted in a lower section of said container; means for electrically connecting the upper coiled portion to a terminal above said container; means for connecting the lower coiled portion to a terminal below said container; a lower conductor brake normally positioned to engage said conductor at a point below said coiled portions and being movable to release said conductor; and an upper conductor brake normally positioned to engage said conductor at a point above said coiled portions and being movable to release said conductor, said upper conductor brake being movable to the release position in response to movement of said lower conductor brake.

6. Apparatus as defined in claim 5 and further comprising means for supporting said container on said pipe string.

7. Apparatus for insertion into a pipe string which comprises: a container having upper and lower coiled portions mounted therein, said coiled portions being wound in opposite hands and having upper and lower means for dispensing portions of conductor from opposite ends of said container, said upper and lower dispensing means being interconnected such that conductor is dispensed from opposite ends of said container at about the same rate.

8. Apparatus as defined in claim 5 wherein said container is free to revolve within said pipe string such that as coiled conductor is dispensed from its opposite ends, said container revolves preventing twists from forming in said conductor.