US3807502A

US3807502A - Method for installing an electric conductor in a drill string

Info

Publication number: US3807502A
Application number: US00350674A
Authority: US
Inventors: J Heilhecker; D Wood
Original assignee: Exxon Production Research Co
Current assignee: ExxonMobil Upstream Research Co
Priority date: 1973-04-12
Filing date: 1973-04-12
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30

Abstract

A method for installing an electric conductor in a drill string during drilling operations wherein an insulated electric conductor is lowered into the drill string and thereafter the drill string and conductor are lengthened as the borehole is advanced by adding lengths of pipe and conductor sections to the drill string and conductor, respectively.

Description

United States Patent [191 Heilhecker et al.

[ METHOD FOR INSTALLING AN ELECTRIC CONDUCTOR IN A DRILL STRING [75] Inventors: Joe Keith l-leilhecker; Donald Bayne Wood, both of Houston, Tex.

[73] Assignee: Esso Production Research Company,

Houston, Tex.

221 Filed: Apr. 12, 1973 211 App]. No.: 350,674

52 us. Cl 166/315, 166/65, 175/50, 339/16 51 Int. Cl. E2lb 47/12 58 Field 61 Search 166/315, 65; 17s/40-50, 104; 174/47 [56] References Cited UNlTED STATES PATENTS 2,096,279 10/1937 Karcher 174/47 [451 Apr.'30, 1974 2,339,274 1/1944 Kothny 1. 339/16 2,370,818 3/1945 Silverrnan 175/40 2,650,067 8/1953 Martin 175/50 2,748,358 5/1956 Johnston 339/16 3,285,629 11/1966 Cullen et al. 175/104 Primary Examiner-James A. Leppink Attorney, Agent, or Firm-Robert L. Graham ABSTRACT A method for installing an electric conductor in a drill string during drilling operations wherein an insulated electric conductor is lowered into the drill string and thereafter the drill string and conductor are lengthened as the borehole is advanced by adding lengths of pipe and conductor sections to the drill string and conductor, respectively.

12 Claims, 12 Drawing Figures PATNTEBAPR30 1914 SHEET 3 BF 4 wzOEbmm FIG.8

FIG. IO

METHOD FOR INSTALLING AN ELECTRIC CONDUCTOR IN A DRILL STRING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved method for performing wellbore telemetry operations. In one aspect it relates to a method for installing an insulated electric conductor in a pipe string used in rotary drilling operations.

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 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 has been that of providing reliable means for transmitting an electric signal between the subsurface and surface location. This problem can best be appreciated by considering the manner in which rotary drilling operations are normally performed. In conventional rotary drilling, a borehole is advanced by rotating a drill string provided with a drill bit. Lengths of drill pipe, usually about 30 feet long, are added to the drill string one at a time as the borehole is advanced in increments. In adapting an electric telemetry system to rotary drilling equipment, the means for transmitting the electric signal through the drill string must be such to permit the connection of additional pipe lengths to the drill string as the borehole is advanced. An early approach to the problem involved the use of continuous electric cable which was adapted to be lowered inside the drill string and to make contact with a subsurface terminal. This technique, however, required withdrawing the cable from the drill string 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. Ea'ch pipe section is provided with connectors which mate with connectors of an adjacent pipe section and thereby provide an electric circuit across the joint (see US. Pat. Nos. 3,518,608 and 3,518,609). Disadvantages of this system include the high cost of the special pipe sections, the need for a large number of electric connections (one at each joint), and the difficulty of maintaining insulation of the electric connectors at each joint.

SUMMARY OF THE INVENTION The purpose of the present invention is to provide an electric circuit between a subsurface location in a well and the surface. The invention permits the monitoring of a subsurface condition or the actuation of a subsurface instrument as drilling operations are in progress.

Briefly, the method involves lowering a drill string in a well by connecting a plurality of pipe sections together in end-to-end relation, lowering an insulated electric conductor in the drill string to extend from a subsurface terminal therein to the surface terminal, incrementally advancing the well a predetermined amount by manipulating the drill string, and for each 2' such advancement adding a length of pipe provided with an electric conductor section to the drill string to lengthen both the drill string and the electric conductor.

An important advantage of the method of the present invention over prior art techniques is that it reduces the number of connectors required in the conductor between the subsurface and surface terminals. The combined length of conductor sections need not exceed the length of one bit run which normally is between about and several thousand feet. This means that the portion of the circuit comprising the conductor sections will normally constitute only a minor fraction of the complete conductor. For most wells, the conductor installed in accordance with the method of the present invention will contain no more than about 30 connectors regardless of the depth of the well. The substantial reduction in the number of connectors increases the reliability of the electric circuit since each connector presents a potential source of failure. Moreover, the improved method permits the use of conventional drill pipe, which is less expensive than a string of pipe especially made for conducting electric energy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of well drilling equipment provided with an electric conductor installed within the drill string in accordance with the present invention.

FIG. 2 is an enlarged sectional view of a portion of the drill string shown in FIG. 1.

FIG. 3 is a transverse sectional view of the assembly shown in FIG. 2 with the cutting plane taken along line 33 thereof.

FIG. 4 is an enlarged exploded view, shown in longitudinal section, of a cable clamp and connector usable in the conductor shown in FIGS. 1 and 2.

FIG. 5 is an enlarged elevation, shown partially in section, of a connector for joining adjacent conductor sections.

FIGS. 6 and 7 illustrate the manner in which a pipe joint provided with a conductor section is added to the upper end of a drill string.

FIGS. -8, 9, and 10 are schematic illustrations showing the relationship of the continuous cable and cable sections for successive bit runs in a drilling operation.

FIG. 11 is a longitudinal sectional view of a cable connector capable of use in the present invention.

. FIG. 12 is a side elevation of a portion of the connector shown in FIG. 11.

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 between the bit 13 and kelly 11; and the term pipe string refers to the complete pipe column including the 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, either drill pipe or drill collars, connected together in end-to-end relation.

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 through a hose (not shown) attached to hose 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 arrangement.)

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 electric 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 a subsurface and surface location, it finds particularly advantageous application in a wellbore telemetry system such as that illustrated in FIG. 1 comprising an instrument 2], conductor 22, and receiver 23.

The instrument 21 capable of measuring a subsurface condition and generating an electric signal indicative or representative of that condition is mounted or adapted to be mounted in the drill string 12. A variety ofdevices 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 electric conductor 22 used to transmit electric energy between surface and subsurface locations and a method for installing the same. The energy 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, as mentioned previously, 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 electric pulses, or it can be transmitted by modulating the frequency or amplitude of the pulsating sig nal. 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 conductor.

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 insulated conductor 22 extends from a subsurface terminal on instrument 21 substantially through the drill string 12, and connects to a suitable surface terminal. The surface terminal in this preferred embodiment is provided by connector 25 of conductor 24. 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 connector 25 at that point. It is preferred, however, that conductor 24 be disposed within kelly 11 as illustrated in FIGS. 1, 6, and 7 and extend a short distance, e.g., one to three feet, below kelly 11 and have connector 25 at its lower end.

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 26 capable of transmitting electric energy from a rotating member to a stationary member. This device 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 27 and ground conductor 28 interconnect the stationary portion of device 26 and receiver 23. If telemetry operations are to be performed at times when the drill string 12 and kelly 11 are stationary, the

conductors

27 and 28 may be connected directly to conductor 24 through a suitable connector. in this situation,

conductors

27 and 28 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 one aspect, the present invention relates to a method for establishing electric continuity between a subsurface location in a well and maintaining electric continuity as the well is advanced. As noted above, the method employs an insulated electric conductor disposed internally of a drill string. The electric conductor will normally be installed after the well has been drilled to a depth where wellbore telemetry operations are to commence. This can be as shallow as a few hundred feet as in the case of directional wells, or several thousand feet deep. The initial step in the improved method is to lower a drill string in a well by connecting a plurality of pipe sections together in end-to-end relation. The drill sstring may be used to drill a well as it is lengthened, or the drill string may be simply lowered in a well already drilled. Next, a continuous electric conductor 30 (also referred to as cable 30 below) is lowered within the drill string 12 to extend from a subsurface terminal, e.g. instrument 21, to a surface terminal, e.g. kelly connector 25. As described in detail below electric continuity between the subsurface and surface terminals, is maintained by adding conductor sections to the continuous conductor 30 as the well is advanced and as the drill string 12 is lengthened.

The term continuous electric conductor or continuous electric cable as used herein means a length of wire or combination of wires suitable for carrying electric current. Preferably, the conductor is free of connectors, (except for its terminal ends) but as a practical matter it may be necessary to connect separate lengths of conductors together using electric connectors. A distinguishing characteristic of the continuous electric conductor is that it normally includes long spans of conductor lengths free of connectors and is electrically continuous which permits it to be lowered in the drill string in a single operation. Preferably, conductor 30 is provided by an armored cable. Armored cable has sufficient strength to permit the use of several thousand feet of cable and to support the instrument 21 during running-in operations.

The surface equipment for lowering the cable 30 in the drill string 12 can be similar to conventional cable handling equipment used in well logging operations. Such equipment normally includes a power winch having a cable wound thereon and a sheave suspended from the rig drawworks for guiding the cable into or out of the drill string 12.

With the instrument 21 properly located at the desired subsurface location preferably in a suitable sub immediately above the drill bit 13 the cable 30 extends internally through the drill string 12 and terminates in a connector 31 at its upper end.

In one embodiment of the invention (illustrated in FIGS. 1-7), the upper end of the continuous cable 30 is supported on a spider 32 or similar support secured to the drill string 12. After the continuous cable 30 has been lowered in the drill string 12, its upper terminal end provided with connector 31 is supported on the drill string 12 by means of spider 32. As described in detail below, spider 32 may be mounted in the box of a pipe section, e.g. pipe section 33, of the drill string 12 (see FIG. 2). Initially, connector 31 of cable 30 is mated with companion connector of kelly conductor 24 completing the electric circuit between instrument 21 and receiver 23. The kelly 11 is then attached to the drill string 12 placing equipment in condition for commencing drilling operations and permitting wellbore monitoring, if desired. If a cable of fixed length is used, it is possible that the connector 31 will not be located exactly opposite a box end of the top pipe section with the cable 30 properly positioned within the drill string 12. However, the length of drill string 12 can be made equal to the length of cable 30 by adding short pipe sections at the upper end of the drill string 12.

While drilling operations are in progress, the next pipe section, e.g. pipe section 34 shown in FIGS. 6 and 7, to be added to the drill string 12 is placed in a shallow borehole 35 (commonly referred to as mouse hole") below the derrick floor. A length of conductor section, preferably a cable section 36, is threaded through pipe section 34. Cable section 36 normally will be slightly longer than pipe section 34 and is provided with

connectors

37 and 38 at its opposite ends.

When the drilling has proceeded to the point that it becomes necessary to insert another pipe section in the drill string 12, the kelly 11 and drill string are elevated, the drill string 12 is supported in the rotary table 16, and the kelly 12 separated from the drill string 12.

Connectors

25 and 31 are manually separated and the kelly 11 is swung over into alignment with pipe section 34. Connector 25 is mated with the upper exposed connector 37 of cable section 36 and kelly 11 is screwed into the box of pipe section 34 (See FIG. 7); this assembly is then elevated above the drill string 12. The length of the cable section 36 is such that it extends a short distance, e.g. about one to three feet, below the lower end of pipe section 34, exposing connector 38. This connector is manually mated with connector 31 which again completes the circuit between the subsurface instrument 21 and the receiver 23. The pin of pipe section 34 is then screwed into the box of thetop pipe section 33 of the drill string 12. This operation lengthens both the drill string 12 and the conductor 22 which now comprises cable 30 and cable section 36.

Drilling operations are resumed and the subsurface condition monitored as desired. The individual sections of drill pipe can be added in the manner described above and illustrated in FIGS. 6 and 7 for each incremental advance of predetermined length of the borehole 17. It should be noted that a spider 32 need not be provided to support the upper end of each cable section. However, a temporary support plate may be employed to facilitate connecting the cable sections together. Such a plate provided with a radial slot can rest on the box shoulder and be adapted to support a connector thereon. After the connectors of adjacent cable sections are mated, the plate is removed.

Drilling operations will continue with the individual pipe sections 34 being added for each incremental advance of the borehole 17 in the manner described above. After drilling has progressed and a number of pipe sections and cable sections have been added to the system, the lower portion of conductor 22 will be provided by the continuous cable 30 and the upper portion by a plurality of cable sections 36 joined in end-to-end relation. This arrangement is illustrated in FIG. 1. Normally, drilling operations will continue in this manner until it becomes necessary to change the drill bit 13. The number of pipe sections and the number of cable sections 36 added during a particular bit run will thus normally be determined by the length of borehole the bit is capable of drilling. This varies within wide limits, but normally ranges from about feet for hard formations to several thousand feet for soft formations.

There are a number of cables commercially available that can serve as cable 30 and cable sections 36 in the present invention. A particularly suitable cable is a single conductor, three-sixteenths inch armored cable manufactured by Vector Cable Company and sold as type I-ISP. This cable is sufficiently strong to support long lengths; it has protective armor which guards against damage; and it is sufficiently flexible to facilitate installation.

Since the combined length of the cable sections 36 will normally be short, these sections in the preferred embodiment of the present invention need not be provided with protective armor. Suitable cable types include a single conductor, 12 AWG, neoprene jacket conductor sold as 8-5025 by Vector Cable Company. The length of each cable section 36 normally will be longer than the average length of pipe section used in the drill string to compensate for variations in the length of pipe sections. The excess length of each cable section also permits the cable to be twisted as pipe sections are screwed together. Moreover, the flexibility of this cable permits cable sections to be overlapped and clamped at the surface or otherwise adjusted to match the length of the pipe sections through which they extend.

As shown in FIGS. 2 and 3, the spider 32 for supporting the upper end of the cable 30 is sized to fit into a box end 40 of pipe section 33. Radial arms 41 rest on internal shoulder 42 of the box 40 and an opening 43 through the axial center of the spider 32 receives the upper end of cable 30. The spider 32 should be designed to minimize the flow restriction through box 40, particularly if internal upset drill pipe is used. A cable clamp 44 comprising

sleeves

45 and 46 anchors the armor of cable 30 as shown in FIG. 4. The cable 30 passes through the center opening of clamp 44. Wire strands 47 stripped from the armor pass around the upper sleeve 45, through suitable axial openings, and between clamping surfaces of

sleeves

45 and 46. Tightening the lower sleeve 46 on upper sleeve 45 thus firmly secures the wire strands. In the installed position, the clamp 44 is supported on the upper surface of spider 32.

The primary function of the spider 32 is to support the upper end of the cable 30 at a fixed location in the drill string 12. This permits the use of unarmored, flexible cable sections in the drill string above the spider 32.

In the embodiment of the invention described above, the connectors,

e.g. connectors

37 and 38, employed to join adjacent cable section 36 are preferably plug type connectors. Such connectors are easily installed, provide water-tight connections, and provide adequate strength. Connector 31 (cable 30), connectors 37 and 38 (cable sections 36), and connector 25 (kelly) may include identical female connectors such as those illustrated in FIG. 4. A double contact plug 50 which is detachable from both female connectors but may be considered a part of either provides electric continuity through each connection. As shown in FIG. 5, the

connection comprising connectors

37 and 38 for joining adjacent cable sections 36 also includes a double contact plug 53. For these connections, it is preferred that a locking sleeve comprising a pair of threaded

metal halves

51 and 52 be employed. The locking sleeve adds strength to the connection. In this regard, it should be noted that the connection for joining a cable section 36 to cable 30 does not include a locking sleeve. Thus, the cable sections 36 joined by connections with locking sleeves can be retrieved as a unit by pulling up on the top cable section 36. Connector 38 will pull free of connector 31 permitting the cable sections 36 to be withdrawn from the drill string in a single operation.

The conductor 22 described above is provided with a single conductor. In such a design, the electric ground circuit may be provided by the armor if armored cable is used to the surface, by the drill pipe itself, or by a combination of cable armor and drill pipe. Alternatively, the cable 30 and cable sections 36 and connectors may be provided with a plurality of conductors and contacts.

In describing the operation of the embodiment of the invention described above, 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 with bit 13 is lowered into the borehole 17 in the usual manner. The instrument 21 is then lowered on cable 30 and located at the proper depth within the drill string 12. The upper end of the cable 30 is provided with the cable clamp 44 and connector 31. The spider 32 is inserted on the cable 30 immediately below the cable clamp 44. This assembly is then seated in the box end 40 of the top section of drill pipe, e.g. pipe section 33. After the kelly connector 25 is mated with connector 31, the kelly 11 is screwed into the box end 40 placing the assembly in condition for drilling and logging. The borehole 17 is advanced in increments of predetermined length about equal to length of pipe to be added to the drill string. Lengths of pipe provided with cable sections 36 are added after each incremental advancement of the borehole in the manner described previously with reference to FIGS. 6 and 7. The cable 30 and drill string 12 are thus lengthened together as the borehole is advanced using conventional drill pipe.

As the drill string is lengthened and as cable sections 36 are added, excess lengths of cable will be introduced into the drill string since each cable section 36 will normally be slightly longer than its companion pipe section. Slack can be periodically removed from the conductor by pulling excess cable from the drill string at the surface, overlapping excess lengths, and clamping the overlapped cable in that configuration. Alternatively, spiders can be provided in certain pipe sections to prevent excess cable from accumulating and snarling within the drill string 12.

When it is desired to interrupt drilling operations, as for example when it is necessary to change the bit 13, the upper portion of the conductor 22 comprising a plurality of cable sections 36 may be retrieved by first disconnecting kelly 11 from the drill string 12, then separating kelly connector 25 from cable connector 37 of the top cable section, and finally reeling in the string of cable sections 36. Connector 38 secured to connector 31 of cable 30 pulls free separating the string of cable sections 36 from cable 30. The drill string 12 then can be withdrawn in the usual manner until the pipe section, e.g., section 33, containing the spider 32 is reached. The continuous cable 30 is then withdrawn by reeling it on a suitable drum. The remainder of the drill string 12 is then withdrawn in the conventional manner.

The drill string that was withdrawn from the borehole is provided with a new bit and rerun into the borehole. A second continuous cable 30 with instrument 21 attached to its lower end is then lowered through the drill string 12 to the instrument setting depth. The second continuous cable may be longer than the previous one by an amount about equal to the advancement of the borehole made by the previous bit run. A new cable may be employed for this purpose or a length of cable about equal to the advancement of the borehole may be attached to the first continuous cable 30. The equipment is assembled in the manner described above, and drilling and telemetry operations resumed. The cable sections 36 withdrawn from the drill string may be reused as individual lengths of pipe are added to the drill string 12.

An important feature of the invention is that the number of connectors required to maintain electric continuity from the subsurface terminal to the surface terminal need be employed only in a minor fraction of the total conductor. This is schematically illustrated in FIGS. 8-10. For purposes of illustration, let it be assumed that the well is about 5,000 feet where wellbore telemetry operations are to commerce; further, each bit is capable of drilling about 500 feet. During the initial bit run at this depth, the borehole is advanced from 5,000 to 5,500 feet. This advancement will be in increments about equal to the length of a pipe section, e.g. about 30 feet. The drill string 12 and conductor 22 are lengthened for each incremental advance in the manner described previously. At the end of the first bit run (see FIG. 8), the continuous cable 30 extends from about 500 to about 5,500 feet and the cable sections 36 connected in end-to-end relation by about 17 connectors (assuming 30-feet joints of drill pipe are used) extend from the top of the drill string 12 to about 500 feet. The drill string 12, and conductor 22, are withdrawn from the borehole and the operations repeated for a second bit run.

At the end of the second bit run (see FIG. 9), the second continuous cable 30 extends from about 500 feet to about 6,000 feet, or 500 feet more than the length of the first continuous cable; and the length of the cable sections 36 remains about the same, extending from the upper end of the drill string 12 to about 500 feet.

The operations are repeated for a third bit run which is illustrated in FIG. 10, showing the third continuous cable 30 now extending from about 500 feet to about 6,500 feet and the cable sections 36 extending from the upper end of the drill string to about 500 feet.

These operations may be repeated several times over; or wellbore telemetry operations may be interrupted for several bit runs and resumed at a later time. Of course it will be understood that there will be variations in the footage that each bit is capable of drilling; that is, some bit runs may be as low as 100 feet or may be as long as 1,000 feet and even longer. It also will be understood that the method is not limited to the drilling capability of the bit. For example, wellbore telemetry operations may be interrupted for reasons other than withdrawing the drill string or replacing the bit. In this regard, it should be noted that the apparatus disclosed in this preferred embodiment permits the cable sections 36 to be withdrawn from the drill string 12 enabling drilling operations to continue in the conventional manner.

A'comparison of FIGS. 8-10 reveals that lengths of the cable sections 36 remain about the same whereas the continuous cable 30 is lengthened for each bit run. Note that the combined length of cable sections 36 never exceeds the length of the continuous cable 30. This method thus permits a substantial reduction in connections required in the conductor over that required in many prior art techniques. In the above example, only 18 connectors were required in each of the three operations. If the cable 30 is lengthened after each bit run by adding a length of cable section equal to the length drilled by that bit run, one additional connector will be required for each successive bit run.

There are a number of arrangements capable of providing the conductor sections in the upper portion of the drill string 12. The conductor sections may be permanently mounted in the drill pipe joints such as those described in US. Pat. Nos. 3,518,608 and 3,518,609. Preferably, however, the conductor sections are provided by a cable section which can be threaded through each length of pipe to be added to the drill string.

The present invention also contemplates that the upper cable sections 36 may be provided by armored cable, in which case the connectors for joining adjacent cable sections must be adapted to anchor the armor as well as provide electric continuity across the connection. The use of armored cable joined by suitable connectors permits the entire conductor to be supported Y on the kelly cable 24, assuming, of course, that this cable is also armored and that connector 25 has sufficient mechanical strength to bear the weight of the entire conductor string 22.

One embodiment of an armored cable connector suitable for use in this second embodiment is shown in FIGS. 11 and 12. The connector assembly designated generally as includes a lower body section 56 and an upper body section 57, each having an axial passage formed therein for receiving the conductor and connectors. A lower cable section 36 which in this embodiment will be provided by armored cable extends upward into the lower end of the body section 56 and terminates in a female connector 62. Strands stripped from the cable section 36 pass through axial openings 58 formed in a clamping sleeve 60. The strands are anchored by means of nut 59 threadedly connected to collar 60. The anchoring assembly is maintained to the lower body section 56 by collar 61.

A bulkhead connector 63 is threadedly connected to the interior of the lower body section 56. The pin (not shown) of the bulkhead connector 63 extends downwardly and mates with the female connector 62. An 0- ring 64 positioned at the base of the bulkhead connector provides a fluid tight seal between the connector 63 and body section 56. A second bulkhead connector 65 is also threadedly connected to the interior of the lower body section 56 and is provided with an upwardly extending pin (not shown). This connector is also provided with an O-ring 66 at its base. An insulated conductor 67 interconnects the interior contacts of

bulkhead connectors

63 and 65.

A second, upper armored cable also illustrated as 36 in FIG. 11 extends downwardly into the upper body section 57 and is similarly provided with a cable anchor comprising sleeve 68, nut 69, and collar 70. The conductor wire of cable 36 extends through the upper body section 57 terminating in the female connector 71. Connector 71 is maintained in place by bushing 72.

The lower and

upper body sections

56 and 57 are separable and are adapted to be joined by coupling 73. Coupling 73 is mounted on the upper body section 57 for relative rotation thereon, and it is provided with internal threads adapted to mate with external threads formed on the lower body section 56. A spring-loaded locking sleeve 74 is also provided to insure that the parts are maintained in assembled relation. The locking sleeve 74 includes a lug 75 adapted to fit snugly into a complementary shaped recess 76 formed in the lower edge of coupling 73 (See FIG. 12). The locking sleeve 74 is mounted for relative axial movement on the body section 56. The connection between the locking sleeve 74 and body v56 may be splined or grooved so as to prevent relative rotational movement.

The female connectors 62 and 71 may be similar to those illustrated in FIG. 4.

During drilling operations, the cable sections 36 may be joined in the manner described previously with ref erence to FIGS. 6 and 7. With the upper cable section 36 positioned above an adjacent cable section (each cable section being provided with complementary halves of the connector assembly 55) the connector 71 is mated with the pin of bulkhead connector 65. The

coupling 73 is then screwed onto the lower body section 56, and finally the locking sleeve 74 which has been maintained in a retracted position, is moved upwardly until the lug 75 enters the recess 76 formed in the lower edge of collar 73. As cable sections 36 are added to the conductor 22, it may be necessary to remove slack from the conductor. This may be achieved by periodically overlapping a portion of a cable section to remove slack from the conductor and securing the overlapped portions; or by using spiders as described above.

Although the present invention has been described with reference to conventional rotary drilling operations, it can also be used with other types of drilling equipment including turbo drills and positive displacement hydraulic motors. These devices normally include a motor or turbine mounted on the lower end of the drill string and adapted to connect to and drive a bit. The motor or turbine powered by the drilling fluid drives the drill bit while the drill string remains stationary. When this type subsurface drilling device is used in directional drilling operations, the present invention provides a highly useful means for transmitting directional data to the surface.

I claim:

1. A method of establishing and maintaining electric continuity between a subsurface terminal in a well and a surface terminal which comprises:

a. lowering a pipe string in said well by connecting a plurality of pipe sections together in end-to-end relation;

b. lowering a first electric conductor in said pipe string to establish electric continuity between said subsurface terminal near the lower end of said pipe string and said surface terminal;

c. repeatedly advancing said well by an amount sufficient to require lengthening said pipe string;

d. for each of such advancements, adding a length of pipe to said pipe string and a conductor section to said first electric conductor.

2. A method as defined in claim 1 wherein said first electric conductor is substantially free of connectors.

3. A method as defined in claim 1 wherein said first electric conductor comprises armored cable.

4. A method as defined in claim 2 wherein each of said conductor sections comprises insulated electric cable free of armor.

5. A method as defined in claim 2 wherein the combined length of the conductor sections added according to step (d) is less than the length of said first conductor.

6. A method of establishing and maintaining electric continuity between a subsurface location within a well and the surface which comprises:

a. lowering in said well a pipe string comprising a plurality of pipe sections connected together in endto-end relation;

b. lowering in said pipe string a continuous electric cable to establish electric continuity from a subsurface terminal and a surface terminal; and

c. advancing said well in increments of predetermined length and for each incremental advancement, lengthening said pipe string and said electric cable by: threading a cable section through a length of pipe to be added to said pipe string;

connecting said cable section to the upper end of the cable in said drill string and said surface terminal; and

connecting said length of pipe into said pipe string.

7. A method as defined in claim 6 wherein the step of lowering said continuous electric cable in said pipe string includes supporting the upper end of said continuous electric cable on said pipe string.

8. A method as defined in claim 6 wherein the total length of cable sections added to the electric cable according to step (c) never exceeds the length of said continuous electric cable.

9. A method of drilling a well while maintaining an electric circuit between a subsurface location in said well and the surface which comprises:

a. lowering a pipe string in said well, said pipe string comprising a plurality of pipe sections;

b. lowering a first electric cable into said pipe string, said first electric cable establishing electric circuit between a subsurface terminal near the lower end of said pipe string and a surface terminal;

0. repeatedly advancing said well in increments sufficient to require lengthening said pipe string, and for each increment so advanced, lengthening said pipe string and electric cable in said pipe string by disconnecting said pipe string and separating electric cable at the surface, threading an electric cable section through a length of pipe, connecting said cable section with the electric cable in the pipe string to reestablish the electric circuit between said terminals, and connecting the length of pipe into said pipe string, the total length of said cable sections being less than the length of said first electric cable.

10. A method as recited in claim 9 and further comprising:

d. withdrawing said pipe string so lengthened, said first electric cable, and said cable sections from said well;

e. lowering said pipe string withdrawn in step (a) into said well; and

f. lowering a second electric cable into said pipe string, said second electric cable being substantially longer than said first electric cable and extending from a subsurface terminal near the lower end of said pipe string to a surface terminal; and

g. repeatedly advancing said well in increments sufficient to require lengthening said pipe string, and for each increment so advanced lengthening said pipe string and electric cable in said pipe string by disconnecting said pipe string and electric cable at the surface, threading an electric cable section through a length of pipe, connecting said cable section with electric cable in the pipe string to reestablish the electric circuit between said terminals, and connecting the length of pipe into said pipe string, the total length of said cable sections being less than the length of said second electric cable.

11. A method of maintaining an electric conductor within a pipe string used to drill a well which comprises:

a. lowering a continuous electric cable through a pipe string which comprises a plurality of pipe sections disposed in a well to provide an electric conductor between a subsurface terminal near the lower end of said pipe string and a surface terminal;

13 14 b. supporting the upper end of said cable on said pipe cable in said pipe string to extend said conductor g; and thereby reestablishing electric continuity berepeatedly advancing Said in increments of tween said subsurface and surface terminals, and predetermined fimoum; and inserting said length of pipe into said pipe to d. for each of said advancements, lengthening said lengthen Said pipe String pipe String and the electric conductor therein by 12. A method as recited in claim 11 and further addisconnecting said pipe string and separating electric cable contained therein at the Surface thread usting the length of at least one cable section used to ing flexible electric cable section free of protective extend Said electric conductor in Said Pip String to armor through a length of pipe to be inserted in the move ce s ack rom Said cable sections. pipe string, connecting said cable section with

Claims

1. A method of establishing and maintaining electric continuity between a subsurface terminal in a well and a surface terminal which comprises: a. lowering a pipe string in said well by connecting a plurality of pipe sections together in end-to-end relation; b. lowering a first electric conductor in said pipe string to establish electric continuity between said subsurface terminal near the lower end of said pipe string and said surface terminal; c. repeatedly advancing said well by an amount sufficient to require lengthening said pipe string; d. for each of such advancements, adding a length of pipe to said pipe string and a conductor section to said first electric conductor.

6. A method of establishing and maintaining electric continuity between a subsurface location within a well and the surface which comprises: a. lowering in said well a pipe string comprising a plurality of pipe sections connected together in end-to-end relation; b. lowering in said pipe string a continuous electric cable to establish electric continuity from a subsurface terminal and a surface terminal; and c. advancing said well in increments of predetermined length and for each incremental advancement, lengthening said pipe string and said electric cable by: threading a cable section through a length of pipe to be added to said pipe string; connecting said cable section to the upper end of the cable in said drill string and said surface terminal; and connecting said length of pipe into said pipe string.

9. A method of drilling a well while maintaining an electric circuit between a subsurface location in said well and the surface which comprises: a. lowering a pipe string in said well, said pipe string comprising a plurality of pipe sections; b. lowering a first electric cable into said pipe string, said first electric cable establishing electric circuit between a subsurface terminal near the lower end of said pipe string and a surface terminal; c. repeatedly advancing said well in increments sufficient to require lengthening said pipe string, and for each increment so advanced, lengthening said pipe string and electric cable in said pipe string by disconnecting said pipe string and separatIng electric cable at the surface, threading an electric cable section through a length of pipe, connecting said cable section with the electric cable in the pipe string to reestablish the electric circuit between said terminals, and connecting the length of pipe into said pipe string, the total length of said cable sections being less than the length of said first electric cable.

10. A method as recited in claim 9 and further comprising: d. withdrawing said pipe string so lengthened, said first electric cable, and said cable sections from said well; e. lowering said pipe string withdrawn in step (a) into said well; and f. lowering a second electric cable into said pipe string, said second electric cable being substantially longer than said first electric cable and extending from a subsurface terminal near the lower end of said pipe string to a surface terminal; and g. repeatedly advancing said well in increments sufficient to require lengthening said pipe string, and for each increment so advanced lengthening said pipe string and electric cable in said pipe string by disconnecting said pipe string and electric cable at the surface, threading an electric cable section through a length of pipe, connecting said cable section with electric cable in the pipe string to reestablish the electric circuit between said terminals, and connecting the length of pipe into said pipe string, the total length of said cable sections being less than the length of said second electric cable.

11. A method of maintaining an electric conductor within a pipe string used to drill a well which comprises: a. lowering a continuous electric cable through a pipe string which comprises a plurality of pipe sections disposed in a well to provide an electric conductor between a subsurface terminal near the lower end of said pipe string and a surface terminal; b. supporting the upper end of said cable on said pipe string; c. repeatedly advancing said well in increments of predetermined amount; and d. for each of said advancements, lengthening said pipe string and the electric conductor therein by disconnecting said pipe string and separating electric cable contained therein at the surface, threading flexible electric cable section free of protective armor through a length of pipe to be inserted in the pipe string, connecting said cable section with cable in said pipe string to extend said conductor and thereby reestablishing electric continuity between said subsurface and surface terminals, and inserting said length of pipe into said pipe to lengthen said pipe string.

12. A method as recited in claim 11 and further adjusting the length of at least one cable section used to extend said electric conductor in said pipe string to remove excess slack from said cable sections.