US3424257A - Device for automatic pulling and running of drilling string - Google Patents

Description

28, 1969 A. M. KOTLYAROV ETAL 3,424,257

DEVICE FOR AUTOMATIC PULLING AND RUNNING OF DRILLING STRING Filed May 5. 1966 Sheet or'ga' F/GJ 6 8, 1969 A. M. KOTLYAROV ETALY 3,424,257

DEVICE FOR AUTOMATIC PULLING AND RUNNING OF DRILLING STRING Filed May 5, 1966 Sheet 2 of 9 Jan. 28. 1969 A. M. KOTLYAROV ETAL 3,424,257

DEVICE FOR AUTOMATIC PULLING AND RUNNING OF DRILLING STRING Filed May 5, 1966 Sheet 3 of 9 Jam 28, 1969 A. M. KOTLYAROV ETAL 3,424,257

DEVICE FO AUTOMATIC PULLING AND RUNNING OF DRILLING STRING Filed May 5. 1966 Sheet 4 0f 9 0 DEA/N 7'0 DEA/IV Jan. 28, 1969 A. M. KOTLYAROV ETAL 3,

DEVICE FOR AUTOMATIC PULLING AND RUNNING OF DRILLING STRING Filed May 5, 1966 Sheet 5 Ora MAM/ 35 H Jan. 28, 1-969 A. M. KOTLYAROV ETAL 3,424,257

DEVICE FOR AUTOMATIC PU LLING AND RUNNING OF DRILLING STRING Filed May 5. 1966 Sheet 6 Jan. 28, 1969 A. M. KOTLYAROV ETAL DEVICE FOR AUTOMATIC PULLING AND RUNNING OF DRILLING STRING f 7 D DEA/IV Sheet 7- of 9 70 Dkn/A/ to ORA/N 28, 1969 A. M. KOTLYAROV ETALY 3,424,257 I DEVICE FOR AUTOMATIC PULLING AND RUNNING OF DRILLING STRING Filed May 5. 1966 Sheet 8 of 9 3 ELK I FIG. 8 W

Jan. 28, 1969 A. M. KOTLYAROV ETAL 3,

DEVICE FOR AUTOMATIC PULLING AND RUNNING OF DRiLLING STRING Filed May 5, 1966 Sheet of 9 United States Patent 18 Claims ABSTRACT OF THE DISCLOSURE A device for the automatic pulling and lowering of a drilling string comp-rising an elevator for gripping the uppermost section of a drill string and driven by a draw means which raises and lowers the elevator at a regulable speed; first and second engager means engage respective adjacent sections of the drill string to selectively unscrew or screw the uppermost section to the remainder of the string; the sections are fed to the string during running and removed from the string during pulling by a handling means. In order to successfully screw and unscrew the sections from the string, a sensing device determines the engagement of both the engager means with their respective sections when the joint between the sections is disposed between the first and second engager means. The control device for the draw means is interconnected with the first and second engager means, the handling means and the locating means such that sections can be automatically added to the string during running and removed from string during pulling.

The present invention relates to devices for automatic pulling and lowering of drilling strings in connection with the rotary method of drilling various purpose holes.

And more particularly, the preferable embodiment described herein'below relates to devices for automatic pulling and running of the drilling string :by a draw for drilling holes 2,000 to 7,000 meters deep.

In the known devices of this type, different working operations are not made fully automatic and as a rule involve manual labor which deduces the efliciency of the automatic working operations when pulling and running drilling string.

As is known, no full automation with the use of draw means for pulling and running drilling strings has ever been attained. Some attemps have been made to develop automatic devices without a draw means; in particular, some designs have been suggested providing for continuous pulling of the drilling string. But they did not provide full automation of operations and were hardly effective from the engineering and economic points of view.

"Dhere is known, for example, a drilling unit which provides for continuous pulling and running of the drilling string with these operations made automatic only along the axis of the hole.

It should be noted that continuous pulling and running of the drilling string involves a number of difficulties to be described below.

The method of continuous pulling and running cannot be implemented with the available equipment and requires different and absolutely novel types of arrangements. This method provides for fixing the gear for screwing and unscrewing the drilling string on the movable part of the .unit which cannot be used in heavy units characterized by high torgues.

Short stands of drill pipes with continuous pulling and running result in a greater number of screwing and "ice unscrewing operations, and thus in a waste of time and wear of tools.

The employment of a hydraulic draw means with screwing and of the drilling string involves great dynamic loads and thus does not warrant high pulling speeds. Under these conditions the speed will be within 0.51 m./sec., while a speed of 2.0-4.0 m./ sec. will be attained if a draw means is employed.

The above arrangement is not universal as it may be employed only with a flanged string precluding the possibility of using a plain string.

The aforementioned disadvantages are also typical of the known drill units providing for continuous pulling and running of the drilling string by means of a chain hoist when the drill pipe stands are stacked horizontally.

The employment of the chain hoist is unjustified due to a comparatively high cost of chains, inevitable .additional expenses or replacements in the course of operation; additionally the device itself is too complicated and heavy.

An object of the present invention is to provide an automatic device for pulling and running the drilling string without the afore-mentioned disadvantages. It is necessary to note the special importance of full automation of such a tedious and labor-consuming work as that of pulling and running the drilling string in deep holes. It should also be noted that full automation of pulling and running operations can substantially reduce the number of failures during drilling.

Another object of the present invention is to provide an automatic device for pulling and running which may be employed both in existing units or those under development.

Still another object of the invention is to provide an automatic device of the simplest possible design which is eflicient in use.

When creating the automatic device for pulling and running the drilling string described hereinafter the applicants proceeded from the principles explained below.

The sequence of operations in pulling and running, as well as the known equipment are revised and completed to provide for easiest automation.

The processes of pulling and running are intermittent, screwing and unscrewing being performed with the string fixed which provide for maximum speeds of pulling and running and for the simplest embodiment of the design and reliability of operation.

Some disadvantages inherent to a draw works are partially eliminated by additional elements relieving it of adjustments, the efiect of it being obvious to those skilled in the art.

The automatic device provides for employing sectionalized stands of a considerable length with a rather rough predetermined length tolerance, and may be employed with both flanged or plain pipe strings, i.e. being universal in this respect.

All gripping arrangements are characterized by selfwedging which provides for holding the string in suspension in the event of a drop of pressure in the hydraulic system.

The device is also provided with an arrangement for automatically halting the automatic system in case of failure or emergency, or when the automatic cycle is disturbed or for various auxiliary operations by remote control.

The automatic cycle is supplemented with conventional operation of the unit without its dismantling in case of emergency.

According to the invention the automatic devicefor pulling and running drilling strings is provided with an arrangement for the location of the joints of the drilling string at a definite level between the screwing/ unscrewing means. This is used to prevent different length stands of the drilling pipe coming into contact when pulling the drilling string from the well. The draw means is provided with an arrangement for controlling the speed of pulling and running, as well as for stopping said draw means. Said arrangement interacts with that used to locate the tool joints.

The object of this arrangement is to maintain the predetermined speeds of pulling and running with a short period of acceleration, constant speed on the major part of the travel, switching over to a lower speed prior to stopping or arresting the draw means at predetermined levels. Said arrangement is interlocked with a device for handling stands of drilling pipe as well as with an arrangement for holding the string in suspension and preventing it from rotation, i.e. provides for successive switching on and off of the working elements of said arrangements in due time. The device for holding the string in suspension and preventing it from rotation is in its turn interlocked with the screwing and unscrewing works of the drilling string. Said screwing and unscrewing means is fixedly mounted coaxially with the arrangement for holding the drilling string in suspension and preventing it from rotation so that the working elements can grip the drilling string preferably at its joints; said screwing and unscrewing means makes it possible to reduce the number of working elements as the arrangement for holding the string in suspension is at the same time used to prevent it from rotating when screwing and unscrewing, as well as to reduce the time of screwing and unscrewing operations since the time necessary for actuating the gripping elements of the screwing and unscrewing means and the arrangement for holding the drilling string is reduced. Besides it provides for the drilling string being gripped at its joints, thus preventing it from being crushed by the working elements and from unscrewing in an unwanted place. The elevator connected with the draw means passes through the mouth of the screwing/ unscrewing arrangement to grip the string at the upper face of the tool joint box thus makin it possible to use plain or flanged drill strings.

The preferable embodiment of the invention provides for a hoisting gear in the form of a draw means with hydraulic brake and travelling block systems.

The latter includes a block with an elevator moving along the guides, said elevator being provided with hydraulic gripping elements.

The gripipng elements of the elevator preferably have an independent source of supply. A hydraulic pump and a hydropneumatic accumulator are housed in the travelling block, the hydraulic pump being driven from a cable roller of the travelling block. The advantage of this embodiment is obvious as it allows to dispense with feeding cables or hoses moving together with the travelling block.

The travelling line of the draw means is provided with a tensioning arrangement for adjusting the elevator travel. The employment of this tensioning arrangement is preferable, as it relieves the draw works and simplifies the automatic cycle. Unless said tensioning gear is employed, the control of the draw works would be more complicated and the wear of brakes more rapid. Besides, the tensioning arrangement relieve the threads of the tool joints, and may be used for feeding the drilling instrument or for non-impact transfer of the load from the device holding the suspended string to the elevator.

The most preferable embodiment of the invention is that in which the screwing/unscrewing arrangement is mounted on the means which holds the string in suspension and prevents it from rotating. It is desirable to provide the screwing/unscrewing arrangement with a freedom of axial and radial movement with respect to the string to minimize the vibration of the string when a section is being screwed or unscrewed.

The device used to locate the joints of the string comprises an arrangement for non-contact signalling of the location of the joints at a level between the working elements of the screwing/unscrewing arrangement, and a signal pickup. The arrangement used for noncontact signalling is at some distance from the end portion of the pipe stand, while the pickup is built in the automatic device.

The arrangement for producing non-contact signals can be made in the form of a diamagnetic ring, for example, rigidly fixed on each section of the string near the end portion of the section, while the signal pickup can be made as an induction coil electrically connected with an electronic transducer unit. The embodiments of said arrangements may vary and may be based, for example, on the principle of radioactivity.

It is most preferable to locate the induction coil of the signal pickup between the screwing/unscrewing means and the means for holding the string in suspension.

The arrangement controlling the speed of pulling and running of the string as well as its arresting comprises: a centrifugal governor coupled to a drum of the draw means by means of a pair of gears, and a throttle used to adjust the pressure of the working fluid in the brake system of the draw works connected to said centrifugal governor by a lever. The centrifugal governor is connected to the electronic transducer unit of the signal pickup by an electric control system. A tachometer, or another arrangement of such type, may be employed instead of the centrifugal governor, the tachometer providing for greater stability in the zone of speed preceding the stop being more effective.

The automatic device is provided with an arrangement for handling stands of pipe so embodied that said stands of pipe are moved by the working elements of the device in the polar system of co-ordinates, which is simpler in design and makes the process of automation easier. The arrangement for handling the stands comprises an element which is rotatable about the vertical axis and carrying working elements fixed thereon. At least one of said working elements can reciprocate radially with respect to the axis of the rotatable element. A chute receives the stands and is provided with longitudinally aligned grooves disposed radially in relation to the vertical axis of the rotatable element.

The working members of the device for handling stands of the pipe are made as two friction grips adapted to engage the upper and the lower end portions of the stand of the pipe.

The working elements may also be made as friction grips for the upper end portion and a fork for holding the lower end portion of the pipe stand.

In this case it is necessary to have a special arrangement to grip the lower end portion of the stand and to center it along the axis of the well. This embodiment is preferable in all cases when the stand is engaged at its upper end portion. With very long stands of the pipe, additional arrangements may be used to center the stands along the axis of the well.

The automatic device also includes an arrangement for cleaning the string in the course of its being pulled out of the well, the device being preferably arranged above the screwing/unscrewing means. The device for cleaning the string is interlocked with the draw means. Cleaning of the string makes possible examination for the purpose of locating faults; cleaning of the threads, and it ensures clean conditions on the drilling platform.

The device is also supplied with an arrangement for lubricating the nipples of the section joints, the latter arrangement being interlocked with the arrangement for handling pipe stands and providing for the automatic lubrication of the nipples before the stands are fed to the axis of the well.

To ensure precise functioning of the automation system, a means for recording the completion of the screwing/unscrewing cycle is built into the interlock system of the screwing/unscrewing means. This may be embodied as, for example, an axial displacement sensing device of the screwing/unscrewing means. A time relay may be also be used for the purpose.

According to the invention the interlocking and release of all the arrangements and devices is effected by hydroelectric or electric sensors which provide for a fully automatic cycle, or, if necessary, a remote control as well as for its automatic stoppage in case of failure.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a front view of the device as employed in a spindle drilling rig with a hydraulic feed and a conventional derrick;

FIG. 2 is a side view of the device in FIG. 1;

FIG. 3 is a sectional view along the line AA of the device as shown in FIG. 2;

FIG. 4 is a sectional 'view along the line BB of the device as shown in FIG. 2;

FIG. 5 is a sectional view along the line CC of the device as shown in FIG. 2;

FIG. 6 is a diagrammatic illustration of a drilling rig with a hydraulic feed;

FIGS. 6a6e are detail views of respective portions of the rig of FIG. 6;

FIG. 7 shows the position of various stands of the pipe along the well axis for the automatic pulling cycle and the sequence of operations;

FIG. 8 is the same in the automatic running cycle;

FIG. 9 diagrammatically shows the string cleaning device; and

FIG. 10 diagrammatically shows a device for lubricating the thread of the tool joint.

On a derrick 1 which may be of various designs are mounted guides 2 carrying a travelling block 3 with an elevator 4 suspended on a cable 5 which passes around a crown block 6 mounted in the upper portion of the derrick, and a tensioning assembly 7 fastened to the rigidly secured end portion of the cable in the bottom portion of the derrick 1. The other end of the cable 5 is secured to a drum 8 of the draw works of the drilling rig 9, said drum 8 being provided with an automatic braking system 10 (FIG. 1, 2, 3).

Fixedly mounted above the well head is a first engager device 11 (FIG. 2) for holding a drill string constituted of threaded sections or stands of pipe in suspension and a second engager device 12 for screwing and unscrewing sections of the string during feeding or withdrawal of the string. The first and second engager devices are coupled together as an assembly. On one side of the derrick, approximately midway thereof is an arrangement 13 for handling stands of pipe (FIGS. 3, 4). Above the screwing/ unscrewing arrangement 12 at the base of the guides 2 is mounted an arrangement 14 for gripping the bottom portion of a stand and centering it on the axis of the well.

On the bottom working platform of the derrick 1 (FIG. 5) there are mounted an oil pump station 15, a panel 16 and a control board 17 of the automatic system, while on the upper working platform of the derrick (FIG. 3) is mounted an oil pump station 18 for the arrangement 13.

Auxiliary arrangements for cleaning the drilling string and lubricating the threads of tool joints are not shown in FIGS. 1-5.

FIG. 6 is a block diagram of a hydro-mechanical automatic system as employed in a spindle drilling rig with hydraulic feed and is a particular case of an embodiment corresponding to the device as shown in FIGS. 15. FIGS.

6a-6e are detailed views of the components of the system illustrated in FIG. 6.

A detailed description of each of the assemblies in operation is given below.

As shown in FIG. 6a a drill string 19 is provided with diamagnetic rings 20 made of aluminum, for example, and mounted at a distance from the end portion of the stands of pipe in the string. The afore-mentioned rings 20 serve as a means for a non-contact signalling of the tool joint location at a certain level. When pulling or withdrawing the string, the rings 20 interact with an induction coil 21 of a signal pickup placed between the arrangements 11 and 12. The coil 21 is electrically connected with an electronic transducer unit 21a. The electronic unit together with the coil 21 and a compensation coil positioned on the panel 16 (FIG. 1) serve to arrest accurately the travelling block 3 when pulling the string, as well as to count the stands of pipe. Travelling switches secured to the guides 2 of the travelling block 3 by means of an electromagnet 22 and a lever 23 are connected to a device for controlling the speed of pulling and arresting of the draw works, the latter being shown in FIG. 6b in an embodiment including the use of a centrifugal governor 24 connected by means of a pair of bevel gears 25 to the drum 8 of the draw works and via a lever 26 to a throttle 27 adjusting the pressure of the working fluid in the hydraulic braking system of the draw works.

To operate the draw works, two power cylinders 28, 29 are employed, one of which is located on the running and the other on the pulling brake. The oil is supplied by a pump 30 of the rig. A slide valve 31 is mounted on the pipe line coming from the pump which serves to supply working fluid either to the hydraulic system of the rig or to the brake system of the draw works.

When feeding or running the string down the well, the working fluid passes from the pump 30 via a set of slide valves, operated by electromagnets, to the throttle 27, and through a separate slide valve to the cylinder 28 located on the running brake. The fluid exerts a force on the piston of the cylinder 28 determined by the pressure in the system. Said pressure is controlled by the throttle 27 the slide valve of which, as mentioned above, is connected to the centrifugal governor through the lever 26. Said governor moves the slide valve of the throttle 27, thus maintaining the pressure in the system necessary to obtain such a braking moment that the string will be run at a predetermined speed; according to the setting of governor 24, the latter may be set for slow or fast speed and be switched over from one speed to the other by means of the electromagnet 22. Switching of the electromagnet 22 is effected by means of hte aforementioned travelling switches mounted on the guides 2.

When switching the corresponding electromagnets for pulling, the working fluid is fed into the cylinders 28, 29 via slide valves. The running brake is released while the pulling brake is set, the string being thus pulled at a speed determined by the operation of the drilling rig.

The maximum pressure in the system is maintained by means of a valve 32. The throttle 27 and the governor 24, when actuated, maintain the pressure necessary to build up a braking moment on the pulling brake and thus maintain the predetermined prior-to-stop speed.

The draw works is stopped by deactivating the electromagnets operating the slide valves, whereupon the working fluid will then pass from the cylinder 28 for dis charge through the slide valves under the effect of a spring 33. The working fluid from the cylinder 29 is also discharged by the operation of a spring 34. A pressure relay 35 in a hydraulic pipe-line of the draw works braking system serves for deactivation of the system in case of emergency, i.e. stopping the system when there is no pressure in the line.

As it was mentioned above, a tachometer may be employed instead of the centrifugal governor 24, but the principles of operation and control of the draw works remain the same.

As seen in FIG. 60, to grip the string when pulling or running, the elevator 4 is provided with hydraulically driven gripping members 36 moving in inclined grooves of the elevator 4 under the pressure of the working fluid actuating a piston 37. The elevator 4 may also rotate with respect to the travelling block 3 by means of its supporting bearings 38. A fluid piston pump 40 driven by a cable roller 41 is built in the travelling block 3 which slides over the guides 2 on rollers 39. Pump 40 drives the piston 37 and the gripping members 36 of the elevator 4. With the travelling block 3 in motion, the pump 40 supplies fluid to a hydropneumatic accumulator 42. The moment the travelling block 3 stops and the corresponding electromagnet is activated, the fluid from the accumulator 42 goes to one or the other chamber of the elevator cylinder 4 via a slide valve 43 controlled by a valve 44. The signal for opening the gripping elements 36 of the elevator 4 is given by a terminal switch 45. When one of the electromagnets is activated by a signal from the switch 45, the fluid from the accumulator 42 passes via the valve 44 to the other end portion of the slide valve 43 pushing the latter; thereby the main pipe line comes into communication with the line supplying the elevator 4 on the other side of the piston 37 which is thereby moved down and the members 36 grip the string. From the other end of the piston 37, the fluid passes to the elevator along passages 46 to a drainage tank 47.

The pressure built up at the end of the gripping process is recorded by a pressure relay 48 which signals the completion of the process.

The device 13 (FIG. 6d) for handling stands of pipe consists of a vertically rotatable unit 49 carrying working members 50 and 51 and a chute 52 for receiving the stands. A hydraulic cylinder 53 is employed to rotate the unit 49. As shown in FIG, 6d, the working member 50 can be subjected to a radial reciprocating movement with respect to the rotatable member 49 by means of a hydraulic cylinder 54, while the working member 51 is rigidly secured to the unit 49. In case the working members 50 and 51 are made with a friction grip, the working member 51 must also be driven with radial movement.

In the embodiment under consideration, the working member 50 is made as a friction element in the form of tongs 55 with a hydraulic cylinder 56 used to close or open said tongs. The tongs 55 can be driven vertically by a cylinder 57. The working member 51 is made as a guiding fork 58 for the bottom end of the stand.

The chute 52 for receiving stands has a lower member 59 and an upper member 60 with longitudinally aligned grooves 61 arranged radially with respect to the vertical axis of the rotating unit 49.

The arrangement 13 for handling stands of pipe is actuated by the oil pump station 18 having two pumps 62 and 63, one of which supplies cylinders 56 and 57 the other supplying the remaining cylinders including 64 and 65 which serve to limit rotation of the working members 50 and 51 together with the rotatable unit 49.

When the electromagnet 66 of a valve 67 is activated, the fluid from the pump 62 passes to the back chamber of the cylinder 56 to drive the piston thereof and close the tongs 55.

When the electromagnet 66 is deactivated and the magnet 68 of the valve 67 is activated, the chamber of the cylinder 56 is brought into communication with the drain line, and the piston is displaced by a spring 69 to discharge the fluid into a tank (not shown) which results in opening of the tongs 55.

When the tongs 55 are closed, the fluid in the cylinder 56 is retained by a non-return valve 70 which prevents the tongs 55 from self-opening. The signal for opening the electromagnets 66 and 68 is given by corresponding terminal switches and pressure relays. A terminal switch 71 opening the tongs 55 and a pressure relay 72 closing them produce signals for continuim the operation and for deactivating the electromagnets 66 and 68.

The vertical movement of the tongs 55 is effected by the cylinder 57 and is performed in a similar manner (FIG. 6d).

The cylinder 54 which radially moves the working member 50, operates at two speeds when pulling or running the string: high forward and reverse and slow forward and reverse speeds. Two reversible electrically controlled slide valves 73, 74, two throttles 75, 76 and a reversible valve 77 are employed for this purpose. When the slide valves 73, 74 are operated, the fluid from the pump 63 passes to the chamber of the cylinder 54. Since the throttle 76 is set so that the speed is high, and the throttle 75 is set for a low speed, the piston of the cylinder 54 moves forward fast. To avoid impact when the tongs 55 approach the stand 19, terminal switches for producing a signal for deactivation of the slide valve 74, are placed in the path of travel of the piston of the cylinder 54.

With the slide valve 74 operates, the fluid passes through the slide valve 73, throttle 75 and 76, while the piston of the cylinder 54 moves forward at a slower speed. With the slide valve 73 actuated, the fluid passage to the cylinder 54 is terminated and the piston is stopped.

To bring the piston of the cylinder 54 to its initial position, the slide valves 73 and 74 are switched over to the opposite extreme positions, the supply line is cut oif and the supply line to the cylinder 54 is switched over for draining. Under the effect of a weight 78, the piston of the cylinder 54 starts moving to the initial position, thus forcing the fluid out the cylinder chamber. As the fluid passes to the drain tank (not shown) through the throttle 76, the piston of the cylinder 54 moves at a higher speed.

To bring the piston of the cylinder 54 backwards at a slow speed, the slide valve 74 is pushed to the left and the fluid passes to the drain tank through the throttles 75, 76 and the slide valve 73. The pressure in the system is controlled by means of a safety valve 79.

The signals for switching the electromagnets of the slide valves 73 and 74, as well for continuing the operation are produced by corresponding terminal switches and pressure relays.

The unit 49 together with the working members 50 and 51 is turned by means of the cylinder 53 from the chute 52 for receiving the stands 19. To achieve this an electromagnet 80 of a control valve 81 is activated, and the fluid from the pump passes to the rod chamber of the cylinder 53 thus turning the working members 50 and 51 towards the well.

To turn the working elements 50 and 51 in the opposite direction, i.e. towards the chute 52 to receive the stands, an electromagnet 82 of the control valve '81 is activated and the fluid passes to the other chamber of the cylinder 53, thus turning the unit 49 in the opposite direction. Said electromagnets are switched by corresponding terminal switches.

In the process of operation, the arrangement 13 for handling the stands 19 may be in one of four pre-determined positions:

(a) An extreme right position with respect to the axis of the well, which is fixed by a stationary stop 83 with a terminal switch 84;

(b) Three predetermined positions in the grooves 61 of the chute 52 for receiving stands, with the position in the extreme left groove being fixed by a stationary stop 85, and in the other two grooves by the rods of two hydraulic cylinders 64 and 65, serving as stops and controlled by valves 86 and 87.

When one of the electromagnets of the control valves 86 or 87 is activated, the fluid is fed from the pump 63 to the chambers of the cylinder 64 or 65 to move the associated piston against the action of spring 88 or 89 thereby extending one or the other stop. Upon switching over of the control electromagnets 86 or 87, the chambers of the cylinders 64 or 65 are communicated with the drain tank. The electromagnets 86 and 87 are controlled by terminal switches.

The device 12 for screwing/unscrewing the string is mounted on the arrangement 11 for holding the string in suspension (FIG. 60). Working members 90 of the device for screwing/ unscrewing the string can perform axial movement as well as a radial movement with respect to the axis of the well in order to compensate the vibration of the string when being screwed and unscrewed. The working members 90 provide for the pasage of the elevator 4 to grip the string at the upper end portion of the joint 91 of the joint box. Working members 92 of the arrangement 11 for holding the string in suspension may be axially moved by a surge damper 93, and, if necessary, may be positioned so that a drilling bit may be passed through when pulling out the string. The working members 92 are actuated by means of hydraulic cylinders 94 and 95 which in turn are operated by a reversible electrically controlled slide valve 96, a throttle 97 and a slide valve 98 controlled by a cam 99 and two pressure relays 100 and 101.

When the slide valve 96 is moved to the right, the fluid is fed from a pump 102 of a set of oil pumps into the rod chambers of cylinders 94 and 95 thereby moving their pistons, which by means of a conical ring 103 actuate the working members 92 gripping the string. From the chambers of the cylinders 94 and 95, the fluid can be discharged via the slide valve 96. The moment the working members 92 grip the string, the pressure in the system builds up rapidly, which is sensed by the pressure relay 100, the latter signalling cut off of the slide valve 96 and continuation of the process by another working arrangement.

To release the working members 92, the slide valve 96 moves to the left and the fluid passes from the pump 102 to the other chambers of the cylinders 94 and 95, whereby the pistons of said cylinder move downwards and release the working members 92 of the conical ring 103. At the end of the stroke, the ring 103 actuates the cam 99 of the slide valve 98, and produces communication between pressure relay 101 with the delivery line. The increase in the pressure of the system at the end of the stroke of the ring 103 actuates the pressure relay 101 which causes deactivation of the slide valve 96 and continuation of the process by means of another working arrangement. From the opposite chambers of the cylinders 94 and 95 the fluid is discharged. The throttle 97 is mounted to control the supply of the fluid to the arrangement 11 which allows control of the speed of the working members 92.

The electromagnets of the slide valve 96 are switched on and off by pulses transmitted by the coil 21 of a signalling arrangement and corresponding pressure relays.

The arrangement for screwing/unscrewing the string is of static action and made as a modified Foster key.

To actuate the working members 90 which eflect screwing and unscrewing of the threaded joints of the string there are employed: a hydraulic motor 104 and a hydraulic cylinder 105 of a post brake 106 of the screwing/ unscrewing arrrangement 12 which are operated by two electrically controlled reversible slide valves 107 and 108 and a slide valve 109 controlled by a cam 10 as well as by throttles 111 and 112. The system is provided with pressure relays 113 and 114 and two reversible valves 115 and 116.

A high pressure gear pump 117 (FIG. 6e) is employed to develop the necessary torque on the arrangement 12 the moment the threaded pipe joint starts moving.

We shall now consider the processes of screwing and unscrewing.

When the slide valve 108 is moved to the left, the fluid passes from the pumps 102 and 117 to the hydraulic motor 104 which is thus started. The motor 104 rotates at a slow speed since the fluid is drainedotf through the slide valve 108 and the throttle 112 is adjusted for a low consumption of the fluid. At the same time the fluid from the pump 102 passes, via the slide valve 118, to the chamber of the post brake 106 thus closing the latter. Therefore, with the motor 104 rotating and the brake 106 operative, the working members 90 are brought together until they grip the joint of the string.

At the moment the working members 90 grip the joint of the string the pressure in the system starts building up.

' This is recorded by the pressure relay 113 which causes activation of the slide valves 107 and 118. At the same time a timer is switched on (not shown) the setting of which is determined by the time necessary for complete unscrewing of the threaded joint. The slide valve 113 moves downwards, thus producing communication between the rod chamber of the cylinder of the post brake 106 with the feed line and the chamber with the drain.

The brake 106 of the screwing/unscrewing arrangement 12 is released while the sliding valve 107 moves to the extreme right position to drain the fluid from the motor 104 through the throttle 111 adjusted to a greater consumption of the fluid than the throttle 112.

With the release of the brake 106 at the maximum increase in pressure, the fluid is passed to the motor 104 by the pump 117 only. With the beginning of unscrewing, the torque decreases, the pressure in the system of the pump 117 drops, the pump 102 is re-engaged with the pump 117 and owing to the rapid draining of the fluid from the motor 104, the threaded joint is quickly unscrewed.

To determine the completion of the unscrewing cycle an axial displacement sensor unit, consisting of said slide valve 109 controlled by the cam and the pressure relay 113, is mounted on the screwing and unscrewing arrangement 12.

When being unscrewed, the stand 19 tarts moving upward along the thread entraining the working members 90 which press on the cam 110 through a tappet 119 thus providing communication between the supply line and the pressure relay 113. The impulse of the pressure relay 113 registering the moment the thread of a nipple 120 and the joint box 91 are disengaged, and the impulse sent with the operation of the time relay (not shown) at the beginning of unscrewing, cause deactivation of the slide valves 107 and 108 and activation of the slide valve 108 which having travelled from the left to the right position will reverse the motor 104; the slide valve 118 moving upwards will thus change the chambers of the cylinder 105, i.e. the brake of the arrangement 12 will be closed. The working members 90 are then drawn apart and reaching their extreme position will cause an increase in pressure which will be registered by the, relay 114, the latter sending an impulse to the set of the slide valves to switch the pump 117 todischarge. To perform the operation of screwing, the slide valve 108 is moved to the left, and a safety valve 121, which was switched off during unscrewing, is now switched on. The hydraulic motor 104 starts rotating at a slow speed as the fluid is drained through the throttle 112, and the post brake 106 of the screwing/unscrewing arrangement is set thus bringing together the working members 90.

Upon engaging the tool joints of the string, the working members 90 cause an increase in the pressure which is registered by the relay 114 switching ofl the slide valves 107 and 118. At the same time the post brake 106 is released, the fluid is drained through the throttle 111 and the threaded joint is quickly engaged.

While the string 19 is threadably engaged, it is lowered thus actuating the axial displacement sensor unit of the working members 90.

The pressure of the fluid in the relay 113 and the increase in pressure in the system of the pump 117 registered by the relay 114 make it possible to transmit the impulse for switching off the slide valves 118 and 107 and for switching over the slide valve 108 which results in releasing the working members 90 on completion of the threaded engagement, said releasing being similar to that in the process of unscrewing.

The arrangement 14 for gripping the bottom portion of the stand 19 and for aligning it with the axis of the well is mounted in the base of the guides 2 and is actuated by two hydraulic cylinders 122 and 123 having slide valves 124' and 125 controlled by eccentric cams 126. To control the arrangment 14, the set of oil pumps 15 is provided with two electrically controlled slide valves 127 and 128. The speed of the arrangement 14 is controlled by a throttle 129 mounted on the supply line.

In the process of operation, the working members 130 of the arrangement 14 may occupy one of the three positions: a first inclined position to grip the bottom. part of the string, a second horizontal position to center the latter, and a third vertical position to let the travelling block pass. By moving the slide valve 127 to the lower position, the fluid is fed from the pump 102 to the rod chambers of the cylinders 122 and 123 via the throttle 129, whereby the working members 130 are brought from the vertical to the inclined position. The fluid is drained from the chambers of the cylinders 122 and 123 via the slide valves 124 and 125. With the working members .130 moving downward, the eccentric cams 126 push the slide valves 124 and 125 to the lower position, thus interrupting the fluid draining from the chambers of the cylinders 122 and 123, while the working members are stopped in the inclined position. The working members 130 are prevented from undergoing impact while moving by the provision of throttles with non-return valves (not shown) on the lines running to the chambers of the cylinders 122 and 123. When the working members 130 are moving, the fluid from the chambers of the cylinders 1'22 and 123 is drained at different speeds due to a throttle, for example, in the drain line of one of the cylinders and a non-return valve in the other.

The working members 130 are brought into the horizontal position by the fluid delivered into the rod chambers of the cylinders 12-2 and 123 by means of said slide valves 127 and 128, and into the vertical position by supplying the fluid to the chambers of the cylinders 122 and 123 via the same slide valves.

The tensioning device 7 (FIG. 62) mounted on the rigidly secured end portion of the cable 5, has a frame 131 with two carriages 132 and 133 mounted therein which can move in opposite directions, each of said carriages being provided with a set of cable rollers 134. The carriages 132 and 133 are actuated by hydraulic cylinders 135 and 136. The cylinders 135 and 136 are controlled by three electrically controlled reversing slide valves 137, 138 and 139. As has been previously mentioned, the tensioning device 7 is used for adjusting the travelling 'block 3 and the elevator 4 When the draw works is not operated. The travelling block 3 and the elevator 4 may be adjusted by moving each of the carriages 132 and 133, each carrying a set of the cable rollers 134.

When raising the travelling block 3 with the carriage 132 of the tensioning device 7, the slide valve 138 moves to the left and the fluid passes from the pump 102 to the chamber of the cylinder 135 thus actuating the piston of said cylinder 135, moving the carriage 132 of the tensioning device 7 upwards, thereupon raising the travelling block 3 and the elevator 4. The terminal switches 140 and 141 transmit impulses for switching off the slide valve 138 when it is in its extreme upper position.

The travelling block 3 and the elevator 4 are lowered by the carriage 133 of the tensioning device 7 when the slide valve 138 moves to the extreme right position, said slide valve providing communication between the chamber of the cylinder 135 and the drain line. Under the weight of the travelling block 3 and the elevator 4, the carriage 132 moves downwards. When the slide valve 138 is shifted to the neutral position, the fluid passage to the cylinder 135 is interrupted. Said neutral position corresponds to the stop position of the carriage 132.

When necessary, the travelling block 3 and the elevator 4 can be raised by the carriage 133 of the tensioning device 7. T do this the slide valve 137 must be shifted to the left, whereupon the fluid will pass from the pump 102 to the chamber of the cylinder 136, and the carriage 133 will go down, while the travelling block 3 and the elevator 4 will move upwards. The carriage 133 is stopped in the extreme position by an impulse sent by the terminal switch 142. The travelling block 3 is lowered as a result of the slide valve 137 being shifted to the right. The process then proceeds in a manner similar to that of the carriage 132.

In the above described cases there have been described relatively fast lowering and raising of the travelling block 3 with the elevator 4.

To perform slow lowering, a delivery slide valve 143 and a throttle 144 are mounted in the drain line of the slide valve 139. The throttle 144 is adjusted to a slow speed for lowering the travelling block 3, while the delivery throttle 143 is adjusted to the pressure developed in the hydraulic cylinder 136 of the carriage 133 under the weight of the travelling block 3 with the elevator 4, and the string 19. When the string 19 is positioned on the end portion of the joint box 91 inside the arrangement 11 for holding the string in suspension, a part of said weight will be resisted by the joint box 91, the pressure in the cylinder 136 will drop and the slide valve 143 will thus go to its lower position and block the drain line; thereby the travelling block will stop lowering. The switching over of the travelling block with the elevator 4 from fast to slow lowering is effected by means of an impulse of the terminal switch 145 which is actuated by the carriage 133 when moving upwards. Then the slide valve 139 is brought to the left position, switching on the corresponding time relay. The slow lowering achieved in this way will be over when the delivery valve 143 operates.

The arrangements for cleaning the string and lubricating threaded joints (FIGS. 9, 10) are auxiliary and are not shown in FIG. 6; their operation will be described hereinafter.

The arrangement for cleaning the string (FIG. 9) in the process of pulling the latter, is a hollow ring 146 with internal nozzle openings 147. The ring 146 is fixed over the arrangement 12 for screwing/unscrewing the string and is connected through a pipe-line 148 with an air or steam supply source. The arrangement is put into operation by an electromagnetic control valve 149 interlocked with the device for starting the draw works (not shown in the drawings) accommodated in the panel box 16. The string is cleaned during the entire cycle of pulling. The arrangement for lubricating the thread of the nipple 120 (FIG. 10) has a hollow ring 150 perforated on its internal tapered face, embracing the thread of the nipple 120 and provided with a centering cylindrical casing 151 and a cone 152 for gripping the bottom end portion of the string (stand of pipe) 19.

The ring 150 is secured on a platform 153 which can be vertically moved in guides 154 by means of a hydraulic cylinder 155.

The interior of the ring 150 is connected, through a pipe line 156, to a piston pump 157 which is housed in a tank 158 filled with lubricant and driven by a hydraulic cylinder 159. The arrangement for lubricating is set in the initial position by the gear 13 for handling stands of pipe and is interlocked therewith by means of switchgear elements in the panel box 16. When the platform 153 is raised and the terminal switch closed, the cylinder 159 is activated and the pump 157 delivers a portion of lubricant; thereupon the cylinder 159 of the pump 157 lifts the piston to the initial position and the platform 153 with the ring 150 moves downwards thus releasing the bottom end portion of the stand which is being moved towards the well.

The folowing is the description of an operation of the units of the automatic plant in the process of operation (FIGS. 6, 7, 8).

Prior to starting the automatic performance cycle, all the arrangements and devices of the automatic plant should be set by means of buttons on the control panel 17 in the following initial positions:

(a) the cylinder 54 and connected thereto the working member 50 of the arrangement for handling the stands 13 (strings) should be retracted and turned in the direction of the axis of the well;

(b) the working members 130 of the arrangement 14 for centering the string (stand) should be brought into the upright position;

(c) the travelling block 3 should be raised close to the terminal switch 161;

(d) the gripping members 36 of the elevator should be disengaged;

(e) the carriages 132 and 133 of the tensioning device should be disengaged;

(f) the working members 92 of the device 11 holding the string in suspension should be engaged;

(g) the tongs 55 of the working members 50 of the arrangement 13 for handling the stands should be drawn apart.

Additionally, during the running (i.e. lowering) cycle the tongs 55 should be lowered and the working members 90 of the screwing/unscrewing arrangement 12 should be drawn apart counter-clockwise. During the pulling cycle, the tongs 55 are raised and the working members 90 of the arrangement 12 are drawn apart clockwise, the cylinder 28 of the running brake is activated and the cylinder 29 of the pulling brake is deactivated; the electric motors of all the pumps and of the drilling rig 9 are switched on; the drilling rig 9 is in its rear position, i.e. retracted from the well head.

The automatic cycle is started by pressing the start button on the panel 17.

By pressing the start button in the running cycle, the cylinder 54 together with the working members 51 are turned to the receiving chute 52. At the end of the turn the switch 162 deactivates the turning cylinder and activates the cylinder 54 which moves the tongs 55 into the receiving chute 52. At the end of this motion, the switch 163 is closed to lower the rate of stroke of the piston of cylinder 54. Thereafter the piston of the cylinder 54 is brought to a stop, and the cylinder 56 brings the tongs 55 together.

With the tongs 55 thus set, the relay 72 is activated causing the tongs 55 to be raised by the cylinder 57 and the cylinder 54, to leave the chute 52.

At the end of the stroke of the cylinder 54, its speed is reduced. In the rear position the switch 164 causes the cylinder 54 to stop and activates the mechanism which turns the cylinder towards the axis of the well. The operation of the switch 84 terminates the turning of the cylinder at the axis of the well.

The preliminary operations are thus completed, and the first automatic cycle is started.

The cylinder 54 holding the stand 19 with the tongs 55 brings it to the well. Simultaneously the arrangement 14 is activated and its working members are set in the inclined position. When the stand 19 reaches the well, the switch 165 deactivates the cylinder 54 and activates the carriage 132 of the tensioning device 7 and the arrangement 14 for lowering.

After the carriage 132 of the tensioning device 7 is lowered, the travelling block 3 is lowered and set onto the stand. This sequence of operations is shown in FIG. 8 (positions I and II). The terminal switch 166 sends an impulse to the elevator 4 to grip the stand. When the stand is gripped by the members 36 of the elevator 4, the pressure relay 48 starts releasing the tongs 55. Then the switch 71 causes the tongs 55 to be lowered by means of the cylinder 57 and the cylinder 54 to be moved away from the well. Upon approaching the switch 164, the latter turns the cylinder 54 to the chute 52. Thereupon the arrangement 13 repeats the entire cycle and also transmits an impulse to other arrangements to operate after the cylinder 54 with the tongs 55 has left the zone of operation of the travelling block 3.

The switch 167 sends a command for lowering the travelling block 3 with the stand 19 (position III, FIG. 8) by means of the carriage 133 of the tensioning device 7 until said block reaches the switch 145. Following a certain delay in time the travelling block 3 comes to a stop and the working members of the arrangement 12 are activated for threadably engaging the pipes (position IV, FIG. 8). The working members 130 of the arrangement 14 are at that time in their upright position. 7

After engaging the working members 90, the relay 114 releases the brake 106 of the arrangement 12 and increases the speed of the motor 104 for screwing on. Then the relay 114 as well as the sensor unit of axial displacement of the working members 90 start operating and the post brake 106 is released. When the working members 90 are disengaged, the relay 114 sends an impulse for moving the working members 92 of the device 11 apart to release the string. Thereafter the relay 101 sends an impulse for lowering the travelling block together with the string. When approaching the lower position, the speed is reduced due to the operation of the switch 168 (position V, FIG. 8). When in the lower position, the travelling block is stopped by the switch 169 which then closes the working members 92 (position VI, FIG. 8).

When the working members 92 are closed, the pressure relay sends an impulse for drawing apart the gripping members 36 of the elevator 4. Thereupon the switch 45 activates the travelling block 3 for hoisting by means of the automatic braking system 10 of the drum 8 of the draw works as well as both carriages 113-2 and 133 of the tensioning device 7 (position VII, FIG. 8).

The carriage 1132 is stopped in its upward travel by the switch 141, and the carriage 133 in its downward travel by the switch 142, the draw works pulling up by means of activation of the pulling brake (the cylinder 29) of the system 10 by the switch 161.

As the travelling block 3 approaches its upper position, the switch 170 starts reducing the speed of pulling.

With the start of the automatic operation of the pulling cycle the travelling block 3 starts going downwards by the operation of the braking system 10 as well as by the carriages 132 and 1133 of the tensioning device 7.

The changeover of the speed of the braking system and of the arrangement for handling the stands is performed by the same terminal switches as in the running cycle. Therefore the procedure of changing over the speed is not discussed hereinbelow.

At the end of downward travel, the switch 169 not only stops the downward travel of the travelling block 3, but also sends an impulse for closing the gripping members 36 of the elevator 4, after which the relay 48 draws the working members 92 apart, whereupon the pressure relay 101 opens the pulling brake (cylinder 29) and the drum 8 of the draw works raises the string (positions I, II and III, FIG. 7).

Pulling of the string is completed when the device locating the tool joints is activated, said device sending an impulse for closing the working members 92 of the device 11 holding the string.

When the members 92 grip the joint of the string, the pressure relay actuates the working members 90 of the arrangement 12 (position IV, FIG. 7) to unscrew the stands of the string. When unscrewing is completed, the pressure relay 114 causes the travelling block 3 with one stand to travel somewhat upwards, which is effected by the upper carriage 13-2 of the tensioning device 7 and also causes the cylinder 54 with the tongs '55 to move towards the axis of the well and bring the working members into the inclined position. The piston of the cylinder 54 stops after approaching the stand 19 retained by the elevator 4, and the switch provides for the stand to be gripped by the tongs 55 (positions V and VI, FIG. 7).

The tongs 55 having gripped the stand, the pressure relay 72 sends a command to open the elevator 4, and then the switch 45 sends an impulse for raising the travelling block 3 by means of the cariage 133. Said block is stopped by the switch 142 which also sends an impulse- 15 to move the piston with the rod of the cylinder 54 together with the stand away from the well (position VII, FIG. 7).

The arrangement 13 for handling the stands operates the same way as it does during the running cycle with the only exception that first the tongs 55 are lowered and then the switch 171 sends an impulse for their being drawn apart, after which the switch 71 sends an impulse for their raising.

After the cylinder 54, together with the tongs 55, have left the zone of the travelling block 3, the switch 167 sends an impulse for setting the working members 130 of the arrangement 14 for centering the end portion of the stand in the Vertical position, then the switches 172 and 173 send impulses for lowering the travelling block 3, and the cylce is repeated.

The oil pumps 15 and 18 are conventional in design and therefore need not be disclosed in detail in the above description What is claimed is:

1. Apparatus for the automatic assembly and disassembly of threaded sections of a drill string during feeding and withdrawal of the string, said apparatus comprising an elevator for gripping the uppermost section of a drill string, draw means for raising and lowering the elevator, control means for regulating the speed of raising and lowering of the elevator and for stopping the draw means, first engager means for engaging a section of the str ng to hold the string in suspension and prevent rotation thereof, second engager means mounted coaxially with the first engager means for engaging the next adacent section to selectively unscrew or screw this section with the section engaged by the first engager means, said first and second engager means being coupled as an assembly and having closed positions for engaging the respective section and open positions for passage of the string and the elevator, handling means for supplying a section to the elevator for addition to the string during feeding and for removal of a section from the string during withdrawal, means for locating adjacent sections in said first and second engager means such that the joint between said sections is disposed between the locations where the first and second engager means engage their respective sections, and means interconnecting the control means with the first and second engager means, the handling means and the means for locating adjacent sections such that sections can be automatically added to the string during feeding and removed during withdrawal.

2. Apparatus as claimed in claim 1, wherein said second engager means is mounted on the first engager means, said first and second engager means including respective working members for engaging their associated sections, and means supporting said working members for axial and radial movement to compensate for vibration of the string during screwing and unscrewing of said sections.

3. Apparatus as claimed in claim 1, comprising means disposed above said second engager means for engaging a section to be added to the string during feeding to align such section axially with the string.

4. Apparatus as claimed in claim 1, comprising means for cleaning the string during withdrawal thereof, the cleaning means being located above said second engager means and coupled to the draw means.

5. Apparatus as claimed in claim 1, comprising means coupled to the handling means for lubricating the threads of the section to be added during feeding.

6. Apparatus as claimed in claim 1, comprising axial displacement sensing means coupled to said second engager means for detecting the completion of screwing or unscrewing of a section with the remainder of the string.

7. Apparatus as claimed in claim 1, wherein said interconnecting means includes means for automatically halting the apparatus in the event of prescribed conditions 16 of emergency, and means for switching to a remote control mode of operation.

8. Apparatus as claimed in claim 1, comprising a traveling block coupled to the elevator for movement therewith, guide means for said traveling block, and cable means connecting said traveling block and the draw means whereby the latter can drive the traveling block and the elevator coupled therewith.

9. Apparatus as claimed in claim 8, wherein said elevator includes hydraulically operated gripping members for engaging the uppermost section of the drill string, and said draw means comprises a hydraulic braking system.

10. Apparatus as claimed in claim 9, comprising a hydraulic pump and hydropneumatic accumulator carried by said block and driven by the travel of said block to operate said gripping members.

11. Apparatus as claimed in claim 9, comprising tensioning means engaging said cable means for adjusting the position of the elevator and the traveling block when the draw means is inoperative.

12. Apparatus as claimed in claim 1, wherein said means for locating adjacent sections in the first and second engager means comprises means disposed in spaced relation from said string for sensing the position of the joints of said string without contacting such string and for producing a signal related to the position of said joints, and means for receiving said signal coupled to the control means for operation thereof.

13. Apparatus as claimed in claim 12, wherein said means for sensing the position of the joints comprises a diamagnetic ring fixed on each section of the drill string, the signal receiving means comprising an induction coil and an electronic transducer unit electrically coupled to said coil.

14. Apparatus as claimed in claim 13, wherein said induction coil is located between the first and second engager means.

15. Apparatus as claimed in claim 1, wherein said handling means comprises a member supported for rotation about a vertical axis, means for rotating said member about said axis, working members for gripping a section of the drill string, said working members being coupled to the last said means for rotation therewith, means supporting at least one of said working members for reciprocal movement in a radial direction with respect to said vertical axis, and a chute for supporting sections of a string, said chute having vertically aligned radial grooves for receiving the said sections, said working members being engageable with a section to remove it from the chute during string feeding and to return it to the chute during string withdrawal.

16. Apparatus as claimed in claim 15, wherein said working members include tongs for gripping a section at upper and lower portions thereof.

17. Apparatus as claimed in claim 15, wherein said working members include tongs for gripping the upper portion of a section and a fork for gripping the lower portion of a section.

18. Apparatus for the automatic assembly and disassembly of threaded sections of a drill string during feeding and withdrawal of the string, said apparatus comprising an elevator for gripping the uppermost section of a drill string, draw means including a hydraulic braking system for raising and lowering the elevator, a centrifugal governor coupled to said draw means, throttle means for controlling the pressure of the fluid in said braking system of the draw means, lever means connecting the throttle means to the governor for control thereby, first engager means for engaging a section of the string to hold the string in suspension and prevent rotation thereof, second engager means mounted coaxially with the first engager means for engaging the next adjacent section to selectively unscrew or screw this section with the section engaged by the first engager means, said first and second engager means being coupled as an assembly and having closed pos1tions for engaging the respective sections and open positions for passage of.the string and the elevator, handling means for supplying a section to the elevator for addition to the string during feeding and for removal of a section from the string during withdrawal, a diamagnetic ring on each section, an induction coil located between said first and second engager means for sensing the passage of a ring therepast, an electronic transducer unit connected to said coil, and an electrical control system connecting said transducer unit to said governor, said governor and throttle means being interlocked with said first engager means for controlling operation thereof.

References Cited UNITED STATES PATENTS Re. 26,284 10/1967 ONeill et a1. 175--85 X 2,450,934 10/ 1948 Calhoun 175-85 X 2,692,059 10/ 1954 Bolling 175-85 X 3,158,211 11/1964 McCue et a1. 175--85 FOREIGN PATENTS 163,563 9/1964 U.S.S.R.

CHARLES E. OCONNELL, Primary Examiner.

R. E. FAVREAU, Assistant Examiner.

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