US3396786A

US3396786A - Depth control methods and apparatus

Info

Publication number: US3396786A
Application number: US576340A
Authority: US
Inventors: Nick A Schuster; William T Bell
Original assignee: Schlumberger Technology Corp
Current assignee: Schlumberger Technology Corp
Priority date: 1966-08-31
Filing date: 1966-08-31
Publication date: 1968-08-13
Anticipated expiration: 1985-08-13

Description

QROSS-REFERENGE SEARCH RUUM Aug. 13, 1968 SCHUSTER ET AL 3,396,786

DEPTH CONTROL METHODS AND APPARATUS 4 Sheets-Sheet 1 Filed Aug. 31, 1966 1N VENTORS Aug. 13, 1968 Filed Aug.

4 Sheets-Sheet 2 W////CZ//7. I Be INVENTORS Aug. 13, 1968 SCHUSTER ET AL 3,396,786

DEPTH CONTROL METHODS AND APPARATUS Filed Aug. 31, 1966 4 Sheets-Sheet 3 Al/CK A. Sc/ruszer W////a//I T B e "3 INVENTORS United States Patent 3,396,786 DEPTH CONTROL METHODS AND APPARATUS Nick A. Schuster and William T. Bell, Houston, Tex.,

This invention relates to methods and apparatus for positioning well tools in a well bore; and, more particularly, to new and improved methods and apparatus for accurately positioning selectively operable well completion devices at predetermined depths in a well 'bore and displaying visual indications of their location therein as Well as their relation to one another.

Once the casing has been set in a well bore, the usual practice is to obtain a log that will in some manner identify at least certain formations and determine their depth. In one manner of doing this, a logging tool is passed through the well bore to simultaneously obtain a log of the natural or induced formation radioactivity as well as some detectable indicia of the positions of the casing collars as a function of well depth. In this manner, the depths of particular formations in relation to certain ones of the collars can be established. Subsequently, by using these logs and, for example, employing a casing collar locator With a completion tool, the completion tool can be located fairly accurately at any particular depth in the well bore. To accomplish this, the position of the completion tool is ascertained by visually comparingthe original collar log with the collar log being obtained as the completion tool is being positioned. Then, by using this comparative data, the cable is payed out or reeled in as required to bring the completion tool to the particular depth desired.

One of the most frequent uses for such a depth-correlating procedure is to position a perforator in a well bore. To perforate a well at several depths, a perforator having a number of selectively operable perforating devices thereon is dependently coupled from a casing collar locator and lowered into the well bore. It will be realized, of course, that although the collar locator is a known distance above each of the perforating devices, these different spacings must be taken into consideration to locate each device. For example, assuming that the first device to be actuated is at the lower end of the tool, a particular correction must be made to compensate for the spacing of the collar locator from that device. Then, as further perforating devices are successively actuated, this spacing will decrease as the devices are tired, with a different spacing correction being required to accurately locate each device.

Accordingly, where a number of completion operations are to be carried out at different depths in a well bore,

it is essential to know at all times not only the spacing between the collar locator and the device next to be actuated but also the actual depth of that device as well. Although the abovementioned procedure itself is basically accurate, where as number of operations are to be made in a Well bore at several depths, it is not at all too uncommon to make some error that causes the well to be completed incorrectly. For example, in addition to making such simple errors as subtracting rather than adding the spacing to the depth indicated by the collar log, it is not at all too uncommon to sometimes even overlook the successive changes in spacing as the various devices are actuated. Thus, where a larger number of completion devices are to be actuated at various depths in a well bore, one or more such human errors can result in the well being incorrectly completed.

Consequently, it is an object of the present invention to provide new and improved methods and apparatus for accurately positioning well tools having a plurality of Patented Aug. 13, 1968 selectively operable devices in a well bore and providing indications and a record of the position of each of the selectively operable devices as well as a visual presentation of which device is being employed at any particular moment.

This and other objects of the present invention are accomplished by obtaining a first log showing thereon one or more distinctive reference points as a function of depth and designating on this log at least one predetermined depth. Then, as a well tool is being positioned, a second log is obtained and correlated with the first log to locate the Well tool at the designated depth. A visual indication is provided of the well tool as well as of the depth at which one of several selectively operable devices thereon are as it is to be actuated. An indication of the position of these selective devices in relation to this predetermined depth is also either made on or related to the first log.

The novel features of the present invention are set forth with particularity in the appended claims. The operation together with further objects and advantages thereof, may best be understood by way of illustration and example of certain embodiments when taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a typical perforator in a Well bore to be perforated at a number of depths;

FIG. 2 is a typical log of the portion of the well bore illustrated in FIG. 1;

FIGS. 3-5 schematically illustrate successive steps in the practice of the present invention; and

FIG. 6 depicts a circuit diagram of apparatus that may be used in the practice of the present invention.

Turning now to FIG. 1, a typical well tool 10 is shown suspended in a Well bore 11 from a cable 12. As is customary, the Well bore 11 is completed by a string of casing joints 13 connected to one another by couplings or collars, as at 14-17, and secured in place in the well bore by cement 18.

It will be understood, of course, that the present invention is applicable to any operation involving the positioning of one or more devices in a well. Moreover, it is to be realized that any one or more means can be used to provide a log indicating the relation of particular earth formations to each other as well as to some identifiable point in the well bore.

As one example of the present invention, however, it is assumed that the well tool 10 is to be used to make a selected number of perforations (not shown) in several producible earth formations 1921. To accomplish this, the well tool 10 is appropriately arranged to include a perforator 22 having thereon a number of perforating devices as, for example, a plurality of shaped charges 23 that may be selectively detonated as required. Inasmuch as the particular arrangement of the perforator 22 plays no part in the present invention, it is necessary only to understand that the perforator is suitably arranged so a predetermined number of one or more of its shaped charges 23 can be detonated upon command from the surface. To assist in positioning the perforator 22 at the correct depth, depth-correlating means, such as a casing anomaly or collar locator 24 which, for example, may be one of those shown in Patent No. 3,144,876 to Nick A. Schuster are mounted on the upper end of the Well tool 10. Such locators, as at 24, can also detect previously located magnetic anomalies as, for example, a short pup joint or other device in the string 13. It should also be understood that any detecting means that can detect an identifiable formation characteristic such as, for example, the natural or induced radioactivity of earth formations can also be used in the place of or in conjunction with the locator 24.

Turning now to FIG. 2, a typical log 25 on paper, film, or the like, is shown of that portion of the well bore 11 illustrated in FIG. 1 such as would customarily be obtained after the casing 13 has been set to provide an accurate indication of the depth of the collars 14-17 and, in one manner or another, their spatial relation to the productive earth formations 19-21. To obtain this log 25, a well tool (not shown) including detecting means for identifying distinctive reference points is passed through the cased well bore 11. In one manner of accomplishing this, the detecting means could include radioactivity-measuring means that can either detect previously placed radioactive markers for depth-reference points in the formations and/or on the collars or also measure only the natural or induced radioactivity of the formations. Irrespective of how a given characteristic of the formations is detected, where the collars, as at 14-17, are used as depth-reference points, another means for determining depth could also be a typical casing collar locator.

Accordingly, although other means of presenting such information can be used, the log 25 will be assumed to include some indicia of some characteristic of at least the formations of interest as, for example, a continuous trace 26 on the left of the log indicating natural or induced radioactivity. For purposes of depth correlation, the relative positions of the collars in the casing string 13 may be assumed as being represented as either a series of separate indicia marks or a continuous trace, as at 27, that is recorded as a function of depth, as at 28 or 29, and having irregularities, as at 30-33, respectively representative of the collars 14-17.

Accordingly, as known by those skilled in the art, once this log 25 has been obtained, the trace 26 can be compared with one or more other logs (not shown) made previously to determine which of the formations are most likely capable of being produced. By comparing previously obtained logs of the same or different nature with the trace 26, the various formations can be identified and their relative locations determined with respect to one another as well as to the casing collars 14-17.

Turning now to the practice of the present invention. As seen in FIG. 3, the log 25 is first marked in some suitable manner, as by the lines at 34-40, to designate the depth at which each perforation is desired. Then, as best seen in FIG. 4, the prepared log 25 is arranged on means, such as a control panel 41, arranged in accordance with the present invention. The completion apparatus is suspended in the well bore 11 from the cable 12 and spooled in the usual manner from a winch 42 with the cable 12 being connected to the control panel 41.

The control panel 41 is comprised of recording means, such as a chart recorder 43 or the like, arranged to accept the log and including selectively responsive marking means, such as a pair of conventional recorder pens 44 and 45, and driving means, such as selsyn motors 46 and 47, that are suitably arranged to drive the spools 48 and 49 on which the log 25 is rolled in either direction. The recorder pen 45 is movably mounted on and arranged for movement along a support 50 parallel to the longitudinal axis of the log 25. Although the recorder pens 44 and 45 can be as normally provided on conventional chart recorders, either one or both of them may be so-called solenoid-actuated event markers that produce a suitable indication upon receiving a signal of a particular nature. Control means 51 and 52 are provided to drive the recorder motors 46 and 47 so that the log 25 will be synchronously advanced or reversed in unison with the unreeling or reeling in of the cable 12.

To actuate the recorder pens 44 and 45, means, as at 53, are provided to respond to a first signal indicative of the depth of the well tool 10 as well as to respond to a second signal indicating that the well tool has been actuated. In one manner of accomplishing this, the recorder pen 44 is coupled through the responsive means 53 to the collar locator 24 to provide a record as desired each time a collar in the casing string 13 is passed by the collar locator. The other recorder pen 45 is coupled through the responsive means 53 to means, as' at'54, on the well tool 10 for detecting the detonation of each of the shaped charges 23 and providing a signal in response thereto for actuating the recorder pen 45. As will subsequently be described in detail with respect to FIG. 6, this actuation-responsive means 54 can be arranged to respond to detonation or concussion shocks of the shaped charges 23 to momentarily interrupt current through the cable 12 and, by virtue of the responsive means 53, actuate the pen 45.

On the right of the control panel 41 and parallel to the longitudinal axis of the log 25, scaled facsimiles of the perforator 22 and collar locator 24 are provided which are preferably comprised of a replaceable template 55 or the like that may be mounted thereon in some suitable manner. As shown in FIG. 4, this template 55 is accurately scaled to represent not only the relative positions 56 and spacing of each of the shaped charges 23 on the perforator 22 but also to show the relative position 57 of the casing collar locator 24. A movable pointer 58 is provided on the control panel 41 adjacent to the template 5-5 and arranged to be moved parallel to the longitudinal axis of the template by a control knob 59 which, by means of a pulley arrangement, gear train, pantograph, or other suitable mechanism 60, will also simultaneously position the shot-indicator recording pen 45. By suitably arranging the mechanism 60, movement of the control knob 59 will shift the pointer 58 a scaled distance along the template 55 that is directly proportional both to the scaled distance that the recorder pen 45 is being simultaneously shifted longitudinally in relation to the scale of the log 25 as well as to the actual distance along the perforator 22 corresponding to the positions 56 being indicated by the pointer.

In other words, by preparing a suitable template 55, the spacing between the casing collar locator position 57 and the particular position 56 of the pointer 58 at any given time will be representative of the actual distance between the collar locator 24 and the corresponding shaped charge 23 on the perforator 22. Similarly, the recording pen 45 will be appropriately adjusted by the control knob 59 and mechanism 60 so that the shot-indicator pen 45 will indicate on the log 25 the true depth of the shaped charge 23 next to be fired on the perforator 22. The collar-locator recording pen 44 always indicates on the log 25 the true depth of the collar locator 24. Thus, the actual distance between the collar locator 24 and a given shaped charge 23 will be simultaneously presented by the scaled spaced or chart divisions on the log 25 between the pens 44 and 45 and the visual portrayal on the template 55 of the spacing between the pointer 58 and the position 57.

After the log 25 has been marked to provide the indications 34-39 representative of the depths at which each of the perforations are to be made, the marked-up log (FIG. 3) is then mounted on the reels 48 and 49 on the control panel 41. A suitable template 55 is prepared and mounted on'the panel 41 and the well completion apparatus 10 is then lowered into the well bore 11.

During the descent of the perforating apparatus 10 into the well bore 11, the log 25 and the usual depthmeasuring totalizers or registers and the like (not shown) as typically used are tied-in to the collars in the casing string. Although this can be done in several manners, by observing the correspondence of the newly-obtained collar log with an older collar log the operator can keep track of just where the apparatus 10 is in the well. Then, since the depth of each collar is known from the older collar log, the operator can adjust the depth-measuring registers as the apparatus 10 is being lowered to keep them in the proper relation to the known depths of the collars. It is, of course, not necessary to actually record a new collar log as the tool 10 is being lowered since visual observation of the measurements being obtained on the measuring instrument typically used will indicate how closely the old collar log is being followed. Thus, in one manner or another, by merely keeping the depth-measuring registers or odometer-like totalizers in step with the old collar log as the apparatus is being lowered, the log will still be unmarked.

The well completion apparatus 10 is preferably lowered below the first depth at which a perforation is to be made. Then, as best seen in FIG. 4, as the well tool 10 is moved upwardly in the well bore 11, the collar locator 24 will detect each of the casing collars as the tool is raised thereby. The control means 51 and 52 and motors 46 and 47 are simultaneously driving the log 25 at a speed directly proportional to the rate of ascent of the perforating apparatus 10. As the log 25 is moved, the collar-locator recorder pen 44 will make a trace 61 having successive irregular marks, such as at 62 and 63, indicative of the casing collars that the well completion apparatus 10 has just passed.

Accordingly, by observing the correspondence (or lack of correspondence) of the marks (as at 33) on the previous collar log trace 27 with those (at at 63) on the newly obtained trace 61, final adjustments may be made on the recorder 43 so as to bring the irregularities 33 and 63 on the two traces 27 and 61, respectively, into register with one another, Once this has been accomplished, it will be appreciated, of course, that the collar-locator recorder pen 44 will indicate and record on the log 25 the precise depth at which the collar locator 24 is at that point. Similarly, the shot-indicator recorder pen 45 will be pointing on the log 25 to the depth at which the particular shaped charge 23 to be fired is then actually positioned. The shot-indicator pen 45 may or may not be providing a continuous trace as desired. Similarly, it is, of course, not necessary to continuously record a trace, as at 61, on the log 25 so long as a record of some nature, as at 62 or 63, is provided of the collars passed.

By keeping the newly recorded collar log trace 61 synchronized with the original collar log trace 27, whenever the well apparatus 10 has reached the depth at which the first perforation is to be made, the shot-indicator recorder pen 45 will provide a visual indication which, when it is brought into register or alignment with the first mark 34 on the log 25, will indicate that the first shaped charge 23a is precisely located at that depth. It is, of course, apparent that with this displayed presentation, no calculation need be made to know positively that the well completion apparatus 10 is correctly positioned at the correct depth in the well bore 11. The correspondence of the collar log traces 27 and 61 'will assure the observer that the tool 10 it as the correct depth. Moreover, once the shot-indicator pen 45 is aligned with the mark 34 previously drawn on the log 25 to designate the precise depth at which the first perforation is to be made, there is no reason to become confused about the precise location of the shaped charge 23a.

Accordingly, once the perforator 22 has been actuated and the concussion-responsive means 54 initiated, the electrical means 53 will actuate the shot-indicator recorder pen 45 to print a mark (not shown in FIG. 4) on the log 25 immediately opposite the mark 34, This will provide a positive permanent indication on the log 25 that this perforation was made at the correct depth.

Once this first perforation has been made, the control knob 59 is then adjusted to shift the pointer 58 upwardly to the next position 561) on the template 55 and, at the same time, also move the shot-indicator recorder pen 45 upwardly on its support 50. This simultaneously shifts the shot-indicator recorder pen 45 relative to the collar-locator recorder pen 44 so as to space the two pens apart a distance which can be scaled on the vertical scale of the log 25 and will also be proportionally scaled to the actual spacing between the casing collar locator 24 and the shaped charge 23b next to be fired.

Turning now to FIG. 5, the well completion tool 10 has been raised in the well bore 11 until it is now adjacent to the formation 19. As the well tool 10 was being raised, it was successively halted as indicated by the correspondence of the pen 45 and the marks 3539 to permit the second through sixth of the shaped charges 23 to be detonated so as to produce corresponding perforations (only the last two being shown at 64 and 65). Then, after making the perforation 65, the control knob 59 was again adjusted to move the movable pointer 58 from opposite the sixth position 56f on the template 55 to the seventh position 56g as seen in FIG. 5. Movement of the control knob 59, of course, simultaneously shifted the shot-indicator recorder pen 45 upwardly on its support 53 to correctly space the pens 44 and 45 relative to one another a scaled distance representative of the actual distance between the shaped charge 23g and the collar 10- cator 22. Once this is done, the cable 12 will be reeled in to raise the tool 10 in the well bore 11 until the mark 40 on the log 25 is brought into alignment with the nowstationary shot-indicator pen 45.

Once the shot-indicator pen 45 and mark 40- are aligned, the observer will be assured that the perforator 22 is correctly positioned in the well bore 11 and is in fact in position to safely make the seventh perforation. When the perforator 22 is actuated, the shaped charge 23g will produce the perforaion 66 and the resultant shock on the electrical means 54 will again actuate the electrical means 52 to cause the shot-indicator pen 45 to make a confirming mark 67 adjacent to the previously drawn mark 40 on the log 25.

Accordingly, this confirming mark 67 will provide a positive and permanent record that the perforation 66 was made while the seventh shaped charge 23g on the perforator 22 was at that depth. Moreover, the correspondence, as at 31 and 62, of the collar logs 27 and 61 will verify that the perforating apparatus 10 was at the correct depth at that time and provide a record thereof. It will be noied that similar confirming marks 6870' were respectively made opposite the pre-drawn marks 37-39.

It will be appreciated that although the procedure has been described as using the collar log trace 27 for depth correlation, the formation log at 26 could be used just as well. This would not change the operation and the pen 44 would instead be appropirately arranged to provide a verifying identification such as a continuous trace similar to that at 27 (but reproducing the log trace 26 of course). In this event, it would not even be necessary to include a collar locator 24 on the apparatus 10.

As an alternate, the log 25 could be obtained at the beginning of the above-described operation. If this were done, the well tool 10 would include the appropriate logging device either alone or in conjunction with the collar locator 24. The tool 10 so equipped would be first used to produce the log 25. Then, after the designations, as at 34-39, are placed, the operation would be conducted as described.

Turning now to FIG. 6, a schematic representation is shown of a suitable firing circuit 71 for selectively detonating the shaped charge-s 23 and the concussion-responsive means 54 for detecting their detonation. Inasmuch as the firing circuit 71 and detecting means 53 and means 54 are respectively arranged in accordance with com monly owned, earlier-filled applications Serial No. 420,345, now Patent No. 3,327,791 filed Dec. 22, 1964, by John W. Harrigan, Jr. and Serial No. 569,316, filed Aug. 1, 1966, by George W. Brock, only a brief explanation of the principles of each of these inventions and their relation to one another and to the present invention is believed to be sufficient.

Briefly stated, the firing circuit 71 is comprised of a solenoid-actuated selector switch 72 that is selectively operated by a DC power source 73 at the earths surface and connected across the inner conductor 74 and outer armor sheath 75 of the monocable 12. To regulate the output of the power source 73, a conventional polarityreversing switch 76 and potentiometer 77 are appropriately arranged. By connecting a polarity-responsive device, such as a diode 78, between the central conductor 74 and the solenoid 79 of the selector switch 72, the selector switch will be actuated only when a voltage of the correct polarity is applied across the monocable 12.

The selector switch 72 includes a rotatable switch contact 80 that is selectively moved by the solenoid 79 around a plurality of contacts 81 spaced around a switch wafer 82. Each of these contacts 81 are connected to one side of a typical detonator 83 (schematically represented as resistors in FIG. 6), with the other sides of these detonators being returned through the body of the perforator 22 to the monocable sheath 75. In this preferred arrangement, the solenoid 79 is arranged to drive a pawl (not shown) that indexes a rotatable ratchet wheel (not shown) connected to the rotatable switch arm 80. By arranging the pawl to remain engaged with the ratchet so long as the solenoid 79 is energized, the switch arm 80 will be indexed only one position at a time to the next contact 81 to be connected. Then, when the solenoid 79 is de-energized, the pawl will be restored to its initial position and come to rest on the next tooth on the ratchet to await another energization. Thus, only by successively energizing and de-energizing the solenoid 79 can the contact arm 80 be advanced around the various contacts 81. To control the detonation of the shaped charges 23, a Zener diode 84 is connected between the polarity-determining diode 78 and the switch contact arm 80. By selecting the Zener diode 84 to have a Zener level somewhat in excess of the voltage required to actuate the solenoid 79, the selector switch 72 can be actuated to connect the next shaped charge 23 into the firing circuit 71 without immediately detonating it. Thus, it is not until after the solenoid 79 has moved the switch arm 80 to the next one of the contacts 81 that the voltage across the monocable 12 will reach the Zener level so as to cause the Zener diode 84 to conduct and apply voltage to the detonator 83 in the circuit at that time. Then, by continuing to advance the potentiometer 77, the voltage will reach a magnitude sufficient to detonate the desired shaped charge 23. It will be recalled, of course, that once the contact arm 80 has been advanced to one of the contacts 81, it can notadvance further until the voltage is first removed and then re-applied to the solenoid 79. This will assure that voltage is at least applied in turn to each of the shaped charges 23 and minimize the risk of unintentionally skipping of a shaped charge.

Turning now to the shot-detecting means 52 and concussion-responsive means 54 depicted in FIG. 6. Briefly, the concussion-responsive means 54 includes signalgenerating means, such as a transducer tor piezoelectric crystal 85, that upon being subjected to a physical shock or the like to the well completion tool will cause a detectable signal to be sent to the earths surface through the cable 12. Once this signal has reached the surface, the shot-detecting means 53 are employed first to ascertain with reasonable certainty that the signal is not spurious and then secondly to actuate the shot-detector pen 45.

To accomplish this, the output of the crystal 85 is amplified by an amplifier 86 and connected, by way of a forwardly-biased diode 87, to the set input of a flipflop circuit 88 that controls an oscillator 89 which, when running, will generate a repetitive output signal such as, for example, a sine wave or a square wave. In one manner of controlling the oscillator 89, one of the outputs of the flip-flop 88 is connected to the control terminal of a gate 90 that is in turn connected to the initiate input of the oscillator as seen in FIG. 6. This gate 90 is of the so-called enable-type wherein application of a signal to its control terminal will cause a very low impedance to be across it. Thus, by connecting the gate 90 between an appropriate connection on the oscillator 89 and ground, as at 91, iniiiation of the gate 90 by the flip-flop 88 will connect the oscillator to ground and start the oscillator. For reasons to be explained shortly, the output of the oscillator 89 is connecied to the control terminal of another so-called enable-type gate 92.

Connected across the monocable 12 is a bridge circuit 93 which, as will be readily appreciated by those skilled in the art, will maintain the polarity of one of its output terminals 94 positive and that of the other output terminal 95 negative in either position of the polarity-reversing switch 76. In this manner, whether the positive terminal of the DC source 73 is connected to the inner conductor 74 or is connected to the sheath 75, the output terminal 94 will always be positive. The purpose of this, however, is to maintain a positive voltage on those conductors, as at 96, supplying B+ voltage to the various components in the downhole circuitry and has no particular bearing on the operation as such as now to be described.

One end of a resistor 97 is connected between the positive terminal 94 of the bridge circuit 93 and the previously mentioned enable-type gate 92 which is in turn connected to ground and the negative terminal 95 'of the bridge circuit. It will be appreciated, of course, that when the gate 92 is not operating, the other end of the resistor 97 is not connected to ground and is merely floating. When the enable-type gate 92 is operated, however, it will connect the floating end of the resistor 97 to ground with a low impedance so that the resistor is then across the

output terminals

94 and 95 of the bridge circuit 93. By using a low value of resistance for the resistor 97, each time it is connected across the bridge circuit 93 by operation of the gate 92, the impedance across the

monocable conductors

74 and 75 will be significantly decreased. Accordingly, since the gate 92 will be repetitively enabled and disabled by the oscillator 89, the impedance across the

monocable conductors

74 and 75 will be changing at the same rate to develop cyclic current changes in the monocable 12 at the same frequency as the oscillator.

To detect these cyclic changes in the current flowing through the monocable 12, the shot-detecting means 52 includes a transformer 98 that has its primary in series with the central monocable conductor 74 and its secondary connected to a bandpass filter network 99 designed to pass only the frequency of the cyclic changes. Thus, the cyclic changes in the current flowing through the monocable 12 will induce a corresponding signal in the secondary of the transformer 98. The signal passing through the filter 99 is rectified by a rectifier 100 and directed through a delay circuit 101 to means, such as a relay solenoid 102 controlled by a silicon-controlled rectifier 103, for actuating the shot-detector pen 45 and opening normally-closed relay switch means 104 in series with the central conductor 74. This delay circuit 101 is of the well-known type wherein a voltage must be present on the input for a given period of time before a signal is generated. The siliconcontrolled rectifier 103 inherently functions to continue conducting once it is initiated so long as power is not re moved. Thus, so long as no signal has been sent through the delay circuit 101, the rectifier 103 will not conduct and the solenoid 102 will remain de-energized. Once it is initiated, the silicon-controlled rectifier 103 will continue conducting to energize the relay solenoid 102 so long as power is applied. When the power is interrupted, however, the silicon-controlled rectifier 103 will discontinue its operation until a second signal is applied through the time-delay circuit 101.

It should be noted in passing that the downhole portion of the circuitry 54 also includes a suitable voltage regulator 105 connected to the positive terminal 94 of the bridge circuit 93. A large capacitor 106 is also connected across the output of the voltage regulator 105 to prevent transients from affecting the B+ voltage to the balance of the circuits.

It will be noted that the time-delay circuit 101 and flip-flop 88 will prevent the presence of transients on the monocable 12 from initiating the shot-detecting means 52.

Since transients are typically of a short interval, a sufficient delay interval in the delay circuit 101 will prevent a transient from actuating the relay solenoid 102. The flipflop 88, will, of course, maintain the oscillator 89 operating so long as power is applied thereto. Thus, the oscillator 89 will continue operating until the relay solenoid 102 is energized. Opening of the relay contacts 104 will remove power from the downhole circuitry.

Because of the inherent nature of flip-flops, however, it is possible that the flip-flop 88 can be set in the wrong state so that it would immediately start the oscillator 89 when sufiicient voltage is first applied across the monocable 12 as the solenoid 79 is being energized. This would, of course, cause the oscillator 89 to operate prematurely without energization of the crystal 85.

Accordingly, to ensure that the flip-flop 88 is properly set so as not to initiate the oscillator 89 until a concussion energizes the crystal 85, a reset circuit comprised of a voltage-sensitive control 107 (such as a Schmitt trigger or the like) connected from the output of the voltage regulator 105 to the control input of a so-called inhibit gate 108 is provided. The inhibit gate 108 is in turn connected between the output of the flip-flop 88 and ground. Thus, until the gate 108 is energized by the trigger 107, the previously mentioned output of the flip-flop 88 is grounded, as at 109, to prevent it from prematurely initiating the oscillator 89. When the output voltage of the voltage regulator 105 reaches a first predetermined value, however, as the potentiometer 77 is being advanced, the connection of this flip-flop output to ground through the gate 108 will ensure that the flip-flop 88 is set in the correct reset state. Then, at some higher second voltage, the voltage-sensitive trigger 107 will supply an output signal to the inhibit gate 108 to disconnect the grounded connection 109 from the output of the flip-flop 88. Once its output is ungrounded, of course, the flip-flop 88 will function as soon as the crystal 85 is energized. It will be understood, of course, that these first and second voltages are well below the voltage required to operate either the solenoid 79 of the Zener level of the Zener diode 84.

In operation, therefore, the perforating apparatus is positioned as already described with reference to FIGS. 4 and 5. When the coincidence of the shot-detector pen 45 with one of the marks, such as 34 for example, indicates that the first shaped charge 23a is at the correct depth, the perforating apparatus 10 is halted. Then, the potentiometer 77 is slowly advanced. As the voltage across the monocable 12 is first increased, the output voltage of the voltage regulator 105 will be below the threshold level of the trigger 107 thereby ensuring that the flip-flop 88 will be placed into the reset state. When the flip-flop 88 is in this reset state the inhibit gate 108 holds the 1 output of the flip-flop at ground potential so that the oscillator 89 cannot be initiated. At some higher voltage output of the voltage regulator 105, the voltage-sensitive trigger 107 will energize the inhibit gate 108 and remove the 1 output of the flip-flop 88 from ground potential so that whenever the crystal 85 is energized by a concussion shock, the set input of the flip-flop will be energized to start the oscillator 89. It will be recognized, of course, that the threshold level of the trigger 107 is well below the voltage necessary to energize the selector switch 72.

The voltage across the monocable 12 will subsequently reach a level whereby the solenoid 79 will index the contact arm 80 to the first cont-act 82a to connect the detonator 83a for the first shaped charge 23a into the firing circuit 71. Then, once the voltage across the monocable 12 has reached the Zener level of the Zener diode 84, voltage will be applied to the detonator 83a. Once the potentiometer 77 has been advanced still further, the detonator 83a will be actuated and the shaped charge 23a detonated if all is functioning properly. If no detonation occurs, failure of the shot-detection circuit 53 to function will immediately give notice to the operator who will then take whatever remedial action is desired.

Assuming, however, that the shaped charge 23a does detonate, the resultant shock to the perforating apparatus 10 will momentarily impulse the crystal 85. This will then energize the flip-flop 88 and start the oscillator 89 which will then cause the resistor 97 to be repetitively connected and disconnected across the monocable 12. As previously explained, this cyclic change of impedance across the monocable 12 will induce a corresponding cyclic signal in the transformer 98. Since the frequency of this signal is in the bandpass range of the filter 99, it will be rectified by the rectifier 100 and applied to the input of the timedelay circuit 101. Once the rectifier signal is applied to the input of the delay circuit 101 for a sufiicient time, the silicon-controlled rectifier 103 will be enabled which in turn energizes the relay solenoid 102.

Once the relay solenoid 102 is energized, the normally-closed relay contacts 104 will open and normally-open relay contacts will be closed. These contacts 110 connect a DC source 111 to an RC circuit 112 that, by way of a diode 113, is connected to the shot-indicator pen 45. The momentary spike produced by the closing of the switch contacts 110 will pulse the shot-indicator pen 45 to produce a mark, as at 67. Opening of the switch contacts 104 will, of course, break the circuit between the monocable 12 and DC power source 73. Once the circuit is broken, no further power can be applied down the monocable 12 since the relay solenoid 102 will continue to draw current through the silicon-controlled rectifier until power to the rectifier 103 is interrupted. Thus, it is necessary -for the operator to return the potentiometer 77 to its original zero position to discontinue the conduction of the rectifier 103 and reclose the normally-closed relay contacts 104 and reopen the normally-open contacts 110. It should be noted in passing that, if desired, an amplifier 11 4 and speaker 115 can be used to provide an audible signal in addition to the permanent record and visual indication provided by the shot-detector pen 45.

The collar-locator 24 is connected across the monocable 12 in the usual manner. Wherea continuous trace, as at 61, is to be made, the recorder pen 44 is connected to the monocable 12 by an amplifier 116. To prevent DC from reaching the amplifier 116, a blocking capacitor 117 is connected. between the amplifier input and the central conductor 74. As a further safety measure, normally-closed relay contacts 118 can be provided so as to momentarily interrupt the circuit whenever the solenoid 102 is energized. It will be understood, of course, that other means can also be employed to translate the output signal of the collar locator 24 into some mark or induction on the log 25.

It will be recognized that so long as the log 25 is in position on the recorder 43, it will be readily determinable that the tool 10 is correctly positioned. Once the log 25 is removed, however, there is nothing by which it can be determined whether the tool 10 was at the correct depth when the shaped charges 23 were detonated. Accordingly, to provide such a record, the event marker or pen 44 could be arranged to also make a characteristic mark (not shown) each time that the event marker or pen 45 makes a mark as at 67-70. In one manner of accomplishing this, a second marker could be aligned horizontally (as seen in the figures) with the pen 44 and connected to make a mark as in the margin of the log 25 each time the pen 45 is actuated.

It will be appreciated, therefore, that the present invention has provided new and improved methods and apparatus for accurately positioning a well tool in a well and providing both visual indications of its location as well as permanent records of the depth of the tool each time it is actuated. In practicing the present invention, it is necessary only to establish that the well tool is tied-in with the earlier log. Then, as desired, a permanent record can be made of some indication that can be compared with the previous log to verify the position of the tool. Each time the tool is actuated, a permanent record is also made on the log to indicate the depth of the tool at that time. In addition to the presentation on the log of the positions of the tool, the scaled facsimile of the tool and movable pointer provide a visual indication of which portion of the tool is in readiness for operation at that time.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A method for completing a well bore at a plurality of depths and which has a distinctive depth-reference point therein at a known depth, comprising: placing into the Well bore, means for detecting the distinctive depthreference point and a well tool having a plurality of completion devices thereon each spaced a known distance from one another and said detecting means; making a chart representative of depth in the well bore and marking on said chart first and second designations respectively of the known depth of the distinctive depth-reference point and of a plurality of desired depths at which the well tool is to be positioned; displaying adjacent to said chart a scaled facsimile of said detecting means and said completion devices on said well tool; moving said detecting means and said well tool into the vicinity of the distinctive depth-reference point for obtaining with first depth-indicating means a first indication in relation to said chart of the apparent depth of said detecting means and for obtaining with second depth-indicating means, a second indication in relation to said chart of the apparent depth of a selected one of said completion devices and a third indication in relation to said facsimile of the spacing between said detecting means and said selected one completion device; correlating said first indication with said first designation to verify the accuracy of said first indication and making adjustments accordingly to obtain with said second depth-indicating means a corrected indication in relation to said chart of the true present depth of said selected one completion device; moving said well tool to bring said second depth-indicating means into correspondence with one of said second designations; operating said selected one completion device while said second depth-indicating means corresponds with said one second designation; adjusting said second depth-indicating means to obtain a different second indication in relation to said chart of the true present depth of another of said completion devices and a different third indication in relation to said facsimile of the spacing between said detecting means and said other completion device; moving said well tool to bring said second depth-indicating means into correspondence with another of said second designations; and operating said other completion device while said second depth-indicating means corresponds with said other second designation.

2. The method of claim 1 further including the step of marking on said chart the position of said detecting means when said second depth-indicating means are first adjusted.

3. The method of claim 1 further including the step of marking on said chart the position of the selected completion devices when said second depth-indicating means are in correspondence with each of said second designations.

4. The method of claim 3 further including the step of marking on said chart the position of said detecting means when said second depth-indicating means are first adjusted.

5. Apparatus for completing a well bore at a plurality of desired depths and in which distinctive depth-reference means are located at a known depth, comprising: a well tool adapted for movement in the well bore and including detecting means for detection of the depth-reference means and a plurality of well-completion means each spaced a known distance from said detecting means; chart means displaying as scaled presentations the known depth of the distinctive depth-reference means and the desired depths at which the well bore is to be completed; facsimile means displaying a scaled representation of the spacings of each of said well-completion means in relation to said detecting means; first means for indicating with respect to said facsimile means a selected one of said well-completion means; second and third means respectively adpated for indicating with respect to said chart means the depths of said detecting means and of one of said well-completion means; means responsive to movement of said well tool in the well bore for maintaining said second and third indicating means and said chart means accurately aligned relative to one another; and means responsive to movement of said first indicating means for positioning said third indicating means to indicate with respect to said chart means the depth of said selected well-completion means.

6. The apparatus of claim 5 wherein said movementresponsive means includes recorder means on which said chart means are carried and moved proportionately to movement of said well tool and further including first and second means for respectively marking on said chart means the depths of said detecting means and of said selected well-completion means.

7. The apparatus of claim 6 wherein said detecting means provide characteristic signals upon detection of the depth-reference means, and further including means responsive to such signals for characteristically marking on said chart means to designate the detection of the distinctive depth-reference means and verify the accuracy of said marking means.

8. The apparatus of claim 7 wherein said second marking means are responsive to operation of said selected we'll-completion means and further including third means for marking on said chart means the depth of said detecting means whenever said selected well-completion means are operated.

References Cited UNITED STATES PATENTS 2,228,623 1/1941 Ennis 166-4 3,268,908 8/1966 Allen 346-17 3,273,639 9/1966 Lebuorg et al. 166-4 3,291,207 12/1966 Rike 1664 DAVID H. BROWN, Primary Examiner.