US3304538A

US3304538A - Acoustic well logging downhole control system

Info

Publication number: US3304538A
Application number: US525502A
Authority: US
Inventors: Fred W Zill
Original assignee: Schlumberger Well Surveying Corp
Current assignee: Schlumberger Well Surveying Corp
Priority date: 1961-08-08
Filing date: 1966-02-07
Publication date: 1967-02-14
Anticipated expiration: 1984-02-14

Description

F. vv. zlLl. 3,304,538

ACOUSTIC WELL: LOGGING DOWNHOLE CONTROL SYSTEM Feb., M, w67

5 Sheets-Sheet 1 Original Filed Aug. 8, 1961 if@ f 5v Feb. 14, 1967 F. w. z|| 3,304,538

ACOUSTIC WELL LOGGING DOWNHOLE CONTROL SYSTEM Original Filed Aug. 8. 1961 5 Sheets-Sheet 2 @ed W Z/// INVENTOR.

ATTOH/VEVS ACOUSTIC WELL LOGGING DOWNHOLE CONTROL SYSTEM Original Filed Aug. 8, 1961 F. W. ZILL Feb. 14, 1967 5 Sheets-Sheet 5 Fred VV Z/ INVENTOR.

F. w. zlLL 3,304,538

ACOUSTIC WELL LOGGING DOWNHOLE CONTROL SYSTEM Feb. 14, 1967 Original Filed Aug. 8. 1961 Z INVENTOR.

@W f J TTO/Q/Vf VS F. w. zlLl. 3,304,538

ACOUSTIC WELL LOGGING DOWNHOLE CONTROL SYSTEM Feb. 14, 1967 5 Sheets-Sheet 5 Original Filed Aug. 8. 1961 Il' Fred W Z/// INVENTOR United States Patent O 3,304,538 ACOUSTIC WELL LOGGING DOWNHOLE CNTRL SYSTEM Fred W. Zill, Houston, Tex., assignor to Schlumberger Well Surveying Corporation, Houston, Tex., a corporation of Texas Original application Aug. 8, 1961, Ser. No. 130,116. Divided and this application Feb. 7, 1966, Ser. No.

is claims. (ci. 34a-1s) This application is a division of my copending application for Acoustic Logging Tool, Serial No. 130,116, tiled VAugust 8, 1961.

This invention relates to exploratory tools for use in well bores and more particularly to tools and systems useful for determining the quality of bonding between a casing and an outer sheath of cement, the location of casing collars, and types of earth formations behind a casing.

In well completion practices, after the selection of a likely production zone, a casing or string of pipe is inserted in the well bore; and cement is pumped into the annulus between the casing and borehole. The cement, upon setting, serves to plug the annular space between the pipe and the borehole to prevent migration of fluids. It is desirable to ascertain after the cementing operation whether the column of cement has adequately plugged the annular space or whether portions of cement failed to completely surround the casing or failed to bond properly to the exterior of the casing. It is also desirable to locate casing collars and the type of formations behind a casing.

In another typical oil eld practice, where a recovery loperation for a stuck drill pipe is contemplated, it is important to know the depth at which the earth formations have seized the pipe. In many instances the packing of the earth formations about the pipe is acoustically analogous to the conditions of a cement bonded pipe in that an acoustic signal is attenuated by the earth formations which are packed about the casing.

Accordingly, it is an object of the present invention Vto provide new and improved apparatus for logging the quality of cementation in a cased well bore.

It is an object of the present invention to provide new and improved apparatus for ascertaining acoustically the packing of earth formations about a pipe string.

A still further object of the present invention is to provide new and improved apparatus for use in a monocable for logging the quality of oementation in a cased well bore.

A still further object of the present invention is to provide new and improved circuit systems useful in the operation of a well tool suspended in a well bore by means of a monocable.

Another object of the present invention is to provide new and improved circuit systems.

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

FIG. 1 illustrates a section of the earth formations traversed by -a cased well bore in which a tool embodying the present invention is disposed.

FIG. 2 illustrates schematicaly a log presentation of typical measurements `obtained by use of the apparatus embodying the present invention.

FIG. 3 is a view in cross-section taken along line 3-3 of FIG. l.

FIG. 4 is a view in cross-section through a section of the earth formations traversed by earth bore and briefly "ice illustrating in cross-section a modified arrangement for the tool illustrated in FIG. l.

FIG. 5 is a schematic illustration of the electrical circuitry in the down hole portion of the apparatus of the present invention.

FIG. 6 is a schematic representation of the electrical circuitry at the earths surface which is coupled to the down hole apparatus for obtaining the log illustrated in FIG. 2.

FIG. 7 is a more detailed circuit illustration of a circuit element schematically illustrated in FIG. 5.

FIG. 8 is a more detailed circuit illustration of a circuit element schematically illustrated in FIG. 5.

FIG. 9 depicts typical electrical wave forms occurring at various points in the circuit illustrated in FIG. 8 for a given input signal.

FIG. l0 depicts typical electrical wave forms occurring at various points in the circuit illustrated in FIG. 84 for another input signal.

Referring now to FIG. l, an apparatus 10 is shown disposed within a casing 11, the casing being firmly coupled to the borehole 12 by means of a column of cement 13. The apparatus 10 is adapted to be suspended in the well bore and passed therethrough by means of a monocable 14 and a conventional winch or pulley (not shown) situated at the surface of the earth. Apparatus 10 is shown positioned to one side of the casing 11 since. in ordinary practice, the casing and/ or well bores invariably are inclined relative to a vertical so that the apparatus naturally gravitates to a lowermost side of a well bore.

The apparatus 10 includes an upper housing section 15 containing a magnet 16 which has longitudinally extending north and south poles arranged parallel to one another and suitably spaced from one 4another to provide magnetic attraction to the upper end `of the housing relative to the casing. The magnet 16 thus offsets resultant forces on the cable which may exist at the upper end of the housing thereby to maintain the upper end of the housing from tilting relative to the casing. Below the upper housing section 1S is an electronic cartridge assembly or housing section 17 which may include a conventional casing collar locator means (not shown) and a conventional radioactivity detector device or means for detecting naturally occurring radioactivity such as gamma rays.

Below the section 17 is the acoustic section 18 which, for example, may be a tubular, rigid housing constructed of steel. A transmitter section T and a receiver section R are spaced from one another along the length of housing section 18, and the interval of housing between the transmitter T and receiver R sections is suitably perforated in a manner calculated to interrupt lengthwise extending acoustic energy along the housing 18 between the transmitter and receiver sections. The transmitter T and receiver R sections may, for example, include longitudinally extending slots 19 equidistantly spaced from one another about the periphery of the member 18; and suitable acoustic transducers (not shown), such as magnetostrictive transducers may be suitably secured relative to the transmitter T and receiver R sections.

The perforations along the length of housing member 18, for example, may include transverse, generally rectangular slots 19a which are staggered or offset relative to one another lengthwise of the housing so that a straight-line acoustic path lengthwise of the housing is substantially interrupted. The perforations may also include circular shaped openings 19b which are illustrated in FIG. 1 in an intermediate position between the transmitter T and receiver R sections. Openings 19b are symmetrically disposed relative to the length of the housing to receive suitable spacing or stand ol plugs 24 which provide a means of spacing the entire assembly a given 3 distance from the wall to the casing. As shown in FIG. 3, the spacing or stand o plugs 24 may be rubber, grommet-like members which are received in openings 1% about the circumference of the housing to provide an overall peripheral coverage to space the housing a given distance from the casing regardless of its relative angular position in the casing.

The function of the tool as thus far briefly described is to obtain, at the surface of the earth, recordings of various measurements plotted against depth. The recording may be more specifically identified as a Gamma Ray Log, (GRL), a Casing Collar Log (CCL), and a Cement Bond Log (CBL).

By Cement Bond Log it is meant that acoustic energy transmitted between an acoustic transmitter and receiver in a cased well bore is measured in a certain manner to provide measurements for obtaining a recorded indication of the quality of cementation. The CBL, as shown in FIG. 2, typically provides a base line indication 32 where the cement is suitably bonded to casing, and where bonding is not present, the signal deviates from the base line 32 to produce typical indications or

excursions

33 and 34. The relative intensity of an

excursion

33 or 34 is believed to be indicative of the relative quality of cementation, i.e., the greater the excursion the less likelihood of bonding, or effectiveness of cementation, or the presence of cement.

As shown in FIG, 2, a typical Gamma Ray Log is a plot of the intensity of radioactivity in the earth formations, and the base line 27 of the log would normally indicate the shale zones since shale generally emits more gamma radiation than other type of formations.

Excursions

28 and 29 of the Gamma Ray Log suggest formations other than shale and may be correlated with the logs of the formations made prior to the casing of the well bore.

The Casing Collar Log provides suitable indications of the location of the casing collar along the length of the casing. As typically shown in FIG. 2, an indication 34) would denote the presence of a collar in the casing string at the depth of the indication.

Referring now particularly to FIG. 5, the travel path 40 of acoustic energy between the Transmitter and Receiver is illustrated in a simplified form in terms of a -ray of energy which travels through the well uid to the casing, along the casing and returns to the receiver. The intensity of the wave front for the acoustic energy traveling path 40 is dependent upon the degree of coupling of the casing to the material surrounding the casing and the characteristics of the material itself.

In FIGS. and 6 the system for deriving the abovedescribed logs include a surface source or power supply 43 of alternating current which is connected to an insulated monocable conductor 44 wherein the metal sheath 44a of the cable 14 forms a ground return. A switch 43a is inserted between the power supply 43 and conductor 44 to disconnect the supply 43 from conductor 44 and also to permit the selective connection of either a positive (B+) or negative (B-) source of direct current (D.C.) to the cable conductor 44. In the position of the switch 43a as illustrated, alternating current (A.C.) is supplied via cable conductor 44 to a conventional shaper circuit 42 in the borehole apparatus (FIG. 5). The secondary winding of the transformer 51 interposed between Conductor 44 and the Shaper circuit 42 does not affect the application of the A.C. signals to the shaper circuit 42 which is arranged to emit pulses to synchronize the master keyer 4l with the A.C. supply. The master keyer 41, which is a conventional multivibrator of free running type synchronized by pulses from the Shaper, triggers the transmitter means 41a. The transmitter means 41a is arranged in a conventional manner to produce an acoustic impulse in response to the trigger from the keyer circuit 41 which impulse subsequently arrives at the receiver means 47a.

The electrical signal or trigger signal from the master keyer 41 which operates the transmitter means 41a also triggers a conventional delay circuit 45 which, after a predetermined time, actuates a conventional time gate circuit 46. The time gate circuit 46, in turn, controls an amplitude sensitive circuit 47 for a preselected time period so that an electrical output signal is developed which is representative of the peak amplitude of signal appearing at the input of the amplitude circuit 47 during the preselected time period. The amplitude circuit 47 is coupled between the receiver means 47a and a low pass filter 48 which serves to perfect -or smooth out the output signal of the amplitude circuit 47. The output signal from amplitude circuit 47 is passed from the lter 48 to an output circuit 49 which is arranged to develop an output signal containing pulses wherein the pulse rate of the output signal is proportional to the amplitude of the peak voltage of the input signal derived from the amplitude circuit 47. The pulses of the output signal are negative relative to a reference value electrical or ground return and are conducted to the monocable conductor 44 via the primary Winding 56 of transformer 51. The secondary winding 52 of transformer 51 is isolated from the electrical ground return 44a by means of a blocking capacitor 53.

From the foregoing it will be appreciated that, at a predetermined time after the acoustic impulse is emitted by the transmitter means, an electrical signal is generated by the receiver means in response to the arrival of the emitted acoustic impulse; and this signal is sensed by the amplitude circuit 47 over a predetermined time period or interval. In this way each of the successive measurements are related to one another since they are consistently sampled at like or given predetermined times after the emission of acoustic impulses and over like or given predetermined time intervals.

In accordance with the foregoing remarks, if it is desired to measure the characteristic of the signal as it initially arrives at the receiver means, the time may be calculated in a well-known manner by a consideration of the stand off distance of the transmitter means and the receiver means from the wall of the casing, the velocity of the fluids, the angle of incidence between the passage ofV acoustic energy when it is transmitted via the fluid into the casing, the velocity of the casing and the spacing between the Transmitter and Receiver. Thus, the stand off plugs 25 as disclosed in FIG. 3 now assume their proper significance and importance in providing a given stand off spacing of the tool from the casing so that the preselected time may be determined with a great deal of certainty. After a precise determination of the preselected time has been calculated, the delay circuit 45 may accordingly be set to operate time gate 46 at a time related to the triggering of the transmitter T. Time gate 46 may have an operational time duration set according to a selected time period (which may be determined from the frequency of the emitted acoustic impulse) to measure only the desired portion of the signal.

For one reason or another it may be desired to change the stand off distance of the tool from the casing Wall. For example, a centralizer unit (FIG. 4) with circumferentially spaced, elastomer constructed arms 65 can be coupled to the apparatus to centralize the same in the casing. Moreover, the desired portion of the signal to be measured may typically arrive either before or after the actuation of time gate 46 while the apparatus is in the well bore. In either of these cases, i.e., to accommodate changes in the stand olf distance yas well as optimize operation of the apparatus, a switching circuit (FIGS. 5 and 7) is connected to the delay circuit 45 and effectively controls the duration of the time delay occurring between the pulsing of the transmitter and the actuation of the time gate circuit 46. Specifically, the switch circuit 70 varies the time delay in circuit 45 by predetermined increments of time and is operated by a surface control signal transmitted via the monocable conductor 44 in a manner which will hereinafter be more fully explained.

Referring to FIG. 7, the switching circuit 70 for changing the time delay of delay circuit 45 is illustrated in detail. In general, the switching circuit 70 is adapted to be normally inoperative whenever the A.C. power source 43 at the earths surface (FIG. 6) is coupled to the conductor 44 of the monocable by switch 43a; and, as explained heretofore, when the A.C. source is disconnected from the conductor 44 by switch 43a, either positive or negative voltage .or control signals may be applied tothe monocable to eifect an operation of the switch circuit 70. In the particular :arrangement hereinafter to be described, a positive D.C. signal or potential serves to step a stepping switch in the switching circuit 70 while a negative D.C. potential or signal serves to reset the aforementioned stepping switch to its starting position. The connections of the various stationary contacts of the steppingr switch provide a control effect by varying the time delay characteristics of the delay circuit 45.

In the switch circuit 70, a first relay or switch 71 is arranged to be operated by virtue of an A.C. current on the -rnonocable 14 to disconnect an input conductor 44b of the monocable conductor 44 from an input conductor 72 in the switch circuit 70. In the absence of A.C. current in the monocable 14,

conductors

44b and 72 are normally connected to one another by a normal closed position of the contacts of switch 71. Switch 71 has a solenoid 72b which is electrically connected between an electrical ground and the downhole D.C. power supply 72a. The D.C. power supply 72a is coupled via a transformer 71a to cable conductor 44 so that the power from the A.C. surface supply 43 is rectified to provide a D.C. output to the solenoid 72b as well as provide DC. outputs or biasing potentials for other downhole circuitry. Hence, when the surface A.C. power supply 43 is connected to conductor 44, solenoid 72b. is energized so that switch 71 disconnects the input conductor 72 in the switch circuit 70 from the cable conductor 44b.

The delay circuit 45 may be a one shot multivibrator which is illustrated in part in the upper portion of FIG. 7 and includes a resistance 73 and capacitance 74 in a network wherein any change of capacitance in the network will alter the time delay operational characteristics of the multivibrator. As such, the capacitor 74 in the multivibrator may be selectively combined with other capacitors 74 (a, b k) with various selected values to selectively ,alter the time delay operational characteristics of the delay circuit 45. The various capacitances 74 (a, b k) may be coupled in parallel to the capacitance 74 by inserting the various capacitors between the respective stationary terminals of a stepping switch 76 tand on terminal of the capacitor 74 and connecting the movable arm 77 of the stepping switch 76 to the remaining terminal of the capacitor 74. The solenoid 78 for operating the stepping switch 76 is coupled to the input conductor 72 via a diode 77a which is connected such that a single positive DC. voltage signal applied to the 'input conductor 72 is conducted via the diode 77a to the solenoid 78, thereby stepping the switch through one step or one position. Hence, for each applied positive pulse the switch 76 may be stepped one position to distinctively change the time delay by a xed preselected increment of time.

Should it be desired to reset the switch 76 at any time to the initial `or home position illustrated in the drawings, the following system is provided. A cam 80 is mechanically coupled (as shown by dashed line 81) to the movable arm 77 of the stepping switch and controls the position of a mechanism of linkage 82 which in turn controls a relay or switch 83. Switch 83 has a movable contact coupled to the input conductor 72 which, in the initial position of the stepping switch 76 shown, couples input conductor 72 to a diode 84 and resistance 85 to electrical ground. The diode 84 is so connected that the diode 84 conducts only when the potential on conductor 72 is negative, and the resistance 85 thereupon provides an electrical load. Switch 83 in its other position connects its movable arm and, accordingly, the input conductor 72 to the movable arm of an interrupter switch 86 which in a closed position completes a circuit to the solenoid 78. Hence, the cam 80 serves to operate the relay switch 83 in a home position of the movable arm 77 of the stepping switch 76 to disconnect or break the electrical path from conductor 72 via the interrupter switch 86 to the solenoid 78.

From the foregoing description it will be appreciated that any time after the cam 80 is stepped one position, the linkage 82 operates switch 83 so that input conductor 72 is connected via switch 83 and interrupter switch 86 to the solenoid 78. Thus, if it is desired to reset the switch 76 to its initial position, a negative potential can be applied to the input conductor 72 via the cable conductor 44, which negative potential causes a current tiow via switch 83, interrupter switch 86 and the relay solenoid 78. Solenoid 78 is then energized to step one position, and in so doing, interrupter switch 86 is opened and closed. The opening of the interrupter switch 86 permits the solenoid 78 to be de-energized while the subsequent closing causes the cycle to repeat. Hence, the stepping switch 76 will be stepped automatically until the cam 80 actuates switch 83 to disconnect the input conductor 72 from interrupter switch S6. Switch 83 when actuated by cam 80 couples the input conductor 72 to the dummy resistance load 85 via the diode 84. Since the diode 77a in switch circuit 70 prevents further actuation of solenoid 78 of switch 76 by the negative potential, the stepping switch 76 is held in its home position. To prevent burning out and sparking of the contact elements of interrupter switch 86, an arc suppression network 90 may be connected across the switch 86.

It should also be appreciated that a purpose of disconnecting the solenoid 78 or dummy load 85 from the conductor 44 is to prevent shorting out of the casing collar signals and the pulse signals.

Referring now to FIG. 5, the amplitude circuit 47 which is controlled by a timed pulse output from time gate 46 includes a triode gating tube 90 with its control grid connected to time gate 46 and its plate coupled via a diode 91 to an amplifier 92 which is, in turn coupled to the receiver means 47a. The diode 91 is connected in this circuit so that voltage signals are eiectively passed to ground via the low impedance path of the triode 90. Also coupled to amplifier 92 is another diode 93 which is connected to a cathode follower 94. Between the diode 93 and cathode follower 94 are a resistance 95 and capacitance 96 which are connected to ground. Diode 93 is similarly connected to pass voltage signals from amplifier 92. The electrical signals generated by the receiver means 47a in response to acoustic impulses are passed via the triode 90 to ground by diode 91 since this is a relatively low impedance path. However, when a control pulse from time gate 46 cuts olf tube 9G, diode 93 conducts in response to the electrical signal and capacitor 96 is charged up to the attained peak value of the applied voltage. Resistor has a value to hold such an attained peak value for an adequate period of time. The resistor 95 and capacitor 96 are provided with a relatively large time constant and cathode follower 94 accordingly produces an output signal which is proportional to the peak value of the signal applied to diode 93 during the period that triode 90 is non-conducting. It has been considered preferable to measure the peak value of only a half cycle of the electrical `signal and, in particular, the second half of the first cycle of the signal.

The voltage output of the Cathode follower 94 is filtered or smoothed out by the lter circuit 48 and passed to the output circuit 49 which is arranged to produce a pulse output having a rate proportional to the amplitude of the input signal from the Cathode follower 94.

Output circuit 49 is shown in detail in FIG. 8, and in the diagram the input to output occurs from right to left. For a complete understanding, certain typical waveforms of the operating conditions at various locations in the circuit are illustrated in FIGS. 9 and 10. In the circuit, the input terminals 100 are arranged to receive the D.C. signal from low pass lter 48 which signal is applied via resistances 98 and 99 to the emitter 101 of a PNP transistor 102. A capacitor 97 is connected across the input terminals 100 to lter A.C. signal components. The collector 104 of transistor 102 is connected via a capacitor 105 to ground. The base 106 of transistor 102 is connected across a resistance load 109 coupled to an emitter 107 of an NPN transistor 108 wherein the collector 110 is connected to a regulated source of positive D.C. voltage and the base 111 is connected to a voltage dividing network comprised of

resistances

112 and 113. This cascaded transistor arrangement permits the voltage drop between the emitter 101 and base 106 0f transistor 102 to be balanced by the voltage drop between the base 111 and emitter 107 of the transistor 108. With the above described arrangement resistances 98 and 99 are made large compared to the input resistance at emitter 101 so that Ein El R1+R2 (1) where Ein represents the input voltage, In, represents the input current, El represents the voltage at the base of transistor 108 and R1, R2 represent the resistance values of resistances 98 and 99. Consequently, the current Ic to the capacitor is equal to the input current lin times the amplification factor ot. Capacitor 105 is charged by a constant current a 1in and acquires charge, and hence voltage, at a rate proportional to Im and therefore proportional to Ein.

Capacitor 105 is connected to a conventional Schmitt trigger circuit 114. In the quiescent condition of circuit 114, an input NPN transistor 115 is normally at cut oif or ott while an output NPN transistor 116 is normally conducting or on. The output conductor 117 of transistor 116 is -connected to the base 118 of an amplifying transistor 119 which, in turn, has its emitter 120 connected to the base 121 of another amplifying transistor 119a. The collector 123 of transistor 11961 is connected to the primary winding 50 of the output transformer 51 which has its secondary winding 52 coupled to the monocable 44. Winding 50 of the transformer 51 is coupled to a D.C. positive potential source.

The output conductor 117 of the Schmitt trigger circuit 114 is also connected via a conductor 122 to the base 124 of a transistor switch 125. Transistor switch 125 has an emitter 126 connected to ground and a collector 127 coupled via a resistance 128 to the capacitor 105,. Transistor switch 125 has normal operating condition at cutolic or oif The operation of the above-described circuit is as follows: at a given time lo (FIG. 9), the transistor 115 is off, transistor 116 is on and transistor 125 is oif. With an applied Em, the voltage EC on the capacitor 105 will reach a value of Et equal to the firing voltage of the transistor 115 of Schmitt trigger at a time IX, which time 1X 1S pfpOltlOIlal to Clef 2 where C `is the capacitance of capacitor 105. When transistor 115 res, or is turned on, transistor 116 is turned off and transistor switch 125 is turned on. Transistor switch 12'5 discharges capacitor 105, with a time constant dependent upon resistance 128 and capacitor 105, and this time constant is made short compared with the minimum period of an output pulse rate to be used. This time constant can be arranged, for example, so that 50 microseconds elapse before capacitor 105 discharges to Iin= a voltage ED. Of course, when the input voltage reaches a value of E0, the transistor of Schmitt trigger 114 is cut off, transistor 116 is turned on and transistor switch is turned off so that the capacitor 105 commences to charge again. With the same input voltage Ein, the time in which the capacitor 10S charges up to the trigger voltage of capacitor 105 is constant and hence it will be appreciated that the spacing or repetition rate of the pulses is dependent upon the amplitude of the input voltage. This is clearly evident from a consideration of FIG. l0 which corresponds to the diagram of FIG. 9 except that a greater slope occurs in the voltage buildup on capacitor 105 between times ta and tb indicating a higher input voltage Ein which permits a faster charging of the capacitor C105. The output pulses 130 of transistor 116 of the Schmitt trigger 114 thus have a xed pulse Width and aVY repetition rate dependent upon the amplitude of the input voltage. The period T of the output voltage of the transistor 125 is inversely proportional to the input voltage Ein, or, stated another way, the frequency of the output voltage of transistor 125 is equal to TOCEin The output signal supplied to the monocable conductor 44 may be detected in terms of the pulse rate which is proportional to the D.C. input voltage Ein, or the output signal can be translated to a D.C. output signal inversely proportional to the input voltage Em.

Returning now briefly to FIG. 5, the gamma ray detector means may consist, for example, of a conventional scintillation counter which detects the existing level of radioactivity and provides an output to a conventional discriminator circuit 141. A conventional scaler circuit 142 may be inserted between the discriminator circuit 141 and a conventional blocking oscillator output circuit 143 to conform the output of the discriminator circuit 141 to a more convenient form for cable transmission. The output of the blocking oscillator circuit 143 is coupled via a transformer 144 to the monocable conductor 44. The output of the gamma ray detector means is typically an -outyput of positive pulses wherein the repetition rate of the pulses provides an indication of the intensity of the radiation.

The conventional casing collar locater as illustrated is connected via a conventional amplier 151 to the monocable and provides typically a D.C. signal whose amplitude varies at a low frequency rate in response to the detecting coil of the collar locater 150 traversing a jointed connection in the pipe string. To prevent shorting out the low frequency casing collar signal, blocking

capacitors

53, 152 and 152a (FIG. 5) are inserted between the conductor 44 of the monocable and the ground return.

As shown in FIG. 6, at the surface of the earth there are essentially three signals which may be arriving either simultaneously or independently relative to one another. These signals are the D.C. casing collar signal, the positive pulses from the gamma ray signals, and the negative pulses of the acoustic logging apparatus. A conventional galvanometer in a recorder 155 at the earths surface is made responsive to the casing collar signals to the exclusion of the pulses from the gamma ray and acoustic circuit by suitable filtering so that the signals indicative of the occurence of casing collars may be recorded on the Casing Collar Log developed by the recorder. The positive and negative pulses of the radioactivity and acoustic circuits in the down hole apparatus are supplied to a filter circuit wherein the secondary winding 161 of the transformer 162 has its end terminals 161g, 161b respectively coupled to conventional detector circuits 162g, 162]). One of the detector circuits 162a is arranged to be responsive to only positive pulses while the other detector circuit 16212 is arranged to be responsive only to negative pulses. The

pulse generators

163a and 163b serve to reshape the pulses at the outputs of the detectors 162a and 162b, respectively. The output of detector 162g is coupled to the pulse generator 163a and also to a gate circuit 164er. The gate circuit 164a is arranged to be responsive to an output of detector 162a to turn off detector 16211 for a given period of time. Hence, if a positive pulse is detected first by the detector 162a, the gate 16451 would turn off the detector 16217 for a given time interval. The output of the pulse generator 163a is supplied to a counter circuit 165a which produces an output voltage representative of the number of pulses per second, which output voltage is supplied to the recorder 155. The output of detector 162b is similarly coupled to the pulse generator 163b and also to a gate circuit 164b. The gate circuit 164b is arranged to be responsive to the output of detector 16211 to turn off the other detector 162a for a given period of time. Hence, if a negative pulse is detected first by the detector 16211, the gate 16412 would turn off the detector 162a for a given time interval. The output of the pulse generator 163b is supplied to a counter circuit 165b which produces an output voltage representative of the number of pulses per second which output voltage is supplied to the recorder 155.

The operation of the apparatus from the foregoing detailed description may be readily appreciated; and, therefore, only a brief description hereafter is provided by way of summary of the more pertinent aspects of the present disclosed invention. In operation the apparatus is lowered in the usual manner to the lowermost depth from which the logging operation is commenced. Thereafter, at this depth the switch 43a at the surface is connected to the A.C. power source 43 so that the signals are sent down the cable conductor 44; and the keyer means 41 periodically pulses the transmitter to emit time spaced acoustic impulses. Since the stand olf device of the apparatus physically spaces the apparatus a given distance from the wall of the casing, the time of arrival of an emitted acoustic impulse at the receiver means 47a can be calculated. Since the emitted acoustic impulse normally consists of a number of cycles of undulating pressure waves, the receiver means 47a will respond to the pressure waves to produce a corresponding electrical signal. In accordance with a preferred operation of the present invention, it is desired to measure only a single pressure peak which, of course corresponds to single peak of the electrical signal. The pressure peak to be measured is preferably the second peak of the first cycle of an acoustic impulse to arrive at the receiver means 47a. Because the time at which such a second peak will arrive `at the receiver ymeans 47a can be precisely calculated, the amplitude circuit means 47 is actuated at a predetermined time after emission of an acoustic impulse for a predetermined time interval. The timing function for circuit means 47 is accomplished by a delay means 45 and time gate 46 which are connected between the transmitter means and the amplitude circuit 47 which is connected to the receiver means. The amplitude of the electrical signal thus sensed by amplitude circuit means 47 is converted into a pulse by output circuit 49 which pulse output has a relatively negative polarity with respect to a reference level and which pulse output has a repetition rate dependent upon the amplitude of the peak of the signal which was sensed. The negative pulses are passed up cable conductor 44 to trigger a detector 162b (FIG. 6) which promptly switch off a positive pulse channel detector 162e and counts the number of pulses and applies a signal to the recorder 155 indicative of the amplitude of the signal detected in the bore hole by the receiver means 47a. From experience it will generally be known what the amplitude of the signal should be in a casing in which the cement is properly bonded thereto; and while the apparatus is thus resting in the lowermost position of the borehole, such an indication should substantially be reproduced by the recorder.

If, however, the amplitude indication initially obtained is not precisely the indication which might be expected, the accuracy of the reading may be checked by changing the predetermined time delay in the following manner: Switch 43a is moved to disconnect the A.C. power source 43 from the cable conductor 44 which immediately disconnects the transmitter means 41a and the power supply 72a in the borehole apparatus and accordingly discontinues the supply of downhole output potentials from the power supply 72a. Thus, the solenoid 72b of the switch 70 in the borehole apparatus (which is connected to the output of the power supply 72) is dce-energized to permit the switch 71 to assume the position shown in FIG. 7 connected the cable connector lead 44b to the input conductor 72 in the switch 70. Now switch 43a at the surface may be moved `to connect the source of potential B+ to the cable conductor 44 at which time a control signal passes down the cable conductor 44 via the switch 71 and diode 77a to actuate a solenoid 78 to step the stepping switch 76 one position. In the home position shown in the drawings, a cam 80 simultaneously moved with the movable arm 77 of switch 76 connects the input conductor 72 via a switch 83 and an interrupter switch 85 to the solenoid 78. The stepping of the switch 76 effectively changes the capacitance in a one-shot multivibrator delay circuit so that the predetermined time at which the time gate 46 is actuated has been changed by an incremental period of time. Next, the A.C. power source 43 can again be connected to the cable conductor 44 to operate the transmitter means 41a and the downhole power supply 72a is again actuated to operate solenoid 72b to disconnect, by means of switch 77, the switch ing circuit from the cable conductor 44. With the transmitter means 41a again emitting impulses, the recorder will as previously described produce an indication of the amplitude signal obtained at the predetermined time and during the predetermined time after the emission of each pulse. The above-described operation may be repeated by disconnecting the power supply 43 and applying a positive control signal at the surface to move the stepping switch to another position. At any time, should it be desired to return the stepping switch to its initial home position, the switch 43a at the surface may be connected to a negative source of potential and this control signal passed via cable conductor 44, the switch 71 and switches 83 and S6 to the solenoid 78. The stepping switch 76 will be continuously actuated as long as the negative source of potential is applied by virtue of the interrupter switch 86 continuously providing the interruption necessary to energize and de-energize solenoid 78 and step the switch. At the time the movable arm 77 of the stepping switch 76 approaches its home position, the cam 80 actuates a linkage 80 to disconnect the circuit through the interrupter switch 86 by opening the switch 83 and connecting the negative source of potential to a dummy load 85 in the switch circuit. Switch 83 when open disconnects the solenoid 78 from being operated by the negative potential signal and the switch thus stops in the home position. It will be appreciated that although a stepping switch and solenoid are specifically disclosed as operated by the switch 71, the principle involved in the surface control of switch 71 by the circuit 72a is applicable to any type of downhole circuit means which may be substituted for the stepping switch and solenoid 78 and selectively operated by a signal which does not actuate circuit 72a.

At the same time that the acoustic probing means above described are probing the material surrounding the Well bore with the acoustic impulses and providing a pulse output with a given polarity to the common cable conductor 44, a scintillation counter which detects radioactivity in the adjacent surrounding media provides a pulse output which is positive with respect to a reference value. The pulse output of the radioactivity means is also applied to the common cable conductor. Hence, both positive and negative pulses with respect to a common reference value are supplied to a common cable conductor. Also imposed upon the common cable conductor are casing collar signals which occur only when the device traverses a jointed section between the casing where the changes in the ferromagnetic configuration of the pipe string causes the casing collar locator to produce a low frequency output signal which is also supplied to the common cable conductor 44. At the earths surface (FIG. 6) the outputs are individually used to develop the individual log presentations as illustrated in FIG. 2.

As shown in FIG. 8 the amplitude to pulse converter uses a well-known Schmitt trigger circuit 114 in a unique arrangement to provide relatively small time duration pulses, i.e. about 50 microseconds with a repetition rate dependent upon the input amplitude. In this arrangement a constant current source is used to charge a capacitor which thereby provides the signal for triggering the Schmitt circuit. A transistor switch is connected to a resistance discharge path and operated upon the triggering of the Schmitt circuit to rapidly discharge the capacitor to turn the Schmitt circuit off again.

The foregoing described features are illustrative of a unique system of acoustic logging both singly and in combination with other systems to provide output pulses suitable for single conductor transmission, unique systems of controlling downhole circuit systems coupled to a single conductor, and unique systems of developing output pulses with a repetition rate dependent upon input amplitudes.

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.

I claim:

l. In a well logging apparatus adapted to be suspended below the earths surface in a Well bore by a cable including a single transmission conductor, a control function circuit operable by signals transmitted from the surface over the conductor, comprising lirst circuit means responsive to first signals on the conductor for developing first output signals, seco-nd circuit means having an input connectable to the conductor and responsive to second signals on such conductor for developing control function signals, and switch means connected between the input of said second circuit means and the conductor, said switch means being responsive to said rst output signals to actuate said switch means to selectively decouple the second circuit means from the conductor.

2. In a well logging apparatus adapted to be suspended below the earths surface by means of a monocable in a well bore, a control function circuit operable by signals transmitted from the surface over the monocable, comprising circuit means responsive to first signals on the monocable for developing rst output signals, stepping switch means including an actuator responsive to second signals on the monocable for providing various connections between movable and stationary contacts, and switch means connected between the actuator of said stepping switch means and the monocable and responsive to said first output signals to actuate said switch means to decouple the stepping switch means from the monocable.

3. In a well logging apparatus adapted to be suspended beneath the earths surface by means of a monocable in a well bore, a control function circuit operable by signals transmitted from the surface over the monocable, comprising a switching circuit responsive to D.C. control signals on the monocable for developing a control function, circuit means responsive to an A.C. signal on the monocable for developing an output signal, and switch means connected intermediate said switching circuit and the monocable and responsive to said output signal for controllably decoupling said switching circuit from the monocable.

4. In a well logging apparatus adapted to be suspended beneath the earths surface by means of a monocable in a well bore, a control function circuit operable by signals transmitted from the surface over the monocable, comprising a switching circuit responsive to D.C. control signals on the monocable for developing a control function, rectifier means responsive to an A.C. signal on the monocable for developing a D.C. output potential, and switch means connected between said switching circuit and the monocable and responsive to the D.C. output potential for controllably decoupling said switching circuit from the monocable.

5. In a well logging apparatus adapted to be suspended beneath the earths surface by means of a monocable in a well bore, a control function circuit operable by signals transmitted from the surface over the monocable, cornprising: a switching circuit including a solenoid operated stepping switch responsive to D.C. control signals on the monocable for developing a control function, a reset switch and an interrupter switch connected in a series circuit with said solenoid, said interrupter switch being operable by said stepping switch to cause said stepping switch to advance a predetermined number of steps for each application of a D.C. control signal of given polarity on the monocable, said reset switch interrupting said series circuit when the stepping switch is in a predetermined position, and a diode connected between the input of said reset switch and said solenoid to bypass said switches while a D.C. control signal of an opposite polarity is applied to the switching circuit; rectifier means responsive to an A.C. signal on the monocable for developing a D.C. output potential; and switch means connected between said series circuit and the monocable and responsive to said D.C. output potential to decouple said switching circuit from the monocable.

6. An electrical system for converting an analog signal into a digital signal including: circuit means having an input and output and operable to develop a pulse output; current storage means coupled to said input to provide an input trigger signal upon charging up to a predetermined value; selectively operable discharge means coupled to said current storage means and responsive to a pulse output signal from said circuit means to discharge said current storage means.

7. An electrical system for producing output pulses at a rate proportional to an input current signal including, a trigger circuit for providing an output pulse in response to an input signal exceeding a given voltage magnitude, storage means coupled to said trigger circuit and adapted to be charged by a current signal to provide an input voltage signal for said trigger circuit, and discharge means coupled to said storage means and said trigger circuit and operable in response to an output pulse to discharge said storage means.

8. An electrical system for producing output pulses at a rate proportional to a current signal including a trigger circuit for providing an output pulse of constant width and constant amplitude i-n response to an input signal exceeding a given voltage magnitude, storage means coupled to said trigger circuit and adapted to be charged by a current signal to provide an input signal for said trigger circuit, means for providing a constant current signal to said storage means, and discharge means coupled to said storage means and said trigger circuit and operable in response to an output pulse to discharge said storage means.

9. An electrical system for producing output pulses at a rate proportional to a current signal including a Schmitt trigger circuit for providing an output pulse of constant width and constant amplitude in response to an input signal exceeding a given voltage magnitude, storage means coupled to the input of said trigger circuit and adapted to be charged by a current signal to provide an input signal for said trigger circuit, means coupled to the input of said storage means to provide a constant current signal to said storage means, and discharge means coupled to said storage means and said trigger circuit and operable in response to an output pulse to discharge said storage means.

10. The apparatus of claim 9 wherein said discharge means includes a resistance and a normally non-conducting switch device, said switch device being operative in response to an output pulse to discharge said storage means.

11. In a well logging apparatus adapted for suspension in a well bore by a single cable conductor, a system for controllably generating a pulse output representing an analog signal, comprising: first circuit means responsive fto Vfirst signals-on the conductor for developing first output signals; second circuit means responsive to second signals on the conductor for developing a control function; switch means connected between the input of said second circuit means and the conductor and being responsive to said first output signals for selectively coupling and decoupling said second circuit means from the conductor; gating means responsive to said control function to provide gating pulses in variable time relation to the occurrence of an amplitude signal; means responsive to the amplitude signal and to said gating pulses to provide an analog signal representative of the strength of said arnplitude signal within the time duration of said gating pulses; and analog to digital converting means including pulse circuit means having an input and output and operable to develop a pulse output, storage means responsive to said analog signal and coupled to said input to provide an input trigger signal upon charging up to a predetermined value, and selectively operable discharge means coupled to said storage means and responsive to a pulse output signal from said pulse circuit means to discharge said storage means.

12. Apparatus in accordance with claim 11 wherein said means responsive to the amplitude signal includes voltage storing means responsive to said amplitude signal for storing a voltage signal proportional to the maximum amplitude of said amplitude signal occurring within the time interval of one of said gating pulses, and means responsive to said voltage signal to produce said analog signal.

13. In well logging apparatus adapted to be suspended by a monocable in a well bore beneath the earths surface, a variable pulse width generating system operable by signals transmitted from the surface over the monocable, comprising: pulse generating means for generating variable time width pulses in synchronism with first signals on the monocable and including timing circuit elements determinative of the pulse time width; switching means responsive to control signals on the monocable for selectively switching different-valued elements into said timing circuit; and circuit means responsive to said first signals on the monocable for rendering said switching means unresponsive to said control signals when said first signals are present.

14. Apparatus as defined in claim 12, wherein said circuit means comprises a switch connected intermediate the monocable and said switching means, and means responsive to said rst signals only for actuating said switch to disconnect said switching means from the monocable.

15. In a well logging apparatus adapted to be susnpended by amonocable in a well bore beneath the eamhs surface, a control function circuit operable by signals transmitted from the surface over the monocable, comprising: a switching circuit including actuator means operative to complete a successive one of a number of electrical connections in response to each application of a first control signal on the monocable, said switching circuit also including means responsive to each application to the monocable of a second control signal distinctive from said first signal for causing the selection by said actuator means of a predetermined one of said electrical connections; circuit means responsive to third signals on the monocable for developing a third control signal; and switch means connected between the actuator means of said switching circuit and the monocable and operable by said third control signal for selectively rendering the switching circuit responsive and unresponsive to said first and second control signals.

References Cited by the Examiner UNITED STATES PATENTS 2,876,434 3/1959 Oberlin 340-18 X 2,901,685 8/1959 Alder 340-18 X 2,963,640 12/1960 Buckner 340-18 X 2,973,505 2/1961 Ioha-nnesen 340-18 3,060,388 10/1962 Ball et al 307-88.5-l8 3,098,947 7/1963 Flieder 320-1 X 3,177,467 4/1965 Brokaw 340-18 3,187,301 6/1965 Summers 181-.5 X 3,191,145 6/1965 Summers 340-18 BENJAMIN A. BORCHELT, Primary Examiner.

R. M. SKOLNIK, Assistant Examiner.

Claims

1. IN A WELL LOGGING APPARATUS ADAPTED TO BE SUSPENDED BELOW THE EARTH''S SURFACE IN A WELL BORE BY A CABLE INCLUDING A SINGLE TRANSMISSION CONDUCTOR, A CONTROL FUNCTION CIRCUIT OPERABLE BY SIGNALS TRANSMITTED FROM THE SURFACE OVER THE CONDUCTOR, COMPRISING FIRST CIRCUIT MEANS RESPONSIVE TO FIRST SIGNALS ON THE CONDUCTOR FOR DEVELOPING FIRST OUTPUT SIGNALS, SECOND CIRCUIT MEANS HAVING AN INPUT CONNECTABLE TO THE CONDUCTOR AND RESPONSIVE TO SECOND SIGNALS ON SUCH CONDUCTOR FOR DEVELOPING CONTROL FUNCTION SIGNALS, AND SWITCH MEANS CONNECTED BETWEEN THE INPUT OF SAID SECOND CIRCUIT MEANS AND THE CONDUCTOR, SAID SWITCH MEANS BEING RESPONSIVE TO SAID FIRST OUTPUT SIGNALS TO ACTUATE SAID SWITCH MEANS TO SELECTIVELY DECOUPLE THE SECOND CIRCUIT MEANS FROM THE CONDUCTOR.