CA1185351A - Borehole televiewer system using multiple transducer subsystems - Google Patents

Abstract

"BOREHOLE TELEVIEWER SYSTEM USING
MULTIPLE TRANSDUCER SUBSYSTEMS"
ABSTRACT OF THE DISCLOSURE
In an acoustic logging system for providing information regarding selected parameters of the wall of a borehole in the earth, and of the rock formation which is adjacent the borehole, in which a single transmit/receive transducer system (T/RTS) mounted on a rotating assembly probes the wall of the borehole in a circular scanning pattern as a function of depth, the improvement which includes at least a second T/RTS mounted on the rotating assembly in known geometrical relation to the first T/RTS, and means to utilize in combination the electrical scan signals from the at least two scanning T/RTS.

Description

35~

"BOREHOLE TELEVIEWER 5YSTEM USING
MULTIPLE TRANSDUCER SUBSYSTEMS"
BACKGROUND OF THE INVENTION
1. Field of the Invention This invention lies in the field of acous~ic 15 logging systems for boreholes. More particularly, it is concerned with the lo~ging of deep boreholes in the earth.
Still more particularly, it concerns the use of an acous-tical transducer which transmits a beam of high frequency acoustic energy into the borehole directed in a radial 20 plane, and receives the returned reflected acoustical energy signal from a reflecting surface, such as the wall of the borehole, and transmits a processed electrical scan signal derived from such received signal, to the surface of the earth, through the cable which supports the instru-25 ment, or sonde, for further processing.
Still more particularly, it concerns improve-ments in such acoustic logging devices and in particular the use of two or more transducer systems on a single rotating assembly so that multiple probing signals are 30 sent outwardly from the axis of the borehole and multiple reflected sonic signals are received, converted to elec-trical scan signals, which are then utilized in various ways.
Still more particularly, this invention concerns 35 improvements in methods and apparatus for processing mul-tiple simultaneous analog electrical scan signals (ESS) in the sonde for transmission to the surface in real time, over conventional logging cables which may have only a single, or possibly only two conventional intermediate frequency signal transmission channels.

2. Description of the Prior Art This field of science and engineering is not 5 new. It has been in useful operation in the logging of boreholes in the earth, such as oil and gas wells, for a number of years. There are various patents issued on selected features of these systems, and including the basic system, which form no part of this invention.
Examples of the prior art are illustrated by U.S. Patent No. 3,369,626 entitled: "METHOD OF AND
APPARATUS FOR PRODUCING A VISUAL RECORD OF PHYSICAL CONDI-TIONS OF MATERIALS TRAVERSED BY A BOREHOLE", issued February 20, 1968 in the name of J. Zemanek, Jr. There is 15 also U.S. Patent No. 3,663,619 entitled: "THREE-DIMEN-SIONAL PRESENTATION OF BOREHOLE LOGGING DATA", patented June 6, 1972 in the name of Charles L. Dennis; U.S. Patent No. 3,550,075 entitled: "SYSTEM FOR DISPLAYING TIME
INFORMATION IN ACOUSTIC WELL LOGGING SYSTEM", issued 20 December 22, 1970 in the name of D. W. Hilchie et al; and U.S. Patent No. 3,835,953 entitled: "ACOUSTIC CALIPER
LOGGING", issued September 17, 1974 in the name of Jerald C. Summers. There is also additional art recorded in the form of other patents, and in technical papers pre-25 sented at technical society meetings, so that furtherdescription or statement of the art is not necessary at this time.

s~

SUMMARY OF THE INVENTION
It is a primary object of this invention to pro-vide a number of improvements in the design and construc-tion of borehole logging instruments employing acoustical S probing beams, and reflected sonic signals, and in the use of data from these instruments.
It is a further object of this invention to pro-vide at least two or more transmitting receiver transducer systems (T/RTS) operating independently to provide mul-10 tiple electrical scan signals~ which are used coopera-tively, in combination, to provide more informat:ion than would be possible by their separate use.
It is another objective of this invention to provide apparatus and methods for processing multiple ESS
15 in a sonde for improved transmission over single or double transmission channels in conventional electrical logging cables.
In the prior art, the rotating system, which is part of the logging instrument, or sonde, is lowered into 20 the borehole in the earth by means of a long cable, unwound from a drum, and passing over a measuring wheel mounted at the mouth of the well, at the surface. Such cables comprise a multiple set of conductors, which can be used in various ways to transmit data from the sonde to 2~ the surface, and also to transmit power and/or control signals from the surface to the sonde. The main limita-tion of these instruments has been the use of only a single transmit/receive transducer system (T/RTS). Thus, in logging a hole it is necessary in advance to make a 30 judgment as to which type of transducer, measuring a selected parameter, will be the most useful in a given subsurface situation.
In this irlvention the improvement lies in the use of two or more T/RTS. These are mounted on the same 35 rotating assembly as the normal single T/RTS~ in a known geometrical relationship to the first one. There may be two, three, four or more additional T/RTS and these may have the same electrical characteristics as the first one, s~

or they may each be differen~ from the other. By the use of different T/RTS, it is possible to probe into the earth to a deeper or shallower depth, depending upon the charac-teristic and the frequency of the T/RTS. For example, one 5 of the problems of the conventional system is that it has a high frequency T/RTS, and high frequency sonic waves in the fluid in the well, such as drilling mud, suffer a high attenuation. Thus, the penetration of the sonic beam is limited by this attenuation, due to the fact that the lO sonic waves must travel a selected distance through the mud, or other fluid in the wellbore. By making the T/RTS
of a lower frequency, the attenuation becomes less, and thus the sonic beam probes to a greater depth, or radial distance from the transducer into the rock wall.
With a plurality of similar transducers, arranged in a common plane transverse to the axis of the rotating assembly of the sonde, equally spaced circumfer-entially, a plurality of scans are made simultaneously, as the sonde is moved vertically at a selected constant rate.
20 Thus, a shorter vertical spacing along the wall of the borehole is provided for each scan. This permits a much finer detail of scanning or probing. Conversely, it per-mits a higher rate of logging to get the same spacing of scan or probe traces The arrangement of multiple T/RTS can be in a horizontal plane circumferentially spaced, or in a ver-tical plane longitudinally spaced. This use of arrays of T/RTS will provide a stronger, better-focused scanning beam, of higher energy. Thus, the penetration of the beam 30 can be greatly increased.
Another problem addressed by the invention is how these multiple ESS can be transmitted to the surface by the use of logging cables which were originally designed for transmitting relatively low frequency elec-35 trical logging signals, and so on, that is, signals ofless than about 50 KHZ. The apparatus and methods of processing the mul tiple ESS form an aspect of this invention. The partic-ular apparatus design depends on a number of factors, such as:
a) the nwmber of separate T/RTS and resulting ESS;
b) whether the frequencies of the T/RTS are the same or different;
c) whether the complete received signals are required~ or simply measurements of ampli-tude of reflection, and time of travel, or depth of penetration, or caliper;
d) whether selective portions of each of two ESS can be gated to combine the two por-tions as a single signal;
e) whether a single transmission channel is provided in the cable, or more parallel channels, f) the nat-ure of the transmission channels, that is, their frequency pass bands; and so on.
These and other aspects of this invention will be described in detail in relation ~o the drawings.

3~i~
BRIEF DESCRIPTION OF THE DRAWINGS
.. . .
These and other objects and advantages of this invention and a better understanding of the principles and details of the invention will be eviden~ from the fol-S lowing description ~aken in conjunction with the append~ddrawings, in which:
FIGURE 1 il]ustrates the prior art simply in the arrangement of the logging sonde held concentric with the wellbore by means of radial centering springs supported by 10 a cable which runs over a measuring wheel, the rotations of which are functions of depth.
FIGURE 2 illustrates one embodiment of this invention employing two T/RTS arranged 180 apart in a horizontal plane on the rotating assembly.
FIGURE 3 illustrates one method of utilizing the two T/RTS of FIGURE 2.
FIGURE 3A illustrates the surface apparatus that might be used in combination with the downhole apparatus of FIGURE 3.
FIGURE 4A illustra~es the relative operation of higher frequency versus lower frequency T/RTS, while FIGURE 4B illustrates the gating operation of the two T/RTS shown in FIGURE 4A.
FIGURE 5 illustrates the received signal from 25 the two transducers of FIGURE 4A.
FIGURE 6 illustrates the use of time delay between the two T/RTS of FIGU~E 3 combined with the gating system of FIGURE 4B.
FIGURES 7 and 7A illustrate two variations of a 30 system employing two separate T/RTS.
FIGURE 8 illustrates the main mechanical con-struction of a single T/RTS mounted on the rotating assembly in the sonde.
FIGURE 9A, 9B, 9C, and 9D illustrate the pos-35 sible arrangement of two, three, four, and six, T/RTS in ahorizontal plane, equally spaced, circumferentially.
FIGURE 10 illustrates a system in which multiple T/RTS are provided on the rotating system~ but these are ~ 3 separated in a longitudinal direction in a common radial plane through the axis of rotation.
FIGURE 11 illustrates the possibility of using multiple T/RTS in a linear array horizontally so that beam 5 formin~ techniqiles may be used to provide a better focused and more penetrating beam than would be provided by a single I'/RTS.
FIGURES 12A, 12B, and 12C represent various methods of transmission and utilization of the scan signal 10 from multiple T/RTS.
FIGURE 13 illustrates a variation of FIGURE 10.
FIGURE 14 is an extension of portions of FIG-URES 2 and 3, illustrating how four separate T/RTS can be mounted on the rotating assembly and can be connected as 15 desired to the pulser and to the cable.
FIGURE 15 is an extension of FIGURE 3, illus-trating the use of multiple pulsers, one for each of the separate T/RTS so that parallel output scan signals are provided simultaneously.
FIGURE 16 is a modification of part of FIGURE 15 showing alternate transmission of two or more electrical scan signals which may be from T/RTS of the same or dif-ferent frequencies.
FIGURE 17 illustrates the time scheduling of the 25 alternate transmissions of the two or more electrical scan signals of FIGURE 15.
FIGURE 18 illustrates one embodiment of appar-atus for transmitting two or more simultaneous analog electrical scan signals by converting them to double fre-30 quency analog electrical scan signals for transmission over a single transmission channel.
FIGURE 19 illustrates the time scheduling of the two simultaneous electrical scan signals and the sequen-tial transmission of the double frequency scan signals.
FIGU~ES 20A, 20B, 20C, 21A, and 21B illustrate different embodiments for transmission of two or more ESS
to the sur~ace, over a single and/or a double transmission channel cable.

FIGURE 22 illustrates one embodiment of surface apparatus for receiving and recording analog and digital ESS.
FIGURE 23 illustrates an apparatus for providing 5 separate digital signals comprising the amplitude of a reflection, and the time of travel, or distance of pene-tration, and multiplexing the two digital signals.
FIGURE 24 illustrates an extension of FIGURE 23, in which plural digital signals of amplitude and caliper 10 from plural ESS are multiplexed and transmitted over a single transmission channel.

~5 3 BRIE~ DESCRIPTION OF THE PREFERRED EMBO~IMENTS
Definitions:
There are a number of words designating elements or parts of the invention that will be us~d frequently 5 during the following description. I propose to define these in advance so that words may be saved in the description. 1. Sonde. This is the sealed logging instrument that contains the transducers, the controls, and power means for driving the transducers. 2. Rotating 10 assembly or drum. This is the assembly on which the transducers are mounted, and which rotates about the axis of the sonde~ 3. The transducers. These are the means to generate a sonic beam responsive to the application of a high frequency voltage or pulses to the transducer. In 15 some instances the sonic generator can also be used as a sonic wave detector. In other ins~ances one of a pair of transducers is used as a detector. These units will be called Transmit/Receive Transducer System or T/RTS.

4. While principal use of this sonde is in logging ver-20 tical boreholes in the earth, it can equally well be usedin horizontal boreholes, etc. The proper word to use for indicating the position of two parts spaced along the axis is longitudinal, but the word vertical will be used when convenient. Also, a plane transverse to the axis of the 25 sonde will be called transverse plane, or horizontal plane, and so on.
Description Referring now to the drawings and in particular to FIGURE 1, which is indicated as prior art, there is 30 indicated generally by the numeral 10, a logging sonde 12 which is supported in a vertical borehole 22, by means of a cable 20 shown passing around a measuring wheel 25 at the surface. The rotations of the wheel ~5 measure the length of cable that has passed over the wheel. The rota-35 tions of the wheel 25 are transmitted by means 26 throughan appropriate drive system, -to control the movement in the direction representing verticality, in any display system that might be used.

~iiS3~

The sonde 12 is supported by radial centering springs 18 so that the axis of the sonde is coaxial with the borehole 22. A section of the sonde indicated by num-eral 14 rotates by motor means in the sonde, at a selected

5 constant rate. A probing beam of sonic energy 16 passes out radially from the rotating portion 14 to probe the wall and provide information regarding the character and the parameters of the wall 22, and the material o~ which the wall is composed. This wall might be a steel casing 10 surrounded by cement in a drilled borehole in a rock for-mation, or it might be an open borehole.
Referrin~ now to ~IGURE 2, there is shown, to a larger scale, a view of parts of a sonde, improved according to the teaching of this invention. Very little 15 information will be provided regarding the normal elec-tronic circuits in the space 31. These are fully described in many configurations in the patent literature referred to earlier. Wherever the circuitry would be dif-ferent in this invention it is, of course, fully described 20 as will be clearly seen in the figures.
The sonde 30 comprises an outer shell 12 o~ con-ventional construction. In the lower portion a cylin-drical bulkhead 50 is fastened rigidly and sealed to the outer shell and a downwardly extending axial post 42.
25 Bearings (not shown) are provided on the post 42, so that a cylindrical tube or sleeve 34 can be rotated about the post 42 by means shown as the dashed line 38, controlled by motor 36. Such a rotating sleeve, as indicated, is common to the prior art design.
On the sleeve 34 is mounted a first T/RTS 46 with its outer face tangential to the surface of revolu-tion, as the sleeve 34 rotates. This T/RTS 46 is periodi-cally excited by electrical circuits which will be described, and transmits radially outwardly a sonic beam 35 indicated by the numeral 16, which passes to the wall 22 o~ the borehole~ which may be cased or uncased. Part of the sonic energy is reflected backwardly to the T/RTS.
The conducting outer surface of the T/RTS is connected to ~5~3S~

a slip ring 44. A brush or electrical contact, stationary in the sonde, contacts the slip ring as the sleeve rotates and transmits on the lead 46' ~he electrical scan signal reflected fro~ the wall of the borehole.
In the normal design of a borehole acoustic logger, or bor~hole televiewer (BHTV), only one such T/RTS
46 is provided, and the signal is collected from the slip ring 44 by the brush and passes by conductor 46' to cir-cuits in the electronic package 31, which are conven-10 tional. The processed signal then passes up through a transmission channel in the cable 20, which is normally a pair of conductors, or a coaxial cable, to the surface, where it is utilized.
In this invention, at least a second T/RTS is 15 mounted on the rotating assembly comprising the sleeve 34, etc. It is energized in a manner similar to that of the T/RTS 46 and produces a scan signal which goes by means of the lead 48' to the electronic package in space 31 and to the surface in a manner similar to that of 46'. As will 20 be discussed in greater detail in connection with FIG-~RES 8, 9A, 9B, 9C, 9D, 10 and 11, various combinations of multiple ~/~TS arranged in a common horizontal plane, equally spaced circumferentially, can be provided which will provide certain benefits. Also the multiple T/RTS
25 can be provided in a longitudinal array, whereby other benefits can be realized, or in some combination of cir-cumferential and longitudinal arrays.
One possible electronic circuit that might be used with the apparatus of FIGURE 2 is illustrated in 30 FIG~RE 3. Here the two T/RTS 46 and 48, labeled A and B
respectively, are rotated by the means 38, as previously described, by the motor 36. The rotating slip rings are shown as 44, four of them are shown, two of them are con-nected internally to the T/RTS ~8 and 46 respectively, and 35 two slip rings are connected to a compass unit 60, which is well known and provides a member which remains in a fixed azimuth as the sonde moves vertically in the hole.
On each rotation of the rotating assembly 34, an ~s~

electrical pulse signal is provided as a selected point on the rotating assembly passes -the constant azimuth angle of the compass. This can be a magnetic compass, which might be useful in logging an open hole, or a gyro compass, or 5 its equivalent, as would be well known in the art. By means of the signal received from 60 that passes inter-nally to the slip ring, and by the collector to line 60', the orientation of the sonde with respect to an absolute azimuth such as north, can be determined. Thus, it can be 10 represented on north/south or east/west displays, etc.
Use of a compass is well known in the prior art The manner in which the T/RTS are used to probe the wall of the borehole is illustrated in F~GURE 3 for completeness as to the electrical circuits in the upper lS righthand portion of the FIG~RE 3. A power supply at 84 supplies power by resistor 176 to capacitor 86, and passes through the primary 88 of a transformer, to junction 90 and ground 78, which is connected ~o the negative poten-tial of the power supply. A triggered rectifier, or gate 20 control rectifier, 80 is connected between the potential at the junction o~ resistor 176 and capacitor 86 to the ground 78.
There is a timing means 74 which is conven-tional, operated by a clock of constant frequency, and 25 including a counter means, such that at a selected time a signal pulse can be placed on line 75 to the trigger con-nection 82 of the controlled rectifier 80. ~hen the trigger pulse arrives, the capacitor having been previ-ously charged to the full potenti~l of 84, now discharges 30 throu~h the rectifier 80 to the ground and this large cur-rent passing through the primary 88 of the transformer generates a corresponding voltage in the secondary 89 of the transformer, which goes by line 92 to the line 68, which can be connected to one or the other of the two 35 T/RTS 46 or 48, as selected by the switch 62.
The switch 62 can be as simple as a relay, which is controlled by a potential on line 64; that is, con-trolled by means of a signal ~rom the surface through one of the multiple conductors of the cable 20, as is we]l known in the art. Cons;der that the pulse of high voltage is delivered by line 92 to the line 48', which means it is delivered to the T/RTS 48 and the transmitter puts out a 5 pulse of sonic energy of selected amplitude and frequency.
This propagates outward radially through the mud in the annulus of the borehole (or liquid o~ selected composi-tion), to an obstruction such as the surface of the casing. Here part of the sonic energy is reflected and 10 passes backward over the same path to the T/RTS 48, where it generates a corresponding received signal, or elec-trical scan signal, which comes back from the T/RTS 48 through line 48' 3 through the switch 62, to the box 66 which is marked S. Box 66 is a switch of a particular 15 nature which is used for cutting off the receiving ampli-~ier 70 from the line 68 during the period that the high voltage is on the line 92 to generate the transmitted sonic pulse. The frequency of the transmitted sonic signal may be as high as l Meg. HZ, or higher, and too 20 high to transmit over the transmission channel of the con-ventional logging cable. It may be necessary to pass this through a signal detector, which converts the high fre-quency ESS to a relatively low frequency unidirectional analog signal, which can be transmitted over the cable.
25 Thus at a selected short time delay after that pulse is sent from line 92 to 48 and transmitted into the liquid, the connection from line 68 through the switch 66 and line 68' to the amplifier 70 is now connected, and the ampli-fied reflected signa] is passed by line 72 which is a high 30 frequency transmission channel, for transmitting the scan signals through the cable to the surface. The timer 74 applied, through 76, the necessary gating potential to the switch 66. This can be as simple as an AN~ gate which is open during the time that the potential is applied to 92, 35 and is closed shortly after that potential disappears.
As will be shown in FIGURE 7, as many parallel transmitted signals as desired can be used, by multiplying the network of the grid controlled rectifier 80 and trans-~3~3~L

former 90. FIGU*E 7 illustrates a case of two separate T/RTS being powered simultaneously, and of course, any number greater than two can likewise be powered by adding on circuits similar to the two shown.
S The particular usefulness of the system of FIGURE 3 will be evident if the two T/RTS 46 and 48 are of different frequencies. If the transducers are of dif-ferent frequencies, the beams of higher frequency have a shorter depth of penetration through media 9 such as the 10 mud in the borehole. Lower frequency sonic beams are less attenuated and have a greater distance of penetration.
Therefore, if it is desired to probe simply the inner wall of the casing or the wall of the borehole, then a high frequency T/RTS would be used.
There is a factor called "aperture" which is a function of the ratio of diameter of the transducer to the wavelength of the sonic signal. The higher the frequency, the shorter the wavelength, and the larger the aperture for a given diameter transducer. The larger the aperture, 20 the sharper the beam width and the bet-ter the "focusing"
of the sonic energy.
A high frequency transducer has better beam forming, but unfortunately, has a shorter penetration.
Therefore, for short distances of probing, a high fre-25 quency transducer would be used. On the other hand, whereit is desired to probe well beyond the wall of the bore-hole, a pulse of sonic energy of a lower frequency that would be less attenuated in its passage through the mud and the material surrounding the borehole would be used.
30 On the other hand, a lower frequency transducer of the same diameter would have a smaller aperture and will not be focused as sharply. Also, the beam focus or image detail will not be as good as it would be for a higher frequency transducer.
In FIGURE 3A a portion of the circuit of FIGURE 3 showing the switch 62, the transmit/receive switch 66, amplifier 70, and cable 20, are connected at the surface to an amplifier 71 and to an analog-to-digital ~ 5 35 converter 73, and to a recorder 77. More will be said about the surface portion of the system later. However, FIGURE 3A provides an indication of how the scan signals provided by the ~wo T/RTS 46, 48, can be successively 5 transmitted by switching the relay 62 by means of the transducer select switch 69.
Referring now to FIGURE 4A and considering the system of FIGURE 3 with two T/RTS 46 and ~8, consider the T/RTS 46 as high frequency, providing a beam 16 as indi-10 cated in FIGURE 1 and the T/RTS ~8 being of lower fre-quency, and having a beam 32 as in FIGURE 2.
The sonic energy delivered to the surrounding liquid by a T/RTS has an optimum zone ZA-100 for the high frequency T/RTS, and a different zone ZB-102 for the lower 15 frequency T/RTS 48. In general, the range, or radius from the T/RTS to the optimum position in the æone A of useful scanning 100, will be shorter for the higher frequency T/RTS, than the zone B-102 for the lower frequency T/RTS.
If 46 is a high frequency T/RTS, and 48 is a corresponding 20 low frequency T/RTS, and if the zones A-100 and B-102 are not mutually overlapping, it is then possible to use the high frequency T/RTS during the time that the pulse of energy traverses the near zone A-100, and use the lower frequency T/RTS 48 during the time that the pulse beam 25 traverses the distant zone B 102. The way to do this is illustrated in FIGURES 4B and 5.
Referring now to FIGURE 5, in line 128 there is a trace called SA, or scan signal of transducer A. Con-sider that the high voltage pulse along line 92 (of 30 FIG~RE 3) occurs at the time T0 and a sonic pulse is sent out from the transducer A. For a short time interval 108, to time Tl, no received signal is passed to the receiving amplifier 70. Then a reflected transmission 106 passes through the fluid in the borehole to the transducer, and 35 at a selected time T2 later, a reflection comes back from the borehole wall, identified as SA'. After a time TS the energy of the sonic beam is insufficient to provide a satisfactory received signal.

If the low frequency transducer is pwlsed at T0 plus one-half revolution and occupies the same position as the high frequency transducer had, the trace will be like SB in line 130, and trace 110 will be the scan signal pro-5 ~ided by the low frequency transducer. Of course, at atime about T2 there will be some reflection SB', probably of lower amplitude and broader time duration than the reflection SA' of the high frequency transducer. There-afte~, there will still be sufficient energy to traverse 10 part of the rock behind the wall of the borehole where there may be a reflecting surface, such as the bottom of a hole or vug, and a signal SB " is provided. There may even be other reflected signals such as the one indicated by SB "'.
It will be clear from examining the traces 106 and 110 that in the region of the reflection SA' that the high frequency transducer whose record is 106 provides a much improved record in the near field than the lower fre-quency transducer 110 does. Consequently, it is desirable 20 to prevent the recording and display of the portion of 110 up to the time TS, and during that period, the gating pulse 116 of FIGURE 4B causes the high frequency signal from transducer A to be present, such as trace 112. At the time TS, the gating pulse 102 passes the signal from 25 the second transducer B to provide the remainder of trace 112 at times T3 and T4.
By this means, it will be clear that by making use of two T/RTS of different frequencies and by proper delay of one electrical scan signal with respect to the 30 other electrical scan signal, and gating the two scan sig-nals appropriately, as has been described, a combination of the two scan signals provides a much improved record in the near fie]d, and having a greater depth of penetration in the far field, than would be provided by either one 35 alone.
In FIG~RE 6 is illustrated the case where the plurality of T/RTS are all of the same frequency, and the cable can transmit only a single electrical scan signal at any one time. One way of handling the plural signals is to delay one with respect to the other and sum the two, to provide a signal of improved signal-to-noise ratio.
FIGURE 6 shows the original scan signal of T/RTSA on line 5 138A which would be identical to the trace 106 of FIGURE 5. Trace 142 shows the same trace 106' provided by the second transducer B, which, of course, is delayed by 180~ of rotation of the rotating system. If trace 106 on line 138 is delayed by the time period 126, or one-half 10 revolution, it appears as 106" on line 140, which would be identical to, and in-phase with, the trace 106' pro-duced by the T/RTS beam B. By summing those two signals 106'' and 106', the results are shown on line 144 as a trace of A ~ B, of improved amplitude and signal-to-noise 15 ratio. Thus, the event on trace 106 which occurs at time T2 will now be much more pronounced on line 144, at the time T2'.
Instead of delaying one trace with respect to the other when the two T/RTS are of the same frequency and 20 summing and transmitting the sum signal to the surfaceg it would be much more desirable to be able to transmit the two signals separately, and cotemporaneously, to the sur-face. This could be done, for example, if there were two transmission channels instead of the cable 20, or if there 25 was a mu]tiplex system by means of which a plurality of N
signals could be sampled at a high rate of sampling, and the successive samples from each of the separate signals would be transmitted in sequence to the surface. There they would be demultiplexed by means which are well known 30 in the art.
Refer now to FIGURE 7 which has been previously mentioned in conjunction with FIGURES 3 and 4. There is shown the situation in which there are two T/RTS as in FIGURE 3, numbers 46 and 48 respectively. Each of the two 35 T/RTS have a transmit signal applied through leads 172 and 174 respectively, to leads 46' and 48' to the T/RTS A
and ~. The timing for these transmit signals is provided by a counter 166 which has a clock signal over lead 18~

from a constant frequency clock or oscillator 164. By prearrangement, the counter counts up to selected numbers, which indicate selected timing; and the two trigger recti-fiers 80 of the transmission source assemblies, which have 5 previously been described in detail in relation to FIGURE 3, are then controlled by the leads 169 and 170 from the counter or timer 166, to the control gate 82 and 82' respectively.
The counter 166 also provides gating pulses or 10 timing pulses on leads 167 and 168 to the transmit/receive switch 150. This disables the detecting apparatus fol-lowing the switch 150 while there is the high potential signal applied to the T/RTS from the transmission elec-tronics over leads 172 and 174. However, a~ter the short 15 in-terval 108 of FIGURE 5 after the transmission pulse is sent, the T/RS 150 will then enable the electronics fol-lowing through leads 46" and 48" to amplifiers 152 and 154, and through gating means 156 as described in relation to FIGURE 4B.
The timing for this gating is derived from the clock 164 over lead 184. The time delay unit 160 wh.ich follows the gating controls 156, 158 is controlled by the counter over lead lB4, 185. The gating units 156, 158 and the delay unit 160 carry out the operations described in 25 connection with FIGURE 5. Following these three units the two signals are added together by means of a pair of resistors 162 being applied together to the input to an amplifier 180, the output of which goes to the transmis-sion channel 178 in the cable 20. Thus, by means of this 30 apparatus so far described in FIGURE 7, the action would be to create the sum trace shown on line 132 of FIGURE 5 and transmit that trace to the surface, for recording and display.
As mentioned previously and shown in FIGURE 7A, 35 the case where there are two transmission channels in the cable 20, such as 186 and 188 of FIGURE 7A, it is then possible to come from a T/RS switch 150 directly to ampli-~iers 152 and 154 and apply the ampli~ied signals, one to each of the two transmission channels.

The situation illustrated in FIGURE 7A is exemplified a little more completely in FIGURE 12B to which reference is now made. Here, the lines 46' and 48' carrying the reflected scan signals from the T/R'rS 46 and 5 48, go to the T/RS switch 150, then to amplifiers 152 and 154. The amplified signals then go to the two sepa-rate channels of transmission through the cable; namely, 186 and 188. The surface end of the cable 20 is similarly shown and the conductors now 186' and 188' go to analog-10 to-digital converters 268 and 270. The digitized signals then go to a digital recorder 266 in a conventional manner. While two separate analog-to-digital converters are shown, they could, of course, be combined into a single instrument, as is well known in the art.
In FIGURE 12A is shown an alternative circuit, in which the signals from the T/RS switch 150 are ampli-fied in amplifiers 152, 154 and then go to a multiplexing means 260, the output of which on a single line goes to amplifier 180 and to a single transmission channel 178 in 20 the cable 20 to the surface. At the upper end of the transmission channel 178' connects to a demultiple~ing unit 261, which converts the combination signal on line 178' back to the two component signals, which were ampli-fied by the amplifiers 152 and 154. These two component 25 signals 46"' and 48" ' on the output of 261 go to ampli-fiers 262 and 264 and then to a conventional digital recorder 266 for later playback and display.
FIGURE 12C illustrates how a playback of the recorder 266 can provide the two original signals 46" ' 30 and 48" ', so that as in the case of FIGURE 7 these two signals can be combined after one of them is delayed in the timed delay unit 272 and combined in the combination of resistors 274 and 276 to the single -trace which goes to the display device.
Therefore, the combination of FIGURES 7, 7A, and 12A, 12B, and 12C provide sy~bolically three separate methods of transmission of the signals from multiple T/RTS
from the subsurface sonde to the surface, to be recorded ~53~

and/or displayed. While it is possible to have any one of many different displays, which do not form a part of this invention, the most common display means can only repre-sent a single scan signal at a given time. It is conven-5 ient, therefore, either to combine two or more signals ashas been described in FIGURE 7. Of course, more than two separate T/RTS scan signals can be summed to provide a single sum signal to transmit to the surface.
Another way of transmitting multiple scan sig-10 nals to the surface is to have a separate transmissionchannel for two or more separate scan signals so that they can be transmitted separately and simultaneously to the surface over independent transmission channels as in FIG-~RES 7A and 12B.
The third method has just been described as the one in which a plurality of simultaneously recorded sig-nals can be transmitted over a single transmission circuit to the surface by the process of multiplexing. Devices for doing multiplexing are commercially available and need 20 not be further described.
In general, it is very desirable to separate out at the surface each of ~he separate electrical scan sig-nals so that they could be recorded as a function of time, or as a function of depth of the sonde below the surface 25 in separate recording channels. The best way of doing this is to record them on separate channels of a multiple channel analog recorder, such as are available in the art, or to digitize each of the separate signals and to record them separately on separate recording channels of a 30 digital magnetic recorder. Another way would be to store the digitized separate signals into one or more separate digital memories, partic-ularly random access memories, such as are now available on the market.
So far in this description of the broad aspects 35 of my invention, I have described the use of multiple T/RTS arranged Oll the ro-tating assembly in a horizontal plane. And, as has been described, there are a number of particular advantages to the use of the multiple T/RTS
arranged at various azimuths on the rotating assembly.

There is one important advantage of multiple similar T/RTS scanning the circular path at slightly delayed time intervals, one after the other. If these multiple signals can be brought to the surface separately, 5 then it is possible to record ~hem and then to play out each of the separate traces sequentially. In view of the continuous vertical motion of the sonde, each of these T/RTS scans a horizontal scan trace on the wall of the borehole which is theoretically independent of each of the 10 others. For example, if there were two similar T/RTS, one spaced 180 behind the other, it would be possible either to show a finer detail of scanning display along the bore-hole, or to permit the sonde to be moved vertically twice as rapidly, and still have the same condition of trace 15 spacing in vertical dimension, as would be obtained at half of the vertical velocity of the sonde with a single T/RTS system, as at present.
One reason for the high cost of logging is because of the time it takes to make a log. The longer it 20 takes, the longer is the commercial use of the well delayed, the longer the logging equipment is utilized, and the greater the cost of the logs. Thus, speeding up the vertical rate of travel of the sonde could materially reduce the cost of logs, without providing any reduced 25 utility or value of the resulting records. It is qui-te possible that as many as four or more T/RTS could be used to obtain a logging speed four times, or more, the present speed of logging with a single T/RTS.
It is also important to use multiple T/RTS in a 30 vertical array that is arranged in a plurality of dif-ferent horizontal planes on the rotating assembly. Such multiple T/RTS would be preferably aligned in a vertical plane throwgh the axis of rotation although this is not required.
For a description of the manner in which the multiple T/RTS can be built in-to the instrument, reference is made to FIGURE 8 which shows the present method of mounting a single T/RTS 200 on the rotating assembly 206.

The rotating assembly has an internal surface 210 which is adapted to fit snugly the outside of the rotating sleeve 34 illustrated in FIGURE 2. Thus a plurality of T/RTS
could be mounted vertically on a suitable cylinder such as 5 206 of sufficient longitudinal dimension as shown in FIGURE 2. Some means such as a set screw or other suitable means 208 would be provided to hold and anchor these rings or cylinders 206 to the rotating sleeve 304 to maintain a rigid rotating assembly. A thin metal 10 sheet 212, preferably made of non-magnetic material, has a central opening which is slightly larger than the diameter of the T/RTS 200. The T/RTS is a thin slab of a cylinder of suitable ~aterial which is piezoelectric or electro-strictive. The slab 200 is anchored to the thin sheet 212 15 by positioning it in the center of the opening and locking the two together by suitable resilient adhesive means, which will anchor the slab but maintain a resilient adhe-sive means, which will anchor the slab but maintain a resilient type of mounting. Thus, no interference is 20 offered to the proper vibration of the transducer, as electrical signals are applied to the electrodes on the top and bottom surfaces.
A volume of backing material indicated as 214 is formed in a suitable shape. The front surface attaches to 25 the sheet 212. This backing material is made of a mixture of a very fine powder of a very dense metal, such as tung-sten mixed and sealed into a resilient plastic material.
The backing serves to absorb the vibrations transmitted by the back side of the T/RTS; that is, the surface of the 30 slab which faces the flat surface of the backing material.
Both surfaces of the piezoelectric slab vibrate in opposition to each other; and unless one of these is greatly attenuated, the two will partially cancel each other. Thus, there will be only a very small part of the 35 energy transmitted perpendicular to the top surface of the slab, or T/RTS 200. The type of backing material which has just been described is conventionally used in the art and forms no part of this invention and need not be described further at this time.

The lead 202 connected to the top surface of the T/RTS 200 goes through a drilled opening 204 as is indi-cated schematically in FIGURE 3. Other openings will also be present for the passage of additional signal leads, 5 like 202 from other T/RTS mounted on the sleeve 34. With this description of the conventional method of mounting and building the rotating assembly, etc., no further description will be made, except to indicate how addi-tional separate transducer slabs, such as 200, can be uti-10 lized.
FIGURES 9A, 9B, 9C, and 9D indicate possiblecombinations of two or more I'/RTS. ~or instance, in FIGURE 9A two slabs 200A and 200B are shown mounted upon a single ring 260 at 180 azimuth from each other. In 15 FIGURE 9B three T/RTS 200A, 200B, and 200C are positioned at 120 azimuth from each other. Similarly, in FIGURE 9C
the spacing is 90 and in FIGURE 9D the spacing is 60.
Other spacing arrangements or construction details can be provided, of course, and those shown in FIGURES 8, 9, 10, 20 11, and 12 are just by way of illustration, and not by way of limitation In FIGURE 10 is shown an embodiment which uti-lizes a plurality of T/~TS units 226A, 226B, and 226C
arranged on a selected rotating assembly 220, each unit 25 having its own backing material 214 and arrayed along a longitudinal plane through the axis of rota~ion. One of the important things that can be done with an array of this sort is to provide, at least in the vertical dimen-sion, a greater dimension of transducer. A larger diam-30 eter transducer, of course, provides a much better colli-mated beam, which is of real value in providing grea-ter detail o-f the reflecting surface which it is designed to probe.
There has been a great deal of theoretical and 35 engineering work done on the transmission of signals from various types of linear arrays of transmitters. The same logic that has been developed can apply to high frequency radar antennas, or to sonar antennas, or seismic antennas, s~
-2~-both transmitting and receiving. These arrays, while important in transmitting a more suitable beam of energy, also provide a greater receiving sensitivity than a single small transducer, as is normally used.
In FIGURE 10 an axis 232 is shown, in a diame-tral plane, of the rotating assembly 220. The oval con-tour 230 indica~es the shape of the beam in rela-tion to its diameter, as a function of the distance, or radius, away from the transmitter along the axis 232. This shape 10 230 can be improved by simultaneously energizing the sepa-rate transducers in accordance with the theory. This theory has been developed over the years and is well known and is fully described in the literature. See, for example, Albers, Underwater Acoustics Handbook II, 15 pp. 180-205. The type of beam form shown in FICURE 10 is indicated as the possible improved type of transmitted beam and receiving sensitivity when the proper theory is used and the individual beam elements 226A, 226B, and 226C
are supplied with transmitting signals in proper phase and 20 amplitude rela-tion. Since the electronics of beam forming is ~ell known, no further description of a beam forming circuit is necessary.
Another capability of a linear antenna, such as shown in the upper part of FIGUR~ 10, is that by proper 25 phase and amplitude control of the electrical signal applied to the transducers, the main axis of the beam which is shown as 232, for example, can be tilted, so that the axis could be along the lines 240A, or 240B, or 240C, etc., for example.
It is possible to use a second similar assembly 224 having a plurality of say three T/RTS, numbers 228A, 228B, and 228C, etc. The beam 231 could likewise be tilted at angles 242A, 242B, or 242C, for e~ample, similar to the angles of 240A, 240B, 240C. It is clear, there-35 fore, if one of these assemblies is used as a transmitter and transmits along the direction 240C and ~he other unit 22~ acts as a receiver and directs its receiving beam along the line or axis 242C, then at a surface such as ~5 ~5 271, there will be a reflection of the transmltted energy.
The beam on axis 242C will be reflected back along axis 242C to the array of the unit 224. Also, by changing the angles or tilt of the beams 230 and 231, the optimum point 5 of reflectivity can be changed from 271 to 271' or 271 ", for example, and so on. The manner in which the tilt of the beam can be changed is something that can be con-trolled by means of the amplitude or frequency of a vol-tage or current supplied to the circuit that does the beam 10 forming, and of course, this control can be provided from the surface ~hrough a control conductor in the cables -to the sonde. Thus, if the received signal as indicated by the beam 231 can be transmitted -to the surface, and viewed on a display, the beam tilting circuits can be varied to 15 change the radius over a wide range for careful explora-tion of the material behind the wall of the borehole.
Of course, as has been described earlier, to get deeper penetration of the beam, it is preferred to use as low a frequency of oscillation of the transducer as pos-20 sible without endangering the precision and detail of the ; measurement.
Also, where the liquid medium in the wellborecan be changed during the period of time the logging is done, it may be wise to provide a suitable liquid medium 25 that offers the lowest attenuation to the sonic signals utilized in the scanning process Referring now to FIGURE 13, there is shown a T/RTS system which is a further extension of FIGURE 10 and includes a plurality of T/RTS in both a horizontal plane 30 and a vertical plane. Thus, assemblies 280, 28~ compare to 220 and 22~ of FIGURE 10, but differ in that there are two sets of vertically spaced T/RTS. Assembly 280 includes also an array 290A, 290B, 290C, and a vertically spaced array 292A, 292B, and 292C. As in FIGURE 10, array 35 286 cooperates with array 288 to provide one transducer 286 for transmission and one transducer for reception, for example. These are preferably multi-element so that beam forming and tilting can be provided.

Similarly, arrays 290 and 292 cooperate with each other in the same way. However, one of the advan-tages of FIGURE 13 is that arrays 286, 288 can be lower frequency, and arrays 290 and 292 can be higher frequency.
5 This is shown in FIGURE 13 by the indicated axes of the two ~/RTS systems. Thus the effective radius of detection of 286, 288 is 294 at radius 294', whereas the radius of detection of 290, 292 is 298, at radius 298', which is considerably shorter than 294'. Of course, both sets of 10 beams would be remotely controllable to different axes and different effective radii.
FIGURE 11 illustrates the use of multiple trans-ducers in a horizontal plane, which can provide beam forming, in a way similar to the arrays of FI~URES lO
15 and 13.
I will now discuss how multiple ESS are trans-mitted to the surface by the use of logging cables which were originally designed for transmitting relatively low frequency electrical logging signals, i. e., signals of 20 less than 50 KHZ.
Referring now to FIGURE 14, here is shown sche-matically a rotating assembly 34, having four separate T/RTS 46A, 46B, 46C and 46D, instead of two as shown in FIGURES 2 and 3. These are arranged in the same tran-25 sverse plane, perpendicular to the axis of rotation. Eachone is connected by conductors 46A', 46B', 46C', 46D', to a multi-point switch 62' which is patterned after the switch 62 of FIGURE 3, controlled by signal over dashed line 64. A pulser, identical in all respects to the 30 pulser of FIGURE 3 shown in the dashed box 81, has three terminals, one being provided with power 84, another pro-viding the power output on lead 92, to transmit a sonic signal, and a third lead 75, which provides a timing signal to the pulser. Although not shown, the lead 75 35 would go to a timing device, such as 74 of FI~URE 3, which would also be connected to time the transfer switch 66 marked T/RTS in FIGURE 14. The output of the T/RTS would then go through an amplifier 70~ through a detector 67 to ~ 3 the transmission channel 72 of the cable 20 as shown in FIGURE 3.
Earlier it was pointed out that any number of T/RTS, as desired, can be provided on the rotating 5 assembly although only two were shown in FIGURE 3 and only a single pulser was shown. In FIGURE 15 a similar circuit is provided in which separate pulsers 81A and 81B are pro-vided so that each of the T/RTS can be operated separately from the others.
In FIGURE 15 each of the pulsers 81A and 81B are supplied by power from the supply 84 through separate leads 84A, 84B, and through separate resistors 16~A and 162B. The timing signal comes from the counter 166, which is supplied with a clock signal from a clock 164 through 15 the line 182. The counter, or control 166 also provides another signal output on leads 167 and 168 to the transmit/receive switch 150. The switch 150 disconnects the ou-tput leads 48" and ~6" whenever the pulser signal is on the leads 46' and 48', which are connected through 20 slip rings to the two transducers T/RTS 46 and 48 respec-tively.
Thus, with the apparatus of FIGURE 15, two sim-ultaneous sonic signal transmissions are being carried on, and the received signals are being transmi~ted through 25 lines 48 " and 46 ". The signals on these output lines can go directly to the cable if there are two separate transmission means. However, they can be combined, as will be described in connection with FIGURES 16 and 18, if there is only a single transmission system in the cable.
30 As also shown in FIGURE 3, a compass, preferably a direct reading compass, such as a flux gate compass, for example, or other available compasses provides a signal pulse on output line 60' whenever the scanning T/RTS crosses a line directed to the north. The pulsers are timed so that the 35 transmission pulses to the multiple T/RTS are synchron-ized.
Since transmission of mu].tiple scan signals involves the logging cable, it might be desirable to look at the subject of the cable, which is the only means of communication between the sonde and the surface. The log-ging cables that are utilized for operating the borehole televiewer are generally the same cables that are used for 5 many other types of sensing apparatus, which are used for the logging boreholes and for the detection of various properties of the subsurface formations. In the logging of electrical resistivity, self-potential, and other types of electrical phenomena, the signals are of much lower 10 frequency than they are in the borehole televiewer. A
cable with an ordinary conductor pair for transmitting the signals is fully adequate. It is generally believed that the commercial logging cables in use at ~he present time, which may be from 20,000 to 30,000 feet in length, will 1~ adequately handle signals in the range of 50 to 100 kilo-hertz (KHZ) or kilobits per second.
The desired resolution of the scan signals that are transmitted to the surface may be set down as the fol-lowing: In the measurement of caliper or the distance of 20 penetration of the sonic signals through mud and the rock wall of the borehole, the minimum resolution desired would be to .05", and 256 units of this would cover a radial distance of penetration of about 13 or 14'l.
In the measurement of azimuth the conventional 25 timing is for 360 transmission pulses in a rotation of 360 giving a minimum angular resolution of 1. In the measurement of signal amplitude, a six-bit digital value for amplitude would indicate a minimal resolution of about 1 1/2%.
To transmit the scan signals with these minimum resolutions would take 256 x 360 x 6 x 3 ~revolutions per second) or 1.6 million bits per second. With such a high data rate, it would obviously be impossib]e to transmit a complete sonic scan signal by digital transmission, 35 although digital transmission would provide more precise amplitude transmission. While there are available in industry high frequency transmission channels, such as coaxial cables and fiber optic channels, these are not 5~3 generally available today in logging service. In the future it is very likely that they will be available, in which case the data rates could be much higher, such as would adequately handle complete scan signal digital 5 transmission.
There is distinct advantage in having multiple T/RTS, such as two T/RTS, of different frequencies. If one T/RTS is in the high frequency range, and the other in a lower frequency range, the precision of amplitude mea-10 surements at short distances from the transmitters wouldbe available with the high frequency unit, and a greater depth of penetration into the rock would be available with the low frequency transducers.
One method of handling this type of signal would 15 be to first delay one with respect to the other, until the two scan signals are in phase, and then gate the high fre-quency scan signal for a certain selected time interval, and then gate the lower frequency scan signal. By this means, a single analog signal can be transmitted over the 20 present cables very satisfactorily and still utilize the benefit of two T/RTS.
Another way of utilizing the present cables effectively with more than one T/RTS is to process the analog scan signals in the sonde to determine khe ampli-25 tudes of the reflected signals, and the correspondingradius of caliper, at the time of the return signal.
These two quantities can be expressed digitally in a rela-tively few bits, so that as many as four such pairs of signals could be transmitted sequentially, as by multi-30 plexing, over the existing single analog transmission cir-cuit in the conventional cables.
One type of present logging cable utilizes seven conductors, of which two would be utilized for the trans-mission channel and the other four would be used for con-35 trol, power supply, etc. However, it could be possible touse four of the conductors to provide two separate con-ductor pairs for analog transmission of the scan signals.
If there are two analog kransmission channels, two ESS

from two T/RTS coul.d be transmitted to the surface independently and simultaneously, as analog signals, in the conventional manner. Or the two transmission channels could provide for transmission of eight separa-te scan sig-5 nals when processed to transmit only the amplitude of thereflected signal and the time of the reflected signal.
With a pair of T/RTS of different frequencies, the ampli-tude of the high frequency reflection and caliper of the low frequency reflection could be combined for transmis-10 sion.
Of course, where the multiple T/RTS are in thesame horizontal plane and spaced circumferentially on the rotating assembly, they can individually be delayed in time until they are all in phase, and they can then be 15 stacked to provide a signal of improved signal-to-noise ratio.
Another combination which would be very useful would be to provide two analog transmission circuits and ~o use two identical T/RTS on the rotating assembly, so 20 that at the surface there would be two scan signals per revolution of the rotating assembly, and thus a shorter vertical spacing between scans on the display could be provided. Conversely, the sonde could be moved vertically at twice the normal ].ogging rate, and still provide the 25 precisely same log that would have been provided with the slower vertical logging rate, and a single T/RTS. Thus, by using two or more identical T/RTS, it would be possible to increase the rate of logging with the borehole telev-iewer by a factor of two, or three, or more, depending 30 upon the number of T/RTS. This would provide a consequent cut in the time for providing a log. Since one of the major components of the cost of logging is for the idle rig time, this could be cut in half if two T/RTS were used, and so on.
Earlier it was mentioned that by means of an apparatus to increase the fre~uency of the scan signals, say b~ a factor of two, ~wo such signals could be trans-mitted over a single transmission channel cable, sequen-3S~L

tially, in the same time that it previously took to transmit one of them. Of course, this would raise the maximum frequencies in the analog scan signals and might not be fully satisfactory. In such a case, it might be 5 desirable to alter the minimum data requirements on one of the several measurements made. For example, it might be possible to transmit one sonic pulse on each of two T/RTS
every two degrees of rotation of the rotating assembly, but alternating the signal from one T/RTS to the other.
10 In this way, the separate ESS would be as normally trans-mitted, and two such scans made by two separate T/RTS
could then be alternately transmitted over a single cable, each in more or less a conventional manner. Of course, another way of doing this would utilize the apparatus of 15 FIGURE 3, except that the switch 62, instead of being a slow mechanical switch, would be a very fast electronic switch capable of alternating connections at millisecond intervals.
This would be a type of multiplexing in which 20 the transmission time is shared between the two trans-ducers sequentially. Of course, the two ESS must be placed in phase by adding time delay to one or the other of the ESS, as shown in FIGURE 6, by the delay means 160.
On this same basis, three or four or more T/RTS can be 25 used sequentially with some lessening of the resolution.
Referring now to FIGURE 16, which is a modifica-tion of FI~URE 15 showing alternating rapid switching of the leads 75A and 75B by switch 21. It is shown as a separate switch for clarity but is most conveniently done 30 in the counter 166. Switch 21 is shown as controlled by means 21' from the counter 166. Thus, instead of trans-mitting signals from both T/RTS, each (say at 1 of rota-tion), the first T/RTS is transmitted say at l; line 402 of FIGURE 17; then one degree later line 404, the other, 35 but not the first; one degree later line 406 the first is again pulsed, and the sequence continues. Only one is pulsed at a time, each degree, to produce sequentially signals 412, 414, 416, 418, and so on.

~s~s~

Of course, the two transducers are not coincident, so the ESS from one of them, say on lead 48"
is delayed by time delay means 160, for one-half period of rotation. This is done by the TD means 160 which can con-5 veniently be one of the charge coupled devices which arecommercially available on the market and need no further description. The two signals are then added by the resi-stor network 385, 385', and applied to amplifier 386 and transmission line 342.
As shown by FIGURE 17, at any one instant there is only one ESS being transmitted so no gating means is re~uired. The two ESS can be identical, that is, from identica] T/RTS. However, they can be from dif~erent T/RTS, such as indicated in FIGURE 17 showing a high fre-15 quency T/RTS on lines l, 3, 5 and a lower frequency signal (having later return of energy) on lines 404 and 408.
With reference to FIGURE 18, there is shown a memory unit 380, which has four separate memory components MlA, MlB, M2A, M2B, etc., numbered respectively 381A, 20 381B, 382A, and 382~. Two switches 374A and 374B are pro-vided, one at the inlets to the memories, and the other at the outlets from the memories. The two leads 370 and 372 -from the A/D converters 268 and 270 go to the two inlet switches 374A, which can alternately connect these two 25 lines to the first pair of memories MlA and MlB respec-tively, and on command, can switch the two lines to the second pair of memories M2A and ~2B, and so on.
The second switch 374B operates in a similar way but is 180 out of phase with the first switch 374A. In 30 other words, when the leads 370 and 372 are connected to the first two memories, and switch 374B is connected to the second two memories, and vice versa. The outputs from the switch 374B ~o to D/A converters 375 and 375', then to gating means 384 and 384', through two equal resistors 385 35 and 385', where they are joined together and to a line drive amplifier 386, the output of which is connected to the transmission charmel 342 of the cable. The bit rate fro~ the analog-to--digital converters 268 and 270 is iden-35~

tical to the rate of bit loading into Lhe memories through switch 374A and is controlled by a clock oE frequency CF1 on line 387A, which comes from a clock C2 164B. The readout from memory through switch 374B is controlled by a 5 higher frequency bit rate CF2, supplied on lead 387B from the clock C2. The bit rate CF2 is normally twice that of CF1. However, if three or more separa-te T/RTS are to be multiplexed on the cable, CF2 would be 3 or more times CFl.
There is a mechanism M, 378 driven by the base clock 164, which controls the switches 374A and 374B
through means indicated by the dashed lines 376. These two switches are switched synchronously, but as mentioned, are out-of-phase. One is loading one pair of memories 15 while the other is reading out of the second pair of memo-ries, and so on. Also, the gating means 384 is controlled by a third frequency from clock Cl, 164A. Each of the clocks Cl, C2 and M are controlled by the base clock C, 164, and frequencies are divi.ded down in a manner well 20 known in the art. However, while the frequencies for each of the controls may be different, they are all synchro-nously related through C.
Refer to FIGURE 19, and consider for purpose of illustration that the two T/RTS are coincident on the 25 rotating. They are not physically coincident, of course, since they are spaced 180 degrees from each other, ~ut this can be taken care of by time delay means 160 as has previously been explained. Thus the delayed signal 436 from A on line 430, which is shown by (A + Delay), is in 30 phase with the signal 438 from B on line 432. Both start at T0 and last till T2. The rectangle between lines 428 and 432, and T0 and T2 is shaded to indicate a first pair of memories MlA, MlB, into which these two ESS are loaded.
The next two ESS 436' and 438' are loaded in the second 35 memories M2A, M2B.
While the second ESS are being loaded, the pre-viously loaded 436 and 438 are being unloaded, in sequence at double rate, as 436A and 438A. This sequence is repeated. When the second memories M2A and M2B are loaded, the next two will switch back to MlA and MlB and so on. Thus, while two separate scan signals are being recorded, simultaneously each one degree of rotation, the 5 two scan signals are being transmitted a~ double frequency in sequence.
Of course, the two T/RTS can be similar, in which case it would be possible to log at double speed, without loss of detail, or they can be different ~one high 10 frequency and one low frequency) in which two separate logs can be recorded. Each of the ESS transmitted can be composite ESS, obtained by first gating a high frequency ESS to provide a short range scan, and then gating a lower frequency ESS for the longer range scan. Thus the two 15 transmitted ESS could be provided from four separate T/RTS, two high frequency and two low frequency, and so on.
Returning to FIGURE 18, the purpose of the gating means 384 is that the two scan sign~ls which are 20 read out at a double bit rate will be transmitted sequen-tially in the time that a pair of transmit-receive signals is loaded into the opposite pair of memories in parallel.
Of course, only one of these 436A and 438A is read out at a time. For example, the switch 374B is connected as 2S shown to the lower pair of memories. I~ may be desired, for example, that M2A should be transmitted first, and so that is read ou-t at double bit rate and passed by the gating means 384 and through resistor 385 and amplifier 386 ~o the line 3~2 to the cable. When that is completed, 30 the second scan signal in M2B controlled by gate 384' is read out at the higher bit rate, and is transmitted in a similar manner to the line 342 in the cable. By the time these two have been read out completely, the next pair of reflection signals have been loaded into the top pair of 35 memories. The switches 374A and 374B are then operated, connecting the inlet switches to the second pair of memo-ries and the outlet switches to the first pair of memo-ries, and so on.

~ 3 While I have shown in FIGURES 16 and 18 only two ESS, it will be clearly understood that this is shown by way of example, and not by way of limitation. Therefore, the apparatus can be extended to transmit 3, 4, or more 5 simultaneous ESS by loading into memory at a first fre-quency, and reading out of memory at a frequency higher by a factor of 2, 3, 4, or more, and transmitting the read-out signals sequentially.
FIGURES 15 through 19 illus~rate the use of mul-10 tiple T/RTS so that in each revolution of the rotaryassembly, 2, 3, 4, or more -times as much information can be recorded on each revolution, without change in the basic mechanical system of the sonde. This provides the opportunity to log at higher speeds without loss of essen-15 tial information, and also provides the opportunity torecord multiple logs at the same or higher speed, pro-viding additional information.
Referring now to FIGURES 20A, 20B, and 20C, there are shown three circuits by means of which two elec-20 trical reflection signals from two T/RTS on line 48' and46' are switched by T/RS 150, and on the output lines 48"
and 46" they go through separate amplifiers 152 and 15~.
One of them (FIGURE 20A) goes to a time delay means 160 as previously discussed, to bring the two signals into phase.
25 They are then stacked by means of the resistor assembly 162A and 162B, and then passed through the amplifier 180 to the single transmission channel 178 of the cable 20.
As previously mentioned, it would be desirable that the two T/RTS be mounted on the same rotating 30 assembly in the same transverse plane so that they would be synchronous and they would be scanning along two sepa-rate closely spaced parallel lines. By adding the two signals the resulting signal, which would be the sum of the two, would be of higher signal-to-noise ratio, and 35 therefore preferable to either one alone.
In FIGURE 20B there is shown a similar system handling two separate T/RTS scan signals which go by means of lines 48" and 46" to amplifiers 152 and 15~. One of these signals goes through a time delay means 160 so that the two signals would be in phase. However, they then go through gating means 156 and 158, which are timed over line 184 from a clock C, 164. If the tw~ ~/RTS are of 5 different frequencies, one, for example, is a high fre-quency conventional type of transducer whose signal, say for example, is on 48" , and a low frequency transducer has its electrical scan signal on 46". Then a portion of the higher frequency scan signal lasting at least as long 10 as the first reflected signal from the wall of the bore-hole is first gated by 156 through the resistor assembly 162A and 162B, through amplifier 180 to line 178 in cable 20. Then the second gate 158 is opened to transmit later arrival of possible reflections from greater dis-15 tances beyond the wall of the borehole. The lower fre-quency scan signal is then transmitted through resistor 162B, a~plifier 180 and through line 178 to the surface.
In this way, two separate T/~TS can each provide valid information best suited to their operating frequency, and 20 the total received signal transmitted up the single trans-mission circuit 178 will be of greater value than either one of the signals from either one of the T/RTS.
FIGURE 20C illustrates another method o han-dling two independent T/RTS scan signals which, passing 25 through the T/RS 150 are then amplified by means 152 and 154 and go to a multiplexer of conventional form 260. As is well known, the multiplexer then combines these two independent signals by, in effect, chopping the analog signals up into short pieces which are then alternately 30 transmitted through the line driver amplifier 180 and through the transmission channel 178'. At the surface the multiplexed signal is then demultiplexed in the box 261, and the original two signals are delivered over lines 46"' and 48"' to amplifiers 262 and 264 to a 35 recorder 266.
A clock 164 in the sonde provides a ~iming signal over line 184 to the multiplexer 260, and also through a control conductor 184' in the cable 20, to line ~ 5 lg4" and the de~ultiplexer 261. These clock signals syn-chronize the operation of the multiplex and demultiplex operations.
The multiplexer can be used with analog or 5 digital signals. Normally the analog signals are sent to a sample and hold circuit and are then sampled at the rate of the clock 164. Their amplitudes are measured ancl con-verted to digital signals of a selec-ted number of bits, say for example, six bits. These sequential digital words 10 of six bits each, one :Erom one T/RTS and the next from the second T/RTS are then transmitted as a string of digi-tal bits over the single transmission channel 178'. At the demultiplexer a reverse action takes place, where the output o~ the demultiplexer on lines 46"' and ~8"' can 15 be, if desired, converted back to analog signals or may very usefully be recorded as digital signals in the recorder 266. The rapid bit stream can be recorded satis-~actorily on digital recorders, such as magnetic tapes or discs and so on. On the other hand, high frequency analog 20 signals can be recorded in analog form on magnetic tape, such as the well-known video tape cassettes. This will be discussed more ~ully in connection with FIGU~E 22.
Referring now -to EIGURES 21A and 21B, there are shown means by which a pair of T/RTS can provide indepen-25 dent electrical scan signals, which passing through theT/RS 150 are amplified through amplifiers 152 and 154 and then are transmit-ted -through the cable 20 on two separate analog transmission circuits 186' and 188'. At the sur-face, the signals transmitted on the two separate lines 30 are converted to digital signals by the ~/D converters 268 and 270, which provide digital signals which can then be recorded on recorder 266 for later playback.
FI~URE 21B illustrates one manner in which the recorded data on recorder 266 can be utilized. The two 35 digital signals are read out from the recorder 266 through the lines 46"' to a time delay device 272, such as was shown in FI~URES 20A and 20B, and through line 48"'. The two signals are then added by means of the resistor ,, ~

~38-combination 274 and 276 to the display, not shown but well known in the art. Ln -this case, what has been ~one is to provide to the recorder signals from two T/RTS of the same frequency, and they are shown being stacked and the 5 stacked signals going -to a display.
Referring now to FIGURE 22, there is shown a typical set of recorders and devices that can be used at the surface to utilize the signal that has been generated in the sonde. While signals from multiple T/RTS can be l0 recorded, FIGURE 22 illustrates the case of a pair of digital signals, such as amplitude and calipers, which are multiplexed on the cable. The cable 20 is shown being metered up and down by means of a wheel 25, driven by the movement of the cable. The wheel as it turns rotates an 15 encoder 350 which transmi-ts pulse signals which are indi-cative of the angle of rotation o~ the wheel 25. The encoder 350 is a conventional device and outputs a signal over line 350' which goes to a digital tape recorder A, 266.
In FIGURE 22 there are shown several types of recorders. One is called a tape recorder 266. The other is 352 and is labelled a CRO recorder, or a cathode ray oscilloscope type recorder. This u-tilizes analog signals, such as the conventional electrical scan signals. The 25 tape recorder is generally a video tape cassette or disc drive~ which records digital signals of high frequencies.
FIGURE 22 is based on the assumption of a digital trans-mission with two signals being multiplexed.
The sonic signals on the cable transmission 30 channel 342 go directly through lead 3~2 to a tape recorder 266. The depth encoder 350 going by lead 350' to the ~ape recorde.r indicates information corresponding -to depth of the sonde. The sync signal, or the north pulse coming from -the compass, is separated out in -the sync sep-35 arator, marked SS 351, and the north indicating pwlsetravels by line 60 " to the tape recorder. Thus, all essential information arriving over the ~ransmission channel is stored in the tape recorder 266 and can be played back later to recover the original signal for display in any one of a number of different ways.
So far as the two scan signals are concerned, they travel over lead 342' to S~ 351. There the sonic 5 signal is separated out and goes over line 316 to the D-MUX 354. The synchronizing signal taken off the line 342' is used over line 318 to control the rate at which the demultiplexer operates so as to be in synchronism with the multiplexer in the sonde. The demultiplexer 354 is 10 indicated as a synchronous switch that transmits the incoming signals on 316 to two separate lines 316' and 318'. Thus digital signals from each of the two T/RTS are then applied to individual digital-to-analog converters 356 and 358 respectively. The individual outpu-ts are then 15 taken by lines 316" and 318" to the cathode ray recorder 352, which is a very fast recorder, responsive to the normal frequencies of the electrical scan signals.
One possible example of the two separated sig-nals calls for one to be a reflection signal and the other 20 to be a caliper signal. These can come from a single T/RTS or can be taken from two separate T/RTS, one of high frequency and one of low frequency, which has previously been discussed. Conventional photographic means are pro-vided to form the logs la~elled 360A and 360C, respec-25 tively amplitude and caliper logs.
The signals on line 316' and 318' from the dem-ultiplexer 354, which are individual digital signals, may also be recorded directly on recorder B 266'. The differ-ence between this recorder 266' and recorder 266 is that 30 the signal recorded on the tape recorder 266 is a multi-plexed signal which can, if desired, be played back later through D-MUX 354, through D/A converters 356, 358 and displayed as individual logs and so on. On the other hand, tape recorder 366' has two channels, each one 35 recording a complete digital signal transmitted from the sonde.
It is possible, o~ course, also to send the analog signals that would come from line 316" and 318"

to an analog tape recorder such as 266" for storage and later playback.
While in FIGURE 22 the two signals are indicated as amplitude and caliper signals, it will be clear that 5 they can be complete digital electrical scan signals or they may be analog electrical scan signals which are transmitted by two separate transmission lines, as in FIGURE 21A.
Referring now to FIGURE 23, there are shown two 10 channels for processing of the ESS. The inputs are taken from the output portion of FIGURE 15 and shows two output signals 48" and 46" from the T/RS 150. One of these goes to the dashed box 302, and the other goes to the box 302', which is identical in all respects to the 15 box 302. However, none of the internal detail of 302' is shown, since it would be identical to that shown in the dashed box 302.
Following the signal on lead 48" from the T/RS 150, the signal is amplified at amplifier 304 and 20 detected at the box DE, 306. Since the received signal is generally a very high frequency electrical signal, it is necessary to process this signal to provide the envelope, which is a lower fre~uency unidirectional analog signal.
The detected signal is the one which is conventionally 25 transmitted to the surface. The deteetor 306 is a conven-tional part of the present-day televiewer and forms no part of this invention.
The detected signal on line 324 goes back to the "amplitude" channel, to amplifier 308, and peak detector 30 310. This peak detector determines the highest amplitude of the received signal, and the sample-and-hold 312 makes a temporary record of the amplitude of the signal. This peak amplitude that is sampled now goes to an analog-to-digital converter 314, which measures the amplitude to six 35 binary bits, and this digital number is transmitted through lines 316 to the multiplexer 320.
At the same time, the signal on line 324 also goes to the detector 306 and to the "caliper" channel, by ~3 -4:L-line 326. This starts with a variable gain amplifier 328.
The need for this arises from the fact that the received signal becomes weaker and weaker, depending on how far it has traveled into and ou~ of the rock wall. Consequently, 5 the signal is amplified in an amplifier that provides increasing gain or amplification, with increasing time of travel of the pulse and its reflection. Thus, even at the remote end of its path, the amplitude of the reflection from a flaw or obstacle, will be large enough to be mea-10 sured.
In the method of determining the precise time ofarrival, the amplified signal from 328 goes to a differen-tiator 330, and to a comparator 332.
The counter 344 is controlled by the sync signal 15 on line 184. The counter provides two different frequen-cies F1 and F2. The high frequency F1 controls the digi-tizer 314 and the counter 322. The lower frequency F2 controls the multiplexer 320, which controls the two six bit signals on input lines 316 and 318. The lines 316 20 carry the six bit signal from the A/~ converter 314. The six bit lines 318 bring the signal from the counter 322, which has counted the time to the reflection in terms of digital bits.
Thus there is on one channel, line 324, a mea-25 sure of the "amplitude" of the signal and on the otherchannel, line 326, a measure of the time of travel, or caliper. These two six bit binary numbers then are passed sequentially to a parallel to-serial converter. Here the parallel words of six bits are converted to serial words 30 of six bit, and transmitted to line drive amplifier 340 and to cable channel 342.
The multiplexing is done by alternately sampling one or the other of the boxes 314 and 322, corresponding to each of the separate initiations of the sonic signal.
35 So for each transmission resulting from the pulsers of FIGURE 15, there is obtained two six bit binary numbers which are alternately transmitted through the parallel-serial- (P/S) converter ~o the cable 342. The switching ~ 3 is accomplished by means of the gate control apparatus 315 over leads 348A and 348B. Also, if a sec~nd scan signal is being provided over line 46" to the signal processor 302'9 the same switch or gate means 315 is also supplied 5 by means of leads 348A' and 348B'.
The compass signal comes in on line 60' from the compass 60 as shown in FIGURE 15, and goes into the ampli-fier 340, and also through lead 60'' to the amplifier 340', which amplifies the output of the second signal pro-10 cessor, and goes by lead 342' to the cable. As shown,there are two transmission channels 342 and 342', each handling the output of a different T/RTS.
Consider again the signal processor in the dashed box 302. If there is a single scan signal on input 15 line 48" , this signal breaks two ways -one through the amplitude branch, and one through the caliper branch. In one mode of operation both measurements of amplitude and caliper are made on the same transducer ESS. As will be discussed in connection with FIGURES 4A and 4B, with the 20 use of two T/RTS, one of high frequency and one of low frequency, the two ESS can be combined into a composite scan signal, which, in the early part is recorded by the high frequency T/RTS, and in the later part is recorded by the low frequency T/RTS.
It will be clear, therefore, that in a second mode of operation, using a composite ESS, that the ampli-tude channel can provide amplitude information from the early part, and caliper information from the later part.
In a third mode of operation a first pair of 30 measurements of amplitude and caliper are made from the early part. The measuring parts of FIGURE 23 are then reset, and the operation is repeated again in the later part of the composite ESS.
Thus it is contemplated in the use of two trans-35 ducers, one of high frequency to provide amplitude at thefirst reflector, the wall of the borehole, and a lower frequency one ~o provide -the time of travel of the cal-iper. By use of switches 324' in line 326, and 324 " in -~3-line 46'', with connector 341, it is possible to utilize a high frequency transdllcer on line 46" so that the caliper measurement in the processor 302 would correspond to the caliper of the lower frequency transducer while the ampli-5 tude would be corresponding to the higher frequency trans-ducer.
I previously pointed out that by use of gating means, a high frequency and a low frequency transducer could be gated sequentially onto a single transmission lO channel and thus, such a composite signal on 48 " would provide, without the switches 3241 and 324 " the amplitude and caliper measurements respectively from both trans-ducers.
In FIGURE 23 I have shown a pair of switches 15 324' and 324". With the switches as shown, a single ESS
on lead 48" could be connected to both the amplitude and caliper channels 324, 326 of processor 302. In another mode of operation, switch 324' is moved to lead 341, as is also switch 324'', so that the ESS on 46" goes to the 20 caliper channel while 48 " goes to the amplitude channel of the processor 302.
While I illustrate in FIGURE 15 a processor that would transmit and receive two sonic signals from two transducers 46 and 48 respectively, it will be obvious 25 that the same apparatus can be used with a transmit/receive switch 150' (FIGURE 24) to handle 3, 4, or more separate signals as it does the two signals on leads 46' and ~i8'. Also, each of these single transducers can be combined as previously mentioned, so that two 30 transducers together provide one pair of signals of ampli-tude and caliper. Thus, to transmit four such signals in digital for~ on a single transmission line it could uti-lize eight separate transducers, four of high frequency and four of low frequency, and so on.
Also, I have shown in FIGURE 23 that two sepa-rate transducers providing signals on lines 48 " and 46"
could each be composed of the gated scan signals from a pair of high and low frequency transducers.

~5 ~ 5 -~4-Referring now to FIGURE 2~, there is shown a modification of FIGURE 23. Briefly, six T/RTS are shown and indicated by letters A, B, C, D, E, and F. These all lead into a transmi-t/receive switch 150A that controls all 5 of the reflected signals on the leads which are identified by the indication HFl, LFl, HF2~ LF2, HF3, and ~F3, etc.
In other words, there are six or more transducers, three of them high frequency, which produce measurements of amplitude, as shown in the amplitude line of 302. The 10 other three transducers are low frequency, and they will pass ~hrough circuits corresponding to the caliper line of box 302 of FIGURE 23.
Since the amplitude signals are taken from the short range transmission, that is, from the wall of the 15 borehole, they will all be multiplexed together by MUXl, 320A. All of the low ~re~uency signals of caliper will be multiplexed in 320B. All of the signals coming into the multiplexer 320A and 320B are now digital. They are con-trolled by the clock signal on 184, which goes by lead 20 184A to the two multiplexers. This timing signal also goes to the parallel-to-serial converter 32~'.
The P/S converter does two things, it stores each of the six signals coming from the two multiplexers and reads out the bits in serial order. Also by means of 25 a switch 391 it reads all of the signals from multiplexer 1 and then switches over and reads them from multiplexer 2, then 1, and so on. Of course, the three pairs of sig-nals can be read out and transmitted in other combina-tions. The output of the P/S converter then goes to the 30 amplifier and line driver 3~0 and to a single transmission channel 342 in the cable 20.
While FIGURE 24 shows that two separate T/RTS, such as HFl and LFl together provide one pair of data, the six T/RTS shown would not even fully load a single trans-35 mission channel.
Another way o~ handling the individual T/RTSwould be as indicated in FIGURE 23 where the jumper lead 341 is not connected, and both the amplitude and caliper -~15-channels process the signal from a single T/RTS. That is, the signal from 48 " goes to both lines 324 and 326 and another signal from T/RTS 46 goes by line 46" to the second processor 302'. In this format, only four T/RTS
5 can be handled on one transmission channel.
Refer back now to FIGURES 4A and 4B. There are shown two T/RTS 46 and 48. One 46 is a high frequency transducer (possibly in the range of .75 to 1.25 MH2), while 48 would be a lower frequency transducer (possibly 10 in the range of 250 KHZ to 850 K~Z). They transmit beams of sonic information 16, and 32 respectively. It is well known that the higher frequency beam has a shorter dis-tance of penetration in a liquid or solid medium. Corre-spondingly, lower frequency beams have a greater distance 15 of penetration.
The best range of usefulness of the high fre-quency T/RTS is ZA, 100, while for the lower frequency T/RTS the best range is ZB. Thus, by using both, a much greater range of usefulness is provided, ZA -~ ZB.
20 FIGU~E 4B shows -the gating time schedule in which the first gate 116 on line 134 passes the high frequency ESS
from T0 to TS, and then the second gate 122 on line 136 passes the low frequency ESS from time TS onward.
While not shown, the multiple pairs of digital 25 numbers transmitted from FIGURE 24, go by conductor 342 -to the surface, along with the clock signal to the multi~
plexers 32A, 32B on lead 184B'. At the surface the digital signals are demultiplexed, converted to analog signals and s-tored or displayed.
What has been described is basically a system of multiple T/RTS in a sonic borehole scanner or borehole televiewer, which has a plurality of transducer assemblies by means of which the combination of scan signals from the plurality of T/RTS can provide information of greater 35 value, more effectively, and more efficiently, than can be done with a single T/RTS.
The multiple T/RTS can, of course, be arranged with respect to each other in azimuthal array in a hori~

zontal plane, or in a vertical array in a vertical plane, or in combinations of multiple horizontal planes and/or multiple vertical planes as has been fully described.
When the words "high frequency" and 1'1Ow fre-5 quency" are used to characterize the properties of thetransducers, they ~ean transducers that have natural oscillation frequencies in the ranges of about 0.5 to about 1.5 M~IZ, and from about 75 to about 750 KHZ, respec-tively.
Also described is a group of embodiments of apparatus for processing multiple analog electrical scan signals detected in the sonde, by means of multiple T/~TS
on the rotating assembly. These can be processed in a number of ways which have been illustrated and described, 15 and transmitted to the surface. This can be by way of a normal single channel logging cable or a multiple channel logging cable or an improved logging cable, which might have very high frequency transmission capability, such as by the use of coaxial cable channels, or optical fiber 20 channels, and so on.
While I have described multiple T/RTS usage when placed in a common transverse plane on the rotating assembly, the apparatus of this invention and the method of opera$ion are equally valid for any type of multiple 25 T/RTS whether placed in vertical arrays or circumferential arrays, or any combination of the two.
While I have shown and described methods and apparatus for processing multiple ESS so as to permit transmission of multiple ESS over presently available low 30 frequency transmission channels to the surface, these sig-nals could of course be transmitted to the surface without processing, where the cable provides single or multiple high frequency channels, and the same processing done at the surface. The point being that the processing is 35 important in the utilization of the multiple ESS~ whether done in the sonde, or at the surface. It is also impor-tant as a basis for transmission over low frequency chan-nels. So, when I speak of processing ESS I mean either processing in the sonde or at the surface, as appropriate.

S~
-~7-This invention makes possible three-dimensional imagery of the rock response surrounding the borehole.
This concept is considered useful in application to any logging parameter that can be focused and beam steered.
While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood 10 that the invention is not limited to the exemplified embodiments set forth herein but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.

Claims (45)

WHAT IS CLAIMED IS:

1. A Method for the volumetric logging of a wellbore drilled in the earth comprising:
generating in said wellbore at a first position a first signal having a frequency f1, generating in said wellbore at a second position in said wellbore a second signal having a frequency f2 which is different from f1, recording first responses from said first signal at said second position, recording second responses from said second signal at said first position.

2. A Method of Claim 1 further comprising generating in said wellbore at the first position a first signal having a frequency f1 and directing said first signal in a 360° horizontal range;
at a vertically displaced second position generating in said wellbore the second signal having a frequency f2 which is different from f1 and directing said second signal in a 360° horizontal range; and recording reflections from said first signal at said displaced second position and reflec-tions from said second signal at said first position.

3. A Method as defined in Claim 2 in which either frequency f1 or f2, or both, are changed from the surface while the generating means and recording means are in the wellbore and generating such signals having such changed frequencies.

4. In a Method as defined in Claim 1 in which there is used an apparatus for recording data obtained from cyclic scanning operations, carried out angularly around the wall of a borehole, by means of a sonde having a rotating assembly, at each of a plurality of different depths;
wherein subsurface parameters are sensed during each scanning cycle by a first transmit/

receive transducer system (T/RTS) mounted on said rotating assembly, the improved method of operation further comprising the steps of:
(a) providing at least a second (T/RTS) in a selected geometric relation to said first (T/RTS) on said rotating assembly;
(b) operating said at least two (T/RTS) in scanning action to provide at least two electrical scan signals (ESS), one from each of said T/RTS; and (c) utilizing said at least two elec-trical scan signals.

5. The Method as in Claim 1 and including means for delaying one of said electrical scan signals a selected time interval with respect to the other, whereby the two signals are in-phase, and adding it to said other of said two electrical signals to provide a sum signal, and means to transmit said sum signal to the surface.

6. The Method as in Claim 5 in which said at least two T/RTS are of the same frequency and said time interval of delay is a function of the angular relation between said first and second T/RTS.

7. The Method as in Claim 5 in which said at least two T/RTS are of different frequency, and including means to gate the time on and time off of said two elec-trical scan signals before adding them together.

8. The Method as in Claim 7 in which the T/RTS
which is of highest frequency is gated on for a first short time interval; then it is gated off, and the T/RTS
which is of a lower frequency is gated on.

9. A Method of Claim 4 further comprising uti-lizing said at least two ESS, comprising the steps of;
(a) processing said at least two analog ESS in preparation for transmission over said at least first analog electrical signal channel to the surface;
(b) combining said two analog ESS; and (c) transmitting said two simultaneous combined analog ESS over said first analog electrical signal channel in said cable to the surface; and uti-lizing at the surface said transmitted first and second analog ESS.

10. The Method as in Claim 9 in which the step of combining said two ESS is carried out after one or the other of said two ESS is delayed until said at least two ESS are in phase.

11. A Method of Claim 4 further comprising uti-lizing said at least two simultaneous analog ESS, com-prising the steps of;
(a) delaying one of said at least two ESS
until the two are in phase;
(b) passing a transmitting pulse sequen-tially to first one and then the other of said at least two T/RTS so that only one is transmitting at a time; and (c) sequentially transmitting said at least two ESS from said at least two T/RTS to the surface.

12. The Method as in Claim 11 in which said at least two T/RTS are of different frequencies, and including the step at the surface of utilizing alternate series of ESS from said at least two different T/RTS to provide two separate logs.

13. A Method of Claim 4 further comprising uti-lizing said at least two simultaneous analog (ESS), com-prising the steps of;
(a) processing and combining said at least two analog ESS in preparation for transmission over said at least first analog electrical signal channel to the surface;
(b) transmitting said two combined, dif-ferent simultaneous analog ESS over said first analog electrical signal channel in said cable to the sur-face; and utilizing at the surface said transmitted combined signal.

14. The Method as in Claim 2 in which the step of combining said two ESS comprises the steps of;
(a) delaying one or the other of said two ESS until said at least two ESS are in phase;
(b) sampling said analog ESS at selected intervals;
(c) loading said samples sequentially into a charge coupled delay line (CCDL) of selected trans-mission rate; and (d) reading out said sequential samples from said CCDL and converting the sequential samples into an analog signal.

15. A System for logging a borehole and pro-viding a first and at least a second electrical scan signal, from cyclic scanning operations carried out angu-larly around the wall of the borehole at each of a plur-ality of different depths by means of a sonde having a rotating assembly wherein subsurface parameters are sensed during each scanning operation by a first transmit/receive transducer system (T/RTS) and at least a second T/RTS in selected geometric relation to said first T/RTS, and means for utilizing said at least two electrical scan signals from said at least two T/RTS and for providing a display of the sensed parameters, wherein:
said at least a second T/RTS comprises (N-1) T/RTS, making a total of (N) T/RTS, each mounted at a selected, equally spaced, azimuthal position with respect to the others, and each pro-ducing electrical scan signals responsive to its scans, for a total of N electrical scan signals.

16. The System as in Claim 15, including a second set of (N) T/RTS in a transverse plane, parallel to and longitudinally displaced from said first set of (N) T/RTS, each T/RTS of said second set of T/RTS spaced in longitudinal alignment with said first set of T/RTS.

17. The System as in Claim 15 in which there a first set of at least three T/RTS, equally spaced vertically along a vertical radial plane; and including means to provide a formed beam of sonic energy; and further comprising means to electronically tilt said formed beam to a selected angle to one side or other perpen-dicular to said axis of rotation; and a second set of at least three T/RTS
similar to said first set, spaced longitudinally a selected distance above or below said first set, and means to adjust the angles of said formed beams so that their axes intersect the perpendicular bisector of the line joining said two sets, at a selected dis-tance from the plane of said T/RTS.

18. A System for logging a wellbore and pro-viding a first and at least a second electrical scan signal from cyclic scanning operations carried out angu-larly around the wall of the wellbore at each of a plur-ality of different depths by means of a sonde having a rotating assembly wherein subsurface parameters are sensed during each scanning operation by a first transmit/receive transducer system T/RTS and at least a second T/RTS in selected geometric relation to said first T/RTS, and means for utilizing said at least two electrical scan signals from said at least two T/RTS and for providing a display of the sensed parameter, the System comprising:
a sonde having the first and the at least a second T/RTS each functional for transmitting a signal and receiving responses from reflecting sur-faces for scanning angularly around a wellbore and for producing respective electrical scan signals rep-resentative of the thus scanned paths, the first T/RTS means being effective for transmitting a first frequency f1 and the second T/RTS means being effec-tive for transmitting a second frequency f2, f2 being different from f1; and means mounted in the sonde for processing the resulting electrical scan signals and for trans-mitting the thus processed electrical scan signals to the surface of the earth.

19. The System as in Claim 18 wherein the means for processing the electrical scan signals for transmis-sion to the surface comprises sampling means for sampling each of the electrical scan signals and for producing a signal representative of the thus sampled electrical scan signals; and means for transmitting the thus produced signal representative of the thus sampled electrical scan signals to the surface on a single transmission line.

20. The System as in Claim 18 wherein the means for processing the electrical scan signals for transmis-sion to the surface comprises means for combining said plurality of electrical scan signals into a single trace for transmission.

21. The System as in Claim 20 wherein:
the means for combining comprises means for delaying each of said electrical scan signals with respect to another electrical scan signal by selected time intervals until all of the plurality of elec-trical scan signals are in time coincidence; and means for summing the thus-delayed signals and providing a single summed electrical scan signal.

22. In a Method for the volumetric logging of a wellbore drilled in the earth which comprises directing a first beam of energy having a first direction and azimuth outwardly from said wellbore into the surrounding forma-tion, receiving a signal indicative of the response of said first beam from at least one point within said forma-tion, directing a beam of energy having a second direction and azimuth outwardly from said wellbore into the sur-rounding formation, and receiving a second signal indica-tive of the response of said second beam from at least one other point within said formation, the steps comprising:
carrying out cyclic scanning operations angularly around the wellbore by transmitting a first signal having a first frequency f1 from a first transmit/receive transducer system (T/RTS) mounted in a sonde and receiving reflected responses to the thus angularly around the wellbore transmitted first signal, and producing a first electrical scan signal representative of the path thus scanned using the first frequency;
carrying out cyclic scanning operations angularly around the wellbore by transmitting a second signal having a second frequency f2 from at least a second T/RTS mounted in said sonde and receiving reflected responses to the second signal and producing at least a second electrical scan signal representative of the path thus scanned using the second frequency; and transmitting signals representative of the thus produced at least two electrical scan signals from the sonde to the surface of the earth.

23. The Method as in Claim 22 wherein the sonde comprises an assembly upon which is mounted said first T/RTS at a first position and said at least a second T/RTS
at at least a second position and including operating the T/RTS in scanning operations and providing the at least two electrical scan signals by transmitting in said well-bore from the first T/RTS at the first position a first signal having the frequency f1 and directing said first signal in a 360° horizontal range, transmitting in said wellbore from the second T/RTS at the second position the second signal having the frequency f2, which is different from f1, and directing said second signal in a 360° hori-zontal range, and receiving responses to said first signal at said second position and responses to said second signal at said first position.

24. The Method as in Claim 22 including gener-ating frequencies f1 and f2 in the wellbore and changing either frequency f1 or f2, or both, from the surface and generating and transmitting first and second signals in the wellbore having such changed frequencies.

25. The Method as in Claim 22 including passing a transmitting pulse sequentially to first one and then to another of the first and the at least a second T/RTS so that only one is transmitting at a time; and sequentially transmitting the at least two electrical scan signals from the first and the at least a second T/RTS to the surface over a single transmission channel.

26. The Method as in Claim 22 comprising:
lowering a the sonde having the first and the at least a second T/RTS mounted therein for cycl-ically scanning angularly around the wellbore into the wellbore with a cable comprising a multiple set of conductors;
moving the sonde vertically at a selected rate and producing the at least two electrical scan signals;
processing the at least two electrical scan signals for transmission to the surface on a single transmission channel; and transmitting the thus processed electrical scan signals on a single transmission channel through the cable to the surface of the earth.

27. The Method as in Claim 26 wherein the step of processing the at least two electrical scan signals for transmission to the surface on the single transmission channel comprises:
summing the at least two electrical scan signals; and transmitting the resulting summed signal to the surface.

28. The Method as in Claim 26 wherein the step of processing the at least two electrical scan signals comprises delaying one or more of the at least two elec-trical scan signals until the electrical scan signals are in time coincidence and summing the thus delayed elec-trical scan signals.

29. The Method as in Claim 26 further com-prising:
generating a plurality of further elec-trical scan signals and delaying and summing all of said electrical scan signals and producing a summed signal which is transmitted to the surface.

30. The Method as in Claim 26 wherein the step of processing the at least two electrical scan signals for transmission to the surface of the earth on the single transmission channel comprises:
sampling each of said at least two elec-trical scan signals and producing a signal representative of the thus sampled electrical scan signals; and transmitting the thus produced signal rep-resentative of the thus sampled electrical scan signals to the surface.

31. The Method as in Claim 22 comprising:
lowering the sonde having the first and the at least a second T/RTS therein for carrying out cyclic scanning operations angularly around the well-bore into the wellbore with a cable comprising a mul-tiple set of conductors;
moving the sonde in the wellbore at a selected rate;
controllably triggering each of the first and the at least a second T/RTS at selected times, transmitting a signal outwardly therefrom and receiving responses thereby and controllably pro-ducing the at least two electrical scan signals; and transmitting signals representative of the at least two electrical scan signals over a single transmission channel to the surface.

32. The Method as in Claim 22 further com-prising:
probing a first zone adjacent the wellbore with the first frequency f1 and producing a first electrical scan signal representative of subsurface parameters; and probing a second zone adjacent the wellbore with the second frequency f2 and producing a second electrical scan signal representative of subsurface parameters.

33. The Method as in Claim 32 further com-prising:
combining the first electrical scan signal and the second electrical scan signal and producing a combined signal representative of a greater depth of penetration than that resulting from second fre-quency f2 alone and having an improved record in the near field as compared with that produced by first frequency f1 alone.

34. The Method as in Claim 22 wherein:
the first and at least a second T/RTS com-prise a vertical array of T/RTS arranged in different horizontal planes on the sonde.

35. The Method as in Claim 22 wherein:
the first and at least a second T/RTS com-prise a horizontal array of T/RTS arranged in a hori-zontal plane on the sonde.

36. The Method as in Claim 35 further com-prising:
simultaneously energizing an array of T/RTS
and transmitting signals in proper amplitude and phase relation for beam forming.

37. The Method as in Claim 35 further com-prising:
simultaneously energizing an array of T/RTS
and transmitting signals in proper amplitude and phase relation for beam forming.

38. The Method as in Claim 22 comprising:
(a) generating the first signal in said wellbore having the frequency f1 and directed along a path in the wellbore;
(b) receiving reflected responses from said first signal and producing the first electrical scan signal;

(c) generating at least a second signal in said wellbore having the frequency f2, f2 being dif-ferent from f1, and directed along essentially said path; and (d) receiving reflected responses from said at least a second signal and producing at least a second electrical scan signal; and (e) delaying the first electrical scan signal until the first electrical scan signal is in time coincidence with the at least a second elec-trical scan signal, summing the thus delayed first electrical scan signal and the at least a second electrical scan signal, producing a summed signal, and transmitting the summed signal to the surface.

39. The Method as in Claim 22 comprising:
(a) generating the first signal having the frequency f1 at a depth in said wellbore;
(b) generating the second signal having the frequency f2 which is less than f1 in said wellbore at approximately said depth;
(c) generating the first electrical scan signal representative of a response to the first signal;
(d) generating the second electrical scan signal representative of a response to the second signal;
(e) discarding all of the first electrical scan signal except a first portion, (f) discarding a first part of said second electrical scan signal and retaining a second por-tion, (g) combining said first portion and said second portion and obtaining a composite signal, and (h) transmitting the composite signal over a single transmission channel to the surface of the earth.

40. The Method as in Claim 39 including gating the time on and time off of the first and at least a second electrical scan signal.

41. The Method as in Claim 39 including gating the time on and time off of the first and at least a second electrical scan signal wherein:
the T/RTS of higher frequency is gated on for a first short-time interval, then gated off, and the T/RTS of lower frequency is gated on.

42. The Method as in Claim 22 including the step at the surface of using alternate series of elec-trical scan signals from said at least two different T/RTS
after transmission to the surface to provide two separate logs.

43. The Method as in Claim 22 including the step of combining said at least two electrical scan sig-nals by:
delaying one or the other of said at least two electrical scan signals until said at least two electrical scan signals are in time coincidence;
sampling said at least two electrical scan signals at selected intervals;
loading said samples sequentially into a charge coupled delay line of selected transmission rate; and reading out said sequential samples from said charge coupled delay lines and converting the sequential samples into an analog signal.

44. The Method of Claim 22 comprising:
generating and directing within the well-bore a first signal from the first T/RTS having the first frequency f1 outwardly toward the wall of the wellbore along a path encircling the wall of the wellbore;
selecting the second frequency f2 different from the first frequency f1 at the surface while gen-erating means for generating the frequencies f1 and f2 and receiving means for receiving reflections are in the wellbore; and generating and directing within the well-bore the at least a second signal from the at least a second T/RTS having the second frequency f2, different from f1, the signal being directed out-wardly toward the wall of the wellbore along paths encircling the wall of the wellbore.

45. The Method of Claim 22 comprising:
generating and directing within the well-bore the first signal from the first T/RTS having the first frequency f1 outwardly toward the wall of the wellbore along a path encircling the wall of the wellbore;
receiving reflected responses to the thus directed first signal and producing respective elec-trical scan signals representative of the paths encircling the wellbore thus scanned using the first frequency f1;
selecting at the surface a different fre-quency f2, different from f1, while generating means for generating the frequencies f1 and f2 are in the wellbore;
generating and directing within the well-bore the at least a second signal from the at least a second T/RTS having the second frequency f2, the second signal being directed outwardly toward the wall of the wellbore along a path encircling the wall of the wellbore; and receiving reflected responses to the thus directed second signal and producing respective elec-trical scan signals representative of the paths encircling the wellbore thus scanned using the second frequency f2.