GB2094473A - Method and apparatus for logging boreholes - Google Patents

Abstract

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 first transmit/receive transducer system (T/RTS) 46 mounted on a rotating assembly 34 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 48 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. <IMAGE>

Description

SPECIFICATION Method and apparatus for logging boreholes This invention lies in the field of acoustic logging systems for boreholes. More particularly, it is concerned with the logging of deep boreholes in the earth. Still more particularly, it concerns the use of an acoustical transducer which transmits a beam of high frequency acoustic energy into the borehole directed in a radial 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 instrument, or sonde, for further.

processing.

Still more particularly, it concerns improvements 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 sent outwardly from the axis of the borehoie and multiple reflected sonic signals are received, converted to electrical scan signals, which are then utilized in various ways.

Still more particularly, this invention concerns improvements in methods and apparatus for processing multiple simultaneous analog electrical scan signals (ESS) in the sonde four 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.

This field of science and engineering is not 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 Conditions of Materials Traversed by a Borehole", issued February 20, 1 968 in the name of J. Zemanek, Jr. There is also U.S. Patent No.

3,668,619 entitled: "Three-dimensional 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 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 presented at technical society meetings, so that further description or statement of the art is not necessary at this time.

It is a primary object of this invention to provide a number of improvements in the design and construction of borehole logging instruments employing acoustical probing beams, and reflected sonic signals, and in the use of data from these instruments.

It is a further object of this invention to provide at least two or more transmitting receiver transducer systems (T/RTS) operating independently to provide multiple electrical scan signals, which are used cooperatively, in combination, to provide more information than would be possible by their separate use.

It is another objective of this invention to provide apparatus and methods for processing multiple ESS 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 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 the surface, and also to transmit power and/or control signals from the surface to the sonde. The main limitation 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 judgement as to which type of transducer, measuring a selected parameter, will be the most useful in a given subsurface situation.

In this invention the improvement lies in the use of two or more T/RTS. These are mounted on the same 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, or they may each be different 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 characteristic and the frequency of the T/RTS. For example, one 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 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 circumferentially, a plurality of scans are made simultaneously, as the sonde is moved vertically at a selected constant rate. 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 permits 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 vertical plane longitudinally spaced. This use of arrays of T/RTS will provide a stronger, betterfocused scanning beam, of higher energy. Thus, the penetration of the beam 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 originaily designed for transmitting relatively low frequency electrical logging signals, and so on, that is, signals of less than about 50 KHZ.

The apparatus and methods of processing the multiple ESS form an aspect of this invention. The particular apparatus design depends on a number of factors, such as: a) the number of separate TORTS 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 m easu re m ents -of amplitude 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 portions as a single signal; e) whether a single transmission channel is provided in the cable, or more parallel channels; f) the nature 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 to 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 evident from the following description taken in conjunction with the appended drawings, in which: Figure 1 illustrates the prior art simply in the arrangement of the logging sonde held concentric withthe wellbore by means of radial centering springs supported by 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 1800 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 illustrates 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 the two transducers of Figure 4A.

Figure 6 illustrates the use of time delay between the two T/RTS of Figure 3 combined with the gating system of Figure 4B.

Figures 7 and 7A illustrate two variations of a system employing two separate T/RTS.

Figure 8 illustrates the main mechanical construction of a single T/RTS mounted on the rotating assembly in the sonde.

Figure 9A, 9B, 9C, and 9D illustrate the possible arrangement of two, three, four, and six, T/RTS in a horizontal plane, equally spaced, circumferentially.

Figure 10 illustrates a system in which multiple T/RTS are provided on the rotating system, but these are 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 forming techniques may be used to provide a better focused and more penetrating beam than would be provided by a singleT/RTS.

Figures 1 2A, 1 2B and 1 2C represent various methods of transmission and utilization of the scan signal from multiple T/RTS.

Figure 13 illustrates a variation of Figure 10.

Figure 14 is an extension of portions of Figures 2 and 3, illustrating how four separate T/RTS can be mounted on the rotating assembly and can be connected as desired to the pulser and to the cable.

Figure 1 5 is an extension of Figure 3, illustrating the use of multiple pulsers, one for each of the separate T/RTS so that parallel output scan signals are provided simultaneously.

Figure 1 6 is a modification of part of Figure 1 5 showing alternate transmission of two or more electrical scan signals which may be from T/RTS of the same or different frequencies.

Figure 17 illustrates the time scheduling of the alternate transmissions of the two or more electrical scan signals of Figure 1 5.

Figure 1 8 illustrates one embodiment of apparatus for transmitting two or more simultaneous analog electrical scan signals by converting them to double frequency 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 sequential transmission of the double frequency scan signals.

Figures 20A, 20B, 20C, 21 A, and 21 B illustrate different embodiments for transmission of two or more ESS to the surface, 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 separate digital signals comprising the amplitude of a reflection, and the time of travel, or distance of penetration, and multiplexing the two digital signals.

Figure 24 illustrates an extension of Figure 23, in which plural digital signals of amplitude and caliper from plural ESS are multiplexed and transmitted over a single transmission channel.

There are a number of words designating elements or parts of the invention that will be used frequently during the following description.

It 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 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 applicaticn of a high frequency voltage or pulses to the transducer. In some instances the sonic generator can also be used as a sonic wave detector. In other instances 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 vertical boreholes in the earth, it can equally well be used in 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 sonde will be called transverse plane, or horizontal plane, and so on.

Referring now to the drawings and in particular to Figure 1, which is indicated as prior art, there is indicated generally by the numeral 10, a logging sonde 1 2 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 25 measure the length of cable that has passed over the wheel. The rotations of the wheel 25 are transmitted by means 26 through an appropriate drive system, to control the movement in the direction representing verticality, in any display system that might be used.

The sonde 12 is supported by radial centering springs 1 8 so that the axis of the sonde is coaxial with the borehole 22. A section of the sonde indicated by numeral 14 rotates by motor means in the sonde, at a selected constant rate. A probing beam of sonic energy 1 6 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 of which the wall is composed. This wall might be a steel casing surrounded by cement in a drilled borehole in a rock formation, or it might be an open borehole.

Referring now to Figure 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 information will be provided regarding the normal electronic circuits in the space 31. These are fully described in many configurations in the patent literature referred to earlier. Wherever the circuitry would be different in this invention it is, of course, fully described as will be clearly seen in the Figures.

The sonde 30 comprises an outer shell 12 of conventional construction. In the lower portion a cylindrical bulkhead 50 is fastened rigidly and sealed to the outer shell and a downwardly extending axial post 42. 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 revolution, as the sleeve 34 rotates. This T/RTS 46 is periodically excited by electrical circuits which will be described, and transmits radially outwardly a sonic beam indicated by the numeral 16, which passes to the wall 22 of 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 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' the electrical scan signal reflected from the wall of the borehole.

In the normal design of a borehole acoustic logger, or borehole 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 circuits in the electronic package 31, which are conventional.

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 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 be discussed in greater detail in connection with Figures 8, 9A, 9B, 9C, 9D, 10 and 11, various combinations of multiple T/RTS arranged in a common horizontal plane, equally spaced circumferentially, can be provided which will provide certain benefits. Also the multiple T/RTS can be provided in a longitudinal array, whereby other benefits can be realized, or in some combination of circumferential and longitudinal arrays.

One possible electronic circuit that might be used with the apparatus of Figure 2 is illustrated in Figure 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 connected internally to the T/RTS 48 and 46 respectively, and 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.

One each rotation of the rotating assembly 34, an 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 its equivalent, as would be well known in the art. By means of the signal received from 60 that passes internally 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 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 Figure 3 for completeness as to the electrical circuits in the upper righthand portion of the Figure 3. A power supply at 84 supplies power by resistor 1 76 to capacitor 86, and passes through the primary 88 of a transformer, to junction 90 and ground 78, which is connected to the negative potential of the power supply. A triggered rectifier, or gate control rectifier, 80 is connected between the potential at the junction of resistor 1 76 and capacitor 86 to the ground 78.

There is a timing means 74 which is conventional, operated by a clock of constant frequency, and including a counter means, such that at a selected time a signal pulse can be placed on line 75 to the trigger connection 82 of the controlled rectifier 80. When the trigger pulse arrives, the capacitor having been previously charged to the full potential of 84, now discharges through the rectifier 80 to the ground and this large current passing through the primary 88 of the transformer aenerates 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 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, controlled by means of a signal from the surface through one of the multiple conductors of the cable 20, as is well known in the art. Consider 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 pulse of sonic energy of selected amplitude and frequency. This propagates outward radially through the mud in the annulus of the borehole (or liquid of selected composition), to an obstruction such as the surface of the casing.

Here part of the sonic energy is reflected and passes backward over the same path to the T/RTS 48, where it generates a corresponding received signal, or electrical scan signal, which comes back from the T/RTS 48 through line 48', through the switch 62, to the box 66 which is marked S. Box 66 is a switch of a particular nature which is used for cutting off the receiving amplifier 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 1 Meg. HZ, or higher, and too high to transmit over the transmission channel of the conventional logging cable. It may be necessary to pass this through a signal detector, which converts the high frequency ESS to a relatively low frequency unidirectional analog signal, which can be transmitted over the cable.

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 amplified reflected signal is passed by line 72 which is a high 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 AND gate which is open during the time that the potential is applied to 92, 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 transformer 90. Figure 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.

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 different frequencies, the beams of higher frequency have a shorter depth of penetration through media, such as the 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 frequencyT/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, the sharper the beam width and the better 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 frequency transducer would be used. On the other hand, where it is desired to probe well beyond the wall of the borehole, 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. 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 a 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 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 two TORTS 46, 48, can be successively 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 48, consider the T/RTS 46 as high frequency, providing a beam 1 6 as indicated in Figure 1 and the T/RTS 48 being of lower frequency, 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-1 02 for the lower frequency T/RTS 48. In general, the range, or radius from the T/RTS to the optimum position in the zone A of useful scanning 100, will be shorter for the higher frequency T/RTS, than the zone B-i 02 for the lower frequency T/RTS.If 46 is a high frequency T/RTS, and 48 is a corresponding low frequency T/RTS, and if the zones As100 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-1 00, and use the lower frequency T/RTS 48 during the time that the pulse beam traverses the distant zone B-i 02. 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.

Consider that the high voltage pulse along line 92 (of Figure 3) occurs at the time TO and a sonic pulse is sent out from the transducer A. For a short time interval 108, to the T1, 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 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 pulsed at TO 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 provided by the low frequency transducer. Of course, at a time 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. Thereafter, there will still be sufficient energy to traverse 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 frequency transducer 110 does. Consequently, it is desirable to prevent the recording and display of the portion of 110 up to the time TS, and during that period, the gating pulse 11 6 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 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 other electrical scan signal, and gating the two scan signals appropriately, as has been described, a combination of the two scan signals provides a much improved record in the near field, and having a greater depth of penetration in the far field, than would be provided by either one alone.

In Figure 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 1 38A 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 1 800 of rotation of the rotating system. If trace 106 on line 138 is delayed by the time period 126, or one-half revolution, it appears as 106" on line 140, which would be identical to, and in-phase with, the trace 106' produced 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 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 summing and transmitting the sum signal to the surface, it would be much more desirable to be able to transmit the two signals separately, and contemporaneously, to the surface.

This could be done, for example, if there were two transmission channels instead of the cable 20, or if there was a multiplex 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 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 T/RTS have a transmit signal applied through leads 1 72 and 1 74 respectively, to leads 46 and 48' to the T/RTS A and B. The timing for these transmit signals is provided by a counter 166 which has a clock signal over lead 1 82 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 rectifiers 80 of the transmission source assemblies, which have previously been described in detail in relation to Figure 3, are then controlled by the leads 169 and 1 70 from the counter or timer 166, to the control gate 82 and 82' respectively.

The counter 166 also provides gating pulses or timing pulses on leads 167 and 168 to the transmit/receive switch 1 50. This disables the detecting apparatus following the switch 1 50 while there is the high potential signal applied to the T/RTS from the transmission electronics over leads 1 72 and 174. However, after the short interval 108 of Figure 5 after the transmission pulse is sent, the T/RS 1 50 will then enable the electronics following through leads 46" and 48" to amplifiers 1 52 and 1 54, and through gating means 1 56 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 which follows the gating controls 1 56, 1 58 is controlled by the counter over lead 184, 185. The gating units 156,158 and the delay unit 1 60 carry out the operations described in connection with Figure 5. Following these three units the two signals are added together by means of a pair of resistors 1 62 being applied together to the input to an amplifier 180, the output of which goes to the transmission channel 178 in the cable 20.

Thus, by means of this 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, 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 1 50 directly to amplifiers 1 52 and 1 54 and apply the amplified signals, one to each of the two transmission channels.

The situation illustrated in Figure 7A is exemplified a little more completely in Figure 1 2B to which reference is now made. Here, the lines 46' and 48' carrying the reflected scan signals from the T/RTS 46 and 48, go to the T/RS switch 150, then to amplifiers 152 and 1 54. The amplified signals then go to the two separate channels of transmission through the cable; namely, 1 86 and 188. The surface end of the cable 20 is similarly shown and the conductors now 186' and 188' go to analog-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 1 2A is shown in an alternative circuit, in which the signals from the T/RS switch 1 50 are amplified 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 the cable 20 to the surface. At the upper end of the transmission channel 178' connects to a demultiplexing unit 261, which converts the combination signal on !ine 178' back to the two component signals, which were amplified by the amplifiers 1 52 and 1 54. These two component signals 46"' and 48"' on the output of 261 go to amplifiers 262 and 264 and then to a conventional digital recorder 266 for later playback and display.

Figure 1 2C illustrates how a playback of the recorder 266 can provide the two original signals 46"' 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 symbolically three separate methods of transmission of the signals from multiple T/RTS from the subsurface sonde to the surface, to be recorded 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 represent a single scan signal at a given time. It is convenient, therefore, either to combine two or more signals as has 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 signals to the surface is to have a separate transmission channel 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 Figures 7A and 128.

The third method has just been described as the one in which a plurality qf simultaneously recorded signals 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 not be further described.

In general, it is very desirable to separate out at the surface each of the separate electrical scan signals so that they could be recorded as a function of time, or as a function of depth of the sonde below the surface 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 digital magnetic recorder. Another way would be to store the digitized separate signals into one or more separate digital memories, particularly random access memories, such as are now available on the market.

So far in this description of the broad aspects of my invention, I have described the use of multiple T/RTS arranged on the rotating assembly in a horizontal plane. And, as has been described, there are a number of particular advantages to the use of the multiplo 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, then it is possible to record them 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 on each of the others.For example, if there were two similar T/RTS, one spaced 1 800 behind the other, it would be possible either to show a finer detail of scanning display along the borehole, or to permit the sonde to be moved vertically twice as rapidly, and still have the same condition of.trace 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 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 utility or value of the resulting records. It is quite 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 vertical array that is arranged in a plurality of different horizontal planes on the rotating assembly. Such multiple T/RTS would be preferably aligned in a vertical plane through the axis of rotation although this is not required.

For a description of the manner in which the multiple T/RTS can be built into the instrument, reference is made to Figure 8 which shows the present method of mounting a signel 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 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 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 material which is piezoelectric or electrostrictive.

The slab 200 is anchored to the thin sheet 212 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 type of mounting. Thus, no interference is 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 the sheet 212. This backing material is made of a mixture of a very fine powder of a very dense metal, such as tungsten 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 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 energy transmitted perpendicular to the top surface of the slab, or T/RTS 200. The type of the 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 indicated schematically in Figure 3.

Other openings will also be present for the passage of additional signal leads, 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 additional separate transducer slabs, such as 200, can be utilized.

Figures 9A, 9B, 9C, and 9D indicate possible combinations of two or more T/RTS. For instance, in Figure 9A two slabs 200A and 2008 are shown mounted upon a single ring 260 at 1800 azimuth for each other. In Figure 9B three T/RTS 200A, 200B, and 200C are positioned at 1200 azimuth from each other. Similarly, in Figure 9C the spacing is 900 and in Figure 9D the spacing is 600. Other spacing arrangements or construction details can be provided, of course, and those shown in Figures 8,9,10,11, and 12 are just by way of illustration, and not by way of limitation.

In Figure 10 is shown an embodiment which utilizes a plurality of T/RTS units 226A, 226B, and 226C arranged on a selected rotating assembly 220, each unit having its own backing material 214 and arrayed along a longitudinal plane through the axis of rotation. One of the important things that can be done with an array of this sort is to provide, at least in the vertical dimension, a greater dimension of transducer. A larger diameter transducer, of course, provides a much better collimated beam, which is of real value in providing greater detail of the reflecting surface which it is designed to probe.

There has been a great deal of theoretical and 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, 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 diametral plane, of the rotating assembly 220.

The oval contour 230 indicates the shape of the beam in relation to its diameter, as a function of the distance, or radius, away from the transmitter along the axis 232. This shape 230 can be improved by simultaneously energizing the separate transducers in accordance with the theory. This theory has been deveioped over the years and is well known and is fully described in the literature. See, for example, Albers, UnderwaterAcoustics Handbook II, pp.180 205. The type of beam form shown in Figure 10 is indicatedas the possible improved type of transmitted beam and receiving sensitivity when the proper theory is used and the individual beam elements 226A, 2268, and 226C are supplied with transmitting signals in proper phase and amplitude relation.Since the electronics of beam forming is well 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 Figure 10, is that by proper 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 example, similar to the angles of 240A, 240B, 240C. It is clear, therefore, if one of these assemblies is used as a transmitter and transmits along the direction 240C and the other unit 224 acts as a receiver and directs its receiving beam along the line or axis 242C, then at a surface such as 271, there will be a reflection of the transmitted 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 of reflectivity can be changed from 271 to 271' or 271", for example, and soon.The manner in which the tiit of the beam can be changed is something that can be controlled by means of the amplitude or frequency of a voltage or current supplied to the circuit that does the beam forming, and of course, this control can be provided from the surface through 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 change the radius over a wide range for careful exploration 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 possible without endangering the precision and detail of the measurement.

Also, where the liquid medium in the wellbore can be changed during the period of time the logging is done, it may be wise to provide a suitable liquid medium 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 and a vertical plane. Thus, assemblies 280, 284 compare to 220 and 224 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, 2928, and 292C. As in Figure 10, array 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 advantages of Figure 13 is that arrays 286, 288 can be lower frequency, and arrays 290 and 292 can be higher frequency. This is shown in Figure 13 by the indicated axes of the two T/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 beams would be remotely controllable to different axes and different effective radii.

Figure 11 illustrates the use of multiple transducers in a horizontal plane, which can provide beam forming, in a way similar to the arrays of Figures 10 and 13.

I will now discuss how multiple ESS are transmitted 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 less than 50 KHZ.

Referring now to Figure 14, here is shown schematically 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 transverse plane, perpendicular to the axis of rotation. Each one 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 pulser of Figure 3 shown in the dashed box 81, has three terminals, one being provided with power 84, another providing 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 would go to a timing device, such as 74 of Figure 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 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 assembly although only two were shown in Figure 3 and only a single pulser was shown. In Figure 1 5 a similar circuit is provided in which separate pulsers 81A and 818 are provided so that each of the T/RTS can be operated separately from the others.

In Figure 15 each of the pulsers 81 A and 81 B are supplied by power from the supply 84 through separate leads 84A, 84B, and through separate resistors 1 62A and 162B. The timing signal comes from the counter 166, which is supplied with a clock signal from a clock 164 through the line 182.

The counter, or control 166 also provides another signal output on leads 167 and 168 to the transmit/receive switch 1 50. The switch 1 50 disconnects the output leads 48" and 46" whenever the pulser signal is on the leads 46' and 48', which are connected through slip rings to the two transducers T/RTS 46 and 48 respectively.

Thus, with the apparatus of Figure 15, two simultaneous sonic signal transmissions are being carried on, and the received signals are being transmitted through 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 1 6 and 1 8, if there is only a single transmission system in the cable. 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 transmission pulses to the multiple T/RTS are synchronized.

Since transmission of multiple 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 logging cables that are utilized for operating the borehole televiewer are generally the same cables that are used for 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 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 the present time, which may be from 20,000 to 30,000 feet in length, will adequately handle signals in the range of 50 to 100 kilohertz (KHZ) or kilobits per second.

The desired resolution of the scan signals that are transmitted to the surface may be set down as the following: In the measurement of caliper or the distance of 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 1 3 or 14".

In the measurement of azimuth the conventional timing is for 360 transmission pulses in a rotation of 360C giving a minimum angular resolution 1 . In the measurement of signal amplitude, a six-bit digital value for amplitude would indicate a minimal resolution of about1 1/2%.

To transmit the scan signals with these minimum resolutions would take 256x360x6x3 (revolutions per second) or 1.6 million bits per second. With such a high data rate, it would obviously be impossible to transmit a complete sonic scan signal by digital transmission, 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 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 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 measurements at short distances from the transmitters would be 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 be to first delay one with respect to the other, until the two scan signals are in phase, and then gate the high frequency 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 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 the amplitudes of the reflected signals, and the corresponding radius of caliper, at the time of the return signal. These two quantities can be expressed digitially in a relatively few bits, so that as many as four such pairs of signals could be transmitted sequentially, as by multiplexing, over the existing single analog transmission circuit in the conventional cables.

One type of present logging cable utilizes seven conductors, of which two would be utilized for the transmission channel and the other four would be used for control, power supply, etc.

However, it could be possible to use four of the conductors to provide two separate conductor pairs for analog transmission of the scan signals.

If there are two analog transmission channels, two ESS from two T/RTS could 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 separate scan signals when processed to transmit only the amplitude of the reflected signal and the time of the reflected signal. With a pair of T/RTS of different frequencies, the amplitude of the high frequency reflection and caliper of the low frequency reflection could be combined for transmission.

Of course, where the multiple T/RTS are in the same 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 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 to use two identical T/RTS on the rotating assembly, so 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 logging rate, and still provide the 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 televiewer-by a factor of two, or three, or more, depending 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.

Eariier it was mentioned that by means of an apparatus to increase the frequency of the scan signals, say by a factor of two, two such signals could be tranmitted over a single transmission channel cable, sequentially, 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 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 if rotation of the rotating assembly, but alternating the signal from one T/RTS to the other In this way, the separate ESS would be as normally transmitted, 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 Figure 3, except that the switch 62, instead of being a siow 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 the transmission time is shared between the two transducers 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 used sequentially with some lessening of the resolution.

Referring now to Figure 16, which is a modification of Figure 1 5 showing alternating rapid switching of the leads 75A and 758 by switch 21. It is shown as a separate switch for clarity but is most conveniently done in the counter 1 66. Switch 21 is shown as controlled by means 21' from the counter 166. Thus, instead of transmitting signals from both T/RTS, each (say at 1 of rotation), the first T/RTS is transmitted say at 1; line 402 of Figure 17; then one degree later line 404, the other, 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.

Of course, the two tranducers 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 1 60 which can conveniently be one of the charge coupled devices which are commercially available on the market and need no further description. The two signals are the added by the resistor 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 required. The two ESS can be identical, that is, from identical T/RTS. However, they can be from different T/RTS, such as indicated in Figure 1 7 showing a high frequency T/RTS on lines 1, 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 Ml A, Ml B, M2A, M2B, etc., numbered respectively 381A, 3818, 382A, and 382B. Two switches 374A and 374B are provided, 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 lines to the first pair of memories Ml A and Ml B respectively, and on command, can switch the two lines to the second pair of memories M2A and M2B, and so on.

The second switch 374B operates in a similar way but is 1 80C out of phase with the first switch 374A. In 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 go to D/A converters 375 and 375', then to gating means 384 and 384', through two equal resistors 385 and 385', where they are joined together and to a line drive amplifier 386, the output of which is connected to the transmission channel 342 of the cable.The bit rate from the analog-to-digital converters 268 and 270 is identical to the rate of bit loading into the memories through switch 374A and is controlled by a clock of frequency CF1 on line 387A, which comes from a clock C2 1 64B. The readout from memory through switch 374B is controlled by a 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 separate T/RTS are to be multiplexed on the cable, CF2 would be 3 or more times CF1.

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 while the other is reading out of the second pair of memories, and so on. Also, the gating means 384 is controlled by a third frequency from clock C1, 1 64A. Each of the clocks C1, C2 and M are controlled by the base clock C, 164, and frequencies are divided down in a manner well known in the art. However, while the frequencies for each of the controls may be different, they are all synchronously related through C.

Refer to Figure 19, and consider for purpose of illustration that the two T/RTS are coincident on the rotating. They are not physically coincident, of course, since they are spaced 1 80 degrees from each other, but 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 phase with the signal 438 from B on line 432.

Both start at TO and last till T2. The rectangle between lines 428 and 432, and TO and T2 is shaded to indicate a first pair of memories Ml A, Ml B, into which these two ESS are loaded. The next two ESS 436' and 438' are loaded in the second memories M2A, M2B.

While the second ESS are being loaded, the previously 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 Ml A and Ml B and so on. Thus, while two separate scan signals are being recorded, simultaneously each one degree of rotation, the two scan signals are being transmitted at 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 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 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 signals which are read out at a double bit rate will be transmitted sequentially 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 shown to the lower pair of memories. It may be desired, for example, that M2A should be transmitted first, and so that is read out at double bit rate and passes by the gating means 384 and through a resistor 385 and amplifier 386 to the line 342 to the cable. When that is completed, 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 memories.

The switches 374A and 374B are then operated, connecting the inlet switches to the second pair of memories and the outlet switiches to the first pair of memories, and so on.

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 simultaneous ESS by loading into memory at a first frequency, 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 1 5 through 19 illustrate the use of multiple T/RTS so that in each revolution of the rotary assembly, 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 essential information, and also provides the opportunity to record multiple logs at the same or higher speed, providing additional information.

Referring now to Figures 20A,20B, and 20C, there are shown three circuits by means of which two electrical reflection signals from two T/RTS on line 48' and 46' are switched by T/RS 1 50, and on the output lines 48" and 46" they go through separate amplifiers 1 52 and 1 54. One of them (Figure 20A) goes to a time delay means 160 as previously discussed, to bring the two signals into phase. They are then stacked by means of the resistor assembly 1 62A and 162B, and then passed through the amplifier 180 to the single transmission channel 1 78 of the cable 20.

As previously mentioned, it would be desirable that the two T/RTS be mounted on the same rotating assembly in the same transverse plane so that they would be synchronous and they would be scanning along two separate 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 therefore preferably 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 154. One of these signals goes through a time delay means 1 60 so that the two signals would be in phase. However, they then go through gating means 1 56 and 158, which are timed over line 184 from a clock C, 164. If the two T/RTS are of different frequencies, one, for example, is a high frequency 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 as the first reflected signal from the wall of the borehole is first gated by 1 56 through the resistor assembly 1 62A and 1 62B, through amplifier 180 to line 1 78 in cable 20. Then the second gate 1 58 is opened to transmit later arrival of possible reflections from greater distances beyond the wall of the borehole. The lower frequency scan signal is then transmitted through resistor 162B, amplifier 180 and through line 178 to the surface.In this way, two separate T/RTS can each provide valid information best suited to their operating frequency, and the total received signal transmitted up the single transmission circuit 1 78 will be of greater value than either one of the signals from either one of the T/RTS.

Figure 20C illustrates another method of handling two independent T/RTS scan signals which, passing through the T/RS 150 are then amplified by means 1 52 and 1 54 and go to a multiplexer of conventional form 260. As is welt known, the multiplexer then combines these two independent signals by, in effect, chopping the analog signals up into short pieces which are then alternately transmitted through the line driver amplifier 1 80 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 46tea and 48"' to amplifiers 262 and 264 to a recorder 266.

A clock 164 in the sonde provides a timing signal over line 184 to the multiplexer 260, and also through a control conductor 184' in the cable 20, to line 184" and the demultiplexer 261. These clock signals synchronize the operation of the multiplex and demultiplex operations.

The multiplexer can be used with analog or 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 and converted to digital signals of a selected number of bits, say for example, six bits. These sequential digital words of six bits each, one from one T/RTS and the next from the second T/RTS are then transmitted as a string of digital bits over the single transmission channel 178'. At the demultiplexer a reverse action takes place, where the output of the demuitiplexer on lines 46"' and 48"' can 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 satisfactorily on digital recorders, such as magnetic tapes or discs and so on.On the other hand, high frequency analog signals can be recorded in analog form on magnetic tape, such as the well-known video tape cassettes. This will be discussed more fully in connection with Figure 22.

Referring now to Figures 21A and 21 B, there are shown means by which a pair of T/RTS can provide independent electrical scan signals, which passing through the T/RS 1 50 are amplified through amplifiers 1 52 and 154 and then transmitted through the cable 20 on two separate analog transmission circuits 186' and 188'. At the surface, the signals transmitted on the two separated lines are converted to digital signals by the A/D converters 268 and 270, which provides digital signals which can then be recorded on recorder 266 for later playback.

Figure 20B illustrates one manner in which the recorded data on recorder 266 can be utilized.

The two digital signals are read out from the recorder 266 through the two separate lines 46"' to a time delay device 272, such as was shown in Figures 20A and 20B, and then added by means of the resistor combination 274 and 276 and to the display, not shown but well known in the art.

In this case, what has been done is to provide to the recorded signals from two T/RTS of the same frequency, and they are shown being stacked and the 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 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 encoder 350 which transmits pulse signals which are indicative of the angle of rotation of the wheel 25. The encoder 350 is a conventional device and outputs a signal over line 350' which goes to 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 utilizes analog signals, such as the conventional electrical scan signals. The 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 transmission with two signals being multiplexed.

Thesonic signals on the cable transmission channel 342 go directly through lead 342 to a tape recorder 266. The depth encoder 350 going by lead 350' to the tape recorder 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 separator, marked SS351, and the north indicating pulse travels by line 60" to the tape recorder. Thus, all essential information arriving over the transmission 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 SS 351. There the sonic signal is separated out and goes over line 31 6 to the D-MUX 354. The synchronizing signal taken off the line 342' is used over line 31 8 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 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 outputs are then taken by lines 31 8" 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 signals calls for one to be a reflection signal and the other 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 provided to form the logs labelled 360A and 360C, respectively amplitude and caliper logs.

The signals on line 316' and 318' from the demultiplexer 354, which are individual digital signals, may also be recorded directly on recorder B 266'. The difference between this recorder 266' and recorder 266 is that the signal recorded on the tape recorder 266 is a multiplexed 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 266' has two channels, each one recording a complete digital signal transmitted from the sonde.

It is possible, of 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 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 channels for processing of the ESS. the inputs are taken from the output portion of Figure 1 5 and shows two output signals 48" and 46" from the T/RS 1 50. 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 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 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 frequency unidirectional analog signal. The detected signal is the one which is conventionally transmitted to the surface. The detector 306 is a conventional 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 31 0. 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 analogto-digital converter 314, which measures the amplitude to six 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 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 travelied into and out of the rock wall. Consequently, 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 flow or obstacle, will be large enough to be measured.

In the method of determining the precise time of arrival, the amplified signal from 328 goes to a differentiator 330, and to a comparator 332.

The counter 344 is controlled by the sync signal on line 1 84. The counter provides two different frequencies F1 and F2. The high frequency F1 controls the digitizer 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 carry the six bit signal from the A/D converter 314. The six bit lines 31 8 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 measure of the "amplitude" of the signal and on the other channel, line 326, a measure of the time of travel, or caliper. These two six bit binary numbers then are passed sequentially to a paraliel-to-serial converter. Here the parallel words of six bits are converted to serial words 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. 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 to the cable 342.

The switching is accomplished by means of the gate control apparatus 315 over leads 348A and 348B. Also, if a second scan signal is being provided over line 46" to the signal processor 302', the same switch or gate means 31 5 is also supplied by means of leads 348At and 348B'.

The compass signal comes in on line 60' from the compass 60 as shown in Figure 1 5, and goes into the amplifier 340, and also through lead 60" to the amplifier 340', which amplifies the output of the second signal processor, 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 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 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 amplitude 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 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 transducers, one of high frequency to provide amplitude at the first reflector, the wall of the borehole, and a lower frequency one to provide the time of travel of the caliper. By use of switches 324' in line 326, and 324" in line 46", with connector 341, it is possible to utilize a high frequency transducer on line 46" so that the caliper measurement in the processor 302 would correspond to the caliper of the lower frequency transducer while the amplitude would be corresponding to the higher frequency transducer.

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 channel and thus, such a composite signal on 48" would provide, without the switches 324' and 324" the amplitude and caliper measurements respectively from both transducers.

In Figure 23 1 have shown a pair of switches 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 caliper channel while 48" goes to the amplitude channel of the processor 302.

While I illustrate in Figure 1 5 a processor that would transmit and receive two sonic signals from two transducers 46 and 48 respectively, it will be obvious 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 48'. Also, each cf these single transducers can be combined as previously mentioned, so that two transducers together provide one pair of signals of amplitude and caliper. Thus to transmit four such signals in digital form on a single transmission line it could utilize eight separate transducers, four of high frequency and four of low frequency, and so on.

Also, I have shown in Figure 23 that two separate 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.

Referring now to Figure 24, 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 transmit/receive switch 1 50A that controls all of the reflected signals on the leads which are identified by the indication HF1, LF1, HF2, LF2, HF3, and LF3, 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 other three transducers are low frequency, and they will pass through 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 borehole, they will all be multiplexed together by MUX1, 320A. Ail of the low frequency signals of caliper will be multiplexed in 320B. All of the signals coming into the multiplexer 320A and 320B are now digital. They are controlled by the clock signal on 184, which goes by lead 1 84A to the two multiplexers. This timing signal also goes to the parallel-to-serial converter 324'.

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 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 signals can be read out and transmitted in other combinations.

The output of the P/S converter then goes to the amplifier and line driver 340 and to a single transmission channel 342 in the cable 20.

While Figure 24 shows that two separate T/RTS, such as HF1 and LF1 together provide one pair of data, the six T/RTS shown would not even fully load a single transmission channel.

Another way of handling the individual T/RTS would be as indicated in Figure 23 where the jumper lead 341 is not connected, and both the amplitude and caliper 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 468 to the second processor 302'. In this format, only four T/RTS 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 MHZ), while 48 would be a lower frequency transducer (possible in the range of 250 KHZ to 850 KHZ). They transmit beams of sonic information 16, and 32 respectively. It is well known that the higher frequency beam has a shorter distance of penetration in a liquid or solid medium. Correspondingly, lower frequency beams have a greater distance of penetration.

The best range of usefulness of the high frequency 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. Figure 4B shows the gating time schedule in which the first gate 11 6 on line 1 34 passes the high frequency ESS from TO 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 numbers transmitted from Figure 24, go by conductor 342 to the surface, along with the clock signal to the multiplexers 32A, 32B on lead 184B'. At the surface the digital signals are demultiplexed, converted to analog signals and stored 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 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 horizontal plane, or in a vertical array in a vertical plane, or in combinattions of multiple horizontal planes and/or multiple vertical planes as has been fully described.

When the words "high frequency" and "low frequency" are used to characterize the properties of the transducers, they mean transducers that have natural oscillation frequencies in the ranges of about 0.5 to about 1.5 MHZ, and from about 75 to about 750 KHZ, respectively.

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/RTS on the rotating assembly. These can be processed in a number of ways which have been illustrated and described, 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 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 operation are equally valid for any type of multiple 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 frequency transmission channels to the surface, these signals 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 important in the utilization of the multiple ESS, whether done in the sonde, or at the surface. It is also important as a basis for transmission over low frequency channels. So, when I speak or processing ESS I mean either processing in the sonde or at the surface, as appropriate.

This invention makes possible threedimensional 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 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 ciaim or claims, including the full range of equivalency to which each element thereof is entitled.

Claims (23)

Claims

1. A method 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, characterized by the further steps of providing at least a second T/RTS in a selected geometric relation to said firstT/RTS on said rotating assembly; 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 utilizing said at least two electrical scan signals.

2. A method as defined in Claim 1 for the volumetric logging of a welibore drilled in the earth which includes generating in said wellbore at said first T/RTS a first signal having a frequency F1; generating in said wellbore at said second T/RTS 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.

3. A method as defined in Claim 1, further comprising generating in said wellbore at the first T/RTS a first signal having a frequency F1 and directing said first signal in a 360 degree horizontal range; at a vertically displaced second T/RTS generating in said wellbore the second signal having a frequency F2 which is different from F1 and directing said second signal in a 360 degree horizontal range; and recording reflections from said first signal at said displaced second T/RTS and reflections from said second signal at said first position.

4. A method as defined in Claim 3 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.

5. A method as in Claim 2 and including the use of 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 1 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 1 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 electrical 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; than it is gated off, and the T/RTS which is of a lower frequency is gated on.

9. A method of Claim 1 further comprising utilizing 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 utilizing 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 utilizing said at least two simultaneous analog ESS, comprising the steps of: (a) delaying one of said at least two ESS until the two are in phase; (b) passing a transmitting pulse sequentially 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 1 further comprising utilizing said at least two simultaneous analog (ESS), comprising 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, different simultaneous analog ESS over said first analog electrical signal channel in said cable to the surface; and utilizing at the surface said transmitted combined signal.

14. The method as in Claim 3 including the step of combining said two ESS by: (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 transmission rate; and (d) reading out said sequential samples from said CCDL and converting the sequential samples into an analog signal.

1 5. Apparatus for use in logging a borehole, and providing at least a first electrical scan signal, 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 operation by a single, first, transmit/receive transducer system (T/RTS); characterised in that there is provided; at least a second T/RTS in selected geometric relation to said first T/RTS, to scan said borehole wall and to provide at least a second electrical scan signal; and means to utilize said at least two electrical scan signals, from said at least two T/RTS, and to provide a display of the sensed parameters.

16. Apparatus as claimed in Claim 1 5 in which said first T/RTS is mounted at a selected point on a selected transverse plane on said rotating assembly; and said second T/RTS is mounted on said rotating assembly on said selected plane displaced from said first T/RTS at a selected azimuthal angle.

1 7. Apparatus as claimed in claim 1 5 in which said at least second T/RTS comprises (N-i) 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 producing electrical scan signals responsive to its scans, for a total of N electrical scan signals.

1 8. Apparatus as claimed in Claim 17, 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 aligment with said first set of T/RTS.

19. Apparatus as claimed in Claim 15 in which said firstT/RTS is mounted on said rotating assembly at a selected first azimuth, and said at least second T/RTS is mounted on said rotating assembly at the same first azimuth, but is displaced longitudinally from said first T/RTS by a selected distance.

20. Apparatus as claimed in Claim 1 5 in which there is: 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 said or other perpendicular 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 distance from the plane of said T/RTS.

21. A method for the volumetric logging of a well bore drilled in the earth which comprises: a) directing a beam of energy having a first direction and azimuth outwardly from said wellbore into the surrounding formation, b) receiving a signal indicative of the response of said beam of step a) from at least one point within said formation, c) directing a beam of energy having a second direction and azimuth outwardly from said wellbore into the surrounding formation, d) receiving a second signal indicative of the response of said beam of step c) from at least one point within said formation at a position different from the point of step b).

22. A method for the logging of a borehole substantially as hereinbefore described with reference to each of the embodiments illustrated in Figures 2 to 24 of the accompanying drawings.

23. Apparatus for use in logging a borehole substantially in accordance with each of embodiments hereinbefore described with reference to and as shown in Figures 2 to 24 of the accompanying drawings.