Process and device for the determination of the characteristics of the geological formations traversed by a borehole

Abstract

Process for determining characteristics of the geological formations traversed by a borehole, making use of a sonde by means of which the intensity of the γ rays naturally radiated from the formations is measured, both longitudinal and transversal acoustic waves are transmitted to the formations, their travel time and their attenuation between two receivers placed in contact with the formations are measured and by combination of the so-obtained values a resulting value is elaborated which is representative of one characteristic of the surveyed formations.

We Claim: 
     
       1. A process for determining the characteristics of the geological formations traversed by a bore hole, making use of a measuring sonde in combination with an automatic system for the treatment of the data delivered by the sonde, comprising the combination of the following steps: a. determining the spectrum of the γ rays naturally radiated from the geological formations in the form of a plurality of quantities associated to said radiation, each of which depends on the intensity of this natural radiation, in a given energy range,   b. alternately transmitting acoustic waves which propagate essentially according to the longitudinal way of propagation and acoustic waves having essentially a transversal way of propagation,   c. successively determining the travel time of said longitudinal waves and of said transversal waves between two receivers placed in contact with the geological formations, by producing two quantities which are functions of the respective travel times of said longitudinal waves and transversal waves,   d. successively determining, between said receivers, the attenuation of said longitudinal and of said transversal waves, by producing two quantities representative of said attenuation respectively for the longitudinal waves and for the transversal waves, and   e. elaborating, on the basis of said quantities, in said automatic system, at least one resulting quantity, representative of a characteristic of said formations, by linearly combining said quantities associated to the γ radiation with said quantities which are functions of the travel time of the longitudinal and transversal waves and with said quantities representative of the attenuations of said acoustic waves.   
     
     
       2. A process for determining the characteristics of the geological formations traversed by a bore hole, comprising the combination of the following steps: a. determining the spectrum of the natural γ rays radiated from the geological formations in the form of a plurality of signals associated to said radiation, each of which depends on the intensity of this natural radiation in a given energy range,   b. alternately transmitting acoustic waves propagating in the geological formations essentially according to the longitudinal way of propagation and acoustic waves propagating essentially according to the transversal way of propagation,   c. successively determining the travel time of said longitudinal waves and of said transversal waves between two receivers placed in contact with the geological formation, by producing two signals related to the respective travel times of the longitudinal waves and the transversal waves,   d. successively determining between said receivers, the attenuation of said longitudinal waves and of said transversal waves, by producing two signals representative of said attenuation respectively for the longitudinal waves and for the transversal waves,   e. recording said signals, and   f. elaborating, on the basis of said recorded signals, at least one resulting signal, representative of a characteristic of said formations, by linearly combining said signals associated to the γ radiation with said signals related to the travel time of said longitudinal and transversal waves, and with said signals representative of the attenuation of said acoustic waves.   
     
     
       3. A device for determining the characteristics of the geological formations traversed by a bore hole, comprising a sonde connected to a surface apparatus through a cable provided with electric conductors, said sonde comprising the combination of: a. means for detecting the natural γ radiation transmitted from the formations, said means delivering electric signals representative of the radiation emanating from the geological formations,   b. means for transmitting acoustic waves, adapted to transmit to the geological formations, acoustic waves having essentially a longitudinal way of propagation,   c. means for transmitting acoustic waves, adapted to transmit to the geological formations, acoustic waves having essentially a transversal way of propagation,   d. means for alternately operating said first and second transmitting means,   e. at least two acoustic wave receivers spaced vertically, adapted to deliver electric signals at the time of reception of said acoustic waves,   f. means for determining the travel time and the waves attenuation between said receivers of said acoustic waves, said means being connected to said receivers and adapted to deliver a first series of electric signals representative of the travel time and a second series of electric signals representative of the attenuation of said acoustic waves, and   g. means for transmitting to the surface all these electric signals.   
     
     
       4. A device according to claim 3, wherein said first and said second transmitting means transmit acoustic waves of a high frequency and said acoustic waves transmitted from said first transmitting means have a frequency different from that of the acoustic waves transmitted from said second transmitting means. 
     
     
       5. A device according to claim 3, wherein said first transmitting means are adapted to transmit acoustic waves whose frequency is at least 20 kHz. 
     
     
       6. A device according to claim 3, wherein said first transmitting means are adapted to transmit acoustic waves whose frequency is in the range of from 20 kHz to 80 kHz. 
     
     
       7. A device according to claim 3, wherein said transmitting means are adapted to transmit acoustic waves whose frequency is at least 80 kHz. 
     
     
       8. A device according to claim 3, wherein said second transmitting means are adapted to transmit acoustic waves whose frequency is in the range of from 80 kHz to 250 kHz. 
     
     
       9. A device according to claim 3, wherein said first and second transmitting means are operating alternately at a recurrence frequency between 5 and 100 Hz. 
     
     
       10. A device according to claim 9, wherein said recurrence frequency is about 50 Hz. 
     
     
       11. A device according to claim 3, wherein said first transmitting means, said second transmitting means and said receivers are placed in the same diametral plane of the sonde. 
     
     
       12. A device according to claim 3, wherein said first transmitting means consist of an acoustic transmitter of the magnetostrictive type. 
     
     
       13. A device according to claim 3, wherein said second transmitting means consist of an acoustic transmitter of the piezo-electric type. 
     
     
       14. A device according to claim 3, wherein said sonde is provided with a movable pad for supporting and for positioning said means for detecting the γ radiation emanating from the geological formations, said second acoustic waves transmitting means and said receivers are supported on the same movable pad of the sonde, so as to come into contact with the wall of the bore hole along a generatrix thereof. 
     
     
       15. A device according to claim 3, wherein said receivers are at a distance from one another equal to a few times the wave length of the transmitted acoustic waves and the distance between said receivers and second acoustic waves transmitting means is greater than ten wave lengths of the transmitted acoustic waves. 
     
     
       16. A device according to claim 3, wherein said means for measuring the attenuation of the acoustic waves comprise a first blocking-lengthening element connected to a first of said receivers, a second blocking-lengthening element connected to the second of said receivers, each of said elements delivering an electric signal of predetermined duration having an amplitude substantially proportional to the peak amplitude of a predetermined half cycle of the electric signals supplied by said receivers, this device also comprising a first analogical gate, a first amplifier and a polarity inverter, said polarity inverter connecting the first element on the one hand, to said first analogical gate and, on the other hand, to said amplifier delivering an electrical signal in the form of a rectangular wave of substantially constant amplitude and of the same duration as that of the signal delivered by said first blocking-lengthening element, a gate of the AND type having a first input connected to said first amplifier, the device further comprising a second analogical gate and a second amplifier said second element being connected, on the one hand, directly to said second analogical gate and, on the other hand, to said second amplifier delivering an electric signal in the form of a rectangular wave of substantially constant amplitude having the same duration than the signal delivered by said second blocking-lengthening element, said second AND gate having a second input connected to said amplifier, said AND gate being connected to said first and second analogical gates and supplying thereto a control signal when it simultaneously receives the signals delivered by each one of said first and second amplifiers, said analogical gates giving passage to the signals supplied by the blocking-lengthening elements only at the time of reception of said control signal, logarithmic amplifiers respectively connected to said first and second analogical gates and delivering signals substantially proportional to the logarithms of the amplitude of the signals supplied by said blocking-lengthening element, a summing amplifier having an input connected to said logarithmic amplifiers said summing amplifier delivering at its output terminal a signal the amplitude of which is substantially proportional to the logarithm of the ratio of the amplitudes of the electric signals supplied by said blocking-lengthening elements, and transmitting means connected to said summing amplifier, said transmitting means comprising a pulse lengthener, adapted to calibrate to a predetermined value the duration of the pulses supplied by said summing amplifier. 
     
     
       17. A device according to claim 16, wherein each of said blockinglengthening elements delivers a signal substantially proportional to the peak amplitude of one of the first five half-cycles of the electric signal delivered by each receiver. 
     
     
       18. A device according to claim 17, wherein each of said blockinglengthening elements delivers a signal substantially proportional to the peak amplitude of the first half-cycle of the electric signal delivered by each receiver. 
     
     
       19. A device according to claim 3, wherein said means for measuring the travel time of the acoustic waves comprises a first one-shot multivibrator connected to said first receiver and a second one-shot multivibrator connected to said second receiver, each of said multivibrators being adapted, when receiving a signal supplied by said receivers, to deliver, at its output terminal, a signal of calibrated amplitude and duration, said first multivibrator being connected to a first and a second gate of the AND type, said second multivibrator being connected to a device which, when it receives a signal supplied by said second multivibrator, delivers at one of its outputs at said second gate a signal identical to the received signal and delivers at its second output terminal connected to said first gate, an electric signal only in the absence of signal delivered by said second multivibrator, said first gate delivering a control signal of a duration equal to the time interval during which signals are simultaneously received at its input terminals, this time interval being substantially equal to the travel time of the acoustic waves between the two receivers, said control signal actuating over its whole duration, an analogical gate connecting to a voltage source, a time-amplitude conversion device, the output of which is connected to amplifying means delivering a signal whose amplitude is proportional to said travel time, said amplifying means being connected, through an analogical gate, controlled by the signal delivered by said second AND gate, to transmitting means comprising a device for lengthening the signal delivered by said amplifying means and a device for resetting to zero said time-amplitude conversion device actuated by the output signal of said second AND gate. 
     
     
       20. A device according to claim 3, wherein the surface apparatus comprises means for recording all the signals delivered by the sonde and means for elaborating in real time from said signals at least one resulting signal representative of a characteristic of said formations, said means for elaborating being connected to said means for recording and linearly combining said signals associated to the γ radiation, said signals being a function of the travel time of the longitudinal and transversal acoustic waves and said signals being representative of the attenuations of said acoustic waves. 
     
     
       21. A device according to claim 20, wherein said means for elaborating in real time comprise a first memory wherein are recorded, in the form of signals, predetermined coefficients, a second memory wherein are recorded said group of signals delivered by the sonde, a group of means for treating said signals, connected to each of said memories actuated by a clock to which they are connected, said means being adapted to combine the signals of said group and to deliver, at their output terminal, at least one digital signal function of the received signals and representative of an information element concerning a characteristic of the geological formations, and a third memory, connected to said treating means, where is recorded said representative signal. 
     
     
       22. A process for .Iadd.quantitatively .Iaddend.determining .[.the characteristics.]. .Iadd.at least one of a lithological and petrophysical characteristic .Iaddend.of the geological formations traversed by a borehole, utilizing a measuring sonde which delivers signals, and an automatic system for treating the signals delivered by the sonde, said process comprising the steps of: a. determining values of coefficients depending on the characteristics of the geological formations and registering the values of the coefficients in the automatic system,   b. determining the spectrum of the γ rays naturally radiated from the geological formations in the form of a plurality of quantities associated to said radiation, each of which depends on the intensity of this natural radiation in a given predetermined energy range of the spectrum, and   c. elaborating on the basis of said quantities in said automatic system at least one resulting quantity representative of a characteristic of said formation by linearly combining said quantities as a function of the values of said coefficients. .[.23. A device for determining the characteristics of the geological formations traversed by a borehole, comprising a measuring sonde placed in the borehole and delivering electrical signals, a surface apparatus combined with said sonde for the automatic treatment of the signals delivered by the sonde, said surface apparatus comprising means for registering values of coefficients depending on the characteristics of the geological formations a cable having electrical conductors, said sonde comprising:   a. means for detecting the natural γ radiation emitted by the formations, and for producing electrical signals representative of the γ radiation emitted by the geological formations each of the signals being a function of the intensity of the natural radiation within a given predetermined energy range of the spectrum, and   b. means for transmitting the electrical signals to the surface   
     
     
        apparatus..]. 24. A device for .Iadd.quantitatively .Iaddend.determining .[.the characteristics.]. .Iadd.at least one of a lithological and petrophysical characteristic .Iaddend.of the geological formations traversed by a borehole, comprising a measuring sonde placed in the borehole and delivering electrical signals, a surface apparatus combined with said sonde for the automatic treatment of the signals delivered by the sonde, values of coefficients depending on the characteristics of the geological formations being registered in the automatic system, a cable having electrical conductors, said sonde comprising: a. means for detecting the natural γ radiation emitted by the formations and for producing electrical signals representative of the γ radiation emitted by the geological formations, each of the signals being a function of the intensity of the natural radiation within a given predetermined energy range of the spectrum, and   b. means for transmitting the electrical signals to the surface apparatus, and   wherein the surface apparatus comprises means for recording said electrical signals delivered by and transmitted form said sonde, and means for elaborating in real time from said electrical signals at least one resulting signal representative of a characteristic of said formations, said means for elaborating being connected to said recording means and linearly combining said electrical signals associated to the γ   
     
     
        radiation. 25. A device according to claim 24, wherein said means for elaborating in real time comprises .[.flat.]. .Iadd.first .Iaddend.memory means to which predetermined coefficients are supplied and are recorded therein in the form of signals, second memory means in which said signals delivered by the sonde are recorded, clock means delivering a clock signal and connected to said first and second memory means, combining means connected to said first and second memory means and responsive to a clock signal for combining the signals from said first and second memory means and providing at least one digital resultant signal which is representative of an information element concerning a characteristic of the geological formations, and third memory means connected to said 
     
     
        combining means for recording said representative resultant signal. 26. A process for .Iadd.quantitatively .Iaddend.determining .[.the characteristics.]. .Iadd.at least one of a lithological and petrophysical characteristic .Iaddend.of the geological formations traversed by a borehole, using a combination a measuring sonde which delivers signals and an automatic system for treating the signals delivered by the sonde, said process comprising the steps of: a. determining values of coefficients depending on the characteristics of the geological formations and registering the values of the coefficients,   b. determining the spectrum of the natural γ rays radiated from the geological formations in the form of a plurality of signals associated to said radiation, each of which depends on the intensity of this natural radiation in a given predetermined energy range of the spectrum,   c. recording said signals, and   d. elaborating on the basis of said signals in said automatic system, at least one resulting signal representative of a characteristic of said formation by linearly combining said signals as a function of the values   
     
     
        of said coefficients. 27. A process for .Iadd.quantitatively .Iaddend.determining .[.characteristics.]. .Iadd.at least one of a lithological and petrophysical characteristic .Iaddend.of a geological formation traversed by a borehole, utilizing a measuring sonde including means delivering measuring signals, and a data processing system for treating said measuring signals, this process comprising the steps of: a. determining from said measuring signals a plurality of quantities associated to the natural γ radiation of the geological formations, each of said quantities depending on the intensity of said natural radiation in a given predetermined energy range of the spectrum,   b. determining the values of .Iadd.calibration .Iaddend.coefficients .[.depending on at least one characteristic of the geological formation.]., and   c. elaborating through said data processing system, on the basis of said measured quantities and of said coefficients, a .[.plurality of.]. resulting .[.quantities.]. .Iadd.quantity .Iaddend.representative of said at least one characteristic of said formation, said resulting .[.quantities.]. .Iadd.quantity .Iaddend.being derived from said measuring quantities through .[.a plurality of.]. .Iadd.at least one .Iaddend.linear .[.relationships.]. .Iadd.relationship .Iaddend.including a plurality of coefficients having said values determined in step (b). .Iadd. 28. A process according to claim 26 wherein the values of the coefficients determined in step (b) depend on at least one lithology characteristic. .Iaddend..Iadd. 29. A process according to claim 28, wherein the at least one lithology characteristic includes the clay content of the geological formation. .Iaddend..Iadd. 30. A process for determining the clay content of a geological formation traversed by a borehole, utilizing a measuring sonde including means delivering measuring signals, and a data processing system for treating said measuring signals, this process comprising the steps of:   (a) determining from said measuring signals a plurality of quantities associated to the natural γ radiation of the geological formations, each of said quantities depending on the intensity of said natural radiation in a given predetermined energy range of the spectrum,   (b) determining the values of calibration coefficients, and   (c) elaborating through said data processing system, on the basis of said measured quantities and of said coefficients, resulting quantity representative of the clay content of said formation, said resulting quantity being derived from said measured quantities through a linear relationship including a plurality of coefficients having said values determined in step (b). .Iaddend..Iadd. 31. A process according to claim 30, wherein said plurality of quantities determined in step (a) depend on the intensity of the natural radiation in a plurality of substantially contiguous energy ranges of the γ radiation spectrum. .Iaddend.