Ultrasonic measurement apparatus

Abstract

Pulse echo apparatus and methods are disclosed for measuring characteristics of a borehole while it is being drilled. A component of a bottomhole assembly, preferably a drilling collar, is provided with one or more ultra-sonic transceivers. A pulse echo sensor of the transceiver is preferably placed in a stabilizer fin of the collar, but may also be placed in the wall of the collar, preferably close to a stabilizing fin. Electronic processing and control circuitry for the pulse-echo sensor is provided in an electronic module placed within such collar. Such pulse echo apparatus, which preferably includes two diametrically opposed transceivers, generates signals from which standoff from a borehole wall may be determined. A method and apparatus are provided for measuring standoff and borehole diameter in the presence of drilling cuttings entrained in the drilling fluid. In a preferred embodiment, such signals are assessed by the electronic processing and control circuity to determine if gas has entered borehole. Three methods and apparatus are provided for such gas entry determination. The first relies on measurement of sonic impedance of the drilling fluid by assessing the amplitude of an echo from an interface between the drilling fluid and a delay-line placed outwardly of a ceramic sensor. The second relies on measurement of drilling fluid attenuation of a borehole wall echo. The third relies on measurement of the phase of oscillations of echoes to identify large gas bubbles entries. The pulse-echo sensor includes a sensor stack including a backing element, a piezo-electric ceramic disk, and a delay-line.

What is claimed is: 
     
       1. Bore hole measurement apparatus comprising, a tool adapted for connection in a drill string in said borehole through earth formations, said tool having a cylindrical body which when disposed in said borehole defines an annulus between a borehole wall and said body, said annulus having drilling fluid with entrained drilling cuttings disposed therein, the distance between said borehole wall and said cylindrical body defining standoff distance,   ultra-sonic transmitter means disposed in said cylindrical body for emitting an ultra-sonic transmitter pulse in said drilling fluid toward said borehole wall, said ultra-sonic pulse being reflected from said borehole wall as a borehole echo adn from said drilling cuttings toward said cylindrical body as a cuttings echo,   ultra-sonic transducer means disposed in said cylinrical body for generating a borehole echo signal representative of said borehole echo and a cuttings echo signal representative of said cuttings echo, and   logic means for distinguishing said borehole echo signal and its time delay from said cuttings echo signal, and means for generating a standoff signal representative of said standoff distance which is .[.inversely related.]. .Iadd.proportional .Iaddend.to said borehole echo time delay, wherein said ultra-sonic transmitter means and said ultra-sonic transducer means includes a single transceiver in which one sensor element serves first as a sonic transmitter and later as a sonic receiver,   wherein said transceiver is disposed in said cylindrical body so that said sensor element faces laterally outwardly from said cylindrical body whereby said ultra-sonic pulses and echoes travel essentially perpendicularly between said borehole wall and said cylindrical body in said annulus, and   wherein said logic means includes   circuit means for storing echoes where each echo is defined as the approximate maximum amplitude and associated delay time of each pulse received by said sensor element after said ultra-sonic transmitted pulse has terminated.   
     
     
       2. The apparatus of claim 1 wherein said drill string is rotating in said borehole, said drilling fluid with entrained drilling cuttings disposed therein is flowing in said annulus, and   wherein said apparatus further includes processing means for generating said standoff signal a plurality of times each second for a predetermined time interval and for generating from said plurality of standoff signals an average standoff signal for said time interval.   
     
     
       3. The apparatus of claim 2 further including memory means for storing a tool diameter signal representative of a diameter of said cylindrical body of said tool, and   processing means for generating a hole diameter signal representative of a diameter of said borehole by adding said diameter signal to a signal equal to twice said average standoff signal.   
     
     
       4. The apparatus of claim 3 further including clock means for generating a time signal, and   memory means for storing said diameter signal as a function of said time signal.   
     
     
       5. The apparatus of claim 3 further including communication means for transmitting said diameter signal to surface instrumentation.   
     
     
       6. The apparatus of claim 1 wherein said single transceiver includes a delay line between said sensor element and said annulus, and wherein a delay-line echo is received by said sensor element as a result of said ultra-sonic pulse being reflected from an interface of said delay- line and said drilling fluid in said annulus. 
     
     
       7. The apparatus of claim 1 wherein said logic means includes delay line echo elimination logic means for eliminating stored echoes having a delay time shorter than a predetermined delay time after said transmitter pulse.   
     
     
       8. The apparatus of claim 1 wherein said logic means includes noise rejection echo elimination logic means for eliminating stored echoes which are noise artifacts of previous echoes rather than reflection from said borehole or said cuttings.   
     
     
       9. The apparatus of claim 8 wherein said noise rejection echo elimination logic means includes a minimum echo amplitude function stored as a function of delay time from said transmitter pulse,   comparison means for identifying stored echoes having amplitudes less than said minimum echo amplitude at its associated delay time, and   means for eliminating said identified echoes from said stored echoes.   
     
     
       10. The apparatus of claim 1 wherein said logic means includes decreasing echo amplitude logic means for eliminating a stored echo, A M , T M , when the amplitude A M+1  of the next in time echo, A M+1 , T M+1 , is larger than A M .   
     
     
       11. The apparatus of claim 1 wherein said logic means includes, time separation logic means for eliminating a stored echo, A M , T M , when the time separation T M  -T M-1  between such stored echo and a preceding stored echo, A M-1 , T M-1  is less than a predetermined minimum time T MIN .   
     
     
       12. The apparatus of claim 1 wherein said logic means includes, noise rejection echo elimination logic means for eliminating stored echoes which result from noise rather than reflection from said borehole or said cutting, decreasing echo amplitude logic means for eliminating a stored echo, A M , T M , when the amplitude A M+1  of the next in time echo, A M+1 , T M+1 , is larger than A M ,   time separation logic means for eliminating a stored echo, A M , T M , when the time separation T M  -T M-1  between such stored echo and a preceding stored echo, A M-1 , T M-1  is less than a predetermined minimum time T MIN ,   temporary formation echo selection logic means for selecting a final echo, A N , T N  of said remaining stored echoes as a temporary formation echo, and   double echo elimination logic means for identifying said temporary formation echo as a double echo if said delay time T N  of said temporary formation echo is equal to approximately twice the delay time of a previous stored echo, and it such temporary formation echo is so identified, eliminating said final echo from said stored echoes, whereby a penultimate echo, A N-1 , T N-1 , becomes said temporary formation echo.   
     
     
       13. The apparatus of claim 12 wherein said logic means further includes echo induced sensor noise elimination logic means for comparing said temporary formation echo A N , T N , with an immediately preceding echo A N-1 , T N-1 , to identify such echo A N , T N  as a formation echo signal if A N  >K*A N-1 , where K is a predetermined minimum ratio of successive amplitudes of echoes above which an echo is unlikely to be an echo induced noise pulse.   
     
     
       14. The apparatus of claim 13 further including control means for generating and storing said formation echo signal A N , T N , a plurality of times each second for a predetermined time interval and for generating from said plurality of standoff signals an average standoff signal for said time interval. 
     
     
       15. The apparatus of claim 14 further including memory means for storing a diameter signal representation of a diameter of said cylindrical body of said tool, and   processing means for generating a hole diameter signal representative of a diameter of said borehole by adding said diameter signal to a signal equal to twice said average standoff signal.   
     
     
       16. Borehole measurement apparatus comprising, a tool adapted for connection in a drill string in said borehole through earth formations, said tool having a cylindrical body which when disposed in said borehole defines an annulus between said borehole wall and said body, said annulus having drilling fluid with entrained drilling cuttings disposed therein,   first and second ultra-sonic transmitter means disposed diametrically opposed from each other in said cylindrical body for emitting first and second ultra-sonic transmitter pulses in said drilling fluid toward said borehole wall, the distance between said borehole wall and said cylindrical body at said first ultra-sonic transmitter means defining a first standoff distance, the distance between said borehole wall and said cylindrical body at said second ultra-sonic transmitting means defining a second standoff distance, said ultra-sonic pulses being reflected from said borehole wall as first and second borehole echoes and from said drilling cuttings toward said cylindrical body as first and second cutting echoes,   first and second ultra-sonic transducer means disposed in said cylindrical body for generating first and second borehole echo signals representative of said first and second borehole echo signals representative of said first and second borehole echo amplitudes and time delays, and first and second cuttings echo signals representative of said cuttings echoes, and   logic means for distinguishing said first borehole echo signal and its time delay in the presence of said first cuttings echo signal and for generating a first standoff signal representative of said first standoff distance which is .[.inversely.]. proportional to said time delay of said first borehole echo signal from said emitting of said first ultra-sonic transmitter pulse and for distinguishing said second borehole echo signal and its time delay in the presence of said second cuttings echo signal and for generating a second standoff signal representative of said second standoff distance which is .[.inversely.]. proportional to said time delay of said second borehole echo signal from said launching of said second ultra-sonic transmitter pulse,   wherein said first and second transmitter means emit said first and second ultra-sonic transmitter pulses alternately in time with said logic means identifying said first borehole echo signal after said first ultra-sonic transmitter pulse is emitted and said logic means identifying said second borehole echo signal after said second ultra-sonic transmitter pulse is emitted, and   processing means for generating a first standoff signal proportional to said time delay of said first borehole echo signal and for generating a second standoff signal proportional to said time delay of said second borehole echo signal,   processing means for generating said first and second standoff signals a plurality of times each second for a predetermined time interval, and for generating from said plurality of standoff signals an average first standoff signal and an average second standoff signal for said time interval,   memory means for storing a diameter signal representative of a diameter of said cylindrical body of said tool, and   processing means for generating a hole diameter signal representative of a diameter of said borehole by adding said diameter signal to a said average first standoff signal and to said average second standoff signal.   
     
     
       17. The apparatus of claim 16 further including clock means for generating a time signal, and memory means for storing said diameter signal as a function of said time signal.   
     
     
       18. The apparatus of claim 16 further including communication means for transmitting said diameter signal to surface instrumentation.   
     
     
       19. The apparatus of claim 16 wherein said first ultra-sonic transmitter means and said first ultra-sonic transducer means and said second ultra-sonic transmitter means and said second ultra-sonic transducer means are each a single transceiver in which one sensor element serves as a sonic transmitter and as a sonic receiver. 
     
     
       20. Borehole measurement apparatus for identifying large gas bubble influxes into a borehole comprising a tool adapted for connection in a drill string in said borehole through each formation, said tool having a cylindrical body defining an annulus between said borehole wall and said body, said annulus having drilling fluid disposed therein,   ultra-sonic transceiver means disposed in said cylindrical body for emitting an ultra-sonic pulse in said drilling fluid toward said borehole wall and for receiving ultra-sonic echo pulses reflected from said borehole wall, and   a phase detector for detecting the phase of said pulses and for generating a signal indicating that an echo has high frequency oscillations which are approximately 180° out of phase from the echo pulse, such signal indicative of the sensing of a large gas bubble.