CA1201797A - Circuit for controlling the magnitude of amplification of signals produced by a borehole televiewer - Google Patents
Circuit for controlling the magnitude of amplification of signals produced by a borehole televiewerInfo
- Publication number
- CA1201797A CA1201797A CA000444718A CA444718A CA1201797A CA 1201797 A CA1201797 A CA 1201797A CA 000444718 A CA000444718 A CA 000444718A CA 444718 A CA444718 A CA 444718A CA 1201797 A CA1201797 A CA 1201797A
- Authority
- CA
- Canada
- Prior art keywords
- circuit
- borehole
- gate
- amplification
- amplifier
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 230000003321 amplification Effects 0.000 title claims abstract description 10
- 238000003199 nucleic acid amplification method Methods 0.000 title claims abstract description 10
- 230000005669 field effect Effects 0.000 claims description 13
- 230000007423 decrease Effects 0.000 claims description 6
- 238000000034 method Methods 0.000 claims 3
- 238000001514 detection method Methods 0.000 abstract 1
- 239000003990 capacitor Substances 0.000 description 5
- 230000001276 controlling effect Effects 0.000 description 3
- 239000012530 fluid Substances 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 241000518994 Conta Species 0.000 description 1
- 241000155250 Iole Species 0.000 description 1
- 241001296096 Probles Species 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000000875 corresponding effect Effects 0.000 description 1
- SAPNXPWPAUFAJU-UHFFFAOYSA-N lofepramine Chemical compound C12=CC=CC=C2CCC2=CC=CC=C2N1CCCN(C)CC(=O)C1=CC=C(Cl)C=C1 SAPNXPWPAUFAJU-UHFFFAOYSA-N 0.000 description 1
- 239000000463 material Substances 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/002—Survey of boreholes or wells by visual inspection
- E21B47/0025—Survey of boreholes or wells by visual inspection generating an image of the borehole wall using down-hole measurements, e.g. acoustic or electric
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers
- H03G3/20—Automatic control
- H03G3/30—Automatic control in amplifiers having semiconductor devices
- H03G3/3052—Automatic control in amplifiers having semiconductor devices in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver
- H03G3/3073—Circuits generating control signals when no carrier is present, or in SSB, CW or pulse receivers
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/002—Survey of boreholes or wells by visual inspection
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
- G01V1/52—Structural details
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Geology (AREA)
- Mining & Mineral Resources (AREA)
- Geophysics (AREA)
- Environmental & Geological Engineering (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Remote Sensing (AREA)
- Acoustics & Sound (AREA)
- Geophysics And Detection Of Objects (AREA)
- Length Measuring Devices Characterised By Use Of Acoustic Means (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
Abstract
A B S T R A C T
CIRCUIT FOR CONTROLLING THE MAGNITUDE OF AMPLIFICATION
OF SIGNALS PRODUCED BY A BOREHOLE TELEVIEWER
An electronic circuit is provided for improving the response of a borehole televiewer in an out-of-round borehole.
The circuit comprises an automatic gain control circuit having time constants that allow detection of borehole anomalies while having a fast enough rise time to adjust for the effects of out-of-roundness.
CIRCUIT FOR CONTROLLING THE MAGNITUDE OF AMPLIFICATION
OF SIGNALS PRODUCED BY A BOREHOLE TELEVIEWER
An electronic circuit is provided for improving the response of a borehole televiewer in an out-of-round borehole.
The circuit comprises an automatic gain control circuit having time constants that allow detection of borehole anomalies while having a fast enough rise time to adjust for the effects of out-of-roundness.
Description
s~7 w ll~ FOR CO~TROLLING THE M~GNITUDE OF AMPLIFICATION
OF SIGN~IS ~ u~ BY A BOFE~IOLE TE~TL~WER
m e invention relates to borehole logging tools and particu larly to a tool that is described as a borehole televiewer. A
borehole televiewer u~ a rotating acoustic tr~n~dll~Pr that is peric~;r~lly pulsed to produce acoustic energy which tr~vels outwardly and strikes ~he borehole wall and is rerlected back to the tr~n~ r. The amplitude of the reflected signal is dis played on a cathode ray tube whose face m~y be ph~LGyLd~iled. The resulting photograph L~L~s~lLs a map of the borehole wall split along the north direction and laid out flat. m e transducer is pulsed at a relatively high rate, for ~x~mrle 1500 pulses per second, while the tr~ns~l~r~r rotation period is 0.333 se~n~
The s~eep of the os~;lloscope is controlled by a north syn~
chronization signal ~hich is produced by a flux gate magneto-me.ter which rotates in unison with the tr~n~ Pr.
While the above tools are useful in obtaining a display of the borehole wall that indicates the loca~ions of fractures or other features, it does have a serious limitation when used in a non-ci~cular or eliptical borehole. m e same problem also arises when the -tool moves off centre as a result of this travel through the borehole. It ccm be shcwn that when the borehole televi~wer is loccited off centre or in a non-circular hole~ the acoustic energy will be scattered at all locati.ons except where the acoustic energy strikes the borehole wall nor~al to a tangent a-t this point. Thus, the reflected ~nergy received by the ~r~n~ r will have four positions where it is at a m~;~ ~ and in the r~m~;nln~ positions the reflected energy will be decreased. The borehole tele~iewer as presently available has various amplifier gain levels that are selected by a rotary .switch controlled frcm the surface~ Since the amplitude is set from ~he surface, it cannot be varied to provide the proper amplification as the tr~n~tl~r rotates. Thus, the resulting display will have li~ht and dark areas where details are lacking. It should be appreciated that in normal operations a fracture or other ancmaly in the borehole wall will not reflect energy and will appear as a dark shadcw on the display.
The present invention solves the proble-ms of u~ ;nf3 a borehole televiewer in a non-circular borehole by providing a circuit for a~L~"~Lically controlling the magnitude of ampli-fication of signals produced by the borehole televiewer, the circuit ccmprising amplifier means having an input and an output, the Lnput of said am~lifier means being coupled to ~he acoustic transducer o the televiewer, gate ~eans having an input, an output and a gate, the input of said gate means being coupled ~o the input of said ~m~lifiPr and the output of the gate means being coupled to ground; and a feed back loop, said feed back loop being coupled to the output of said ~mpl;~;Pr and to ~he gate of said gate means to control said gate means in r~ n~e to the output signal of said ~mrl;f;~r. In a suitable ~mhc~;mPnt of the invention the circuit has a relatively slow rise time and a very fast decay or fall time. It is observed that the circuit is not a true autcmatic gain contxol circult m the sense that the gain of the ~m~lif;pr is changed but rather a voltage dividing circuit that shorts part of the ;nc~m;ng signal to ground and thus decreases the input signal to the ~m~l;fiPr. m is allows the ~rl;fier to retain the gain setting selected from the surface while in-creasing the signal level to provide details whe~ the reflected signal is weak.
In an attractive ~mhc~im~nt of the invention the decay constan-t for the circuit is less than the cycle time of the tr~n~ r~r so that the ~mrlif;~r will not saturate when the reflected signal suddenly increases in amplit~de. Preferably, the rise time of the circuit extends over several cycles so that the ~mrl;f;~r Will not obscure fractures or other ~n~mAl;e~ in the borehole wall that have a short circumferential extent along the wall.
In a preferred embodiment of the i~vention the gate means of the circuit is a field effect transistor whose gate voltage is controlled to control its conduction to ground. Thus, the field effect transistor acts as a voltage divider circuit in the input circuit of the amplifier.
m e invention will be more easily unders~ood from the following description wh n taken in conjunction with the attached drawings in which:
Figure 1 is a schematic elevation view Of a borehole televiewer.
Figure 2 is a waveform o-f the s:ignals produced by the borehole televiewer.
Figure 3 is a graphic L~es~.Lation of the borehole televiewer located in a non-circular borehole~
Figure 4 is a schematic drawing of the dU~ull~LiC gain control circuit of the invention.
Referring now to Figure 1, there i5 shown the borehole televiewer that includes an acoustic tr~n~ rPr 10 and a flux gate magn~L~,~Ler ll which are mounted on a ccmmon shaft. m e shaft is rotated by motor 12 about the axis 14 of the borehole televiewer. Electronics for control of the p~ ;n~ of the trAnq~l-rPr and the trAnYmi~ion of the reflected signals to the surface i5 conta med in a section 16 of the tool while a pressure equalization chamber 15 is mounted in the bottom portion of the tool. The pressure ec~lalization ~hAmhPr serves to equalize the pressure on the interior of the acoustic windcw 13 with the pressure of the fluid in the borehole. By e~~ ing the pressure the required mP~h~niç~l ~LL~ly~h of the acoustic window can be reduced and allow the use of materials which provide a gcod acoustic match between the fluid filling the borehole televiewer and the borehole fluid.
Referring to Figure 2, there is shcwn the waveforms of the signals produced by the borehole televiewer. In particular, the signal 20 represents the acoustic p~Lse produced by the trans-ducer ~Thile the signal 21 represents the reflected signal received by the tr~n~dll~Pr. As shownl a time interval of approximately 100 microseconds elapses between the production of the acoustic pulse and the receipt oi- the reflected signal. The tlme lapse~ of course, ~PpPn~ upon the diameter of the borehole but lO0 micro~ec~n~ is representati~Te. m e actual borehole televiewer tool that is available commercially has a repetition or cycle rate of the acoustic tr~n~ r that is approximdtel.y 1500 cycles per second while the rotational cycle of the trans-ducer is 0.333 sec~n~.~. Thus, the borehole televiewer provides approximately 500 acoustic pulses per rotation of the tr~n~ Pr for sc~nnlng the borehole wall.
Referring to Figure 3, there is shcwn a schematic arrange-ment of the borehole televiewer in a borehole wall that illus-tra-tes the proble~ produced by a non-circular borehole or a borehole televiewer positioned off centre. As shcwn, the trans-ducer 10 is located at approxima~ely the y~ Lic ce~tre of the non-circular borehole 31. When the acoustic pulse travels along the path 32, it is dy~reciated that it strikes the borehole normal to a tangent at the point at which it strikes and is reflected back to the tr~n~ c~r 10. In contrast, when the acoustic energy travels along the path 34, it strikes the borehole wall at an angl.e to a tangent at the point at which it strikes and instead of being re~lect~ back, the major portion of the energy is scattered or reflect~d along the path 35. Frcm the above description, it can be readily appreciated that the energy received by the transducer along the path 32 will greatly exceed the acoustic energy received along the path 34. Thus if ~26~ 7 details of the borehole are to be displayed some means must be taken for increasing the gain of the transducer amplifier as it rotates from the posi-tion 32 to the position 34. While the gain must be adjusted, it must be adjusted slowly since the change in the path of acoustic energy occurs at a slow rate. While the gain must be adjusted slowly there are positions where the energy may be reflected directly bac3s to the acoustic tr~ns~ Pr due to a fracture or other anGmaly in the borehole wall. At these positions, the gain of the amplifier must be decreased very rapidly so tnat the ancmaly is not obscured in the final display of borehole televiewer data.
Referring to Figure 4, there is shown a simple autcmatic gain control circuit for controlling the transducer amplifier.
~ The input 41 of the circuit is coupled to the trAn~ Pr (not shown). The circuit ~ es a field effect transistor 47 which i5 operated as a voltage divider to shunt a portion of the input signal of the amplifier 40 directly to ground. The gain control circuit does not adjust the gain of an ~m~l;fi~r as is traditional with duL~LLLcLLic gain control circuits but rather is a voltage dividing circuit formed by the resistor 42~ and the resistance of the field effect transistor 47. The resistance of the field effect transistor 47 is ~Lo~v~Lional to the voltage applied to the gate 46. The input 41 is both resistivel~ and capacitively callpl~ to the Amplif;~r 40 through a circuit 42 ccmprising a resist~nce 42A and a capacitance 42Bo The output 49 of the ~mrl;f;~r is coupled to an ;m~rl~nre 43 which is used to match the output signal of the A~rl;fi~r to a logging cable 52. The autcmatic gain control is provided by a fee~back lcop 44 which signal is rectified by a diode 45. ~le rectified signal is applied to the gate 46 o~ the field effect transistor 47 to control the c~ ion thereof. By controlling -the conduction of the field effect transistor 47 ~he input voltage ~L~Pli~ to the amplifier 40 can ke controlled. The fee~hA~k si~nal charges a resistance capacitance circuit comprising a resistance 50 and a ~2~3L7~3~
capacitance 51, which circuit couples the f~h~k loop 44 resistively and capacitively to ground. The values of the resistance 50 and the capacit~nce 51 are chosen to provide an amplifier gain rise time of ~L~imately 20 m;ll;~r~n~ and a decay time of 600 microseconds. Thus, the decay time is slightly shorter than the time between the successive cycles of the acoustic trAn~u~r lO. As can be appreciated if the output vo1tage of the ~m~lif;~r 40 increases to a high value, the capacitor 51 wculd be ;m~ tely charged and the voltaye Oll the gate 46 will be an extre~ely high voltage thus re~ ;ng the resistance of the field effect transistor 47 and the corre-sponding signal voltage ~pllfA to the input of the amplifier 40. The charging rate of the capacitor 51 is controlled by the ~nt~rn~l resistance of the diode 45 which is relatlvely low and thus the 600 microsecond decay tlme of the au~oma~ic gain control circuit can be readily achieved. As the voltage on the output of the amplifier 40 decreases the capacitor 51 will ~ h~rge to ground through the resistance 50 thus re~ ;ng the voltage on the gate 46. This ~;~rh~rge rate is largely controlled by the product of resistance 50 and capacitor 51 and is chosen to be on the order of 20 m; 11;~econds. miS will increase the resistance of the field effect transistor 47 and raise the voltage le~el of the input to the a~plifier 40. When the voltage on the capacitor is completely discharged the field effect transistor 47 will act as a very hlgh resistance and apply the m,~xlml~m voltage signal to the input of the ~mrl;fl~r 40.
From the above description, it is seen that the invention provides a simple gain control for the tr~ns~ r ~rli~;~r which has a slow rise time therefore increasing the output voltage of the ~mrl;f;~r at a slcw rate but has a very fast cutoff so that the amplifier will not: saturate. m e a~ ~Lic gain cont~ol circuit will allow the borehole televiewer to abtain an accurate representation of the wall of ~he borehole and the presence of fractures an~ other ~nf~lie~ in the bore-3~9 hole wall will not be lost because of the saturation of theamplifier. Likewise, when the signal increases as the transducer approaches a position w~ere the path of acoustic energy will be normal to the borehole wall the gain of the amplifier will be reduced. Thus, signals providing an accurate representation of the borehole wall will be obta m ed. It is to be understood that when the term "gain of the ~m~l; F;~r" is used, it is to describe the voltage di~iding circuit formed by the resistance 42 and the field effect transistor 47 that effectively control the voltage level of the input signal supplied to the amplifier 40. As explained, this is ~ot a true autcmatic gain control circuit but functions m the same manner as an autcmatic gain control circuit.
OF SIGN~IS ~ u~ BY A BOFE~IOLE TE~TL~WER
m e invention relates to borehole logging tools and particu larly to a tool that is described as a borehole televiewer. A
borehole televiewer u~ a rotating acoustic tr~n~dll~Pr that is peric~;r~lly pulsed to produce acoustic energy which tr~vels outwardly and strikes ~he borehole wall and is rerlected back to the tr~n~ r. The amplitude of the reflected signal is dis played on a cathode ray tube whose face m~y be ph~LGyLd~iled. The resulting photograph L~L~s~lLs a map of the borehole wall split along the north direction and laid out flat. m e transducer is pulsed at a relatively high rate, for ~x~mrle 1500 pulses per second, while the tr~ns~l~r~r rotation period is 0.333 se~n~
The s~eep of the os~;lloscope is controlled by a north syn~
chronization signal ~hich is produced by a flux gate magneto-me.ter which rotates in unison with the tr~n~ Pr.
While the above tools are useful in obtaining a display of the borehole wall that indicates the loca~ions of fractures or other features, it does have a serious limitation when used in a non-ci~cular or eliptical borehole. m e same problem also arises when the -tool moves off centre as a result of this travel through the borehole. It ccm be shcwn that when the borehole televi~wer is loccited off centre or in a non-circular hole~ the acoustic energy will be scattered at all locati.ons except where the acoustic energy strikes the borehole wall nor~al to a tangent a-t this point. Thus, the reflected ~nergy received by the ~r~n~ r will have four positions where it is at a m~;~ ~ and in the r~m~;nln~ positions the reflected energy will be decreased. The borehole tele~iewer as presently available has various amplifier gain levels that are selected by a rotary .switch controlled frcm the surface~ Since the amplitude is set from ~he surface, it cannot be varied to provide the proper amplification as the tr~n~tl~r rotates. Thus, the resulting display will have li~ht and dark areas where details are lacking. It should be appreciated that in normal operations a fracture or other ancmaly in the borehole wall will not reflect energy and will appear as a dark shadcw on the display.
The present invention solves the proble-ms of u~ ;nf3 a borehole televiewer in a non-circular borehole by providing a circuit for a~L~"~Lically controlling the magnitude of ampli-fication of signals produced by the borehole televiewer, the circuit ccmprising amplifier means having an input and an output, the Lnput of said am~lifier means being coupled to ~he acoustic transducer o the televiewer, gate ~eans having an input, an output and a gate, the input of said gate means being coupled ~o the input of said ~m~lifiPr and the output of the gate means being coupled to ground; and a feed back loop, said feed back loop being coupled to the output of said ~mpl;~;Pr and to ~he gate of said gate means to control said gate means in r~ n~e to the output signal of said ~mrl;f;~r. In a suitable ~mhc~;mPnt of the invention the circuit has a relatively slow rise time and a very fast decay or fall time. It is observed that the circuit is not a true autcmatic gain contxol circult m the sense that the gain of the ~m~lif;pr is changed but rather a voltage dividing circuit that shorts part of the ;nc~m;ng signal to ground and thus decreases the input signal to the ~m~l;fiPr. m is allows the ~rl;fier to retain the gain setting selected from the surface while in-creasing the signal level to provide details whe~ the reflected signal is weak.
In an attractive ~mhc~im~nt of the invention the decay constan-t for the circuit is less than the cycle time of the tr~n~ r~r so that the ~mrlif;~r will not saturate when the reflected signal suddenly increases in amplit~de. Preferably, the rise time of the circuit extends over several cycles so that the ~mrl;f;~r Will not obscure fractures or other ~n~mAl;e~ in the borehole wall that have a short circumferential extent along the wall.
In a preferred embodiment of the i~vention the gate means of the circuit is a field effect transistor whose gate voltage is controlled to control its conduction to ground. Thus, the field effect transistor acts as a voltage divider circuit in the input circuit of the amplifier.
m e invention will be more easily unders~ood from the following description wh n taken in conjunction with the attached drawings in which:
Figure 1 is a schematic elevation view Of a borehole televiewer.
Figure 2 is a waveform o-f the s:ignals produced by the borehole televiewer.
Figure 3 is a graphic L~es~.Lation of the borehole televiewer located in a non-circular borehole~
Figure 4 is a schematic drawing of the dU~ull~LiC gain control circuit of the invention.
Referring now to Figure 1, there i5 shown the borehole televiewer that includes an acoustic tr~n~ rPr 10 and a flux gate magn~L~,~Ler ll which are mounted on a ccmmon shaft. m e shaft is rotated by motor 12 about the axis 14 of the borehole televiewer. Electronics for control of the p~ ;n~ of the trAnq~l-rPr and the trAnYmi~ion of the reflected signals to the surface i5 conta med in a section 16 of the tool while a pressure equalization chamber 15 is mounted in the bottom portion of the tool. The pressure ec~lalization ~hAmhPr serves to equalize the pressure on the interior of the acoustic windcw 13 with the pressure of the fluid in the borehole. By e~~ ing the pressure the required mP~h~niç~l ~LL~ly~h of the acoustic window can be reduced and allow the use of materials which provide a gcod acoustic match between the fluid filling the borehole televiewer and the borehole fluid.
Referring to Figure 2, there is shcwn the waveforms of the signals produced by the borehole televiewer. In particular, the signal 20 represents the acoustic p~Lse produced by the trans-ducer ~Thile the signal 21 represents the reflected signal received by the tr~n~dll~Pr. As shownl a time interval of approximately 100 microseconds elapses between the production of the acoustic pulse and the receipt oi- the reflected signal. The tlme lapse~ of course, ~PpPn~ upon the diameter of the borehole but lO0 micro~ec~n~ is representati~Te. m e actual borehole televiewer tool that is available commercially has a repetition or cycle rate of the acoustic tr~n~ r that is approximdtel.y 1500 cycles per second while the rotational cycle of the trans-ducer is 0.333 sec~n~.~. Thus, the borehole televiewer provides approximately 500 acoustic pulses per rotation of the tr~n~ Pr for sc~nnlng the borehole wall.
Referring to Figure 3, there is shcwn a schematic arrange-ment of the borehole televiewer in a borehole wall that illus-tra-tes the proble~ produced by a non-circular borehole or a borehole televiewer positioned off centre. As shcwn, the trans-ducer 10 is located at approxima~ely the y~ Lic ce~tre of the non-circular borehole 31. When the acoustic pulse travels along the path 32, it is dy~reciated that it strikes the borehole normal to a tangent at the point at which it strikes and is reflected back to the tr~n~ c~r 10. In contrast, when the acoustic energy travels along the path 34, it strikes the borehole wall at an angl.e to a tangent at the point at which it strikes and instead of being re~lect~ back, the major portion of the energy is scattered or reflect~d along the path 35. Frcm the above description, it can be readily appreciated that the energy received by the transducer along the path 32 will greatly exceed the acoustic energy received along the path 34. Thus if ~26~ 7 details of the borehole are to be displayed some means must be taken for increasing the gain of the transducer amplifier as it rotates from the posi-tion 32 to the position 34. While the gain must be adjusted, it must be adjusted slowly since the change in the path of acoustic energy occurs at a slow rate. While the gain must be adjusted slowly there are positions where the energy may be reflected directly bac3s to the acoustic tr~ns~ Pr due to a fracture or other anGmaly in the borehole wall. At these positions, the gain of the amplifier must be decreased very rapidly so tnat the ancmaly is not obscured in the final display of borehole televiewer data.
Referring to Figure 4, there is shown a simple autcmatic gain control circuit for controlling the transducer amplifier.
~ The input 41 of the circuit is coupled to the trAn~ Pr (not shown). The circuit ~ es a field effect transistor 47 which i5 operated as a voltage divider to shunt a portion of the input signal of the amplifier 40 directly to ground. The gain control circuit does not adjust the gain of an ~m~l;fi~r as is traditional with duL~LLLcLLic gain control circuits but rather is a voltage dividing circuit formed by the resistor 42~ and the resistance of the field effect transistor 47. The resistance of the field effect transistor 47 is ~Lo~v~Lional to the voltage applied to the gate 46. The input 41 is both resistivel~ and capacitively callpl~ to the Amplif;~r 40 through a circuit 42 ccmprising a resist~nce 42A and a capacitance 42Bo The output 49 of the ~mrl;f;~r is coupled to an ;m~rl~nre 43 which is used to match the output signal of the A~rl;fi~r to a logging cable 52. The autcmatic gain control is provided by a fee~back lcop 44 which signal is rectified by a diode 45. ~le rectified signal is applied to the gate 46 o~ the field effect transistor 47 to control the c~ ion thereof. By controlling -the conduction of the field effect transistor 47 ~he input voltage ~L~Pli~ to the amplifier 40 can ke controlled. The fee~hA~k si~nal charges a resistance capacitance circuit comprising a resistance 50 and a ~2~3L7~3~
capacitance 51, which circuit couples the f~h~k loop 44 resistively and capacitively to ground. The values of the resistance 50 and the capacit~nce 51 are chosen to provide an amplifier gain rise time of ~L~imately 20 m;ll;~r~n~ and a decay time of 600 microseconds. Thus, the decay time is slightly shorter than the time between the successive cycles of the acoustic trAn~u~r lO. As can be appreciated if the output vo1tage of the ~m~lif;~r 40 increases to a high value, the capacitor 51 wculd be ;m~ tely charged and the voltaye Oll the gate 46 will be an extre~ely high voltage thus re~ ;ng the resistance of the field effect transistor 47 and the corre-sponding signal voltage ~pllfA to the input of the amplifier 40. The charging rate of the capacitor 51 is controlled by the ~nt~rn~l resistance of the diode 45 which is relatlvely low and thus the 600 microsecond decay tlme of the au~oma~ic gain control circuit can be readily achieved. As the voltage on the output of the amplifier 40 decreases the capacitor 51 will ~ h~rge to ground through the resistance 50 thus re~ ;ng the voltage on the gate 46. This ~;~rh~rge rate is largely controlled by the product of resistance 50 and capacitor 51 and is chosen to be on the order of 20 m; 11;~econds. miS will increase the resistance of the field effect transistor 47 and raise the voltage le~el of the input to the a~plifier 40. When the voltage on the capacitor is completely discharged the field effect transistor 47 will act as a very hlgh resistance and apply the m,~xlml~m voltage signal to the input of the ~mrl;fl~r 40.
From the above description, it is seen that the invention provides a simple gain control for the tr~ns~ r ~rli~;~r which has a slow rise time therefore increasing the output voltage of the ~mrl;f;~r at a slcw rate but has a very fast cutoff so that the amplifier will not: saturate. m e a~ ~Lic gain cont~ol circuit will allow the borehole televiewer to abtain an accurate representation of the wall of ~he borehole and the presence of fractures an~ other ~nf~lie~ in the bore-3~9 hole wall will not be lost because of the saturation of theamplifier. Likewise, when the signal increases as the transducer approaches a position w~ere the path of acoustic energy will be normal to the borehole wall the gain of the amplifier will be reduced. Thus, signals providing an accurate representation of the borehole wall will be obta m ed. It is to be understood that when the term "gain of the ~m~l; F;~r" is used, it is to describe the voltage di~iding circuit formed by the resistance 42 and the field effect transistor 47 that effectively control the voltage level of the input signal supplied to the amplifier 40. As explained, this is ~ot a true autcmatic gain control circuit but functions m the same manner as an autcmatic gain control circuit.
Claims (10)
1. A circuit for automatically controlling the magnitude of amplification of signals produced by a borehole televiewer in response to acoustic waves reflected by a borehole wall, said waves being received by and emanated from a rotating acoustic transducer that is periodically pulsed to produce acoustic energy, the circuit comprising:
amplifier means having an input and an output, the input of said amplifier means being coupled to the acoustic transducer;
gate means having an input, an output and a gate, the input of said gate means being coupled to the input of said amplifier and the output of the gate means being coupled to ground; and a feedback loop, said feedback loop being coupled to the output of said amplifier and to the gate of said gate means to control said gate means in response to the output signal of said amplifier.
amplifier means having an input and an output, the input of said amplifier means being coupled to the acoustic transducer;
gate means having an input, an output and a gate, the input of said gate means being coupled to the input of said amplifier and the output of the gate means being coupled to ground; and a feedback loop, said feedback loop being coupled to the output of said amplifier and to the gate of said gate means to control said gate means in response to the output signal of said amplifier.
2. The circuit of claim 1, wherein said gate means provides a variable resistance to ground, the magnitude of said variable resistance being proportional to the feedback signal being transferred to the gate of the gate means via the feedback loop.
3. The circuit of claim 2, wherein said gate means is a field effect transistor.
4. The circuit of claim 3, wherein the feedback loop includes control means for providing a feedback signal with a variable voltage for controlling the gate of the field effect transistor.
5. The circuit of claim 4, wherein the control means provides a feedback signal with a slow rise time and a rapid decrease.
6. The circuit of claim 5, wherein the rise time does not exceed one-quarter of the time required for the borehole tele-viewer to make one complete scan of the borehole.
7. The circuit of claim 6, where m the rapid decrease does not exceed the time elapsing between successive pulses of the borehole televiewer.
8. The circuit of claim 4, wherein the control means couples the feedback loop resistively and capacitively to ground and ccmprises a resistance capacitance circuit whose time constant provides a slow rise time and a fast decay time for the feedback signal.
9. A method for improving the response of a borehole tele-viewer in an out-of-round borehole, the method comprising:
amplifying the signal of the borehole televiewer downhole;
and controlling the magnitude of said amplification in response to the amplified signal.
amplifying the signal of the borehole televiewer downhole;
and controlling the magnitude of said amplification in response to the amplified signal.
10. The method of claim 9, wherein said controlling increases the amplification slowly in response to a decrease in the amplified signal and decreases the amplification rapidly in response to an increase in the amplification above a desired level.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US45944383A | 1983-01-20 | 1983-01-20 | |
| US459,443 | 1983-01-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1201797A true CA1201797A (en) | 1986-03-11 |
Family
ID=23824793
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000444718A Expired CA1201797A (en) | 1983-01-20 | 1984-01-05 | Circuit for controlling the magnitude of amplification of signals produced by a borehole televiewer |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS59137808A (en) |
| CA (1) | CA1201797A (en) |
| FR (1) | FR2539880B1 (en) |
| GB (1) | GB2133882B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5212353A (en) * | 1984-12-17 | 1993-05-18 | Shell Oil Company | Transducer system for use with borehole televiewer logging tool |
| CA1250944A (en) * | 1985-03-11 | 1989-03-07 | Edward A. Clerke | Method for lithology detection |
| US4646565A (en) * | 1985-07-05 | 1987-03-03 | Atlantic Richfield Co. | Ultrasonic surface texture measurement apparatus and method |
| US4855965A (en) * | 1986-11-26 | 1989-08-08 | Shell Oil Company | Time ramped gain for borehole televiewer |
| US20030205376A1 (en) | 2002-04-19 | 2003-11-06 | Schlumberger Technology Corporation | Means and Method for Assessing the Geometry of a Subterranean Fracture During or After a Hydraulic Fracturing Treatment |
Family Cites Families (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1036647A (en) * | 1963-07-26 | 1966-07-20 | Jersey Prod Res Co | Seismic amplifier |
| GB1109443A (en) * | 1964-05-29 | 1968-04-10 | Smiths Industries Ltd | Echo-sounding apparatus for examining strata below the sea-bed |
| DE1516629B2 (en) * | 1965-11-29 | 1970-10-29 | Electroacustic Gmbh, 2300 Kiel | Method and device for recording two closely spaced submarine hall signals on current-sensitive paper |
| US3474878A (en) * | 1967-07-28 | 1969-10-28 | Shell Oil Co | Acoustic well logging system and method for detecting fractures |
| US3724589A (en) * | 1969-05-26 | 1973-04-03 | Schlumberger Technology Corp | Well logging methods and apparatus |
| US3904971A (en) * | 1971-09-29 | 1975-09-09 | Us Navy | Automatic gain control amplifier circuit |
| FR2160263B1 (en) * | 1971-11-16 | 1978-01-06 | Chauchat Jean | |
| FR2171957B1 (en) * | 1972-02-17 | 1974-09-13 | Schlumberger Prospection | |
| GB1473345A (en) * | 1973-04-26 | 1977-05-11 | Olympus Optical Co | Automatic gain control circuit |
| JPS5011111A (en) * | 1973-05-29 | 1975-02-05 | ||
| US3924260A (en) * | 1974-06-27 | 1975-12-02 | Petty Ray Geophysical Inc | Method and apparatus for suppression of noise in seismic data |
| GB1495767A (en) * | 1975-05-01 | 1977-12-21 | Mark Products | Apparatus and method for adjusting the output of a plurality of geophones to compensate the effect of variations in the near surface character of the earth |
| IL51708A (en) * | 1976-04-22 | 1979-03-12 | Motorola Inc | Automatic gain control circuit |
| JPS5647757A (en) * | 1979-09-28 | 1981-04-30 | Hitachi Ltd | Ultrasonic probe driver |
| JPS6227891Y2 (en) * | 1981-03-30 | 1987-07-17 | ||
| IT1190872B (en) * | 1982-06-17 | 1988-02-24 | Sgs Microelettronica Spa | AUDIO AMPLIFICATION SYSTEM WITH INCREASE IN THE AVERAGE LISTENING POWER |
-
1984
- 1984-01-05 CA CA000444718A patent/CA1201797A/en not_active Expired
- 1984-01-18 GB GB08401298A patent/GB2133882B/en not_active Expired
- 1984-01-18 JP JP59007006A patent/JPS59137808A/en active Granted
- 1984-01-18 FR FR8400726A patent/FR2539880B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2133882A (en) | 1984-08-01 |
| FR2539880A1 (en) | 1984-07-27 |
| GB2133882B (en) | 1986-09-03 |
| FR2539880B1 (en) | 1988-03-18 |
| JPH0432961B2 (en) | 1992-06-01 |
| JPS59137808A (en) | 1984-08-08 |
| GB8401298D0 (en) | 1984-02-22 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |