CA1231377A - Apparatus for focusing electrode induced polarization logging - Google Patents
Apparatus for focusing electrode induced polarization loggingInfo
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- CA1231377A CA1231377A CA000454307A CA454307A CA1231377A CA 1231377 A CA1231377 A CA 1231377A CA 000454307 A CA000454307 A CA 000454307A CA 454307 A CA454307 A CA 454307A CA 1231377 A CA1231377 A CA 1231377A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/18—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
- G01V3/20—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with propagation of electric current
- G01V3/24—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with propagation of electric current using ac
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- Environmental & Geological Engineering (AREA)
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- Engineering & Computer Science (AREA)
- General Physics & Mathematics (AREA)
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Abstract
A B S T R A C T
APPARATUS FOR FOCUSED ELECTRODE
INDUCED POLARIZATION LOGGING
An induced polarization logging tool for measuring para-meters of a formation surrounding a borehole comprises a survey current electrode and two focusing electrodes disposed on opposite sides of the survey current electrode. The tool further comprises monitoring electrodes for monitoring the current flow in the formation between the survey current and focusing electrodes. The monitoring electrodes are coupled to circuit means, wherein a first current control means is directly coupled to said survey current electrode and said circuit means for control of the current flow to said survey current electrode in response to and in phase with the monitored current flow, and a second current control means is directly coupled to said focusing electrodes to control the current flow to said focusing electrodes in response to and in phase with the monitored current flow.
APPARATUS FOR FOCUSED ELECTRODE
INDUCED POLARIZATION LOGGING
An induced polarization logging tool for measuring para-meters of a formation surrounding a borehole comprises a survey current electrode and two focusing electrodes disposed on opposite sides of the survey current electrode. The tool further comprises monitoring electrodes for monitoring the current flow in the formation between the survey current and focusing electrodes. The monitoring electrodes are coupled to circuit means, wherein a first current control means is directly coupled to said survey current electrode and said circuit means for control of the current flow to said survey current electrode in response to and in phase with the monitored current flow, and a second current control means is directly coupled to said focusing electrodes to control the current flow to said focusing electrodes in response to and in phase with the monitored current flow.
Description
~3~L3'~
APPARATUS PHARAOH FOCUSES) ODE
INDUCED POI~IZATICN IOG~;ING
me invention relates to an induced polarization logging system such as described in U.S. Patent No. 4,359,687 by Harold J. Vinegar and Monroe H. Wan an issued November 16, 1982. In this patent there is described an induced polarization logging 5 tool and method or determining the cation exchange capacity per unit pore volleyer electrolyte cor~dustivity Ow and water saturation So of shyly sand formations using in situ measure-mints. In particular, the patent described a logging tool having an insulated Sunday with current and return electrodes together 10 with voltage measurement and reference electrodes and means to determine oath the in-phase and quadrature conductivity. The induced polarization logging tool described in Patent No.
4,359,687 provides means for determiT g the value of TV Ow and So from in situ measurements thereby greatly improving the evaluation of a formation penetrated by the Barlow.
The above mentioned invention has several limitations, however. The presence of the Barlow filled with conductive drilling Bud requires use ox Barlow correction curves to obtain a true indication of the actual formation parameters.
When the formation resistivity is considerably greater than the mud resistivity, very large Barlow Corrections are required.
The problem is cG~pounded in the case of formations heavily invaded by mud filtrate, where several different array spacings are required for a complete formation evaluation. Another problem occurs in logging thin formations, where the measured induced polarization is only a fraction ox the true ovation values. The formation thickness must be several times the AM
array spacing in a normal array to obtain a good approximation to the true formation values. The limitations of the above-mentioned logging device arise from induced polarization currents channeling through the Barlow and invaded zones, rather than into the uninvaded formation adjacent to the tool.
Object of the present invention is to provide an induced polarization logging method whereby the induced polarization currents are focused into the uninvaded formation.
In accordance with the invention this object is acccmr polished by an induced polarization logging tool comprising:
a plurality of electrodes disposed on a non-conductive logging Sunday, said electrodes including at least a survey current electrode and two focusing electrodes disposed on opposite sides of said survey current electrode, monitoring electrodes a voltage measuring electrode and voltage reference and current return electrodes;
circuit means coupled to said monitoring electrodes for neutering the current flow in the formation between the survey current and focusing electrodes, a first current control means directly coupled to said survey current electrode and said circuit means for control of the current flow to said survey current electrode in response Jo and in phase with the Nitride current flow, a second current control means directly coupled to said focusing electrodes to control the current flow to said focusing electrodes Lo response to and in phase with the monitored current flow;
a source of alternating current located at the surface, one end of said source being coupled to the two current control means and the other to the current return electrodes, said source being capable of supplying alternating current at various discrete frequencies;
measurement means coupled to said voltage measurement and survey current electrodes to measure the amplitude and phase of ~3.~'7'7 the voltage induced in the formation and the amplitude and phase o-f the cur-rent flow to the survey current electrode; and transmission means for transmitting said measurements to the surface.
In the logging tool according to the invention the hocusing elect--troves inject current which is in phase with the current injected a-t the survey current electrode.
It is observed that although it is common practice in the industry to use focused electrode arrays for resistivity logging, none of the prior art would be suitable for an induced polarization logging tool such as desk cried in patent No. ~,359,687. This is because all prior devices use focusing electrodes which are transformer or capacitor coupled to the current source.
Either transformer or capacitor coupling will create phase shifts between the focusing currents and the survey current that will distort the measurement of the formation phase shift, which is extremely small (I 1 milliradian). This is no-t a problem in resistivity logging where the phase shift is not measured.
Since formation phase shift is the primary quantity measured in the induced polarization logging tool of patent No. ~,359,687, this would prevent obtain-in accurate values for TV' Ow and So using in situ measurements.
According to another aspect, the present invention provides an induced polarization logging tool for measuring parameters of a formation sun-rounding a Barlow, said logging tool comprising: a non-conductive logging Sunday; a plurality of electrodes disposed on said Sunday, said electrodes including at least a survey current electrode and guard electrodes disposed on opposite sides OX said survey current electrode, a voltage measuring elect trove and reference and current return electrodes; a first control means directly coupled to said survey current electrode, said control means control-Jo I I;
I
-pa-lying the current slow to said survey current electrode in response to and in phase with the monitored current flow; a second control means directly coupled to said guard electrodes to control the current -flow to said guard electrodes in response to and in phase with the monitored current -flow; a source of alter-noting current located at the surface, one end of said source being coupled to the two current control means and the other to the current return electrodes, said source being capable of supplying alternating current at various discrete frequencies between 0.01 and 100 Ho; measurement means directly coupled to said voltage measurement and survey current electrodes to measure the amply-tune and phase of the voltage induced in the formation and the amplitude and phase of the current flow to the survey current electrode; and transmission means for transmitting said measurements to the surface.
The invention will be more easily understood from the following detailed description when taken in conjunction with the attached drawings in which Figure 1 is a block diagram of a logging system constructed according to the invention.
Figure 2 is a vertical section of a silver/silver chloride elect trove used in the logging system of Figure 1.
Figure 3 is a modified electrode array of that shown in Figure 1.
Figure is a different -focusing electrode array.
Figure 5 is a plot of the measurement signals obtained with the logging tool of Figure 1.
Figure 6 is a modified focusing electrode array.
I
I
Referrmg to Figure l, there is shown a representative embodiment of the apparatus constructed in accordance with the teachings of this invention. m e apparatus investigates sub-surface earth formations 10 traversed by a Barlow 11 that is filled with a conductive drilling fluid or mud 12 as is ccm~on practice in the industry. m e logging apparatus includes a cylindrical support or housing member 13 to which are secured the electrodes of the present invention. Secured to the upper end of the support member 13 is the cylindrical fluid-tight housing 14. Housing 14 contains various electrical circuits used in the operation of the electrodes mounted on support member 13.
m e dcwnhole apparatus, including support member 13 and fluid-tight housing 14, is suspended from the surface of the earth by means of a multi conductor cable 15, the lower hundred feet or so of which is covered with an electrical insulation material 16.
At the surface, the cable 15 is reeled in and out of the bore-hole by a drum and winch mechanism (not shown).
The electrode system consists of a centrally located survey current electrode A attached to and supported by the support means 13, an upper focus my electrode Al situated above survey current electrode A and a lower focusing electrode A situated a symmetrical distance below survey current electrode A. An upper pair of monitor electrodes Ml and Ml' are located on support means 13 between survey current electrode A and upper focusing electrode Alto Similarly, a lower pair of nutria electrodes My and My' are situated on support means 13 between survey current electrode A and layer focusing electrode A.
Located equidistant button the upper pair of monitor electrodes Ml and Ml' is the potential measurement electrode MO. Located 30 avow the fluid-kight housmg 14 on the insulated portion 16 owe anr.oured n~lticonductor cable 15 is the potential reference electrode N. Located at safe given d.istaTlce awe the potential reference electrode N is the current return electrode B.
_ 5 3-71`~
The positions of the various electrodes shown in the drawing can vary somewhat depending on the Barlow size, the desired depth of investigation, and the monomania bed thickness to be resolved on the log. Typically, the distance from survey current electrode A to the potential measurement electrode My is made equal to twice the Barlow diameter. Ire minimum bed thickness will then be approximately twice the AMY distance.
The distance from the survey current electrode A to the focusing electrodes Al and A is made between 2 and 3 times the AMY
distance. The distance between survey current electrode A and the potential reference electrode N is about 6 or 7 times the distance between survey current electrode A and focusing electrodes Al or A. The current return electrode B is prey-drably a relatively great distance from potential reference electrode N, and can be located at the surface. The Allah and AYE distances are at least 10 times the Sunday diameter In order to generate a symmetric electrical response the electrode pairs located at equal distances on opposite sides of survey current electrode A ye connected by insulated con doctors of negligible resistance. Thus, upper monitor electrode Ml is connected to fewer monitor electrode My, upper monitor electrode My' is connected to lower monitor electrode My', and upper focusing electrode Al is connected to lower focusing electrode A.
All of the monitor electrodes Ma, My', I, My', as well as the potential measurement electrode My and the potential reference electrode N are norl-polarizing, reversible electrodes such as silver/sil~er Shelley A de electrodes. mix prevents erroneous phase shifts due to electroche~ical surface Polaris ration, as would exist from the standard lead electrodes used in resistivity logging. Still another advantage of the silver/
silver chloride electrode is the very low offset potential which or lies the apparatus to employ the full dynamic range of the dcwnhole amplifiers. One implementation of a high-pressure, high I
temperature silver/silver chloride electrode is shown in Figure
APPARATUS PHARAOH FOCUSES) ODE
INDUCED POI~IZATICN IOG~;ING
me invention relates to an induced polarization logging system such as described in U.S. Patent No. 4,359,687 by Harold J. Vinegar and Monroe H. Wan an issued November 16, 1982. In this patent there is described an induced polarization logging 5 tool and method or determining the cation exchange capacity per unit pore volleyer electrolyte cor~dustivity Ow and water saturation So of shyly sand formations using in situ measure-mints. In particular, the patent described a logging tool having an insulated Sunday with current and return electrodes together 10 with voltage measurement and reference electrodes and means to determine oath the in-phase and quadrature conductivity. The induced polarization logging tool described in Patent No.
4,359,687 provides means for determiT g the value of TV Ow and So from in situ measurements thereby greatly improving the evaluation of a formation penetrated by the Barlow.
The above mentioned invention has several limitations, however. The presence of the Barlow filled with conductive drilling Bud requires use ox Barlow correction curves to obtain a true indication of the actual formation parameters.
When the formation resistivity is considerably greater than the mud resistivity, very large Barlow Corrections are required.
The problem is cG~pounded in the case of formations heavily invaded by mud filtrate, where several different array spacings are required for a complete formation evaluation. Another problem occurs in logging thin formations, where the measured induced polarization is only a fraction ox the true ovation values. The formation thickness must be several times the AM
array spacing in a normal array to obtain a good approximation to the true formation values. The limitations of the above-mentioned logging device arise from induced polarization currents channeling through the Barlow and invaded zones, rather than into the uninvaded formation adjacent to the tool.
Object of the present invention is to provide an induced polarization logging method whereby the induced polarization currents are focused into the uninvaded formation.
In accordance with the invention this object is acccmr polished by an induced polarization logging tool comprising:
a plurality of electrodes disposed on a non-conductive logging Sunday, said electrodes including at least a survey current electrode and two focusing electrodes disposed on opposite sides of said survey current electrode, monitoring electrodes a voltage measuring electrode and voltage reference and current return electrodes;
circuit means coupled to said monitoring electrodes for neutering the current flow in the formation between the survey current and focusing electrodes, a first current control means directly coupled to said survey current electrode and said circuit means for control of the current flow to said survey current electrode in response Jo and in phase with the Nitride current flow, a second current control means directly coupled to said focusing electrodes to control the current flow to said focusing electrodes Lo response to and in phase with the monitored current flow;
a source of alternating current located at the surface, one end of said source being coupled to the two current control means and the other to the current return electrodes, said source being capable of supplying alternating current at various discrete frequencies;
measurement means coupled to said voltage measurement and survey current electrodes to measure the amplitude and phase of ~3.~'7'7 the voltage induced in the formation and the amplitude and phase o-f the cur-rent flow to the survey current electrode; and transmission means for transmitting said measurements to the surface.
In the logging tool according to the invention the hocusing elect--troves inject current which is in phase with the current injected a-t the survey current electrode.
It is observed that although it is common practice in the industry to use focused electrode arrays for resistivity logging, none of the prior art would be suitable for an induced polarization logging tool such as desk cried in patent No. ~,359,687. This is because all prior devices use focusing electrodes which are transformer or capacitor coupled to the current source.
Either transformer or capacitor coupling will create phase shifts between the focusing currents and the survey current that will distort the measurement of the formation phase shift, which is extremely small (I 1 milliradian). This is no-t a problem in resistivity logging where the phase shift is not measured.
Since formation phase shift is the primary quantity measured in the induced polarization logging tool of patent No. ~,359,687, this would prevent obtain-in accurate values for TV' Ow and So using in situ measurements.
According to another aspect, the present invention provides an induced polarization logging tool for measuring parameters of a formation sun-rounding a Barlow, said logging tool comprising: a non-conductive logging Sunday; a plurality of electrodes disposed on said Sunday, said electrodes including at least a survey current electrode and guard electrodes disposed on opposite sides OX said survey current electrode, a voltage measuring elect trove and reference and current return electrodes; a first control means directly coupled to said survey current electrode, said control means control-Jo I I;
I
-pa-lying the current slow to said survey current electrode in response to and in phase with the monitored current flow; a second control means directly coupled to said guard electrodes to control the current -flow to said guard electrodes in response to and in phase with the monitored current -flow; a source of alter-noting current located at the surface, one end of said source being coupled to the two current control means and the other to the current return electrodes, said source being capable of supplying alternating current at various discrete frequencies between 0.01 and 100 Ho; measurement means directly coupled to said voltage measurement and survey current electrodes to measure the amply-tune and phase of the voltage induced in the formation and the amplitude and phase of the current flow to the survey current electrode; and transmission means for transmitting said measurements to the surface.
The invention will be more easily understood from the following detailed description when taken in conjunction with the attached drawings in which Figure 1 is a block diagram of a logging system constructed according to the invention.
Figure 2 is a vertical section of a silver/silver chloride elect trove used in the logging system of Figure 1.
Figure 3 is a modified electrode array of that shown in Figure 1.
Figure is a different -focusing electrode array.
Figure 5 is a plot of the measurement signals obtained with the logging tool of Figure 1.
Figure 6 is a modified focusing electrode array.
I
I
Referrmg to Figure l, there is shown a representative embodiment of the apparatus constructed in accordance with the teachings of this invention. m e apparatus investigates sub-surface earth formations 10 traversed by a Barlow 11 that is filled with a conductive drilling fluid or mud 12 as is ccm~on practice in the industry. m e logging apparatus includes a cylindrical support or housing member 13 to which are secured the electrodes of the present invention. Secured to the upper end of the support member 13 is the cylindrical fluid-tight housing 14. Housing 14 contains various electrical circuits used in the operation of the electrodes mounted on support member 13.
m e dcwnhole apparatus, including support member 13 and fluid-tight housing 14, is suspended from the surface of the earth by means of a multi conductor cable 15, the lower hundred feet or so of which is covered with an electrical insulation material 16.
At the surface, the cable 15 is reeled in and out of the bore-hole by a drum and winch mechanism (not shown).
The electrode system consists of a centrally located survey current electrode A attached to and supported by the support means 13, an upper focus my electrode Al situated above survey current electrode A and a lower focusing electrode A situated a symmetrical distance below survey current electrode A. An upper pair of monitor electrodes Ml and Ml' are located on support means 13 between survey current electrode A and upper focusing electrode Alto Similarly, a lower pair of nutria electrodes My and My' are situated on support means 13 between survey current electrode A and layer focusing electrode A.
Located equidistant button the upper pair of monitor electrodes Ml and Ml' is the potential measurement electrode MO. Located 30 avow the fluid-kight housmg 14 on the insulated portion 16 owe anr.oured n~lticonductor cable 15 is the potential reference electrode N. Located at safe given d.istaTlce awe the potential reference electrode N is the current return electrode B.
_ 5 3-71`~
The positions of the various electrodes shown in the drawing can vary somewhat depending on the Barlow size, the desired depth of investigation, and the monomania bed thickness to be resolved on the log. Typically, the distance from survey current electrode A to the potential measurement electrode My is made equal to twice the Barlow diameter. Ire minimum bed thickness will then be approximately twice the AMY distance.
The distance from the survey current electrode A to the focusing electrodes Al and A is made between 2 and 3 times the AMY
distance. The distance between survey current electrode A and the potential reference electrode N is about 6 or 7 times the distance between survey current electrode A and focusing electrodes Al or A. The current return electrode B is prey-drably a relatively great distance from potential reference electrode N, and can be located at the surface. The Allah and AYE distances are at least 10 times the Sunday diameter In order to generate a symmetric electrical response the electrode pairs located at equal distances on opposite sides of survey current electrode A ye connected by insulated con doctors of negligible resistance. Thus, upper monitor electrode Ml is connected to fewer monitor electrode My, upper monitor electrode My' is connected to lower monitor electrode My', and upper focusing electrode Al is connected to lower focusing electrode A.
All of the monitor electrodes Ma, My', I, My', as well as the potential measurement electrode My and the potential reference electrode N are norl-polarizing, reversible electrodes such as silver/sil~er Shelley A de electrodes. mix prevents erroneous phase shifts due to electroche~ical surface Polaris ration, as would exist from the standard lead electrodes used in resistivity logging. Still another advantage of the silver/
silver chloride electrode is the very low offset potential which or lies the apparatus to employ the full dynamic range of the dcwnhole amplifiers. One implementation of a high-pressure, high I
temperature silver/silver chloride electrode is shown in Figure
2 and described below. The survey current electrode A, focusing electrodes Al and A, and current return electrode B may be constructed from standard lead electrodes.
m e electrical circuitry which is connected to the electrodes, is shown within dotted line box 14 which corresponds to the fluid-tight housing 14. The power for the dcwnhole circuitry is supplied by DC power from the surface power supply 17 to the regulated dcwnhole power supplies 18 through the armored multi conductor cable 15. One end of the alternating current source 19 located at the surface is connected via mNlticonductor cable 15 to the current return electrode B. The other end of the alternating current source 19 is connected via multi conductor cable 15 to voltage-controlled resistors 20 and 21. Voltage controlled resistor 21 is connected through reference resistor R0 to survey current electrode A. Voltage-controlled resistor 20 is connected through reference resistor Al to focusing current electrodes Al and Aye Thy voltage-controlled resistors are to be construed as any implementation whereby a series resistance is varied by means of I Al a control voltage. m e voltage-controlled resistors and may be field effect power transistors whose source to drain resistance varies m response to the voltage applied to the gate. Monitor electrodes Ml and My æ e connected to one input of differential amplifier 22. Monitor electrodes Ml' and My' are connected to the other input of differential amplifier 22.
Amplifier 22 is a differential-Lnput, differential output amplifier with very high input impedance. One differential output from amplifier 22 is the control for voltage-controlled resistor 21. The other differential output is the control for voltage-controlled resistor 20. The combination of the differ-entail amplifier 22 and the voltage controlled resistors I and 21 maintain substantially zero potential difference between nK~itor'electrc~es Ml and Ml' and also between monitor electrodes My and My'.
Potential measurement electrode My is connected to one end of voltage amplifier 23 while the potential reference electrode N is connected to the other end of voltage amplifier 23. Voltage amplifier 23 is a direct-coupled, very high put impedance differential amplifier which amplifies the potential difference generated by the applied A current in the earth formation. The output of voltage amplifier 23 is connected to low-pass filter 25 whose function is to prevent aliasing of the voltage signal when it it converted to a digital signal. The output of the low pass filter is sampled by the track-and-hold amplifier 27 which is controlled by the clock and control logic circuit 30.
m e sampled output from the track-and-hold amplifier 27 is digitized by the dcwnhole analog-to-digital converter 23. m e track-and-hold circuit follows the voltage signal and when actuated by the clock and logic circuit 30 samples the amplitude of the voltage signal.
Dcwnhole current measurement is obtained by measurillg the voltage across dcwnhole reference resistor R0, using current amplifier 24. The output of current amplifier 24 is connected to low-pass filter 26, whose function is to prevent aliasing of the digital current signal. Lcw-pass filters 25 and 26 æ e sub Stan-tidally identical in order to prevent any differential phase shift from being introduced between the dcwnhole measured current and ~ol~age. m e output of low-pass filter 26 is con-netted to track-and-hold amplifier 28. Track-and-hold amplifier 28 is substantially identical to rewakened hold amplifier 27 and is controlled by clock and control logic 30. Lowe same control pulse is used for both track-and-hold amplifiers 27 and 28 so that the current and voltage are sampled simultaneously. is prevents differential phase shift between the dcwnhole measured current and voltage signals. The sampled output of track-and-hold amplifier 28 is applied to analog-to-digital converter 29.
The sampled outputs from track-and-hold amplifiers 27 and 28 are multiplexed to the analog-to-digital converter 29 by the clock Jo and control logic 30. Therefore, any drift in the analog-to-digital converter 20 characteristics occurs equality in current and voltage channels. The digitized current and voltage signals from the analog-to-digital converter 29 are digitally encoded into transmission code by the digital encoder 31 whose output go s to line driver 32 m e line driver 32 is connected to the surface via the central conductor of multi conductor cable 15.
The central conductor has been fount to allow rapid transmission of digital signals without spurious cable reflections.
At the surface, the digital current and voltage signals are received by digital receiver 33, which decades the transmission code. The digital receiver supplies the current and voltage signals to the digital computer which computes spontaneous potential, resistivity and phase shift. The computer is con-netted to recording means 38 and storage means 39. me digital receiver 33 is also connected to digital-to-analog converter 35, which converts the digital current and voltage signals to analog form m e analog current and voltage signals from the digital-to analog converter 35 go to analog phase meter 36 which measures spontaneous potential (SUP), resistivity (R) and phase shift (9).
The output from analog phase moire 36 is recorded by recording means 37. A depth encoder 40 inputs depth information from the winch snot shown) to thy cc~puterO
The silver/silver chloride electrode shown in Figure 2 consists of a housing 50 having a silver electrode 51 disposed therein. m e surface of the silver electrode is converted to silver chloride by chloridization. The silver electrode is secured to the end of an electrode element 52 that projects outside of the housing. The electrode clement is sealed in the housing by an "oaring 53 that is compressed by a threaded packing gland 54. The volume 56 of the housing is filled with a saturated potassium chloride reference solution. A porous fruit 55 in the end of the housing allows the potassium chloride solution to contact the Barlow fluid.
I
g Now, concerning the operation of the logging apparatus in Figure 1, the AC current source supplies a constant amplitude alternating current of few frequency in the range .001 lo Ho, and preferably between 1 and 10 Ho. The frequency is usually selected less than 100 Ho to prevent phase shifts from inductive coupling in the earth formation. If the frequency is too few, the logging speed becomes prohibitively long in order to prevent waveform distortion. A logging speed of lo feet per minute has been found satisfactory with an AC current frequency of 10 Ho.
The alternating current is applied both to the survey current electrode A and the focusing electrodes Al and A. The pro-portion of current split between survey and focusing electrodes is controlled by the voltage-controlled resistors 20 and 21, which function as a resistor-di~ider network. eye voltage-controlled resistors are purely resistive so that no phase shifts introduced between the current supplied to the survey current electrode A and the current supplied to the focusing electrodes Al and A. me current injected into the formation through the survey current electrode is measured across the reference resistor R0. In a homogeneous and isotropic earth formation, the resistance ratio of voltage-controlled resistor 20 to volkaga-controlled resistor 21 is approximately:
VFl~VRO - 0.5 ~n2-1)2 on where n is the ratio of the AYE distance to the MOE distance (The reference resistors an formation resistance is assumed to be small relative to the voltage-controlled resistors). However, opposite a thin resistive bed, the resistance of voltage-controlled resistor 20 is reduced relative to voltage-controlled resistor 21 in order to inject more current into focusing electrodes Al and A than into A. reference resistor R1 can be used to monitor the focusing current (not shown). Values of reference resistors R0 and R1 ox about 1 Ohm have been found to give satisfactory signal levels. ale differential clmplifier 22 monitors the potential difference between Ml and Ma' and between My and My'. me differential output from differential amplifier 22 adjusts the ratio between current injected in-to survey current electrode A and current injected into focusing electrodes Al and A. This is accomplished by varying the resistance ratio between voltage-controlled resistors 20 and 21 until the potential difference between Ml and Ml' and My and My' is substantially equal to zero Differential amplifier 22 and voltage-controlled resistors 20 and 21 must have sufficiently fast response relative to the AC current frequency that sub-staunchly zero additional phase shift is added by this control loop.
m e survey current and the generated earth potential are both measured and digitized dcwnhole. This avoids sending analog signals to the surface which would suffix large phase shifts from cable capacitance. A clock frequency of 4.4 OH has been found satisfactory. mix gives a current and voltage sample every 7 milliseconds. The Nyquist frequency is then 71 Ho The lcw-pass filters are of the maxImally-flat Butter worth type and are designed to give at least 48 dub attenuation a the Nyquist frequency. m e analog-to-digital converter must haze sufficient number of bits to achieve substantially low digitization noise.
A 12-bit analog-to-digital converter has been found satisfactory to reduce phase noise below 1 milliradian. m e gain of amplifiers 23 and 24 are automatically adjusted to keep at least eight significant bits at all times by suitable circuit means (not shown).
The digitized current and voltage signals are analyzed by a digital computer 34 which computes resistivity and phase shift of the earth formation from the measured current and voltage dcwnhole. Since the entire current and voltage waveform including both AC and DC cc~ponents) have been digitized, the computer can also compute spontaneous earth potential, SPY
The data received at the surface by the digital receiver 33 will correspond to a series of points txi,yi) on an ellipse as shown in Figure 5. m e vertical offset of the centre of the ellipse is the self potential of the formation while horizontal offset is the offset current. By proper control of AC input signal a zero current offset can be achieved The present invention allows focusing of the survey current in the horizontal plane, so that the measured resistivity and the measured phase shift are substantially those of the formation adjacent to the tool. m e focused induced polarization tool obtains substantially more accurate induced polarization measure-mints of the earth formation when the formation resistivity is much greater than the mud resistivity. Still another advantage of this focused induced polarization apparatus is the accurate response to thin resistive beds.
It should be apparent to one skilled in the art that various modifications of the basic implementation shown in Figure 1 are possible without violating the essence of this invention. Thus, the phasemetre and cc~puter located at the surface could also have been located Donnelly within house my 14.
In this case, digital transmission to the surface is not required. Another v æ ration is the use of one of the monitoring electrodes Ma, Ma' or My, My' as the voltage measuring electrode instead of using a separate voltage measuring electrode My.
Also, within the spirit of this invention are other focused electrode arrays, such as the embed m en shown in Figure 3. In this arrangement the survey current electrode A is divided into two electrodes A and A' and the voltage measurement electrode My is placed between the two electrodes A and A'. This arrange-mint has the advantage of tailoring current applied to the formation to obtain improved response from thin beds. The two survey current electrodes will provide a different focused pancake current pattern that has three positions of zero potential difference, i.e., between Ml-Ma', M2-M2' and My. The I to - I -spacing between the survey current electrodes can be adjusted to determine the thickness of a thin bed that can be measured ace-rarely. Still another embodiment would allow separate dip-ferential amplifiers for each pair of monitor electrodes My, Ml' and My, My' as shown in Figure 4. This arrangement allows independent control of the focusing elec~rcdes Al and A that will compensate for any distortion of the current field caused by resistance i~hcmo~eneity in the formation. For example, if a thin bed has a high resistivity formation on one side and low resistivity formation on the other side, the current field will be distorted with the apparatus of Figure 1. The system Chicano in Figure 4 will compensate for this distortion and provide a more uniform current flow through the thin bed. The dynamic range required from voltage-eontrolled resistors is also reduced in this configuration in contrast to Figure 1.
Still another embodiment would utilize long cylindrical guard current electrodes, as shown in Figure 6, in place of the mc~ltor electrodes My, My' and My, My'. The current guard electrodes Al and A in Figure are elee~rieal conductors in contact with the Barlow fluid and therefore autom~tieally have zero potential difference along thwacks length. Current guard electrodes Al and A are electrically connected by a wire of negligible resistance which maintains them at the same potential. m e current guard electrodes Al and A are physically and electrically separated frock the split survey current electrodes A and A' by thin insulating disks. The voltage measurement electrode My is located midway kitten split s~vey current electrodes A and A' and is electrically insulated frock A and A' by thin insulating disks. The split survey current electrodes A and A' are electrically connected by a wire of negligible resistance which maintains them at the same potential.
The total length L of the long cylindrical focusing array must be greater than the Sunday diameter to Obtain good current focusing. In practice, L can be made approximately 10 feet ~3.05 m). me total length Q of the split survey current electrode must be much less than L, for example, to 1 foot (0.15 to 0.30 m). m e 1 ngth Q will be the minlm~n thickness of thin bed that can be accurately measured by the focused induced polarization tool.
The major advantage of the long cylindrical focused electrode array is the tighter focusing of the survey current beam in the vertical direction. This allows thinner beds to be accurately measured than with the array shown in Figure 3.
Still another modification is the use of a different type of input current signal, such as a square wave, triangular wave, time-dcmain waveform (i.e., bipolar square wave with dead time) or multi frequency rather than the sinusoidal current waveform disclosed in this embodiment. These and similar modifications are to be construed as covered within this invention.
.
m e electrical circuitry which is connected to the electrodes, is shown within dotted line box 14 which corresponds to the fluid-tight housing 14. The power for the dcwnhole circuitry is supplied by DC power from the surface power supply 17 to the regulated dcwnhole power supplies 18 through the armored multi conductor cable 15. One end of the alternating current source 19 located at the surface is connected via mNlticonductor cable 15 to the current return electrode B. The other end of the alternating current source 19 is connected via multi conductor cable 15 to voltage-controlled resistors 20 and 21. Voltage controlled resistor 21 is connected through reference resistor R0 to survey current electrode A. Voltage-controlled resistor 20 is connected through reference resistor Al to focusing current electrodes Al and Aye Thy voltage-controlled resistors are to be construed as any implementation whereby a series resistance is varied by means of I Al a control voltage. m e voltage-controlled resistors and may be field effect power transistors whose source to drain resistance varies m response to the voltage applied to the gate. Monitor electrodes Ml and My æ e connected to one input of differential amplifier 22. Monitor electrodes Ml' and My' are connected to the other input of differential amplifier 22.
Amplifier 22 is a differential-Lnput, differential output amplifier with very high input impedance. One differential output from amplifier 22 is the control for voltage-controlled resistor 21. The other differential output is the control for voltage-controlled resistor 20. The combination of the differ-entail amplifier 22 and the voltage controlled resistors I and 21 maintain substantially zero potential difference between nK~itor'electrc~es Ml and Ml' and also between monitor electrodes My and My'.
Potential measurement electrode My is connected to one end of voltage amplifier 23 while the potential reference electrode N is connected to the other end of voltage amplifier 23. Voltage amplifier 23 is a direct-coupled, very high put impedance differential amplifier which amplifies the potential difference generated by the applied A current in the earth formation. The output of voltage amplifier 23 is connected to low-pass filter 25 whose function is to prevent aliasing of the voltage signal when it it converted to a digital signal. The output of the low pass filter is sampled by the track-and-hold amplifier 27 which is controlled by the clock and control logic circuit 30.
m e sampled output from the track-and-hold amplifier 27 is digitized by the dcwnhole analog-to-digital converter 23. m e track-and-hold circuit follows the voltage signal and when actuated by the clock and logic circuit 30 samples the amplitude of the voltage signal.
Dcwnhole current measurement is obtained by measurillg the voltage across dcwnhole reference resistor R0, using current amplifier 24. The output of current amplifier 24 is connected to low-pass filter 26, whose function is to prevent aliasing of the digital current signal. Lcw-pass filters 25 and 26 æ e sub Stan-tidally identical in order to prevent any differential phase shift from being introduced between the dcwnhole measured current and ~ol~age. m e output of low-pass filter 26 is con-netted to track-and-hold amplifier 28. Track-and-hold amplifier 28 is substantially identical to rewakened hold amplifier 27 and is controlled by clock and control logic 30. Lowe same control pulse is used for both track-and-hold amplifiers 27 and 28 so that the current and voltage are sampled simultaneously. is prevents differential phase shift between the dcwnhole measured current and voltage signals. The sampled output of track-and-hold amplifier 28 is applied to analog-to-digital converter 29.
The sampled outputs from track-and-hold amplifiers 27 and 28 are multiplexed to the analog-to-digital converter 29 by the clock Jo and control logic 30. Therefore, any drift in the analog-to-digital converter 20 characteristics occurs equality in current and voltage channels. The digitized current and voltage signals from the analog-to-digital converter 29 are digitally encoded into transmission code by the digital encoder 31 whose output go s to line driver 32 m e line driver 32 is connected to the surface via the central conductor of multi conductor cable 15.
The central conductor has been fount to allow rapid transmission of digital signals without spurious cable reflections.
At the surface, the digital current and voltage signals are received by digital receiver 33, which decades the transmission code. The digital receiver supplies the current and voltage signals to the digital computer which computes spontaneous potential, resistivity and phase shift. The computer is con-netted to recording means 38 and storage means 39. me digital receiver 33 is also connected to digital-to-analog converter 35, which converts the digital current and voltage signals to analog form m e analog current and voltage signals from the digital-to analog converter 35 go to analog phase meter 36 which measures spontaneous potential (SUP), resistivity (R) and phase shift (9).
The output from analog phase moire 36 is recorded by recording means 37. A depth encoder 40 inputs depth information from the winch snot shown) to thy cc~puterO
The silver/silver chloride electrode shown in Figure 2 consists of a housing 50 having a silver electrode 51 disposed therein. m e surface of the silver electrode is converted to silver chloride by chloridization. The silver electrode is secured to the end of an electrode element 52 that projects outside of the housing. The electrode clement is sealed in the housing by an "oaring 53 that is compressed by a threaded packing gland 54. The volume 56 of the housing is filled with a saturated potassium chloride reference solution. A porous fruit 55 in the end of the housing allows the potassium chloride solution to contact the Barlow fluid.
I
g Now, concerning the operation of the logging apparatus in Figure 1, the AC current source supplies a constant amplitude alternating current of few frequency in the range .001 lo Ho, and preferably between 1 and 10 Ho. The frequency is usually selected less than 100 Ho to prevent phase shifts from inductive coupling in the earth formation. If the frequency is too few, the logging speed becomes prohibitively long in order to prevent waveform distortion. A logging speed of lo feet per minute has been found satisfactory with an AC current frequency of 10 Ho.
The alternating current is applied both to the survey current electrode A and the focusing electrodes Al and A. The pro-portion of current split between survey and focusing electrodes is controlled by the voltage-controlled resistors 20 and 21, which function as a resistor-di~ider network. eye voltage-controlled resistors are purely resistive so that no phase shifts introduced between the current supplied to the survey current electrode A and the current supplied to the focusing electrodes Al and A. me current injected into the formation through the survey current electrode is measured across the reference resistor R0. In a homogeneous and isotropic earth formation, the resistance ratio of voltage-controlled resistor 20 to volkaga-controlled resistor 21 is approximately:
VFl~VRO - 0.5 ~n2-1)2 on where n is the ratio of the AYE distance to the MOE distance (The reference resistors an formation resistance is assumed to be small relative to the voltage-controlled resistors). However, opposite a thin resistive bed, the resistance of voltage-controlled resistor 20 is reduced relative to voltage-controlled resistor 21 in order to inject more current into focusing electrodes Al and A than into A. reference resistor R1 can be used to monitor the focusing current (not shown). Values of reference resistors R0 and R1 ox about 1 Ohm have been found to give satisfactory signal levels. ale differential clmplifier 22 monitors the potential difference between Ml and Ma' and between My and My'. me differential output from differential amplifier 22 adjusts the ratio between current injected in-to survey current electrode A and current injected into focusing electrodes Al and A. This is accomplished by varying the resistance ratio between voltage-controlled resistors 20 and 21 until the potential difference between Ml and Ml' and My and My' is substantially equal to zero Differential amplifier 22 and voltage-controlled resistors 20 and 21 must have sufficiently fast response relative to the AC current frequency that sub-staunchly zero additional phase shift is added by this control loop.
m e survey current and the generated earth potential are both measured and digitized dcwnhole. This avoids sending analog signals to the surface which would suffix large phase shifts from cable capacitance. A clock frequency of 4.4 OH has been found satisfactory. mix gives a current and voltage sample every 7 milliseconds. The Nyquist frequency is then 71 Ho The lcw-pass filters are of the maxImally-flat Butter worth type and are designed to give at least 48 dub attenuation a the Nyquist frequency. m e analog-to-digital converter must haze sufficient number of bits to achieve substantially low digitization noise.
A 12-bit analog-to-digital converter has been found satisfactory to reduce phase noise below 1 milliradian. m e gain of amplifiers 23 and 24 are automatically adjusted to keep at least eight significant bits at all times by suitable circuit means (not shown).
The digitized current and voltage signals are analyzed by a digital computer 34 which computes resistivity and phase shift of the earth formation from the measured current and voltage dcwnhole. Since the entire current and voltage waveform including both AC and DC cc~ponents) have been digitized, the computer can also compute spontaneous earth potential, SPY
The data received at the surface by the digital receiver 33 will correspond to a series of points txi,yi) on an ellipse as shown in Figure 5. m e vertical offset of the centre of the ellipse is the self potential of the formation while horizontal offset is the offset current. By proper control of AC input signal a zero current offset can be achieved The present invention allows focusing of the survey current in the horizontal plane, so that the measured resistivity and the measured phase shift are substantially those of the formation adjacent to the tool. m e focused induced polarization tool obtains substantially more accurate induced polarization measure-mints of the earth formation when the formation resistivity is much greater than the mud resistivity. Still another advantage of this focused induced polarization apparatus is the accurate response to thin resistive beds.
It should be apparent to one skilled in the art that various modifications of the basic implementation shown in Figure 1 are possible without violating the essence of this invention. Thus, the phasemetre and cc~puter located at the surface could also have been located Donnelly within house my 14.
In this case, digital transmission to the surface is not required. Another v æ ration is the use of one of the monitoring electrodes Ma, Ma' or My, My' as the voltage measuring electrode instead of using a separate voltage measuring electrode My.
Also, within the spirit of this invention are other focused electrode arrays, such as the embed m en shown in Figure 3. In this arrangement the survey current electrode A is divided into two electrodes A and A' and the voltage measurement electrode My is placed between the two electrodes A and A'. This arrange-mint has the advantage of tailoring current applied to the formation to obtain improved response from thin beds. The two survey current electrodes will provide a different focused pancake current pattern that has three positions of zero potential difference, i.e., between Ml-Ma', M2-M2' and My. The I to - I -spacing between the survey current electrodes can be adjusted to determine the thickness of a thin bed that can be measured ace-rarely. Still another embodiment would allow separate dip-ferential amplifiers for each pair of monitor electrodes My, Ml' and My, My' as shown in Figure 4. This arrangement allows independent control of the focusing elec~rcdes Al and A that will compensate for any distortion of the current field caused by resistance i~hcmo~eneity in the formation. For example, if a thin bed has a high resistivity formation on one side and low resistivity formation on the other side, the current field will be distorted with the apparatus of Figure 1. The system Chicano in Figure 4 will compensate for this distortion and provide a more uniform current flow through the thin bed. The dynamic range required from voltage-eontrolled resistors is also reduced in this configuration in contrast to Figure 1.
Still another embodiment would utilize long cylindrical guard current electrodes, as shown in Figure 6, in place of the mc~ltor electrodes My, My' and My, My'. The current guard electrodes Al and A in Figure are elee~rieal conductors in contact with the Barlow fluid and therefore autom~tieally have zero potential difference along thwacks length. Current guard electrodes Al and A are electrically connected by a wire of negligible resistance which maintains them at the same potential. m e current guard electrodes Al and A are physically and electrically separated frock the split survey current electrodes A and A' by thin insulating disks. The voltage measurement electrode My is located midway kitten split s~vey current electrodes A and A' and is electrically insulated frock A and A' by thin insulating disks. The split survey current electrodes A and A' are electrically connected by a wire of negligible resistance which maintains them at the same potential.
The total length L of the long cylindrical focusing array must be greater than the Sunday diameter to Obtain good current focusing. In practice, L can be made approximately 10 feet ~3.05 m). me total length Q of the split survey current electrode must be much less than L, for example, to 1 foot (0.15 to 0.30 m). m e 1 ngth Q will be the minlm~n thickness of thin bed that can be accurately measured by the focused induced polarization tool.
The major advantage of the long cylindrical focused electrode array is the tighter focusing of the survey current beam in the vertical direction. This allows thinner beds to be accurately measured than with the array shown in Figure 3.
Still another modification is the use of a different type of input current signal, such as a square wave, triangular wave, time-dcmain waveform (i.e., bipolar square wave with dead time) or multi frequency rather than the sinusoidal current waveform disclosed in this embodiment. These and similar modifications are to be construed as covered within this invention.
.
Claims (13)
1. An induced polarization logging tool for measuring para-meters of a formation surrounding a borehole, said logging tool comprising:
a plurality of electrodes disposed on a non-conductive logging sonde, said electrodes including at least a survey current electrode and two focusing electrodes disposed on opposite sides of said survey current electrode, monitoring electrodes, a voltage measuring electrode and voltage reference and current return electrodes;
circuit means coupled to said monitoring electrodes for monitoring the current flow in the formation between the survey current and focusing electrodes;
a first current control means directly coupled to said survey current electrode and said circuit means for control of the current flow to said survey current electrode in response to and in phase with the monitored current flow;
a second current control means directly coupled to said focusing electrodes to control the current flow to said focusing electrodes in response to and in phase with the monitored current flow;
a source of alternating current located at the surface, one end of said source being coupled to the two current control means and the other to the current return electrodes, said source being capable of supplying alternating current at various discrete frequencies;
measurement means directly coupled to said voltage measure-ment and survey current electrodes to measure the amplitude and phase of the voltage induced in the formation and the amplitude and phase of the current flow to the survey current electrode;
and transmission means for transmitting said measurements to the surface.
a plurality of electrodes disposed on a non-conductive logging sonde, said electrodes including at least a survey current electrode and two focusing electrodes disposed on opposite sides of said survey current electrode, monitoring electrodes, a voltage measuring electrode and voltage reference and current return electrodes;
circuit means coupled to said monitoring electrodes for monitoring the current flow in the formation between the survey current and focusing electrodes;
a first current control means directly coupled to said survey current electrode and said circuit means for control of the current flow to said survey current electrode in response to and in phase with the monitored current flow;
a second current control means directly coupled to said focusing electrodes to control the current flow to said focusing electrodes in response to and in phase with the monitored current flow;
a source of alternating current located at the surface, one end of said source being coupled to the two current control means and the other to the current return electrodes, said source being capable of supplying alternating current at various discrete frequencies;
measurement means directly coupled to said voltage measure-ment and survey current electrodes to measure the amplitude and phase of the voltage induced in the formation and the amplitude and phase of the current flow to the survey current electrode;
and transmission means for transmitting said measurements to the surface.
2. The induced polarization logging tool of claim 1, wherein said circuit means comprises a differential-in/differential-out amplifier and said first and second current control means comprise voltage variable resistances.
3. The induced polarization logging tool of claim 2, wherein said monitoring electrodes comprise an upper and lower pair of electrodes, one pair being located on each side of said survey current electrode, said voltage measuring electrode being disposed between one pair of said monitoring electrodes.
4. The induced polarization logging tool of claim 3, wherein said circuit means includes a pair of differential-in/differen-tial-out amplifiers, one of said amplifiers having its input coupled to one pair of said monitoring electrodes, the other of said amplifiers having its input coupled to the other pair of said monitoring electrodes, said amplifiers jointly controlling said first current control means and individually controlling the second current control means to individually control the focusing electrode adjacent the pair of monitoring electrodes connected to said individual amplifier.
5. The induced polarization logging tool of claim 3, wherein the upper and lower focusing electrodes are placed at equal distances on each side of said survey current electrodes, the upper and lower pairs of monitoring electrodes are placed between the survey current and focusing electrodes on either side of said survey current electrode, the voltage measurement electrode is located between one pair of said monitoring electrodes, and the voltage reference and current return electrodes are both located at a greater distance from said survey current electrode than said focusing electrodes.
6. The induced polarization logging tool of claims 1 and 5, wherein said circuit means comprise a differential-in/
differential-out amplifier, one monitoring electrode of each pair being direct coupled to one input of the amplifier, the other monitoring electrode of each pair being direct coupled to the other input of said amplifier, the first output of said differential-in/differential-out amplifier being direct coupled to said first current control means and the second output of said differential-in/differential-out amplifier being direct coupled to said second current control means; the circuit means further comprising a reference resistor coupling the survey current electrode to said first current control means; said measurement means comprising first measurement means direct coupled to the voltage measurement and voltage reference electrodes to measure amplitude and phase of the voltage induced in the formation, and second measurement means direct coupled across the reference resistor to measure the amplitude and phase of the current flow to said survey current electrode; and said transmission means being coupled to said first and second measurement means to transmit said voltage and current measurements to the surface.
differential-out amplifier, one monitoring electrode of each pair being direct coupled to one input of the amplifier, the other monitoring electrode of each pair being direct coupled to the other input of said amplifier, the first output of said differential-in/differential-out amplifier being direct coupled to said first current control means and the second output of said differential-in/differential-out amplifier being direct coupled to said second current control means; the circuit means further comprising a reference resistor coupling the survey current electrode to said first current control means; said measurement means comprising first measurement means direct coupled to the voltage measurement and voltage reference electrodes to measure amplitude and phase of the voltage induced in the formation, and second measurement means direct coupled across the reference resistor to measure the amplitude and phase of the current flow to said survey current electrode; and said transmission means being coupled to said first and second measurement means to transmit said voltage and current measurements to the surface.
7. The induced polarization logging tool of claim 1, wherein said transmission means include analog-to-digital conversion means for converting the voltage and current measurements to related digital quantities for transmission to the surface, the conversion means comprising a pair of track-and-hold circuits, one for measuring the amplitude and phase of the induced voltage and the other for measuring the amplitude and phase of the current, both said track-and-hold circuits being controlled by a single logic circuit.
8. The induced polarization logging tool of claim 1, wherein said survey current electrode is divided into two electrodes and connected by a wire of negligible resistance and said voltage measurement electrode is positioned between said two survey current electrodes.
9. The induced polarization logging tool of claim 1, wherein said measuring electrode, reference electrode, and monitoring electrodes are non-polarizable silver/silver chloride electrodes.
10. The induced polarization logging tool of claim 1, wherein said source of alternating current is a time-domain source, said source being capable of supplying alternating current at various discrete frequencies between 0.01 and 100 Hz.
11. An induced polarization logging tool for measuring parameters of a formation surrounding a borehole, said logging tool comprising:
a non-conductive logging sonde;
a plurality of electrodes disposed on said sonde, said electrodes including at least a survey current electrode and guard electrodes disposed on opposite sides of said survey current electrode, a voltage measuring electrode and reference and current return electrodes;
a first control means directly coupled to said survey current electrode, said control means controlling the current flow to said survey current electrode in response to and in phase with the monitored current flow;
a second control means directly coupled to said guard electrodes to control the current flow to said guard electrodes in response to and in phase with the monitored current flow:
a source of alternating current located at the surface, one end of said source being coupled to the two current control means and the other to the current return electrodes, said source being capable of supplying alternating current at various discrete frequencies between 0.01 and 100 Hz;
measurement means directly coupled to said voltage measure-ment and survey current electrodes to measure the amplitude and phase of the voltage induced in the formation and the amplitude and phase of the current flow to the survey current electrode;
and transmission means for transmitting said measurements to the surface.
a non-conductive logging sonde;
a plurality of electrodes disposed on said sonde, said electrodes including at least a survey current electrode and guard electrodes disposed on opposite sides of said survey current electrode, a voltage measuring electrode and reference and current return electrodes;
a first control means directly coupled to said survey current electrode, said control means controlling the current flow to said survey current electrode in response to and in phase with the monitored current flow;
a second control means directly coupled to said guard electrodes to control the current flow to said guard electrodes in response to and in phase with the monitored current flow:
a source of alternating current located at the surface, one end of said source being coupled to the two current control means and the other to the current return electrodes, said source being capable of supplying alternating current at various discrete frequencies between 0.01 and 100 Hz;
measurement means directly coupled to said voltage measure-ment and survey current electrodes to measure the amplitude and phase of the voltage induced in the formation and the amplitude and phase of the current flow to the survey current electrode;
and transmission means for transmitting said measurements to the surface.
12. The induced polarization logging tool of claim 11, wherein said guard electrodes are long cylindrical electrodes in contact with the borehole fluid and electrically connected to each other.
13. The induced polarization logging tool of claim 12, wherein said guard electrodes have a total length of at least 10 times greater than the sonde diameter.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/505,623 US4583046A (en) | 1983-06-20 | 1983-06-20 | Apparatus for focused electrode induced polarization logging |
| US505,623 | 1983-06-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1231377A true CA1231377A (en) | 1988-01-12 |
Family
ID=24011124
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000454307A Expired CA1231377A (en) | 1983-06-20 | 1984-05-15 | Apparatus for focusing electrode induced polarization logging |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4583046A (en) |
| JP (1) | JPS6014190A (en) |
| AU (1) | AU569004B2 (en) |
| CA (1) | CA1231377A (en) |
| FR (1) | FR2548388B1 (en) |
| GB (1) | GB2146125B (en) |
| NO (1) | NO160480C (en) |
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| CA2930251C (en) * | 2012-11-20 | 2019-10-29 | Rutgers, The State University Of New Jersey | Intelligent spectral induced polarization measurement module |
Family Cites Families (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2592125A (en) * | 1949-11-18 | 1952-04-08 | Schlumberger Well Surv Corp | Method and apparatus for logging static spontaneous potentials in wells |
| US2824279A (en) * | 1953-01-19 | 1958-02-18 | Schlumberger Well Surv Corp | Control circuit for electrical logging apparatus |
| US2988690A (en) * | 1956-08-17 | 1961-06-13 | Newmont Mining Corp | Method and apparatus for geophysical exploration |
| US2884590A (en) * | 1956-10-16 | 1959-04-28 | Schlumberger Well Surv Corp | Electrical well logging systems |
| US3132298A (en) * | 1959-06-16 | 1964-05-05 | Schlumberger Well Surv Corp | Methods and apparatus for investigating earth boreholes by means of electrodes constructed to contact the borehole walls |
| US3054046A (en) * | 1959-09-17 | 1962-09-11 | Seismograph Service Corp | Electrodes for electrical well logging |
| GB1071414A (en) * | 1963-01-10 | 1967-06-07 | British Petroleum Co | Method of and apparatus for logging boreholes |
| FR2128200B1 (en) * | 1971-03-11 | 1974-03-01 | Schlumberger Prospection | |
| US4087739A (en) * | 1974-07-22 | 1978-05-02 | Schlumberger Technology Corporation | Earth formation permeability determining technique using synthetic resistivity parameters |
| JPS5433866A (en) * | 1977-08-22 | 1979-03-12 | Babcock Hitachi Kk | Method and device for cooling reducing agent injection tube |
| US4122387A (en) * | 1977-08-24 | 1978-10-24 | Halliburton Company | Apparatus and method for simultaneously logging an electrical characteristic of a well formation at more than one lateral distance from a borehole |
| GB2019004B (en) * | 1978-01-21 | 1982-12-08 | Schlumberger Ltd | Well logging methods and apparatus |
| US4282486A (en) * | 1978-12-04 | 1981-08-04 | Dresser Industries, Inc. | Dual focused resistivity logging method and apparatus with dynamic range reduction |
| US4335353A (en) * | 1979-06-18 | 1982-06-15 | Schlumberger Technology Corporation | Method and apparatus for detecting an anomaly in a resistivity measurement of an earth formation |
| US4359687A (en) * | 1980-01-25 | 1982-11-16 | Shell Oil Company | Method and apparatus for determining shaliness and oil saturations in earth formations using induced polarization in the frequency domain |
| US4471307A (en) * | 1982-04-02 | 1984-09-11 | Halliburton Company | Amplitude modulated resistivity logging system |
| US4578675A (en) * | 1982-09-30 | 1986-03-25 | Macleod Laboratories, Inc. | Apparatus and method for logging wells while drilling |
-
1983
- 1983-06-20 US US06/505,623 patent/US4583046A/en not_active Expired - Fee Related
-
1984
- 1984-05-15 CA CA000454307A patent/CA1231377A/en not_active Expired
- 1984-06-18 GB GB08415495A patent/GB2146125B/en not_active Expired
- 1984-06-18 AU AU29479/84A patent/AU569004B2/en not_active Ceased
- 1984-06-18 JP JP59125004A patent/JPS6014190A/en active Pending
- 1984-06-18 NO NO842439A patent/NO160480C/en unknown
- 1984-06-18 FR FR8409498A patent/FR2548388B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NO160480C (en) | 1989-04-19 |
| FR2548388A1 (en) | 1985-01-04 |
| AU2947984A (en) | 1985-01-03 |
| NO160480B (en) | 1989-01-09 |
| GB8415495D0 (en) | 1984-07-25 |
| JPS6014190A (en) | 1985-01-24 |
| AU569004B2 (en) | 1988-01-14 |
| NO842439L (en) | 1984-12-21 |
| FR2548388B1 (en) | 1988-07-08 |
| GB2146125B (en) | 1987-07-15 |
| US4583046A (en) | 1986-04-15 |
| GB2146125A (en) | 1985-04-11 |
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