US3772589A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Apparatus for determining the resistivity of a subsurface earth formation at different lateral distances from a bore hole wall
Assignee: Schlumberger Technology Corp
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Filing: 1972-03-10
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Granted: 1973-11-13
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Expires: 1992-03-10
Abstract
Abstract Apparatus for investigating subsurface earth formations traversed by a borehole comprising a system of electrodes consisting of a central electrode Ao and four pairs of electrodes M1-M''1, M2-M''2, A1-A''1, A2-A''2 respectively short-circuited and aligned symmetrically on both sides of the electrode Ao. This apparatus comprises arrangements which, for a frequency f2, establish a potential gradient between electrodes A1-A''1 and A2A''2. A source of alternating current of frequency f1 is connected between the electrodes A1-A''1 and A2-A''2 and a source of alternating current of frequency f2 between a surface electrode B and electrodes A2-A''2. The potential difference between electrodes M1-M2 and M''1-M''2 is maintained substantially at zero by circulating a current between electrodes A1-A''1 and electrode Ao. Such an apparatus allows simultaneous measurement in a borehole of the electrical resistivities of the subsurface earth formations extending over relatively small and relatively large lateral distances from the wall of the borehole.
Inventors
- 👤 A Scholberg
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 18:40
CPC Classifications
G; G01; G01V; G01V3/00; G01V3/18; G01V3/20; G01V3/24
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
233 words
An apparatus for the electrical investigation of earth formations traversed by a borehole, comprising: a. an electrode system comprising a central electrode and four pairs of electrodes respectively short-circuited and aligned symmetrically about said central electrode at increasing distances therefrom, the central electrode and the electrodes of the third and fourth pairs being called current electrodes, the electrodes of the first and second pairs being called voltage electrodes; b. means for producing an alternating current at a first frequency, f1, coupled between the electrodes of the fourth pair and at least one of the other current electrodes; c. means for producing an alternating current at a second frequency, f2, coupled between one of the current electrodes and an electrode at electrical infinity with respect to the electrode system; d. means for maintaining the potential difference between the first and second pairs of electrodes at substantially zero, said means adapted to monitor the potential difference between the first and second pairs of electrodes and to emit current from the central current emitting electrode in response to the measured potential difference to reduce the potential difference to zero; and e. means for measuring the electrical potential proximate to one of the first and second pairs of electrodeS and the current emitted from the central electrode to produce therefrom signals representative of the electrical resisitivity of the formation located at different lateral distances from the borehole.
Claim 2
Independent Claim
233 words
An apparatus for the electrical investigation of earth formations traversed by a borehole, comprising: a. an electrode system comprising a central electrode and four pairs of electrodes respectively short-circuited and aligned symmetrically about said central electrode at increasing distances therefrom, the central electrode and the electrodes of the third and fourth pairs being called current electrodes, the electrodes of the first and second pairs being called voltage electrodes; b. means for producing an alternating current at a first frequency, f1, coupled between the electrodes of the fourth pair and at least one of the other current electrodes; c. means for producing an alternating current at a second frequency, f2, coupled between one of the current electrodes and an electrode at electrical infinity with respect to the electrode system; d. means for maintaining the potential difference between the first and second pairs of electrodes at substantially zero, said means adapted to monitor the potential difference between the first and second pairs of electrodes and to emit current from the central current emitting electrode in response to the measured potential difference to reduce the potential difference to zero; and e. means for measuring the electrical potential proximate to one of the first and second pairs of electrodeS and the current emitted from the central electrode to produce therefrom signals representative of the electrical resisitivity of the formation located at different lateral distances from the borehole.
Claim 3
Dependent Claim
52 words
The apparatus of claim 1 wherein said means for producing an alternating current at frequency f1 is coupled between said third and fourth pairs of electrodes and said means for producing an alternating current at frequency f2 is coupled between the fourth pair of current electrodes and the electrode at electrical infinity.
Claim 4
Dependent Claim
31 words
The apparatus of claim 2 further comprising means for maintaining at the frequency f2 a potential gradient of predetermined value between the electrodes of the third and fourth pairs of electrodes.
Claim 5
Dependent Claim
26 words
The apparatus of claim 3 wherein the potential gradient between the third and fourth pairs of electrodes at frequency f2 is maintained at substantially zero volts.
Claim 6
Dependent Claim
108 words
The apparatus of claim 3 wherein the means for maintaining a predetermined potential gradient between the third and fourth pairs of electrodes comprises; a. a fifth pair of electrodes positioned one on each side of the central electrode between the third and fourth pairs of electrodes; and b. means for measuring the potential gradient at frequency f2 between the fourth and fifth pairs of electrodes and adapted to supply a current to the formation at the frequency f2 in response to the potential difference between the fourth and fifth pairs of electrodes to maintain the potential difference between the fourth and fifth electrodes at the predetermined potential gradient.
Claim 7
Independent Claim
257 words
An apparatus for investigating earth formations traversed by a borehole, comprising: a. a plurality of electrodes adapted for movement through a borehole, said electrodes comprising a central current emitting electrode, first and second pairs of potential monitoring electrodes positioned on opposite sides of the central electrode and first and second pairs of current electrodes positioned on opposite sides of the central current emitting electrode and further from the central electrode than the potential monitoring electrodes; b. means for producing a current at frequency f1 coupled between the first and second pairs of current emitting electrodes; c. means for producing a current at frequency f2 coupled between the second pair of current emitting electrodes and a point at electrical infinity from said plurality of electrodes; d. means for maintaining the impedance between the first and second pair of current emitting electrodes at frequency f2 substantially equal to zero; e. means for maintaining the potential difference between the first and second pairs of potential monitoring electrodes substantially at zero volts said means adapted to monitor the potential difference between the first and second pairs of potential electrodes and to supply current from the central current emitting electrode in response to the potential difference between the first and second pairs of potential electrodes to maintain the potential difference substantially equal to zero; and f. means for measuring the potential proximate to the potential monitoring electrodes and the current emitted from the central electrode and to provide output signals representative of the resisitivity at different lateral distances from the borehole wall.
Claim 8
Independent Claim
257 words
An apparatus for investigating earth formations traversed by a borehole, comprising: a. a plurality of electrodes adapted for movement through a borehole, said electrodes comprising a central current emitting electrode, first and second pairs of potential monitoring electrodes positioned on opposite sides of the central electrode and first and second pairs of current electrodes positioned on opposite sides of the central current emitting electrode and further from the central electrode than the potential monitoring electrodes; b. means for producing a current at frequency f1 coupled between the first and second pairs of current emitting electrodes; c. means for producing a current at frequency f2 coupled between the second pair of current emitting electrodes and a point at electrical infinity from said plurality of electrodes; d. means for maintaining the impedance between the first and second pair of current emitting electrodes at frequency f2 substantially equal to zero; e. means for maintaining the potential difference between the first and second pairs of potential monitoring electrodes substantially at zero volts said means adapted to monitor the potential difference between the first and second pairs of potential electrodes and to supply current from the central current emitting electrode in response to the potential difference between the first and second pairs of potential electrodes to maintain the potential difference substantially equal to zero; and f. means for measuring the potential proximate to the potential monitoring electrodes and the current emitted from the central electrode and to provide output signals representative of the resisitivity at different lateral distances from the borehole wall.
Claim 9
Dependent Claim
98 words
The apparatus of claim 6 wherein the means for producing currents at frequencies f1 and f2 comprise: a. a current amplifier, the output of the amplifier being coupled between the first and second pairs of current electrodes and having an output impedance substantially equal to zero at the frequency f2; b. a source of alternating current of frequency f1 coupled to the input of the current amplifier; and c. a source of alternating current of frequency f2 coupled betwen the second pair of current elEctrodes and a point at a substantial electrical distance from the plurality of electrodes.
Claim 10
Dependent Claim
32 words
The apparatus of claim 7 wherein the sources of alternating current of frequencies f1 and f2 each comprise a variable gain amplifier allowing an adjustment of the amplitude of the said currents.
Claim 11
Dependent Claim
18 words
The apparatus of claim 8 wherein said sources of alternating current of frequencies f1 and f2 are synchronized.
Claim 12
Dependent Claim
143 words
The apparatus of claim 6 wherein the means for maintaining the impedance of frequency f2 between the first and second pairs of current electrodes substantially equal to zero, comprises: a. a third pair of electrodes positioned between said first and second pairs of current emitting electrodes; and b. current amplifier means having an input coupled between the second pair of current emitting electrodes and the third pair of electrodes and an output coupled between the first and second pairs of current emitting electrodes, the amplifier means being adapted to supply current at frequency f2 to the formation in response to a potential difference at frequency f2 measured between the second pair of current emitting electrodes and the third pair of electrodes to maintain the potential difference between the first and second pairs of current emitting electrodes at frequency f2 substantially equal to zero.
Claim 13
Dependent Claim
110 words
The apparatus of claim 6 further comprising: a. means coupled to said current and voltage measuring means adapted to separate the measured currents and voltages into components at frequencies f1 and f2 and to provide signals representative of the current and voltage at frequencies f1 and f2; b. means adapted to receive the current and voltage signals at frequency f1 and to provide a first output signal representative of the resistivity of a first zone in the formation; and c. means adapted to receive the current and voltage signals at frequency f2 and to provide a second output signal representative of the resisitivity of a second zone in the formation.
Claim 14
Dependent Claim
30 words
The apparatus of claim 11 further comprising means adapted to receive said first and second output signals for recording said first and second output signals as a function of depth.
Claim 15
Dependent Claim
28 words
The apparatus of claim 12 wherein one of the input terminals of the said voltage measuring means is connected to the electrodes of the second pair of electrodes.
Claim 16
Dependent Claim
112 words
The apparatus of claim 11 wherein the means adapted to separate the measured current and voltage signals comprise: a. two frequency modulators, the input of one coupled to the output of the voltage measuring means and the input of the other coupled to the output of the current measuring means and operating respectively at frequencies f3 and f4; b. two filters coupled respectively to the outputs of the modulators, one filter adapted to pass the signals of frequency f3 and the other filter adapted to pass the signals of frequency f4; and c. two demodulators coupled to the outputs of the filters adapted to demodulate the signals at frequencies f3 and f4.
Claim 17
Dependent Claim
124 words
The apparatus of claim 11 further comprising means adapted to receive said current and voltage signals at frequency f1 and to produce a first error signal representative of the difference between the product of the voltage multiplied by the current and a reference value and means adapted to receive the current and voltage signals at frequency f2 and to produce a second error signal representative of the difference between the product of the voltage multiplied by the current and a reference value, said first and second error signals being supplied respectively to the sources of alternating current of frequencies f1 and f2 to control the gain of the output of said sources to as to keep the product of the current and voltage constanT.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-11-12 | 1977-05-14 | 1977-11-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-11-12 | 1981-05-14 | 1981-11-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-11-12 | 1985-05-14 | 1985-11-13 | $7700.00 | Window Closed / Lapsed |