US3702436A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Methods and apparatus for investigating the spontaneous potential of earth formations
Assignee: Scientific Atlanta LLC
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Filing: 1971-10-26
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Granted: 1972-11-07
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Expires: 1991-10-26
Abstract
Abstract In accordance with illustrative embodiments of the present invention, a technique is disclosed for substantially eliminating noise from measurements of the spontaneous potential made in a borehole drilled into the earth. An exploring device in the borehole carries two closely spaced electrodes and the potential is measured between these two electrodes to provide a first differential type measurement as a function of the movement of the electrodes. A converting circuit converts this first measurement from a function of such movement to a function of time. The potential between one of these two electrodes and a remote point is measured to produce a second measurement. The converted first measurement and the second measurement are combined to provide a substantially error free spontaneous potential measurement. To compensate for errors produced in the converting circuit by acceleration of the electrodes, the low frequency components of the first measurement are eliminated prior to combining the two measurements.
Inventors
- 👤 Billy G Pollard
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 10:25
CPC Classifications
G; G01; G01R; G01R23/00
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
200 words
Apparatus for investigating earth formations traversed by a borehole, comprising: a. support means adapted to carry at least one electrode through a borehole; b. a cable supporting said support means for movement through a borehole; c. means for measuring the potential gradient over a distance in the borehole in the vicinity of said at least one electrode to produce a first measurement; d. means for measuring the difference between the potential at said at least one electrode and the potential at a relatively remote point to produce a second measurement; and e. means for combining said first and second measurements to produce an output signal which is representative of a formation characteristic, said combining means including means responsive to the velocity (dZ/dt) of said cable through said borehole for converting said first measurement from a function of distance (dZ) to a function of time (dt), thereby to permit said combining means to operate as a function of time, first filter means for filtering out the low-frequency components of said first measurement to produce a filtered first measurement, and means for subsequent frequency selective combination of said converted, filtered first measurement with said second measurement to thereby produce said output signal.
Claim 2
Dependent Claim
200 words
Apparatus for investigating earth formations traversed by a borehole, comprising: a. support means adapted to carry at least one electrode through a borehole; b. a cable supporting said support means for movement through a borehole; c. means for measuring the potential gradient over a distance in the borehole in the vicinity of said at least one electrode to produce a first measurement; d. means for measuring the difference between the potential at said at least one electrode and the potential at a relatively remote point to produce a second measurement; and e. means for combining said first and second measurements to produce an output signal which is representative of a formation characteristic, said combining means including means responsive to the velocity (dZ/dt) of said cable through said borehole for converting said first measurement from a function of distance (dZ) to a function of time (dt), thereby to permit said combining means to operate as a function of time, first filter means for filtering out the low-frequency components of said first measurement to produce a filtered first measurement, and means for subsequent frequency selective combination of said converted, filtered first measurement with said second measurement to thereby produce said output signal.
Claim 3
Dependent Claim
65 words
The apparatus of claim 1 wherein said converting means is operative to convert said filtered first measurement from a function of distance (dZ) to a function of time (dt) to produce a filtered, converted first measurement, and said combining means includes second filter means responsive to said filtered, converted first measurement and said second measurement for producing said output signal representative of a Formation characteristic.
Claim 4
Dependent Claim
196 words
Apparatus for investigating earth formations traversed by a borehole, comprising: a. support means adapted to carry at least two electrodes separated by a distance a through a borehole, b. a cable support means for movement through a borehole; c. means for measuring the difference between the potentials on said two electrodes to produce a first measurement Delta SP; d. means for measuring the difference between the potential on one of said two electrodes and the potential at a relatively remote point to produce a second measurement SP; e. filter means for filtering out the low frequency components of said first measurement to produce a filtered first measurement e1, said filter means having a transfer function of ST3/1 + ST3 where S is the Laplace operator, and T3 is the time constant of said filter means; and f. combining means responsive to the velocity (dZ/dt) of said cable through the borehole for combining said first and second measurements to produce an output signal e0 which is representative of a formation characteristic and defined by the expression where T1 and T2 are time constants given by said combining means, and u is the velocity (dZ/dt) of said cable.
Claim 5
Dependent Claim
196 words
Apparatus for investigating earth formations traversed by a borehole, comprising: a. support means adapted to carry at least two electrodes separated by a distance a through a borehole, b. a cable support means for movement through a borehole; c. means for measuring the difference between the potentials on said two electrodes to produce a first measurement Delta SP; d. means for measuring the difference between the potential on one of said two electrodes and the potential at a relatively remote point to produce a second measurement SP; e. filter means for filtering out the low frequency components of said first measurement to produce a filtered first measurement e1, said filter means having a transfer function of ST3/1 + ST3 where S is the Laplace operator, and T3 is the time constant of said filter means; and f. combining means responsive to the velocity (dZ/dt) of said cable through the borehole for combining said first and second measurements to produce an output signal e0 which is representative of a formation characteristic and defined by the expression where T1 and T2 are time constants given by said combining means, and u is the velocity (dZ/dt) of said cable.
Claim 6
Independent Claim
165 words
A method of investigating earth formations traversed by a borehole, comprising: a. moving at least one electrode through a borehole; b. measuring the potential gradient over a distance in the borehole in the vicinity of said at least one electrode to produce a first measurement; c. measuring the difference between the potential on said at least one electrode and the potential at a relatively remote point to produce a second measurement; and d. combining said first and second measurements to produce an output signal which is representative of a formation characteristic, including (1) filtering out the low-frequency components of said first measurement to produce a filtered first measurement, (2) converting said filtered first measurement from a function of distance (dZ) to a function of time (dt), thereby permitting the combining of said first and second measurements to be carried out as a function of time, and (3) frequency selectively combining said converted, filtered first measurement with said second measurement to thereby produce said output signal.
Claim 7
Independent Claim
165 words
A method of investigating earth formations traversed by a borehole, comprising: a. moving at least one electrode through a borehole; b. measuring the potential gradient over a distance in the borehole in the vicinity of said at least one electrode to produce a first measurement; c. measuring the difference between the potential on said at least one electrode and the potential at a relatively remote point to produce a second measurement; and d. combining said first and second measurements to produce an output signal which is representative of a formation characteristic, including (1) filtering out the low-frequency components of said first measurement to produce a filtered first measurement, (2) converting said filtered first measurement from a function of distance (dZ) to a function of time (dt), thereby permitting the combining of said first and second measurements to be carried out as a function of time, and (3) frequency selectively combining said converted, filtered first measurement with said second measurement to thereby produce said output signal.
Claim 8
Independent Claim
171 words
A method of investigating the spontaneous potential of earth formations traversed by a borehole, comprising: a. carrying at least two electrodes through a borehole with a cable; b. measuring the difference between the potentials at said two electrodes to produce a first measurement which is proportional to dV/dZ, where V is potential and Z is distance; c. measuring the difference between the potential at one of said two electrodes and the potential at a relatively remote point to produce a second measurement; d. filtering out the low frequency components of said first measurement to produce a filtered first measurement; e. detecting the velocity (dZ/dt) of movement of said cable through the borehole; f. employing said velocity detection to convert said filtered first measurement from a function of distance (dZ) to a function of time (dt) to produce a converted, filtered first measurement; and g. frequency selectively combining said converted, filtered first measurement with said second measurement to produce a measure of the spontaneous potential in the formation adjacent said two electrodes.
Claim 9
Independent Claim
171 words
A method of investigating the spontaneous potential of earth formations traversed by a borehole, comprising: a. carrying at least two electrodes through a borehole with a cable; b. measuring the difference between the potentials at said two electrodes to produce a first measurement which is proportional to dV/dZ, where V is potential and Z is distance; c. measuring the difference between the potential at one of said two electrodes and the potential at a relatively remote point to produce a second measurement; d. filtering out the low frequency components of said first measurement to produce a filtered first measurement; e. detecting the velocity (dZ/dt) of movement of said cable through the borehole; f. employing said velocity detection to convert said filtered first measurement from a function of distance (dZ) to a function of time (dt) to produce a converted, filtered first measurement; and g. frequency selectively combining said converted, filtered first measurement with said second measurement to produce a measure of the spontaneous potential in the formation adjacent said two electrodes.
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) | 1975-11-07 | 1976-05-08 | 1976-11-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-11-07 | 1980-05-08 | 1980-11-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-11-07 | 1984-05-08 | 1984-11-07 | $7700.00 | Window Closed / Lapsed |