Patent US3838335A successfully refreshed from Google Patents.
US3838335A
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US
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Method and apparatus for determining the presence of and depth to a horizontal electrical resistivity contrast beneath the earth surface
Assignee: ConocoPhillips Co
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Filing: 1973-02-23
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Granted: 1974-09-24
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Expires: 1993-02-23
Abstract
Abstract Method and apparatus for determining the presence of and depth to a horizontal electrical resistivity contrast lying beneath the bottom of a borehole. The apparatus comprises a surface generator for applying a low frequency sinusoidal current between a long downhole current electrode unit and a distant surface current electrode. The apparatus further includes a voltage-measuring device for recording the resulting potential difference between two long downhole potential electrode units. The centers of the two long downhole potential electrode units are equally spaced several hundred feet above and below the long downhole current electrode unit, respectively. The exact spacing is chosen according to the desired depth of investigation. Another aspect of the apparatus is that the length of each downhole current and potential electrode unit is made equal to about one-tenth the chosen vertical electrode spacing. The method includes measuring the amplitude of the potential difference measured between the two long downhole potential electrode units and displaying in a log-log plot the potential difference over the low frequency sinusoidal current versus the difference of the electrode array above the bottom of the borehole and determining therefrom the distance from the bottom of the borehole to the level of electrical resistivity contrast.
Inventors
- 👤 D Miller
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 05:15
CPC Classifications
G; G01; G01V; G01V3/00; G01V3/18; G01V3/20; G01V3/24
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
192 words
A method of determining the depth of a substantially horizontal electrical resistivity contrast below the bottom of a substantially vertical borehole of known depth extending downwardly from the earth surface, comprising the steps of: inducing a low frequency alternating current in the earth between a first position on the earth surface at a large distance from the borehole and a second position in the borehole a known distance above the bottom of said borehole and a greater distance above the resistivity contrast the depth of which is to be determined; measuring the voltage level at a third position in the borehole a fixed distance above the second position; measuring the voltage level at a fourth position in the borehole a fixed distance below the second position, said fixed distance being substantially equal to the fixed distance between the second and third positions; measuring the current between the first and second positions; measuring the difference in voltage levels at the third and fourth positions; and processing the difference in the measured voltage levels and the measured current to determine the depth of the horizontal electrical resistivity contrast below the bottom of said borehole.
Claim 2
Independent Claim
192 words
A method of determining the depth of a substantially horizontal electrical resistivity contrast below the bottom of a substantially vertical borehole of known depth extending downwardly from the earth surface, comprising the steps of: inducing a low frequency alternating current in the earth between a first position on the earth surface at a large distance from the borehole and a second position in the borehole a known distance above the bottom of said borehole and a greater distance above the resistivity contrast the depth of which is to be determined; measuring the voltage level at a third position in the borehole a fixed distance above the second position; measuring the voltage level at a fourth position in the borehole a fixed distance below the second position, said fixed distance being substantially equal to the fixed distance between the second and third positions; measuring the current between the first and second positions; measuring the difference in voltage levels at the third and fourth positions; and processing the difference in the measured voltage levels and the measured current to determine the depth of the horizontal electrical resistivity contrast below the bottom of said borehole.
Claim 3
Dependent Claim
29 words
The method as defined in claim 1 wherein the frequency of the alternating current induced in the earth is within the range from zero to five cycles per second.
Claim 4
Dependent Claim
17 words
The method as defined in claim 1 wherein the alternating current induced in the earth is sinusoidal.
Claim 5
Dependent Claim
26 words
The method as defined in claim 3 wherein the frequency of the sinusoidal alternating current is within the range from zero to five cycles per second.
Claim 6
Dependent Claim
145 words
The method as defined in claim 4 wherein the fourth position is located a distance ''''x'''' above the bottom of the borehole, the second position is located a distance ''''a'''' above the fourth position, and the third position is the same distance ''''a'''' above the second position, and wherein the step of processing the difference in voltage levels and the measured current comprises the additional step of: converting thE difference in voltage levels and the measured current by approximating a solution to the equation; log V/I log( Rho 1k/4 pi a) + log( 1/(2 x/a + 2 d/a + 1) -1/(2 x/a + 2 d/a + 3)). where '''' Rho 1'''' is the resistivity of an infinite homogeneous medium, ''''k'''' is a constant resistivity reflection factor, and ''''d'''' is the vertical distance from the bottom of the borehole to a substantially horizontal resistivity contrast therebelow.
Claim 7
Dependent Claim
28 words
The method as defined in claim 5 characterized further to include the additional step of: recording log V/I and log x/a; and plotting log V/I vs. log x/a.
Claim 8
Dependent Claim
261 words
Apparatus for determining the depth of a horizontal resistivity contrast below the bottom of a borehole of known depth extending downwardly from the earth surface, comprising: a surface current electrode positioned on the earth surface at a relatively large distance from the borehole; a downhole current electrode disposed within the borehole and spaced a known distance above the bottom of the borehole and a greater distance above the resistivity contrast the depth of which is to be determined; an upper potential electrode disposed within the borehole and spaced a distance above the downhole current electrode; a lower potential electrode disposed within the borehole and spaced a distance below the downhole current electrode, the distance between the lower potential electrode and the downhole current electrode being substantially equal to the distance between the downhole current electrode and the upper potential electrode; the effective lengths of said upper and lower potential electrodes each being equal to approximately one tenth the distance said upper and lower potential electrodes are spaced, respectively, above and below said downhole electrode; means electrically connected to the upper and lower potential electrodes for continuously measuring and recording any potential difference between voltages at the upper and lower potential electrodes; means electrically connected between the surface current electrode and the downhole current electrode for applying a low frequency alternating current between the surface current electrode and the downhole current electrode; and means electrically connected between the surface current electrode and the downhole current electrode for measuring and recording current flow between the surface current electrode and the downhole current electrode.
Claim 9
Dependent Claim
261 words
Apparatus for determining the depth of a horizontal resistivity contrast below the bottom of a borehole of known depth extending downwardly from the earth surface, comprising: a surface current electrode positioned on the earth surface at a relatively large distance from the borehole; a downhole current electrode disposed within the borehole and spaced a known distance above the bottom of the borehole and a greater distance above the resistivity contrast the depth of which is to be determined; an upper potential electrode disposed within the borehole and spaced a distance above the downhole current electrode; a lower potential electrode disposed within the borehole and spaced a distance below the downhole current electrode, the distance between the lower potential electrode and the downhole current electrode being substantially equal to the distance between the downhole current electrode and the upper potential electrode; the effective lengths of said upper and lower potential electrodes each being equal to approximately one tenth the distance said upper and lower potential electrodes are spaced, respectively, above and below said downhole electrode; means electrically connected to the upper and lower potential electrodes for continuously measuring and recording any potential difference between voltages at the upper and lower potential electrodes; means electrically connected between the surface current electrode and the downhole current electrode for applying a low frequency alternating current between the surface current electrode and the downhole current electrode; and means electrically connected between the surface current electrode and the downhole current electrode for measuring and recording current flow between the surface current electrode and the downhole current electrode.
Claim 10
Dependent Claim
243 words
Apparatus for determining the depth of a horizontal electrical resistivity contrast below the bottom of a borehole of known depth extending downwardly from the earth surface, comprising: a surface current electrode positioned on the earth surface a large distance from the borehole; a lower potential electrode disposed within the borehole a distance ''''x'''' above the bottom of the borehole and a distance greater than ''''x'''' above the resistivity contrast the depth of which is to be determined; a downhole current electrode disposed within the borehole a distance ''''a'''' above the lower downhole potential electrode and a distance greater than the total distance ''''x'''' plus ''''a'''' above the resistivity contrast the depth of which is to be determined; an upper potential electrode disposed within the borehole a distance ''''a'''' above the downhole current electrode; the effective lengths of said upper and lower potential electrodes each being equal to approximately one tenth the distance ''''a''''; means connected to the upper and lower potential electrodes for continuously receiving, measuring and recording any potential difference between voltages at the upper and lower potential electrodes; means electrically connected between the surface current electRode and the downhole current electrode for applying a low frequency sinusoidal alternating current between the surface current electrode and the downhole current electrode; and means electrically connected between the surface current electrode and the downhole current electrode for receiving, measuring and recording the current flow between the surface current electrode and the downhole current electrode.
Claim 11
Dependent Claim
243 words
Apparatus for determining the depth of a horizontal electrical resistivity contrast below the bottom of a borehole of known depth extending downwardly from the earth surface, comprising: a surface current electrode positioned on the earth surface a large distance from the borehole; a lower potential electrode disposed within the borehole a distance ''''x'''' above the bottom of the borehole and a distance greater than ''''x'''' above the resistivity contrast the depth of which is to be determined; a downhole current electrode disposed within the borehole a distance ''''a'''' above the lower downhole potential electrode and a distance greater than the total distance ''''x'''' plus ''''a'''' above the resistivity contrast the depth of which is to be determined; an upper potential electrode disposed within the borehole a distance ''''a'''' above the downhole current electrode; the effective lengths of said upper and lower potential electrodes each being equal to approximately one tenth the distance ''''a''''; means connected to the upper and lower potential electrodes for continuously receiving, measuring and recording any potential difference between voltages at the upper and lower potential electrodes; means electrically connected between the surface current electRode and the downhole current electrode for applying a low frequency sinusoidal alternating current between the surface current electrode and the downhole current electrode; and means electrically connected between the surface current electrode and the downhole current electrode for receiving, measuring and recording the current flow between the surface current electrode and the downhole current electrode.
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) | 1977-09-23 | 1978-03-25 | 1978-09-24 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-09-23 | 1982-03-25 | 1982-09-24 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-09-23 | 1986-03-25 | 1986-09-24 | $7700.00 | Window Closed / Lapsed |