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US3697864A
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Method of detecting geologically anomalous bodies lateral to a borehole by comparing electrical resistivity measurements made using short-range measuring means and a long-spaced electrode array
Assignee: Chevron USA Inc
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Filing: 1970-11-16
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Granted: 1972-10-10
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Expires: 1990-11-16
Abstract
Abstract An improved method of detecting geologically anomalous bodies lateral to a borehole and determining the distance thereto utilizes a long-spaced electrode array with a current source and a current sink electrode located within the borehole. A shortspaced electrode array or other short-range electrical resistivity measuring means such as an induction log is used to obtain resistivity values for the formation surrounding the borehole. A long-spaced electrode array comprising two potential measuring electrodes, M and N, and two current electrodes, A and B, positioned within the borehole, is utilized to make resistivity measurements of the formation surrounding the borehole, said measurements reflecting the presence of electrically resistive geologically anomalous bodies located at lateral distances from the borehole up to a distance on the order of twice the spacing between the source or sink electrode and the closest potential measuring electrode. The electrodes of the long-spaced array are positioned so that B lies within the borehole and above N, N is positioned above M, M is positioned above A, and the BN distance is approximately equal to the AM distance. The short-range resistivity values are then compared with the resistivity measurements from the long-spaced electrode array, significant differences therebetween indicating the presence of an electrically resistive anomaly lateral to the borehole and the magnitude of said differences indicating the distance from the borehole to said anomaly.
Inventors
- 👤 Richard J Runge
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 20:20
CPC Classifications
G; G01; G01V; G01V3/00; G01V3/18; G01V3/34
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
354 words
A method of prospecting for electrically resistive anomalies lateral to, and not cut by, a borehole which avoids the introduction of error effects due to partial casing of the upper portion of said borehole comprising: measuring a first electrical characteristic representative of the resistivity of formations cut by and surrounding the borehole with short-range logging means over a given depth interval below the cased portion of said borehole; measuring the apparent resistivity of the formations surrounding the borehole including any resistivity anomalies lateral to and not cut by said borehole over said given depth interval with a long-spaced electric logging array consisting of two current electrodes, A and B, and two potential measuring electrodes, M and N, positioned so that B is within said borehole and lies both below said cased portion thereof and above N, N is positioned above M, M is positioned above A, and the BN distance is approximately equal to the AM distance; obtaining expected long-spaced apparent resistivity values over said given depth interval for spacings equal to the distance between electrodes M and N from said first electrical characteristic values by machine processing said measured first electrical characteristic values with a digital computer programmed to average said values over said distance by a program selected from the group consisting of the Dakhnov algorithm and a distance averaging algorithm; comparing expected apparent resistivity values with the apparent resistivity values measured by said long-spaced electric logging array, a significant dIsparity indicating that an electrically resistive anomaly that is not cut by said borehole lies at a lateral distance from the borehole, said distance being determined by the following formula: Rho s/ Rho (GB + IB(x) ) /GB where Rho s is the apparent resistivity measured in the presence of a resistive anomaly; Rho is the apparent resistivity expected if no resistive anomaly is present; x is the apparent distance from the borehole to the flank of the anomaly; GB is the geometric factor of the long-spaced electrode array 2/AM - 2/ANIB(x)is the image term for the long-spaced electrode array 2/ square root (AM)2 + 4x2 2/ square root (AN)2 + 4x2
Claim 2
Independent Claim
354 words
A method of prospecting for electrically resistive anomalies lateral to, and not cut by, a borehole which avoids the introduction of error effects due to partial casing of the upper portion of said borehole comprising: measuring a first electrical characteristic representative of the resistivity of formations cut by and surrounding the borehole with short-range logging means over a given depth interval below the cased portion of said borehole; measuring the apparent resistivity of the formations surrounding the borehole including any resistivity anomalies lateral to and not cut by said borehole over said given depth interval with a long-spaced electric logging array consisting of two current electrodes, A and B, and two potential measuring electrodes, M and N, positioned so that B is within said borehole and lies both below said cased portion thereof and above N, N is positioned above M, M is positioned above A, and the BN distance is approximately equal to the AM distance; obtaining expected long-spaced apparent resistivity values over said given depth interval for spacings equal to the distance between electrodes M and N from said first electrical characteristic values by machine processing said measured first electrical characteristic values with a digital computer programmed to average said values over said distance by a program selected from the group consisting of the Dakhnov algorithm and a distance averaging algorithm; comparing expected apparent resistivity values with the apparent resistivity values measured by said long-spaced electric logging array, a significant dIsparity indicating that an electrically resistive anomaly that is not cut by said borehole lies at a lateral distance from the borehole, said distance being determined by the following formula: Rho s/ Rho (GB + IB(x) ) /GB where Rho s is the apparent resistivity measured in the presence of a resistive anomaly; Rho is the apparent resistivity expected if no resistive anomaly is present; x is the apparent distance from the borehole to the flank of the anomaly; GB is the geometric factor of the long-spaced electrode array 2/AM - 2/ANIB(x)is the image term for the long-spaced electrode array 2/ square root (AM)2 + 4x2 2/ square root (AN)2 + 4x2
Claim 3
Dependent Claim
71 words
The method of claim 1 in which said first electrical characteristic is resistivity and said short-range logging means is a short-spaced electrode array which has the potential measuring electrodes positioned less than 25 feet apart and in which said long-spaced electrode array has distances between said AM and BN of at least 75 feet, and in which the AN and BM distances are more than twice said AM and BN distances.
Claim 4
Dependent Claim
60 words
The method of claim 1 in which said first electrical characteristic is conductivity and said short-rage logging means is an induction logging tool and in which said long-spaced electrode array has distances between said AM and BN distances of at least 75 feet, and in which the AN and BM distances are more than twice said AM and BN distances.
Claim 5
Dependent Claim
270 words
In a method for exploring for salt domes or other electrically resistive bodies lateral to and not intercepted by a borehole, said borehole being partially cased with an electrically conductive casing in its upper portion, which comprises the steps of measuring a first electrical characteristic of the formation directly surrounding and intercepted by the borehole with short-range logging means over a given depth interval in said borehole below said conductive casing, measuring over the same depth interval the apparent resistivity of the formations surrounding the borehole including formations not intercepted by said borehole, with long-spaced electric logging means, obtaining expected long-spaced apparent resistivity values from said first electrical characteristic values by machine processing said first electrical characteristic values with a digital computer programmed to average said values over said given depth interval including the Dakhnov algorithm and a distance averaging algorithm, and comparing the computed apparent resistivity for at least a part of said given depth interval with the apparent resistivity measured by the long-spaced electric logging means for the same part of said interval, a significant disparity therebetween indicating that an electrically resistive anomaly lies at some lateral distance from the borehole less than the distance between the source electrode and the nearest potential measuring electrode, the improvement comprising utilizing a long-spaced electrode array consisting of two current electrodes, A and B, and two potential measuring electrodes, M and N, positioned so that B is within said borehole and lies below said electrically conductive casing and above N, N is positioned above M, M is positioned above A, and the BN distance is approximately equal to the AM distance.
Claim 6
Dependent Claim
270 words
In a method for exploring for salt domes or other electrically resistive bodies lateral to and not intercepted by a borehole, said borehole being partially cased with an electrically conductive casing in its upper portion, which comprises the steps of measuring a first electrical characteristic of the formation directly surrounding and intercepted by the borehole with short-range logging means over a given depth interval in said borehole below said conductive casing, measuring over the same depth interval the apparent resistivity of the formations surrounding the borehole including formations not intercepted by said borehole, with long-spaced electric logging means, obtaining expected long-spaced apparent resistivity values from said first electrical characteristic values by machine processing said first electrical characteristic values with a digital computer programmed to average said values over said given depth interval including the Dakhnov algorithm and a distance averaging algorithm, and comparing the computed apparent resistivity for at least a part of said given depth interval with the apparent resistivity measured by the long-spaced electric logging means for the same part of said interval, a significant disparity therebetween indicating that an electrically resistive anomaly lies at some lateral distance from the borehole less than the distance between the source electrode and the nearest potential measuring electrode, the improvement comprising utilizing a long-spaced electrode array consisting of two current electrodes, A and B, and two potential measuring electrodes, M and N, positioned so that B is within said borehole and lies below said electrically conductive casing and above N, N is positioned above M, M is positioned above A, and the BN distance is approximately equal to the AM distance.
Claim 7
Dependent Claim
71 words
The method of claim 4 in which said first electrical characteristic is resistivity and said short-range logging means is a short-spaced electrode array which has the potential measuring electrodes positioned less than 25 feet apart and in which said long-spaced electrode array has said distances between AM and BN of at least 75 feet, and in which the AN and BM distances are more than twice said AM and BN distances.
Claim 8
Dependent Claim
59 words
The method of claim 4 in which said first electrical characteristic is conductivity and said short-range logging means is an induction logging tool and in which said long-spaced electrode array has distances between said AM and BN of at least 75 feet, and in which the AN and BM distances are more than twice said AM and BN distances.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-10-10 | 1976-04-10 | 1976-10-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-10-10 | 1980-04-10 | 1980-10-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-10-10 | 1984-04-10 | 1984-10-10 | $7700.00 | Window Closed / Lapsed |