US4587641A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Downhole fracture analysis
Assignee: Shell USA Inc
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Filing: 1984-02-07
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Granted: 1986-05-06
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Expires: 2004-02-07
Abstract
Abstract A method and apparatus using a multiple transducer acoustic logging tool to detect fractures surrounding a borehole, particularly fractures that do not intersect the borehole wall. The transducers are actuated to produce broad band width pulses and signal enhancement techniques are used to determine fracture width, orientation and distance from the borehole wall.
Inventors
- 👤 Rocco DiFoggio
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 12:32
CPC Classifications
G; G01; G01V; G01V1/00; G01V1/40; G01V1/44; G01V11/00; G01V11/002; G01V11/005
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
186 words
A method for detecting fractures in a formation surrounding a borehole wall comprising irradiating the formation with a broad band width acoustic pulse produced by a transducer in response to a broad band irradiating electrical signal pulse; receiving the acoustic energy that is reflected from the formation while discriminating by the time of arrival against energy that is reflected from the borehole wall; converting the received acoustic signal to a corresponding electrical signal; determining the maxima and minima of the power spectrum of the electrical signal; determining the frequency difference between two adjacent power spectrum maxima and minima; calculating the width of the fracture using the frequency difference between peaks in the power spectrum from the expression ##EQU1## wherein Δf=frequency difference between peaks in the power spectrum V=velocity of sound in the fluid filling the fracture w=width of the fracture θ=angle between beam of acoustic pulse and plane containing the probed region of the fracture and; determining the depth of the fracture using velocity of sound in the formation and the time required for the acoustic pulse to travel through the formation and be reflected back.
Claim 2
Independent Claim
186 words
A method for detecting fractures in a formation surrounding a borehole wall comprising irradiating the formation with a broad band width acoustic pulse produced by a transducer in response to a broad band irradiating electrical signal pulse; receiving the acoustic energy that is reflected from the formation while discriminating by the time of arrival against energy that is reflected from the borehole wall; converting the received acoustic signal to a corresponding electrical signal; determining the maxima and minima of the power spectrum of the electrical signal; determining the frequency difference between two adjacent power spectrum maxima and minima; calculating the width of the fracture using the frequency difference between peaks in the power spectrum from the expression ##EQU1## wherein Δf=frequency difference between peaks in the power spectrum V=velocity of sound in the fluid filling the fracture w=width of the fracture θ=angle between beam of acoustic pulse and plane containing the probed region of the fracture and; determining the depth of the fracture using velocity of sound in the formation and the time required for the acoustic pulse to travel through the formation and be reflected back.
Claim 3
Dependent Claim
28 words
The method of claim 1 wherein a plurality of acoustic pulses are used, said pulses being equally spaced around the periphery of the borehole and produced in sequence.
Claim 4
Dependent Claim
17 words
The method of claim 2 wherein said pulses are produced in close proximity to the borehole wall.
Claim 5
Dependent Claim
20 words
The method of claim 1 wherein said acoustic pulse comprises a short wave train of not more than five cycles.
Claim 6
Dependent Claim
23 words
The method of claim 1 wherein the electrical signals are enhanced using cross-correlation of the irradiating electrical signal with the reflected electrical signal.
Claim 7
Dependent Claim
22 words
The method of claim 5 wherein the maximum value of the cross-correlation function is related to twice the depth of the fracture.
Claim 8
Dependent Claim
55 words
The method of claim 1 wherein the autocorrelation function of the electrical signal is obtained by correlating the electrical signal with a time delayed copy of the electrical signal and taking the Fourier transform to get the power spectrum from which the spacing between adjacent maxima and minima is determined to obtain the frequency difference.
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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) | 1989-05-05 | 1989-11-04 | 1990-05-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-05-05 | 1993-11-04 | 1994-05-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-05-05 | 1997-11-04 | 1998-05-06 | $7700.00 | Window Closed / Lapsed |