Acoustic borehole logging
First Claim
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1. An acoustic borehole logging method comprising the steps of:
- (a) traversing a borehole with a borehole logging tool containing a transmitter of acoustic energy having a free-field frequency spectrum with at least one characteristic resonant frequency of vibration and a spaced-apart receiver,(b) repeatedly exciting said transmitter with a swept frequency tone burst of a duration sufficiently greater than the travel time of acoustic energy between said transmitter and said receiver to allow borehole cavity resonances to be established within the borehole cavity formed between the borehole logging tool and the borehole wall,(c) detecting acoustic energy amplitude modulated by said borehole cavity resonances with said spaced-apart receiver, and(d) recording an amplitude versus frequency output of said receiver in correlation with depth as a log of the borehole frequency spectrum representative of the subsurface formation comprising the borehole wall.
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Abstract
An acoustic borehole logging system employs an acoustic tranmitter excited by a sweep frequency tone burst to produce an acoustic output having a free-field frequency spectrum of at least one resonant frequency of vibration. A closely-spaced acoustic receiver detects a borehole frequency spectrum that is representative of the acoustic transmitter free-field frequency spectrum altered by the effects of the properties of the subsurface formulation materials comprising the borehole wall. Such detected borehole frequency spectrum is recorded in correlation with depth as a log of the material properties of the subsurface formations surrounding the borehole.
46 Citations
9 Claims
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1. An acoustic borehole logging method comprising the steps of:
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(a) traversing a borehole with a borehole logging tool containing a transmitter of acoustic energy having a free-field frequency spectrum with at least one characteristic resonant frequency of vibration and a spaced-apart receiver, (b) repeatedly exciting said transmitter with a swept frequency tone burst of a duration sufficiently greater than the travel time of acoustic energy between said transmitter and said receiver to allow borehole cavity resonances to be established within the borehole cavity formed between the borehole logging tool and the borehole wall, (c) detecting acoustic energy amplitude modulated by said borehole cavity resonances with said spaced-apart receiver, and (d) recording an amplitude versus frequency output of said receiver in correlation with depth as a log of the borehole frequency spectrum representative of the subsurface formation comprising the borehole wall. - View Dependent Claims (2, 3, 4, 5)
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6. An acoustic well logging method comprising the steps of:
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(a) traversing a borehole with a well logging tool containing an acoustic transmitter having a free-field acoustic energy frequency spectrum with at least one characteristic resonant frequency of vibration and an acoustic receiver spaced no greater than two feet from the transmitter, (b) repeatedly exciting said transmitter as the logging tool traverses the borehole with a swept frequency tone burst having a duration of at least one second to allow borehole cavity resonance to be established within the borehole cavity formed between the borehole logging tool and the borehole wall which cause the frequency sweep of said acoustic energy to be amplitude modulated by at least one borehole cavity resonance affected by the borehole wall, and (c) recording the output of said receiver as an amplitude versus frequency log of the borehole frequency spectrum of the borehole. - View Dependent Claims (7, 8, 9)
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Specification