Acoustic impedance logging using reflection coefficients

Claim 3

The method of claim 1 wherein the step of generating a signal representative of the acoustic reflection coefficient in the frequency region above a predetermined lower cutoff frequency includes the steps of: transmitting a component of acoustic energy radially outwardly from a fluid-filled borehole into the surrounding earth formations; receiving a reflected portion of said transmitted energy and generating signals representative thereof; and integrating the portion of said received signal in the frequency region above said predetermined lower cutoff signal to generate a reflection coefficient signal.

Claim 4

The method of claim 2 and further including the step of linearly transforming said reflection coefficient signal in a predetermined manner to calibrate said reflection coefficient signal for a given well logging tool.

Claim 5

The method of claim 1 wherein the step of combining in a predetermined manner said reflection coefficient signal and said drilling fluid impedance signal includes multiplying said drilling fluid impedance signal by a predetermined function of said reflection coefficient signal.

Claim 6

The method of claim 4 wherein the combining step is performed by multiplying the drilling fluid impedance signal Zf by a signal representative of the ratio: (1 + Q)/(1 - Q) where Q is the magnitude of the signal representative of the reflection coefficient in the frequency region above a predetermined lower cutoff frequency.

Claim 7

The method of claim 1 wherein said predetermined lower cutoff frequency is approximately 5 KHZ.

Claim 8

The method of claim 1 wherein the steps are performed repetitively at different depths in the well borehole and said signal representative of the acoustic impedance of earth formations surrounding the borehole is recorded as a function of borehole depth.

Claim 11

The method of claim 8 wherein the steps are performed repetitively at different borehole depths and the signals representative of the acoustic impedance are recorded as a function of borehole depth.

Claim 12

The method of claim 8 wherein said predetermined lower cutoff frequency is approximately 5 KHZ.

Claim 13

The method of claim 8 wherein said combining step is performed by multiplying said signal representative of the acoustic impedance of the drilling fluid in the borehole Zf by a signal representative of the ratio: (1 + Q)/(1 - Q) where Q is the magnitude of the signal representative of the calibrated acoustic reflection coefficient to generate a signal representative of the acoustic impedance of earth formations surrounding the borehole.

Claim 14

Apparatus for determining the acoustic impedance of earth formations surrounding a fluid-filled well borehole comprising: a body member sized for passage through a well bore; acoustic transmitting means carried by said body member for transmitting a component of acoustic energy radially outwardly from the borehole into the surrounding earth formation; receiving means for receiving a reflected portion of said transmitted energy and generating signals representative thereof; means for integrating the portion of said receivEd signal in the frequency region above a predetermined lower cutoff frequency to generate a signal proportional to the acoustic reflection coefficient; means for linearly transforming said reflection coefficient signal in a predetermined manner to generate a calibrated reflection coefficient signal; and means for combining said calibrated reflection coefficient signal and a signal representative of the acoustic impedance of the drilling fluid in a predetermined manner to generate a signal representative of the acoustic impedance of the earth formation surrounding the borehole.

Claim 15

Apparatus for determining the acoustic impedance of earth formations surrounding a fluid-filled well borehole comprising: a body member sized for passage through a well bore; acoustic transmitting means carried by said body member for transmitting a component of acoustic energy radially outwardly from the borehole into the surrounding earth formation; receiving means for receiving a reflected portion of said transmitted energy and generating signals representative thereof; means for integrating the portion of said receivEd signal in the frequency region above a predetermined lower cutoff frequency to generate a signal proportional to the acoustic reflection coefficient; means for linearly transforming said reflection coefficient signal in a predetermined manner to generate a calibrated reflection coefficient signal; and means for combining said calibrated reflection coefficient signal and a signal representative of the acoustic impedance of the drilling fluid in a predetermined manner to generate a signal representative of the acoustic impedance of the earth formation surrounding the borehole.

Claim 16

The apparatus of claim 12 and further including: means for moving said body member through the borehole; means for repetitively actuating said transmitter means and said receiver means at different borehole depths; and means for recording said signal representative of the acoustic impedance of earth formations surrounding the borehole as a function of the depth of said body member in the borehole.

Claim 17

The apparatus of claim 12 wherein said means for integrating the received signal in the frequency region above a predetermined lower cutoff frequency includes filter means for passing substantially only the frequency components of the received signal above the lower cutoff frequency and integrator means coupled to the output of said filter means.

Claim 18

The apparatus of claim 14 wherein said filter means passes substantially only frequencies above 5 KHZ.

Claim 19

The apparatus of claim 12 wherein the means for combining said calibrated reflection coefficient signal and a signal representative of the acoustic impedance of the drilling fluid includes means for generating a signal representative of the quantity: (1 + Q)/(1 - Q) where Q is the magnitude of the signal representative of the calibrated reflection coefficient, together with means for multiplying this latter signal by said signal representative of the acoustic impedance of the drilling fluid.