Methods and apparatus for acoustic logging in cased well bores

Claim 2

Apparatus for investigating characteristics of the media forming a cased well bore having a cement annulus between the casing and the surrounding earth formations, comprising: a well tool having an acoustic transmitter and two acoustic receivers spaced therefrom at different distances; means for repetitively energizing said acoustic transmitter to emit energy into the media surrounding said well tool and producing timing pulses representative of the times of energization, at least a portion of said energy being received by said acoustic receivers which produce electrical signals representative of said received energy; means for measuring the amplitude of a selected portion of at least some signals produced by the receiver nearest said transmitter in response to acoustic energy transmitted to said nearest receiver at least in part through the casing to produce an output signal representative of the bonding between the casing and cement surrounding said casing; means for recording said output signal to produce a log indicative of the bonding between the casing and cement; and means responsive to selected timing pulses and selected signals produced by the receiver farthest from said transmitter in response to acoustic energy transmitted to said farthest receiver at least in part through the media surrounding the casing for producing a variable density record of the signals produced by said farthest receiver, whereby said variable density record can be used in conjunction with said cement bond log to evaluate the cement bonding.

Claim 3

The apparatus of claim 1 wherein said means for producing a variable density record includes a record medium, means for sweeping a radiant energy beam across said record medium, means responsive to selected timing pulses for initiating the sweep of said beam, and means for modulating the intensity of said beam with representations of signals produced by said farthest receiver to thereby produce a variable density record on said record medium.

Claim 4

The apparatus of claim 1 wherein said receiver nearest said transmitter is located approximately three feet from said transmitter and said receiver farthest from said transmitter is located approximately five feet from said transmitter.

Claim 5

Apparatus for investigating characteristics of the media forming a cased well bore having a cement annulus located between the casing and the surrounding earth formations, comprising: a well tool having an acoustic transmitter and two acoustic receivers spaced therefrom at different distances; means for repetitively energizing said acoustic transmitter to emit energy into the media surrounding said well tool and producing timing pulses representative of the times of energization, at least a portion of said energy being received by said acoustic receivers which produce electrical signals representative of said received energy; means operative in a time relationship with each emission of energy for selecting the electrical signal from one of said receivers for each energy emission for transmission to the surface of the earth; means for transmitting said selected electrical signals and timing pulses to the surface of the earth; control means located at the surface of the earth for producing control signals representative of which receiver signal has been selected for transmission; means adapted for measuring the amplitude of a selected portion of a signal produced by the receiver nearest said transmitter in response to acoustic energy transmitted to said nearest receiver at least in part through the casing to produce an output signal; variable density means adapted to produce a variable density display of the signals produced by the receiver farthest from said transmitter in response to acoustic energy transmitted to said receiver at least in part through the media surrounding the casing; means responsive to said control signals for gating a timing pulse to said amplitude means whenever a signal produced by the receiver nearest said transmitter is selected for transmission to the surface of the eArth and for gating a timing pulse to said variable density means whenever a signal produced by the receiver farthest from said transmitter is selected for transmission to the surface of the earth, said gated timing pulses acting to enable the operation of one of said amplitude means or variable density means; and means for recording said output signal and variable density display to produce logs indicative of the bonding of the cement to the casing and formations.

Claim 6

Apparatus for investigating characteristics of the media forming a cased well bore having a cement annulus located between the casing and the surrounding earth formations, comprising: a well tool having an acoustic transmitter and two acoustic receivers spaced therefrom at different distances; means for repetitively energizing said acoustic transmitter to emit energy into the media surrounding said well tool and producing timing pulses representative of the times of energization, at least a portion of said energy being received by said acoustic receivers which produce electrical signals representative of said received energy; means operative in a time relationship with each emission of energy for selecting the electrical signal from one of said receivers for each energy emission for transmission to the surface of the earth; means for transmitting said selected electrical signals and timing pulses to the surface of the earth; control means located at the surface of the earth for producing control signals representative of which receiver signal has been selected for transmission; means adapted for measuring the amplitude of a selected portion of a signal produced by the receiver nearest said transmitter in response to acoustic energy transmitted to said nearest receiver at least in part through the casing to produce an output signal; variable density means adapted to produce a variable density display of the signals produced by the receiver farthest from said transmitter in response to acoustic energy transmitted to said receiver at least in part through the media surrounding the casing; means responsive to said control signals for gating a timing pulse to said amplitude means whenever a signal produced by the receiver nearest said transmitter is selected for transmission to the surface of the eArth and for gating a timing pulse to said variable density means whenever a signal produced by the receiver farthest from said transmitter is selected for transmission to the surface of the earth, said gated timing pulses acting to enable the operation of one of said amplitude means or variable density means; and means for recording said output signal and variable density display to produce logs indicative of the bonding of the cement to the casing and formations.

Claim 7

The apparatus of claim 4 wherein said control means operates to transmit representations of said control signals to said well tool to control the energization of said transmitter and the selection of receiver signals for transmission to the surface of the earth whereby the operation of said well tool will be slaved to said control means.

Claim 8

The apparatus of claim 4 wherein said control means is responsive to at least said timing pulses for producing said control signals whereby said control means will be slaved to the operation of said well tool.

Claim 11

A method according to claim 7 further comprising: selecting the spacing between the transmitter and the nearest receiver such that the acoustic energy arriving at said nearest receiver through the casing is measurably distinguishable from energy arriving at the nearest receiver through other media surrounding the well tool; and selecting the spacing between the transmitter and the farthest receiver such that the acoustic energy arriving at the farthest receiver through the media surrounding the casing is substantially stronger than the interfering energy arriving at the farthest receiver through the casing.