Methods of preventing cycle skipping in processing acoustic well-logging signals

Claim 1

A method of correcting random errors in the measurement of the transit time between two points of an acoustic wave in earth formations traversed by a borehole, comprising the steps of lowering an acoustic well-logging probe into a borehole, generating successive acoustic waves by means of said probe, generating a composite electric signal corresponding thereto, generating measurement signals responsive to said composite electric signal and representative of the transit time of said acoustic waves between first and second points during successive measurement sequences, said first and second points in successive measurement sequences being respectively relatively close to each other, comparing the measurement signals representative of successive measurements, whether or not valid, to determine whether their difference in absolute value exceeds a threshold value, and making a record as a function of depth of valid measurements, said valid measurements corresponding, in cases where said difference is smaller than said threshold, to the later of said measurement signals and, in other cases, to the measurement signal representative of the latest previous valid measurement.

Claim 2

A method of correcting random errors in the measurement of the transit time between two points of an acoustic wave in earth formations traversed by a borehole, comprising the steps of lowering an acoustic well-logging probe into a borehole, generating successive acoustic waves by means of said probe, generating a composite electric signal corresponding thereto, generating measurement signals responsive to said composite electric signal and representative of the transit time of said acoustic waves between first and second points during successive measurement sequences, said first and second points in successive measurement sequences being respectively relatively close to each other, comparing the measurement signals representative of successive measurements, whether or not valid, to determine whether their difference in absolute value exceeds a threshold value, and making a record as a function of depth of valid measurements, said valid measurements corresponding, in cases where said difference is smaller than said threshold, to the later of said measurement signals and, in other cases, to the measurement signal representative of the latest previous valid measurement.

Claim 6

A method of correcting random measurement errors due to occasional reduction of the signal-to-noise ratio of reception signals corresponding to acoustic measurement waves which are sequentially generated in a borehole traversing earth formations and of which the transit time between two points in the borehole is measured in successive measuremtn sequences to produce an acoustic log, comprising the steps of comparing two signals respectively representative of the measurements, whether or not valid, of the transit times of said acoustic waves between two points in the borehole during a given measurement sequence and the measurement sequence immediately preceding said given measurement sequence, producing an enabling signal to permit recording of said signal representative of said transit time during said given measurement sequence only in the case where the difference in absolute value between said two signals is smaller than a given threshold, and recording said signal representative of said transit time during said given measurement sequence only if said enabling signal is produced.

Claim 7

A method of correcting random measurement errors due to occasional reduction of the signal-to-noise ratio of reception signals corresponding to acoustic measurement waves which are sequentially generated in a borehole traversing earth formations and of which the transit time between two points in the borehole is measured in successive measuremtn sequences to produce an acoustic log, comprising the steps of comparing two signals respectively representative of the measurements, whether or not valid, of the transit times of said acoustic waves between two points in the borehole during a given measurement sequence and the measurement sequence immediately preceding said given measurement sequence, producing an enabling signal to permit recording of said signal representative of said transit time during said given measurement sequence only in the case where the difference in absolute value between said two signals is smaller than a given threshold, and recording said signal representative of said transit time during said given measurement sequence only if said enabling signal is produced.