Shot to shot processing for measuring a characteristic of earth formations from inside a borehole

A method for measuring slowness of acoustic waves introduced into earth formations from inside a borehole penetrating the earth formations wherein the acoustic waves are caused by acoustic pulses generated by a repetetively actuated source located on a tool which is moved along the borehole to generate waveform signals representative of acoustic waves detected at a plurality of receiver locations spaced along the direction of the borehole axis of the tool comprising the steps of:

• selecting a depth interval which is less in length than the distance between the farthest of said receiver locations;
• identifying signals relevant to said selected depth interval;
• converting identified signals which are attributable to effectively common times of operation of the source to a domain of signals representating values of a coherence as a function of values of said slowness:
• combining coherence values of converted signals attributable to different times of operation of the source in a preselected manner to determine at least one value for said slowness for that depth interval;
• repeating said steps for different depth intervals;
• and
• forming a tangible record as a function of borehole depth from the determined values of the slowness.

A method for measuring a slowness of acoustic waves introduced into earth formations from inside a borehole which penetrates the earth formations wherein the acoustic waves are caused by acoustic pulses generated by a repetetively actuated source located on a tool which is moved along the borehole to generate waveform signals representative of acoustic waves detected at a plurality of receiver locations spaced along the direction of the borehole axis of the tool, comprising the steps of:

• selecting a depth interval which is less in length than the distance between the farthest of said receiver locations;
• identifying signals relevant to said selected depth interval;
• converting sub-arrays of identified signals which relate to a common depth and are attributable to effectively different times of operation of the source while it is located within the selected depth interval to a domain of signals representing values of a coherence as a function of values of said slowness;
• combining coherence values for sub-arrays of converted signals attributable to effectively common times of operation of the source while it is located within the selected depth interval to determine at least one value for said slowness for that depth interval;
• repeating said steps for different depth intervals;
• and
• forming a tangible record as a function of borehole depth from the determined values of the slowness.

An apparatus for measuring a characteristic of earth formations penetrated by a borehole from investigative energy generated by a source located on a tool which is moved along the borehole and wherein signals are generated respectively representative of the energy detected along an aperture defined by receivers spaced at locations along the direction of the borehole axis of the tool, comprising:

• means for defining successive depth intervals which are less in length than said aperture;
• means for identifying signals relevant to respective selected depth intervals and including signals generated as a result of different times of operation of the source;
• means for transforming for each selected depth interval sub-arrays of identified signals to a domain of signals representing values of a coherence between the signals in a respective sub-array as a function of values of said characteristic;
• means for combining coherence values corresponding to common characteristic values and relevant to respective depth intervals;
• means for deriving from the combined coherence values at least one value for said characteristic for said selected depth intervals;
• and
• means for generating a tangible record as a function of borehole depth from the derived values of the characteristic for said selected depth intervals.

An apparatus for measuring slowness of acoustic waves introduced into earth formations from inside a borehole penetrating the earth formations wherein the acoustic waves are caused by acoustic pulses generated by a repetetively actuated source located on a tool which is moved along the borehole to generate waveform signals representative of acoustic waves detected at a plurality of receiver locations spaced along the direction of the borehole axis of the tool comprising:

• means for selecting depth intervals which are less in length than the distance between the farthest of said receiver locations;
• means for identifying signals relevant to said selected depth intervals;
• means for converting identified signals which are attributable to effectively common times of operation of the source to a domain of signals representating values of a coherence as a function of values of said slowness;
• means for combining coherence values of converted signals attributable to different times of operation of the source in a preselected manner to determine at least one value for said slowness for the depth interval;
• and
• means for forming a tangible record as a function of borehole depth from the determined values of the slowness.

An apparatus for measuring a slowness of acoustic waves introduced into earth formations from inside a borehole which penetrates the earth formations wherein the acoustic waves are caused by acoustic pulses generated by a repetetively actuated source located on a tool which is moved along the borehole to generate waveform signals representative of acoustic waves detected at a plurality of receiver locations spaced along the direction of the borehole axis of the tool, comprising:

• means for selecting depth intervals which are less in length than the distance between the farthest of said receiver locations;
• means for identifying signals relevant to said selected depth intervals;
• means for converting sub-arrays of identified signals which relate to a common depth and are attributable to effectively different times of operation of the source while it is located within the selected depth interval to a domain of signals representing values of a coherence as a function of values of said slowness;
• means for combining coherence values for sub-arrays of converted signals attributable to effectively common times of operation of the source while it is located within the selected depth interval to determine at least one value for said slowness for that depth interval;
• and
• means for forming a tangible record as a function of borehole depth from the determined values of the slowness.

A method for measuring a characteristic of earth formations penetrated by a borehole from a plurality of waveforms generated by an array of receivers spaced from each other on a tool along the axis of the borehole and generating the waveforms in sets in response to respective repetetive actuations of a source of energy spaced from the receivers on the tool comprising the steps of:

• selecting a depth interval which is less in length than the length of the array of receivers and is representative of a desired depth resolution of the measured characteristic;
• identifying those sets of waveforms generated in response to different actuations of the source and as to which sets the energy of the source traversed said selected depth interval;
• identifying from the latter sets of waveforms a plurality of sub-arrays of waveforms attributable to different actuations of the source, with the waveforms in each sub-array being generated by receivers while they are located in said selected depth interval;
• converting each sub-array of waveforms to a domain of signals representing values of a coherence between the signals in a sub-array as a function of values of the characteristic;
• combining coherence values of common characteristic values of converted signals from different sub-arrays to determine values of said characteristic for that depth interval;
• repeating said steps for different depth intervals;
• and
• forming a tangible record as a function of borehole depth from the determined values of the characteristic.

A method for measuring a characteristic of earth formations penetrated by a borehole from a plurality of waveforms generated by an array of receivers spaced from each other on a tool along the axis of the borehole and generating the waveforms in sets in response to respective repetetive actuations of a source of energy spaced from the receivers on the tool comprising the steps of:

• selecting a depth interval which is less in length than the length of the array of receivers and is representative of a desired depth resolution of the measured characteristic;
• identifying those sets of waveforms generated in response to different actuations of the source and as to which sets the energy of the source traversed said selected depth interval;
• identifying from the latter sets of waveforms a plurality of sub-arrays of waveforms attributable to different actuations of the source, with the waveforms in each sub-array being generated by different receivers while they are located at a common depth while said source is located within the selected depth interval;
• converting each sub-array of waveforms to a domain of signals representing values of a coherence between the signals in a sub-array as a function of values of the characteristic;
• combining coherence values of common characteristic values of converted signals from different sub-arrays to determine values of said characteristic for that depth interval;
• repeating said steps for different depth intervals;
• and
• forming a tangible record as a function of borehole depth from the determined values of the characteristic.