Enhanced-resolution sonic data processing for formation body wave slowness with full offset waveform data

1. A method of determining body wave slowness values for a target formation zone, the method comprising:

selecting a target axial resolution based on the size of a receiver array;

obtaining, by an acoustic logging tool having the receiver array, a plurality of waveform data sets corresponding to a target formation zone, wherein each waveform data set is acquired at a different shot position;

reconstructing the plurality of waveform data sets to generate a plurality of subarray data sets corresponding to the target formation zone;

determining a slowness value for each subarray data set;

determining a slowness versus offset value for each subarray data set;

generating a borehole model having at least one alteration formation zone and a virgin formation zone;

generating a slowness versus offset model based at least in part on the borehole model;

optimizing the parameters in the borehole model by minimizing a misfit between the slowness value for each subarray data set and the borehole model and the slowness versus offset model to generate an optimized borehole model and an optimized slowness versus offset model;

extracting a virgin formation zone slowness from the optimized slowness versus offset model based on the slowness with the longest offset predicted by the model; and

extracting an alteration formation zone slowness from the optimized slowness versus offset model based on the slowness with the shortest offset predicted by the model.

2. The method of claim 1 , further comprising determining the radial depth of the at least one alteration formation zone based on the optimized slowness versus offset model.

3. The method of claim 2 , wherein determining the radial depth of the at least one alteration formation zone based on the optimized slowness versus offset model comprises calculating the radial depth of the at least one alteration formation zone using a ray-model.

4. The method of claim 1 , wherein the plurality of waveform data sets comprises lower monopole (LMP), far monopole (FMP), and ultrafar monopole (UFMP) data.

5. The method of claim 1 , wherein the slowness versus offset model is generated using forward modeling.

6. The method of claim 1 , wherein generating a slowness versus offset model comprises generating a look-up table comprising slowness values and related offset values.

7. The method of claim 6 , wherein the look-up table is generated using forward modeling.

8. The method of claim 1 , wherein optimizing the parameters in the borehole model comprises generating, using forward modeling, a look-up table that includes optimized slowness versus offset values.

9. The method of claim 1 , further comprising:

running the acoustic logging tool to a plurality of shot positions in the wellbore; and

actuating the one or more transmitters at each of the plurality of shot positions so as to obtain a plurality of waveform data sets at the receiver array corresponding to the target formation zone, wherein each waveform data set is acquired at the different shot position.

10. A method of determining body wave slowness values for a target formation zone, the method comprising:

selecting a target axial resolution based on the size of the receiver array;

obtaining, by an acoustic logging tool having a receiver array, a plurality of waveform data sets corresponding to a target formation zone, wherein each waveform data set is acquired at a different shot position of a plurality of shot positions and each waveform data set comprises lower monopole (LMP), far monopole (FMP), and ultrafar monopole (UFMP) data gathered at each shot position of the plurality of shot positions;

determining reconstructed sets of waveform data for the target formation zone, wherein each reconstructed set of waveform data corresponds to a particular shot position;

determining a semblance map, a variable density log (VDL), and a slowness value for each reconstructed set of waveform data;

stacking the VDLs; and

extracting body wave slowness values from the stacked VDLs.

11. The method of claim 10 , further comprising:

running the acoustic logging tool to the plurality of shot positions in the wellbore, the acoustic logging tool comprising one or more transmitters and the receiver array; and

actuating the one or more transmitters at each of the plurality of shot positions so as to obtain a plurality of waveform data sets at the receiver array corresponding to the target formation zone, wherein each waveform data set is acquired at a different shot position.

12. An apparatus comprising:

an acoustic logging tool having a receiver array, the acoustic logging tool configured to acquire a plurality of waveform data sets corresponding to a target formation zone, wherein each waveform data set is acquired at a different shot position;

at least one processor in communication with the acoustic logging tool, wherein the processor is coupled with a non-transitory computer-readable storage medium having stored therein instructions which, when executed by the at least one processor, causes the at least one processor to:

select a target axial resolution based on the size of a receiver array;

obtain a plurality of waveform data sets corresponding to a target formation zone, wherein each waveform data set is acquired at a different shot position;

reconstruct the plurality of waveform data sets to generate a plurality of subarray data sets corresponding to the target formation zone;

determine a slowness value for each subarray data set;

determine a slowness versus offset value for each subarray data set;

generate a borehole model having at least one alteration formation zone and a virgin formation zone;

generate a slowness versus offset model based at least in part on the borehole model;

optimize the parameters in the borehole model by minimizing the misfit between the slowness value for each subarray data set and the borehole model and the slowness versus offset model to generate an optimized borehole model and an optimized slowness versus offset model;

extract a virgin formation zone slowness from the optimized slowness versus offset model based on the slowness with the longest offset predicted by the model; and

extract an alteration formation zone slowness from the optimized slowness versus offset model based on the slowness with the shortest offset predicted by the model.

13. The apparatus of claim 12 , wherein the non-transitory computer-readable storage medium further contains a set of instructions that when executed by the at least one processor, further causes the at least one processor to determine the radial depth of the at least one alteration formation zone based on the optimized slowness versus offset model.

14. The apparatus of claim 13 , wherein determining the radial depth of the at least one alteration formation zone based on the optimized slowness versus offset model comprises calculating the radial depth of the at least one alteration formation zone using a ray-model.

15. The apparatus of claim 12 , wherein the plurality of waveform data sets comprises lower monopole (LMP), far monopole (FMP), and ultrafar monopole (UFMP) data.

16. The apparatus of claim 12 , wherein the acoustic logging tool is configured to acquire lower monopole (LMP), far monopole (FMP), and ultrafar monopole (UFMP) data.

17. The apparatus of claim 12 , wherein generating a slowness versus offset model comprises generating a look-up table comprising slowness values and related offset values.

18. The apparatus of claim 12 , wherein optimizing the parameters in the borehole model comprises generating, using forward modeling, a look-up table that includes optimized slowness versus offset values.