Systems and methods for analyzing casing bonding in a well using ultrasound velocity filtering

1. A method for isolation detection in a wellbore, the method comprising:

obtaining an axial acoustic signal, the axial acoustic signal captured using an axial sensor deployed in a structure in a subterranean surface;

determining one or more velocities of one or more waveforms included in the axial acoustic signal;

separating the axial acoustic signal into a first wave region and a second wave region by applying velocity filtering to the one or more velocities;

generating an axial log indicating an axial symmetry of a portion of the structure based on at least one of the first wave region or the second wave region;

generating a radial log indicating a radial symmetry of the portion of the structure based on a radial acoustic signal; and

combining the axial log and the radial log to generate an isolation characterization for the portion of the structure.

2. The method of claim 1 , wherein the first wave region corresponds to a first propagation mode and the second wave region corresponds to a second propagation mode, the first propagation mode being different than the second propagation mode.

3. The method of claim 2 , wherein the first propagation mode includes Rayleigh waves and the second propagation mode includes P waves.

4. The method of claim 2 , wherein the first propagation mode corresponds to a first velocity and the second propagation mode corresponds to a second velocity.

5. The method of claim 2 , wherein the first propagation mode corresponds to a first penetration and the second propagation mode corresponds to a second penetration.

6. The method of claim 5 , wherein the first penetration is lower than the second penetration.

7. The method of claim 1 , wherein at least one isolation region corresponding to the portion of the structure is detected based on the axial symmetry.

8. The method of claim 1 , wherein an axial log is generated based on the axial acoustic signal, and the velocity filtering separates the axial log into the first wave region and the second wave region.

9. The method of claim 1 , wherein the first wave region corresponds to return signals of the axial acoustic signal receives below than a threshold and the second wave region corresponds to return signals of the axial acoustic signal received over the threshold.

10. The method of claim 9 , wherein the threshold is 500 microseconds.

11. The method of claim 1 , wherein a presence of cement at the portion of the structure is determined using the second wave region.

12. The method of claim 1 , wherein the axial symmetry includes an absence of returns corresponding to the first wave region and a presence of returns corresponding to the second wave region.

13. A method for isolation detection in a wellbore, the method comprising:

obtaining an axial acoustic signal, the axial acoustic signal captured using an axial sensor deployed in a structure in a subterranean surface;

determining a first velocity of a first waveform included in the axial acoustic signal, and a second velocity of a second waveform included in the axial acoustic signal;

separating the axial acoustic signal into a first wave region and a second wave region by applying velocity filtering to the first velocity and the second velocity;

determining an axial symmetry of a portion of the structure based on at least one of the first wave region or the second wave region;

determining a radial symmetry of the portion of the structure based on at least a radial acoustic signal; and

generating an isolation characterization for the portion of the structure based on both the axial symmetry and the radial symmetry.

14. One or more tangible non-transitory computer-readable storage media storing computer-executable instructions for performing a computer process on a computing system, the computer process comprising:

obtaining an axial acoustic signal using an axial sensor deployed in a structure in a subterranean surface;

obtaining a radial acoustic signal using a radial sensor deployed in the structure;

determining one or more velocities of one or more waveforms included in the axial acoustic signal;

separating the axial acoustic signal into a first wave region and a second wave region by applying velocity filtering to the one or more velocities; and

generating an axial log indicating an axial symmetry of a portion of the structure based on at least one of the first wave region or the second wave region;

generating a radial log indicating a radial symmetry of the portion of the structure based at least partly on the radial acoustic signal;

determining if the portion of the structure is axially or radially homogenous by combining the axial log with the radial log.

15. The one or more tangible non-transitory computer-readable storage media of claim 14 , wherein the first wave region corresponds to a first propagation mode and the second wave region corresponds to a second propagation mode, the first propagation mode being different than the second propagation mode.

16. The one or more tangible non-transitory computer-readable storage media of claim 15 , wherein the first propagation mode includes Rayleigh waves and the second propagation mode includes P waves.

17. The one or more tangible non-transitory computer-readable storage media of claim 15 , wherein the first propagation mode corresponds to a first velocity and the second propagation mode corresponds to a second velocity.

18. The one or more tangible non-transitory computer-readable storage media of claim 17 , wherein the first velocity is slower than the second velocity.

19. The one or more tangible non-transitory computer-readable storage media of claim 15 , wherein the first wave region corresponds to return signals of the axial acoustic signal receives below than a threshold and the second wave region corresponds to return signals of the axial acoustic signal received over the threshold.

20. The one or more tangible non-transitory computer-readable storage media of claim 15 , wherein the axial symmetry includes an absence of returns corresponding to the first wave region and a presence of returns corresponding to the second wave region.