Methods and apparatus for cement bond evaluation through production tubing
Various downhole logging tools and methods of using and making the same are disclosed. In one aspect a method evaluating cement bond quality in a well is provided. In a well with a particular casing/tubing configuration, waveforms of acoustic energy returning from the tubing and the casing with the tubing present are recorded. A frequency spectrum from the recorded waveforms is determined. Amplitudes of the returning acoustic energy at one or more preselected frequency(s) of interest of a range of frequencies at which the amplitudes are noticeably affected by cement bond quality for the particular casing/tubing configuration are determined. The determined amplitudes are compared with one or more baseline amplitudes to look for indications of cement bond quality. Other aspects involve time domain analysis.
1. A method for evaluating cement bond quality in a well, comprising:
in a well with a particular casing/tubing configuration, recording waveforms of acoustic energy returning from the tubing and the casing with the tubing present;
determining the lengths of wave cycles of the recorded waveforms for at least one preselected time window for the particular casing/tubing configuration; and
determining if the lengths of the wave cycles are longer or shorter than a baseline wave cycle length and;
determining, based on whether the length of the wave cycles are longer or shorter than a baseline wave cycle length, at what depths to look for indications of cement bond quality.
2. The method of claim 1 , wherein the wave cycles comprise the time between every other zero crossing of the recorded waveforms.
3. The method of claim 1 , wherein the wave cycles comprise the time between adjacent amplitude peaks or adjacent amplitude troughs of the recorded waveforms.
4. A method for evaluating cement bond quality in a well with a particular casing/tubing configuration using waveforms of acoustic energy returning from the tubing and the casing with the tubing present, comprising:
determining the lengths of wave cycles of the recorded waveforms for at least one preselected time window for the particular casing/tubing configuration; and
determining if the lengths of the wave cycles are longer or shorter than a baseline wave cycle length and;
determining, based on whether the length of the wave cycles are longer or shorter than a baseline wave cycle length, at what depths to look for indications of cement bond quality.
5. The method of claim 4 , wherein the wave cycles comprise the time between every other zero crossing of the recorded waveforms.
6. The method of claim 4 , wherein the wave cycles comprise the time between adjacent amplitude peaks or adjacent amplitude troughs of the recorded waveforms.
7. An apparatus for evaluating cement bond quality in a well with a particular casing/tubing configuration, the apparatus comprising:
a storage device for storing recorded waveforms of acoustic energy returning from the tubing and from the casing with the tubing present; and
a processor programmed to:
determine the lengths of wave cycles of the recorded waveforms for at least one preselected time window for the particular casing/tubing configuration;
determine if the lengths of the wave cycles are longer or shorter than a baseline wave cycle length; and
determine, based on whether the length of the wave cycles are longer or shorter than a baseline wave cycle length, at what depths to provide indications of cement bond quality.
8. The apparatus of claim 7 , comprising a downhole logging tool, the storage device and processor contained in the downhole logging tool.
9. The apparatus of claim 7 , comprising a downhole logging tool, the storage device and processor not contained in the downhole logging tool.
10. A computer readable medium having computer-executable instructions for performing a method of evaluating cement bond quality in a well with a particular casing/tubing configuration using waveforms of acoustic energy returning from the tubing and the casing with the tubing present comprising:
determining the lengths of wave cycles of the recorded waveforms for at least one preselected time window for the particular casing/tubing configuration; and
determining if the lengths of the wave cycles are longer or shorter than a baseline wave cycle length and;
determining, based on whether the length of the wave cycles are longer or shorter than a baseline wave cycle length, at what depths to look for indications of cement bond quality.