System and method for detection of near-wellbore alteration using acoustic data
A method for monitoring a formation property includes determining at least two slowness values from at least two datasets each characterizing an acoustic wave having a different frequency traversing a formation; and deriving an indicator based on the at least two slowness values. A system for monitoring a formation property includes a process and a memory, wherein the memory stores a program having instructions for: determining at least two slowness values from at least two datasets each characterizing an acoustic wave having a different frequency traversing a formation; and deriving an indicator based on the at least two slowness values.
1. A method for monitoring a near wellbore formation property using acoustic waveforms, comprising:
filtering the acoustic waveforms with a first bandpass filter to obtain first signals;
filtering the acoustic waveforms with a second, different bandpass filter to obtain second signals;
processing the first and second signals to obtain first and second slowness values each characterizing an acoustic wave having a different frequency;
making a comparison between the first and second slowness values at a reference depth;
detecting a near wellbore alteration based on the comparison; and
outputting the results of the detecting to a user.
2. The method of claim 1 , wherein the first filter comprises a low-band-pass filter and the second filter comprises a high-band-pass filter.
3. The method of claim 1 , wherein the acoustic waveforms are from Stoneley mode.
4. The method of claim 1 , wherein the acoustic waveforms are from a monopole, dipole, quadrupole, or higher-order-pole mode.
5. The method of claim 1 , wherein the comparison comprises deriving an indicator based on a difference between the first and second slowness values.
6. The method of claim 5 , wherein the indicator is a change in the difference between the first and second slowness values as a function of measured depth.
7. The method of claim 1 , wherein processing the first and second signals uses a slowness-time-coherence (STC) algorithm.
8. The method of claim 1 , wherein the acoustic waveforms are obtained from while-drilling togging measurements.
9. The method of claim 1 , wherein the acoustic waveforms are obtained from wireline logging measurements.
10. The method of claim 1 , wherein the first and second signals are obtained from separate measurements of the waveforms.
11. A system for monitoring a near wellbore formation property using acoustic waveforms, comprising:
a processor and a memory, wherein the memory stores a program having instructions for:
filtering the acoustic waveforms with a first bandpass filter to obtain first signals;
filtering the acoustic waveforms with a second, different bandpass filter to obtain second signals;
processing the first and second signals to obtain first and second slowness values each characterizing an acoustic wave having a different frequency;
making a comparison between the first and second slowness values at a reference depth;
detecting a near wellbore alteration based on the comparison,
wherein the first and second signals are obtained from separate measurements of the waveforms.
12. The system of claim 11 , wherein the first filter comprises a low-band-pass filter, the second filter comprises a high-band-pass filter, and wherein the program has instructions for performing the low-band-pass and high-band-pass filtering.
13. The system of claim 11 , wherein the acoustic waveforms are from Stoneley mode.
14. The system of claim 11 , wherein the acoustic wave forms are from a monopole, dipole, quadrupole or higher-order-pole mode.
15. The system of claim 11 , wherein the comparison comprises deriving an indicator based on a difference between the first and second slowness values.
16. The system of claim 15 , wherein the indicator is a change in the difference between the first and second slowness values.
17. The system of claim 11 , wherein processing the first and second signals uses a slowness-time-coherence (STC) algorithm.
18. The system of claim 11 , wherein the system is part of a downhole tool.