Acoustic array signal processing for flow detection
Disclosed are tools, systems, and methods for detecting one or more underground acoustic sources and localizing them in depth and radial distance from a wellbore, for example, for the purpose of finding underground fluid flows, such as may result from leaks in the well barriers. In various embodiments, acoustic-source detection and localization are accomplished with an array of at least three acoustic sensors disposed in the wellbore, in conjunction with array signal processing.
1. A method, comprising:
substantially simultaneously measuring acoustic signals with each of at least three sensors disposed in an array within a wellbore;
using an array-processing technique to compute, from the measured acoustic signals, a fused-signal parameter as a function of depth and radial distance from the wellbore; and
determining a depth and radial distance from the wellbore of an acoustic source based on a local maximum of the fused-signal parameter.
2. The method of claim 1 , further comprising using a binary hypothesis test applied to the local maximum of the fused-signal parameter to determine whether the acoustic source corresponds to an underground flow.
3. The method of claim 2 , wherein the binary hypothesis test comprises a comparison of the local maximum against a detection threshold, flow being detected based on the local maximum of the fused-signal parameter exceeding the detection threshold, the threshold being based on empirical data for a plurality of flow and non-flow scenarios.
4. The method of claim 1 , wherein the empirical data comprises fused-signal data derived from logging data for confirmed flow cases as well as in the absence of flow conditions.
5. The method of claim 4 , wherein creating the forward model comprises modifying a free-space steering vector to account for non-uniformities in the configuration of the wellbore and surrounding formation.
6. The method of claim 4 , wherein creating the forward model comprises modifying a free-space steering vector to account for the acoustic source being a near-field source.
7. The system of claim 6 , wherein the binary hypothesis test comprises a comparison of the local maximum against a detection threshold, the data-processing facility to detect flow based on the local maximum of the fused-signal parameter exceeding the detection threshold, the threshold being based on empirical data for a plurality of flow and non-flow scenarios.
8. The method of claim 1 , wherein the detection threshold is derived from the empirical data bases on one or statistical metrics comprising at least one of a sensitivity, a false-alarm rate, or a false-negatives rate.
9. The method of claim 8 , wherein the non-uniformities comprise at least one of multiple barriers to fluid flow or multiple media between the acoustic source and the sensors.
10. The system of claim 9 , wherein the data-processing facility is further to use a binary hypothesis test applied to the local maximum of the fused-signal parameter to determine whether the acoustic source corresponds to an underground flow.
11. The system of claim 9 , wherein the data-processing facility, in computing the fused-signal parameter, is to create a forward model of acoustic wave propagation based at least in part on a configuration of the wellbore and surrounding formation, the configuration being modelled as non-uniform.
12. The system of claim 9 , wherein the acoustic sensors comprise omnidirectional hydrophones, FBG sensors, or fiber-optic cables.
13. The system of claim 9 , wherein the acoustic sensors form a linear array disposed along a longitudinal axis of the wellbore.
14. The method of claim 1 , wherein computing the fused-signal parameter comprises creating a forward model of acoustic wave propagation based at least in part on a configuration of the wellbore and surrounding formation, the configuration being modelled as non-uniform.
15. A system comprising:
a sensor array disposed within a wellbore, comprising at least three acoustic sensors for substantially simultaneously measuring acoustic signals received thereat; and
a data-processing facility to use an array-processing technique to compute, from the measured acoustic signals, a fused-signal parameter as a function of depth and radial distance from the wellbore compute, and to determine a depth and radial distance from the wellbore of an acoustic source based on a local maximum of the fused-signal parameter.
16. The system of claim 15 , wherein the empirical data comprises fused-signal data derived from logging data for confirmed flow cases as well as in the absence of flow conditions.
17. The system of claim 16 , wherein the data-processing facility, in creating the forward model, is to modify a free-space steering vector to account for non-uniformities in the configuration of the wellbore and surrounding formation.
18. The system of claim 15 , wherein the data-processing facility is to derive the detection threshold from the empirical data bases on one or statistical metrics comprising at least one of a sensitivity, a false-alarm rate, or a false-negatives rate.
19. The system of claim 18 , wherein the non-uniformities comprise at least one of multiple barriers to fluid flow or multiple media between the acoustic source and the sensors.
20. The system of claim 18 , wherein the data-processing facility, in creating the forward model, is to modify a free-space steering vector to account for the acoustic source being a near-field source.