Subterranean formation monitoring using frequency domain weighted analysis

1. A method of seismic monitoring of a subterranean formation comprising:

receiving resulting signals emanating from the subterranean formation, wherein the resulting signals are caused, at least in part, by incident signals emitted from a plurality of seismic sources located above the subsurface formation and wherein the resulting signals are received for a predetermined emission length of time;

dividing a total time length of at least a part of the resulting signals into a plurality of sub-samples such that each sub-sample has a time length smaller than the total time length;

for one or more of the sub-samples:

determining a frequency content of the sub-sample in a frequency domain; and

assigning a weight to one or more components of the frequency content of the sub-sample to produce a weighted frequency content of the sub-sample, wherein the assigned weight is based, at least in part, on a comparison of (1) the frequency components of the sub-sample to (2) frequency components of received signals from previous times;

combining the weighted frequency contents of the sub-samples to produce a weighted sample; and

determining one or more properties of the subsurface formation based, at least in part, on the weighted sample.

2. The method of claim 1 , wherein the step of assigning a weight to one or more components of the frequency content of the sub-sample to produce a weighted frequency content of the sub-sample is based, at least in part, on an estimate of the amount of noise present in the frequency content of the sub-sample and further comprises:

determining one or more amplitudes of frequency components of the sub-sample that are adjacent to one or more frequencies of the incident signals.

3. The method of claim 2 , further comprising:

determining a set of median value for frequency components that are adjacent to one or more frequencies of the incident signals; and

wherein assigning a weight to one or more components of the frequency content of the sub-sample to produce a weighted frequency content of the sub-sample further comprises determining if the amplitude a frequency component of the sub-sample is above a corresponding median value for the frequency component and, if so, removing the frequency component from the sub-sample.

4. The method of claim 1 , wherein determining one or more properties of the subsurface formation based, at least in part, on the weighted sample further comprises:

combining a plurality of weighted samples, wherein the weights samples correspond to a plurality of received resulting signals based on monofrequency incident signals with different frequencies; and

determining one or more properties of the subsurface formation based, at least in part, on the combined plurality of weighted samples.

5. The method of claim 1 , further comprising:

controlling the plurality of seismic sources to each emit an incident signal having a selected frequency for a predetermined emission length of time.

6. The method of claim 5 , wherein the selected frequency for two or more of the seismic sources is the same.

7. The method of claim 1 , wherein determining one more properties of the subsurface formation based, at least in part, on the frequency content of the sub-samples, as weighted by the weight of the sub-sample comprises:

monitoring fluid production from the subsurface formation.

8. The method of claim 1 , wherein determining one more properties of the subsurface formation based, at least in part, on the frequency content of the sub-samples, as weighted by the weight of the sub-sample comprises:

monitoring a steam injection operation in the subsurface formation.

9. The method of claim 1 , wherein the sub-samples have equal lengths.

10. A seismic monitoring system, comprising:

one or more seismic sources to emit incident signals into a subterranean formation for a predetermined emission length of time;

one or more seismic receivers to receive resulting signals emanating from the subsurface formation;

at least one processor; and

a memory including non-transitory executable instructions that, when, executed cause the at least one processor to:

divide a total time length of at least a part of the resulting signals into a plurality of sub-samples such that each sub-sample has a time length smaller than the total time length;

for one or more of the sub-samples:

determine a frequency content of the sub-sample in a frequency domain; and

assign a weight to one or more components of the frequency content of the sub-sample to produce a weighted frequency content of the sub-sample, wherein the assigned weight is based, at least in part, on a comparison of (1) the frequency components of the sub-sample to (2) frequency components of received signals from previous times;

combine the weighted frequency contents of the sub-samples to produce a weighted sample; and

determine one or more properties of the subsurface formation based, at least in part, on the weighted sample.

11. The seismic monitoring system of claim 10 , wherein the executable instructions that cause the at least one processor to assigning a weight to one or more components of the frequency content of the sub-sample to produce a weighted frequency content of the sub-sample, wherein the assigned weight is based, at least in part, on an estimate of the amount of noise present in the frequency content of the sub-sample comprises further causes the at least one processor to:

determine one or more amplitudes of frequency components of the sub-sample that are adjacent to one or more frequencies of the incident signals.

12. The seismic monitoring system of claim 10 , wherein the executable instructions further cause the at least one processor to:

determine a set of median value for frequency components that are adjacent to one or more frequencies of the incident signals; and

wherein the executable instructions that case the at least one processor to assign a weight to one or more components of the frequency content of the sub-sample to produce a weighted frequency content of the sub-sample further cause the at least one processor to:

determine if the amplitude a frequency component of the sub-sample is above a corresponding median value for the frequency component and, if so, removing the frequency component from the sub-sample.

13. The seismic monitoring system of claim 10 , wherein the executable instructions further cause the at least one processor to:

combine a plurality of weighted samples, wherein the weights samples correspond to a plurality of received resulting signals based on monofrequency incident signals with different frequencies; and

determine one or more properties of the subsurface formation based, at least in part, on the combined plurality of weighted samples.

14. The seismic monitoring system of claim 10 , wherein the executable instructions that cause the at least one processor to determine a frequency content of the sub-sample further causes the at least one processor to:

determine whether the sub-sample includes frequency components that are indicative of impulsive signals or noise.

15. The seismic monitoring system of claim 10 , wherein the executable instructions further cause the at least one processor to:

control the plurality of seismic sources to each emit an incident signal having a selected frequency for a predetermined emission length of time.

16. A non-transitory computer-readable medium, comprising instructions that, when executed by a processor, cause the processor to:

receive resulting signals emanating from the subterranean formation, wherein the resulting signals are caused, at least in part, by incident signals emitted from a plurality of sources located above the subsurface formation and wherein the resulting signals are received for a predetermined emission length of time;

divide a total time length of at least a part of the resulting signals into a plurality of sub-samples such that each sub-sample has a time length smaller than the total time length;

for one or more of the sub-samples:

determine a frequency content of the sub-sample in a frequency domain; and

assign a weight to one or more components of the frequency content of the sub-sample to produce a weighted frequency content of the sub-sample, wherein the assigned weight is based, at least in part, on a comparison of (1) the frequency components of the sub-sample to (2) frequency components of received signals from previous times;

combine the weighted frequency contents of the sub-samples to produce a weighted sample; and

determine one or more properties of the subsurface formation based, at least in part, on the weighted sample.

17. The non-transitory computer-readable medium of claim 16 , wherein the executable instructions that cause the at least one processor to assign a weight to one or more components of the frequency content of the sub-sample to produce a weighted frequency content of the sub-sample, and wherein the assigned weight is based, at least in part, on an estimate of the amount of noise present in the frequency content of the sub-sample, further causes the at least one processor to:

determine one or more amplitudes of frequency components of the sub-sample that are adjacent to one or more frequencies of the incident signals.

18. The non-transitory computer-readable medium of claim 16 , wherein the executable instructions further cause the at least one processor to:

determine a set of median value for frequency components that are adjacent to one or more frequencies of the incident signals; and

wherein the executable instructions that case the at least one processor to assign a weight to one or more components of the frequency content of the sub-sample to produce a weighted frequency content of the sub-sample further cause the at least one processor to:

determine if the amplitude a frequency component of the sub-sample is above a corresponding median value for the frequency component and, if so, removing the frequency component from the sub-sample.

19. The non-transitory computer-readable medium of claim 16 , wherein the executable instructions that cause the processor to determine a frequency content of the sub-sample further cause the processor to:

determine whether the sub-sample includes frequency components that are indicative of impulsive signals or noise.

20. The non-transitory computer-readable medium of claim 16 , further comprising executable instructions that cause the processor to: control a plurality of seismic sources to each emit an incident signal having a selected frequency for a predetermined emission length of time.