Surface wave tomography using sparse data acquisition
Method and system for ongoing monitoring for underground structure at or near a production wellpad is provided. The system includes a sparse acquisition grid and utilizes information obtained from Rayleigh waves to monitor subsurface structures.
1. A method for monitoring a frozen subsurface structure to detect thawing-related problems, the method comprising:
obtaining seismic data;
estimating travel time or phase delay or both of Rayleigh waves in the seismic data at a central frequency;
performing tomography to the travel time or the phase delay estimated at the central frequency to obtain a slice of seismic velocity at the central frequency;
repeating the estimating of the travel time or phase delay or both and the performing of the tomography to the travel time or the phase delay for a range of central frequencies;
performing a dispersion inversion on slices of seismic velocity for the range of central frequencies to obtain a 3-D velocity cube in depth, the 3-D velocity cube in depth providing an indication of thawing of the frozen subsurface structure; and
monitoring the thawing of the frozen subsurface structure via repeating at least the obtaining of the seismic data every day, every few days, or bi-weekly to determine a progression of the thawing.
2. The method of claim 1 , wherein the subsurface structure includes a near surface layer over a hydrocarbon production reservoir.
3. The method of claim 1 , wherein the seismic data is obtained using a sparse acquisition grid that includes between about 1 to about 25 seismic sources.
4. The method of claim 1 , wherein the seismic data is obtained using a non-uniform grid of seismic sources.
5. The method of claim 1 , wherein the seismic data is obtained using a non-uniform grid of seismic receivers.
6. The method of claim 1 , wherein the range of central frequencies is between about 0.1 Hz or about 50 Hz.
7. The method of claim 1 , wherein the monitoring is continuous for at least about one month.
8. The method of claim 1 , wherein the monitoring is continuous for at least about a year.
9. The method of claim 1 , wherein the monitoring monitors production anomalies.
10. A method for monitoring a frozen subsurface structure to detect thawing-related problems, the method comprising:
obtaining seismic data using a sparse acquisition grid;
estimating travel time or phase delay or both of Rayleigh waves in the seismic data at a central frequency;
performing tomography to the travel time or the phase delay estimated at the central frequency to obtain a slice of seismic velocity at the central frequency;
repeating the estimating of the travel time or phase delay or both and the performing of the tomography to the travel time or the phase delay for a range of central frequencies;
performing a dispersion inversion on slices of seismic velocity for the range of central frequencies to obtain a 3-D velocity cube in depth, the 3-D velocity cube in depth providing an indication of thawing of the frozen subsurface structure; and
f) monitoring the thawing of the frozen subsurface structure via repeating at least the obtaining of the seismic data every day, every few days, or bi-weekly to determine a progression of the thawing.
11. The method of claim 10 , wherein the sparse acquisition grid includes less than about 25 seismic sources.
12. The method of claim 10 , wherein the sparse acquisition grid includes less than about 10 seismic sources.
13. The method of claim 10 , wherein the sparse acquisition grid includes 1 seismic source.
14. The method of claim 10 , wherein the subsurface structure includes a near surface layer over a hydrocarbon production reservoir.
15. The method of claim 10 , wherein the range of central frequencies is between about 0.1 Hz or about 50 Hz.
16. The method of claim 10 , wherein the monitoring is continuous for at least about one month.
17. The method of claim 10 , wherein the monitoring is continuous for at least about one year.
18. The method of claim 1 , wherein the thawing-related problems include deformation or compaction of the frozen subsurface structure.
19. The method of claim 1 , wherein the thawing is caused by steam-assisted production.
20. The method of claim 1 , wherein the seismic data is obtained via emitting a shot from at least one seismic source.