Discrimination of P-Wave Interval  in Time-Quefrency Analysis  for Proximity Microseismic Doublets Koji Nagano Muroran Ins...
What we want to know  Fine structures Flow paths in geothermal reservoir Cloud Soultz in France Geothermal fracture reserv...
Proximity microseismic doublets <ul><li>Similar waveforms </li></ul><ul><li>Interval between events is short,  <1s. </li><...
Accurate location in proximity MS doublets  microseismic doublets with long interval long  interval different velocity mod...
Relative location P-wave interval Relative location Fine structure of fracture reservoir The relative location estimated b...
Cepstrum analysis for proximity MS doublets <ul><li>Cepstrum analysis is used to detect interval </li></ul>
Cepstrum  Interval
Two cepstrum peaks <ul><li>Which is the P-wave interval in the two cepstrum peaks ?  </li></ul>P S P ? S ?
Time-quefrency analysis -  Window function suppresses data after the onset of the  2nd S-wave. -  I shorten the window fun...
Contour plot and cepstrum graph Contour plot:  To discriminate the P-wave peak    from the S-wave peak identification of t...
4 check points in contour plot P-wave interval peak <ul><li>starts more early. The window function suppresses the 2nd S-wa...
Soultz geothermal field 15089 MS events were located during hydraulic injection in 1993.  The data were monitored at 4 sta...
Typical result of the time-quefrency analysis Early start Stable, low, and narrow peak Some artifacts are visible quefrenc...
9 events show P-wave interval peak The P-wave interval should be detected at 4 stations  to determine relative location. q...
Relative location The P-wave intervals in the Proximity MS doublets are compared among the 4 stations.  Moriya 2003 showed...
Conclusions <ul><li>Proximity MS doublets are a good tool to estimate fine structures of a geothermal reservoir. </li></ul...
difficult result of the time-quefrency analysis Which peak starts more early  ???? The upper peak is  more stable, lower, ...
Cepstrum and auto-correlation
Rotation of coordinates 3 component seismic detector was used. 3D particle motion associated with seismic waves was measur...
A result of the rotation X-Y-Z P-S1-S2 S1: the maximum variance on S-wave plane S2: P and S1 are perpendicular  P-wave pol...
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DISCRIMINATION OF P-WAVE INTERVAL IN TIME--QUEFRENCY ANALYSIS FOR PROXIMITY MICROSEISMIC DOUBLETS.ppt

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  • Thank you, Vern Singhroy, Canada Centre for Remote Sensing and Jill Pearse, Alberta Geological Survey Good morning, everybody. My name is Koji Nagano, From Muroran Institute of Technology, Japan. Today I will talk about proximity microseismic doublets. This is the proximity microseismic doublets. These microseismic events have a potential to reveal a fine structure of a geothermal fracture reservoir.
  • Measurement of a geothermal fracture reservoir is important in geothermal engineering. We locate MS sources to know the fracture reservoir. However, the locations of MS events look like clouds. Information such clouds can provide is not sufficient to make the geothermal system. We want to know a fine structure of fracture networks and flow paths which water runs through
  • I have studied similar events, doublets and multiplets. Analyses of such similar events have provided precise relative location. In my presentation, I will talk about proximity MS doublets. This is proximity MS doublets. They have a similar waveform. Interval between the events is very short. It is shorter than 1 s. When the interval is so short, the 2nd event arrives before attenuation of the 1st event.
  • When the proximity MS doublets can be analyzed, the relative location is more precise than the conventional similar event analysis. Similar MS events that have long interval have been studied. The similar event analysis has provided good information about a fracture reservoir. However, the similar event analysis has a problem on its accuracy. In the similar event analysis, when the 2nd event occurs, velocity of the media is different because of induced fracture. On the other hand, in the analysis of the proximity MS doublets, the velocity is constant. Therefore, The relative location between the proximity MS doublets is more precise than that between the similar events with long interval.
  • When we can estimate P-wave interval between the proximity MS doublets, We can calculate relative location between the 1st event and the 2nd event. The relative location estimated based on the interval is much precise than that calculated from the each sources We can know a fine structure from the relative locations.
  • I use capstrum analysis to estimate the interval between the proximity MS doublets. The cepstrum shows clear peaks at the intervals.
  • Cepstrum is inverse Fourier transform of the logarithm of the power spectrum. When two events overlap and its interval is T, the cepstrum shows a clear peak at the interval T because of this additive periodic component .
  • I use capstrum analysis to estimate the interval between the proximity MS doublets. However, there are two peaks in the cepstrum. One peak indicates interval between arrivals of P-wave. Another peak indicates interval between arrivals of S-wave. We can not determine which peak represents the P-wave interval peak by using the cepstrum analysis alone.
  • I design time-quefrency analysis to discriminate the P-wave interval peak from the S-wave interval peak in the cepstrum. Window function isolates the 1st and the 2nd P-waves. I shorten the window function to suppresses the data after the 2nd S-wave arrival. The results of the windowed data are represented in a contour plot of 3 dimensional data, time-quefrency-cepstrum. The time axis means the terminal of the window function. Two dimensional graphs, quefrency-cepstrum, are also plotted to detect the precise interval.
  • We have the two figures to understand the results of the time-quefrency analysis. The contour plot has some advantages to discriminate the P-wave interval peak from the S-wave interval peak. We can identify the cepstrum peaks in the contour plot. Continuity of a peak is important information in the contour plot. We examine its length and its start time to discriminate the P-wave interval peak. Width of the peak is also important information. Artifact peaks are identified in the contour plot. The Cepstrum-quefrency graph is better to detect the precise quefrency of the peak than the contour plot. It is difficult to exclude the artifacts in the cepstrum-quefrency graph alone.
  • 4 check points are used to discriminate the P-wave interval peak. The P-wave interval peak starts more early. The P-wave interval peak is more stable than the S-wave interval peak. The window function suppressed the 2nd S-wave. The S-wave loses its similarity and its peak is not stable. The P-wave interval peak is lower than the S-wave peak because P-wave is smaller than S-wave. The P-wave interval peak is narrower than the S-wave peak. I examine these 4 check points to discriminate the P-wave interval in the contour plot.
  • I analyzed MS data that were recorded in Soultz geothermal field in France. Hydraulic injection was carried out in 1993 and a lot of MS events were observed. Fifteen thousand MS events were located. I checked all waveforms whose source were located and 230 proximity MS doublets were detected.
  • This is a typical result of the time-quefrency analysis of the proximity MS doublets. Rough estimates of the interval are detected in the time domain waveform. This is a cepstrum of the total waveform. We can see two peaks here. This contour plot shows two peaks. This peak starts early. Therefore , I conclude that this is the P-wave interval peak. However, we cannot determine the precise quefrency of the P-wave peak in the contour plot. I also make these cepstrum-quefrency graphs to detect the precise quefrency of the P-wave interval.
  • I analyzed 9 events of the proximity MS doublets that were recorded in 4 stations. These are the results of the time-quefrency analysis. 230 proximity MS doublets were observed. But, quality of the data that were recorded in one station was not good to detect the P-wave interval. Therefore, I located just only 9 events and the number of the located events was small. When the P-wave intervals are estimated at 4 stations, we can estimate its relative location between the 1st event and the 2nd event.
  • This figure shows the relative locations of the proximity MS doublets. The arrows show the relative location. Moriya analyzed similar MS events in the same data. The similar MS events had long interval. The longest interval was a day. He showed 4752 relative location. I have not yet analyzed relationship between the relative locations. I will examine my relative locations and Moriya’s relative locations.
  • This is another result of the time-quefrency analysis. Two peaks are visible in the contour plot. But the two peaks start at the almost same time. We cannot determine the P-wave interval peak based on only the start time of the peaks. I examine the other check points in the contour plot and cepstrum graphs . The upper peak is more stable in the cepstrum-quefrency graph. It is lower and narrower than the lower peak. Therefore, I conclude that the upper peak represents the P-wave interval.
  • A three component seismic detector is used to detect the microseismic events. The 3C detector measures 3 dimensional particle motion associated with the seismic waves. Data in the direction of the P-wave polarization is analyzed because P-wave is larger than that in the other directions.
  • This is a result of the coordinate rotation. We can analyzed the data that is independent from the sensor location.
  • DISCRIMINATION OF P-WAVE INTERVAL IN TIME--QUEFRENCY ANALYSIS FOR PROXIMITY MICROSEISMIC DOUBLETS.ppt

    1. 1. Discrimination of P-Wave Interval in Time-Quefrency Analysis for Proximity Microseismic Doublets Koji Nagano Muroran Institute of Technology Muroran, Hokkaido, 050-8585, Japan [email_address]
    2. 2. What we want to know Fine structures Flow paths in geothermal reservoir Cloud Soultz in France Geothermal fracture reservoir
    3. 3. Proximity microseismic doublets <ul><li>Similar waveforms </li></ul><ul><li>Interval between events is short, <1s. </li></ul>
    4. 4. Accurate location in proximity MS doublets microseismic doublets with long interval long interval different velocity model 1st event 2nd event proximity microseismic doublets More precise than doublets with long interval
    5. 5. Relative location P-wave interval Relative location Fine structure of fracture reservoir The relative location estimated based on the interval is much precise than that calculated from the each sources.
    6. 6. Cepstrum analysis for proximity MS doublets <ul><li>Cepstrum analysis is used to detect interval </li></ul>
    7. 7. Cepstrum Interval
    8. 8. Two cepstrum peaks <ul><li>Which is the P-wave interval in the two cepstrum peaks ? </li></ul>P S P ? S ?
    9. 9. Time-quefrency analysis - Window function suppresses data after the onset of the 2nd S-wave. - I shorten the window function. - When the window function suppresses the 2nd S-wave, S-waves lose similarity and the S-wave peak decreases. cepstrum quefrency quefrency Terminal of window <ul><li>Cepstrum-quefrency graph is used to detect the interval. </li></ul>cepstrum
    10. 10. Contour plot and cepstrum graph Contour plot: To discriminate the P-wave peak from the S-wave peak identification of the cepstrum peaks - continuity of the peak, - comparison of the peak width - exclusion of artifacts - low resolution in quefrency Cepstrum graph: - precise detection of quefrency - difficult discrimination from artifacts quefrency Terminal of window cepstrum quefrency
    11. 11. 4 check points in contour plot P-wave interval peak <ul><li>starts more early. The window function suppresses the 2nd S-wave. The 1st and 2nd P-waves are isolated. </li></ul><ul><li>is more stable. The S-wave peak decreases because the S-wave loses similarity </li></ul><ul><li>is lower. The P-wave is smaller than the S-wave </li></ul><ul><li>is narrower. </li></ul>P S quefrency Terminal of window cepstrum
    12. 12. Soultz geothermal field 15089 MS events were located during hydraulic injection in 1993. The data were monitored at 4 stations Data length was 1.6 s. Sampling frequency was 5000 Hz. Proximity MS doublets were 230
    13. 13. Typical result of the time-quefrency analysis Early start Stable, low, and narrow peak Some artifacts are visible quefrency Terminal of window cepstrum quefrency
    14. 14. 9 events show P-wave interval peak The P-wave interval should be detected at 4 stations to determine relative location. quefrency Terminal of window quefrency Terminal of window quefrency Terminal of window quefrency Terminal of window
    15. 15. Relative location The P-wave intervals in the Proximity MS doublets are compared among the 4 stations. Moriya 2003 showed 4752 relative locations of MS doublets with long interval. We will examine my relative locations and his data.
    16. 16. Conclusions <ul><li>Proximity MS doublets are a good tool to estimate fine structures of a geothermal reservoir. </li></ul><ul><li>Time-quefrency analysis can provide the P-wave interval between the proximity MS doublets. </li></ul><ul><li>4 check points are indicated to discriminate the P-wave interval in a contour plot of the time-quefrency analysis. </li></ul><ul><li>I have estimated relative locations of 9 events recorded in Soultz geothermal field. </li></ul>
    17. 17. difficult result of the time-quefrency analysis Which peak starts more early ???? The upper peak is more stable, lower, and narrower than the lower peak. S P quefrency Terminal of window cepstrum quefrency
    18. 18. Cepstrum and auto-correlation
    19. 19. Rotation of coordinates 3 component seismic detector was used. 3D particle motion associated with seismic waves was measured. Data in the direction of the P-wave polarization is analyzed in the time-quefrency analysis. The data is larger than that in the other directions We have clear P-wave peak in the contour plot when the data in the direction of the P-wave polarization is analyzed in the time-quefrency analysis.
    20. 20. A result of the rotation X-Y-Z P-S1-S2 S1: the maximum variance on S-wave plane S2: P and S1 are perpendicular P-wave polarization is estimated in the data at the onset of the P-wave

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