Seismic 2D Reflection Processing and Interpretation of ... - Posiva

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16Figure 11. First three shots with AGC from the line S28 after the preliminary filteringand refraction statics. Trace number on X-axis and two way travel time in seconds onY-axis.Deconvolution (Table 2, item 8) applied Wiener predictive error filtering. Aim was torecover high frequencies, attenuate multiples, equalize amplitudes, produce a zerophasewavelet and generally affect the wave shape. Deconvolution was performedusing the following parameters and is one of the most important processing steps.First lag of prediction filter: 0,0001 sOperator length: 0,040 sStart of autocorrelation window: min offset 0,1 s, max offset 0,12 sEnd of autocorrelation window: min offset 0,3 s, max offset 0,4 sNoise: 1 %Stacked sections were compared with and without deconvolution in Figure 21 a) andFigure 21 b), respectively. Figures indicate the effect of deconvolution. After thedeconvolution the data was filtered (Table 2, item 9) with similar filter as beforedeconvolution, using parameters shown below.0-100 mslower cutoff frequency: 70 Hzlower plateau frequency: 140 Hzupper plateau frequency: 300 Hzupper cutoff frequency: 450 Hz
1750-200 mslower cutoff frequency: 60 Hzlower plateau frequency: 120 Hzupper plateau frequency: 300 Hzupper cutoff frequency: 450 Hz150-500 mslower cutoff frequency: 50 Hzlower plateau frequency: 100 Hzupper plateau frequency: 270 Hzupper cutoff frequency: 400 HzShot gather after the deconvolution and the second filtering is shown in Figure 12.Now the reflectors after 130 ms and 200 ms are seen. It is hard to see these reflectors inthe shot gathers where the shot point is located between the geophones because of theairwave.Figure 12. Shot gather from the line S28 after deconvolution and second filtering withAGC. Reflectors can be seen under 130 ms and 200 ms marked with red and bluearrows respectively. Airwave is marked with orange arrow. Trace number on X-axisand two way travel time in seconds on Y-axis. First 6 shots on line.The behaviour of records according to shot offset was viewed in common offsetgathers (Figure 13). The airwave (red line) was removed by muting (Table 2, item 10)at velocity 340 m/s vs offset. The air blast duration was set as a function of offset.Number of points to taper before hard mute was set to 1000. Common offset gather
Page 1 and 2: Working Report 2006-114Seismic 2D R
Page 3 and 4: Seismic 2D Reflection Processing an
Page 5: 1TABLE OF CONTENTSABSTRACTTIIVISTEL
Page 9 and 10: 52 SOURCE DATA2.1 Surface seismic d
Page 11 and 12: 7Figure 2. Survey array. At the lin
Page 13 and 14: 93 DATA PROCESSINGThe aim was to pe
Page 15 and 16: 11Processing was performed using fr
Page 17 and 18: 13Figure 7. Original spectrum from
Page 19: 15new datum and elevation differenc
Page 23 and 24: 19Original first breaks were picked
Page 25 and 26: 21Figure 17. Shot gather from the l
Page 27 and 28: 23a)CDP position b)CDP numberFigure
Page 29 and 30: 25a) b)Figure 21. a) Final stacked
Page 31 and 32: 27Figure 23. Stacked section withou
Page 33 and 34: 294 INTERPRETATIONAfter the seismic
Page 35 and 36: 31events) indicates presence of off
Page 37 and 38: 33Table 4. Positions and dips for m
Page 39 and 40: 35In Figure 28 are shown the picked
Page 41 and 42: 37Figure 30. 3D view (from the sout
Page 43 and 44: 39Figure 32. Matching events in the
Page 45 and 46: 415 CONCLUSIONSAim of this work was
Page 47 and 48: 43REFERENCESAhokas, H. & Vaittinen,
Page 49 and 50: 45APPENDIX 1. STACKED SEISMIC SECTI
Page 51 and 52: 47Figure 3. Stacked section from th
Page 59 and 60: 55Figure 11. Stacked section from t
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67Figure 23. Stacked section from t
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Figure 41. Stacked section from the
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Figure 45. Stacked section from the
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Seismic 2D Reflection Processing and Interpretation of ... - Posiva

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