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

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18after the muting is shown in Figure 14. After the muting automatic gain control (AGC)was applied (Table 2, item 11) to data in order to improve visibility of late-arrivingevents in which attenuation or wavefront divergence has caused amplitude decay.Figure 13. Offset gather from the line S28. Airwave with the velocity of 340 m/s ismarked with red line.Figure 14. Common offset gather from the line S28 after muting.The calculated refraction statics were quite good on basis of lining up of P-arrival (seeFigure 12). Some residual errors still remain, which must be corrected for. Theseerrors can be seen after deconvolution as displacements in first breaks and the reflectedevents. The residual statics (Table 2, item 12) are plus-minus errors with respect to thelong wavelength trend of travel time anomalies due to the near-surface effects (Li1999). Corrections were applied to traces by picking the first break maxima andcomputing their differences to the theoretical first breaks, which were computed duringthe refraction statics.
19Original first breaks were picked to zero amplitude (crossover). This work appliedmaximum amplitude, so datum was shifted half a wavelength (2-3 ms). After this shift,datum was 0 m +/- 2 m. This is because before the residual statics datum was 5 m +/- 2m which corresponds to 2 ms shift in two way travel time. In Figure 15 is shown ashot gather and in Figure 20 b) a stacked section before the residual statics and inFigure 16 a shot gather and in Figure 21 a) a stacked section after the residual statics(see also Figure 23 and Figure 24).Residual statics makes the reflecting events clearer and straighter. Residual staticswere not applied to the data from the survey lines S33 and S34 because reliable pickingof first break maxima was not possible due to noisy data (see Figure 4).Figure 15. Shot gather from the line S28 after the muting but before residual statics.Trace number on X-axis and two way travel time in seconds on Y-axis. First 4 shots online.
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 and 20: 15new datum and elevation differenc
Page 21: 1750-200 mslower cutoff frequency:
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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69Figure 25. 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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