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

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10Figure 5. Raw shot gather from the line S28 with automatic gain control. First nineshots on line. Trace number on X-axis and two way travel time in seconds on Y-axis.Table 2. Processing flow and parameters.Processing stepParameters1. Convert SEG2 data into SEGY (Figure 5)2. Remove noisy traces3. Set geometry4. Geometric spreading correction 1,5Multiply by t5. Bandpass filter (Figure 8) 30-60-400-600 Hz6. Refraction statics (Figure 11)7. Set CDP numbers8. Deconvolution (Figure 12) Minlag: 0,01msMaxlag: 40 msStart of autocorrelation: 0 offset: 100 ms; maxoffset: 120 sEnd of autocorrelation: 0 offset: 300 ms; maxoffset: 400 msNoise: 1 %9. Bandpass filter 0-100 ms: 70-140-300-450 Hz50-200 ms: 60-120-300-450 Hz150-500 ms: 50-100-270-400 Hz10. Mute (Figure 14) Linear velocity: 340 m/sWidth: 0 offset: 10 ms; max offset: 15 msTaper before hard mute: 1000 samples11. Automatic Gain Control (AGC) Window: 50 ms12. Residual statics (Figure 16)13. Normal Moveout (NMO) (Figure 17) Velocity: 5000 m/sStretch mute: 4Number of points to taper: 100014. Stack (Figure 21 a) )
11Processing was performed using free seismic data processing package Seismic Unix(SU) (Stockwell & Cohen 2002). Refraction seismic data SEG-2 format was convertedinto SEG-Y format before importing into SU (Table 2, item 1), using sharewaresoftware IXseg2segy (Interpex Ltd). Number of samples in SEG-2 format was limited,and conversion was preferred rather than down sampling. In down sampling somefeatures of the data could have been lost.Bad traces to be removed (Table 2, item 2) were selected visually using ReflexWsoftware (ReflexW) and then removed in SU. Typically these geophones are locatednear the shots or the geophones were not properly mounted into the ground.The next step after removing the noisy traces was setting the geometry (Table 2, item3). As described in Chapter 2 the geophone spacing and shot spacing are irregular.Line number S28 consists of 432 seismic traces and for each trace, trace number, shotnumber, geophone number, shot position, geophone position, common depth point(CDP) position and offset must be set. Common depth point is a common reflectingpoint at depth on a reflector (see Figure 6). In the case of planar layers, CDP is ahalfway point between a source and a receiver as illustrated in Figure 6. In this workthe CDP locations have been computed assuming that reflectors are planar. Geometrywas read from the ASCII file, which was created with Microsoft Excel, and applied todata using Seismic Unix. Example of geometry file is shown inFigure 6. Definition of a common depth point in the case of a planar reflector.
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: 93 DATA PROCESSINGThe aim was to pe
Page 17 and 18: 13Figure 7. Original spectrum from
Page 19 and 20: 15new datum and elevation differenc
Page 21 and 22: 1750-200 mslower cutoff frequency:
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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61Figure 17. 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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