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# ÖNCEL AKADEMİ: INTRODUCTION TO GEOPHYSICS

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Seismic Reflection: Acquisiton, Processing, and Waveform Analysis

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• Normal Incidence: Reflections from the common source/receiver positions result from ray paths striking reflectors at 90.
• An unmigrated time section , presents each seismic trace as if a source and a receiver were in the same position.
• ### ÖNCEL AKADEMİ: INTRODUCTION TO GEOPHYSICS

1. 1. Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Seismic Reflection: Acquisiton, Processing, and Waveform Analysis Introduction to Geophysics-KFUPM
2. 2. Review: Travel-Time Curves Measurable features in the shot record <ul><li>X crit (Critical distance) - distance at which first head wave arrive at surface </li></ul><ul><li>X cross (Cross-over distance) - is point at which head wave overtakes direct wave </li></ul>• slope is 1/V 1 for direct wave and 1/V 2 for head wave • direct wave travels at velocity V 1 and head wave at V 2 <ul><li>Intercept time t i - the time at which back-extrapolated refractor curve intersects time axis </li></ul>Introduction to Geophysics-KFUPM
3. 3. Seismic Reflection <ul><li>Refraction and reflection studies are complimentary. </li></ul><ul><li>Refraction providing gross crustal velocities and thickness, </li></ul><ul><li>Reflection showing finer details of structure and stratigraphy. </li></ul>Introduction to Geophysics-KFUPM Fig. 5.1 of Lillie
4. 4. Requirements for successful works by Reflection and Refraction <ul><li>Refraction requires that receivers extend to well beyond the X cr , so that refraction spread lengths need to be five to ten times the depth to the deepest refractor of interest . </li></ul><ul><li>Reflections require usually vertically arriving which is less than the X c . Then, reflection spread lengths therefore approximate the depth of the deepest reflector of interest. </li></ul>Introduction to Geophysics-KFUPM Fig. 5.1 of Lillie
5. 5. Seismic Reflection <ul><li>Since it was developed in the 1920s and 30s as a tool for oil and gas exploration (Petty, 1976). </li></ul><ul><li>It has been used mostly as a Geophysical Technique for </li></ul><ul><li>Petroleum Application </li></ul><ul><li>In Conjunction with Refraction </li></ul><ul><li>Land and at Sea </li></ul><ul><li>On a Variety of Scales - 10’s of Meters to </li></ul><ul><li>Crust and Mantle </li></ul>Introduction to Geophysics-KFUPM
6. 6. Objectives <ul><li>Visualizing high resolution of subsurface detail based upon the Seismic Velocity Inversion as: </li></ul><ul><li>Structure and Stratigraphy </li></ul><ul><li>Physical Properties of Rock/Sediment Layers </li></ul>Introduction to Geophysics-KFUPM
7. 7. Seismic Reflection - Onland Introduction to Geophysics-KFUPM
8. 8. Oncel, 2004 Kadif Area Introduction to Geophysics-KFUPM
9. 9. Qatif Area Oncel, 2004 Introduction to Geophysics-KFUPM
10. 10. Oncel, 2004 Introduction to Geophysics-KFUPM Qatif Area
11. 11. Introduction to Geophysics-KFUPM Vibrator Truck Oncel, 2004
12. 12. Introduction to Geophysics-KFUPM Vibrator Truck Oncel, 2004
13. 13. At Sea
14. 14. Introduction to Geophysics-KFUPM Oncel, 2004 Recording Truck
15. 15. Introduction to Geophysics-KFUPM Oncel, 2004 Recording Truck
16. 16. Introduction to Geophysics-KFUPM Oncel, 2004 Inside the Recording Truck
17. 17. Introduction to Geophysics-KFUPM Oncel, 2004
18. 18. Introduction to Geophysics-KFUPM
19. 19. Introduction to Geophysics-KFUPM
20. 20. Introduction to Geophysics-KFUPM
21. 21. Introduction to Geophysics-KFUPM
22. 22. Introduction to Geophysics-KFUPM
23. 23. Normal Incidence Seismic Section = Resulting from raypaths Striking reflectors at 90°. What is a Seismic Section? Introduction to Geophysics-KFUPM
24. 24. What is a Seismic Section? Introduction to Geophysics-KFUPM
25. 25. Seismic Line Hundreds to Thousands of Seismic Traces Introduction to Geophysics-KFUPM
26. 26. <ul><li>Composed of individual seismograms or seismic traces </li></ul><ul><li>Reflector or Event has a two-way traveltime and amplitude </li></ul><ul><li>Reflector or Event as a Wavelet </li></ul>Nature of Seismic Section Introduction to Geophysics-KFUPM
27. 27. <ul><li>Acoustic Impedance </li></ul>Introduction to Geophysics-KFUPM
28. 28. Most geophones are designed to respond the motions that are the vertical. Reflected compressional waves (vertical particle motion) are enhanced, at the expense of events that produce horizontal motions at the surface (direct compressional waves; reflected shear waves). Enhancement: Compressional Waves Introduction to Geophysics-KFUPM
29. 29. Single Channel Seismic Reflection Introduction to Geophysics-KFUPM
30. 30. Seismic Profile <ul><li>Produce Quasi-Cross-Section or 3-D Volume </li></ul><ul><li>Translation from 2-way Travel Times to Depth </li></ul>Introduction to Geophysics-KFUPM
31. 31. Reading Assignment For next time read over pages 100 -110 in Chapter 5 Introduction to Geophysics-KFUPM