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Chapter 7

Chapter 7. 3-D Seismic Exploration. Introduction. What is 3-D seismic? It is a group of closely spaced 2-D source and receiver lines forming a grid that covers an area. Receiver and source lines may be perpendicular or at an angle. Why 3-D seismic?

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Chapter 7

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  1. Chapter 7 3-D Seismic Exploration

  2. Introduction • What is 3-D seismic? • It is a group of closely spaced 2-D source and receiver lines forming a grid that covers an area. • Receiver and source lines may be perpendicular or at an angle. • Why 3-D seismic? • 3-D migration eliminates misties over dipping reflectors. • presents a more detailed image of the subsurface

  3. 3-D Terminology (Cordsen et al., 2000)

  4. 3-D Terminology (Cordsen et al., 2000)

  5. 3-D Terminology • Inline: direction parallel receiver lines. • Crossline: direction orthogonal receiver lines. • CMP bin: a small rectangle (1/2 RI x 1/2 SI) that contains all the traces which belong to the same CMP. • Box (unit cell): area bounded by two adjacent receiver lines and two adjacent source lines. • Patch (template): area of all live receivers recording from the same source. • Swath: length over which sources are recorded without crossline rollover.

  6. 3-D Swath Shooting Method • Receiver lines are laid in parallel lines. • Source lines are laid in parallel lines in a direction orthogonal to receiver lines. • An area of receivers (patch) is activated. • Source at patch center is shot and recorded. • Patch is moved crossline one source interval. • Source at new patch center is shot and recorded. • Repeat this until source line is finished. • This is one swath. • Roll over one source-line interval and begin recording the next swath. • Keep doing this until the survey is finished.

  7. 3-D Swath Shooting Method Crossline rollover Swath 1 Swath 2 SP # 6 SP # 5 SP # 4 SP # 3 SP # 2 SP # 1 Crossline rollover

  8. 3-D Land Survey Designs • Grid geometry • full fold • parallel • orthogonal • non-orthogonal • brick • Zigzag • Non-grid geometry • star • radial • random

  9. 3-D Land survey designsFull-fold (Cordsen et al., 2000)

  10. 3-D Land survey designsParallel (Cordsen et al., 2000)

  11. 3-D Land survey designsOrthogonal (Cordsen et al., 2000)

  12. 3-D Land survey designsNon-orthogonal (Cordsen et al., 2000)

  13. 3-D Land survey designsBrick (Cordsen et al., 2000)

  14. 3-D Land survey designsZigzag (Cordsen et al., 2000)

  15. 3-D Land survey designsStar (Cordsen et al., 2000)

  16. 3-D Land survey designsRadial (Cordsen et al., 2000)

  17. 3-D Land survey designsRandom (Cordsen et al., 2000)

  18. Factors Controlling 3-D Survey Design • Shallowest reflector of interest • Deepest reflector of interest • Target Size • Target dip • Multiples • Cost

  19. Parameters of 3-D Survey Design • RI and SI • RLI and SLI • CMP Fold • Maximum Offset • Minimum Offset • Record length • Frequency • Migration Aperture

  20. 3-D Marine Surveys • Shoot closely spaced parallel 2-D lines. • Cable may drift with water cross currents (feathering). • Correct for feathering effect using compasses along cable to determine source and receiver locations.

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