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Understanding Reflection Coefficients in Seismic Exploration

This overview explores the concept of reflection coefficients (RC) in seismic exploration, specifically in relation to the angle of incidence (qi) and the properties of different media. It clarifies when normal-incidence assumptions are valid (qi ≤ 15°) and when they are not (qi > 15°), highlighting the importance of the Zoeppritz equations for high deviations in incidence. The document also discusses typical reflection coefficient magnitudes for various rock and fluid interfaces, providing essential insights for effective seismic analysis.

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Understanding Reflection Coefficients in Seismic Exploration

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  1. Sr Pr Pi fr qi qr a1, b1 a2, b2 qt ft Pt St Sinqi Sinqr Sinqt Sinfr Sinft a1 a1 a2 b1 b2 Reflection coefficients

  2. r - r V V 2 2 1 1 RC = r + r V V 2 2 1 1 Reflection coefficientsqi ≈ 0 r1: density in incident medium r2: density in refraction medium V1: seismic velocity in incident medium V2: seismic velocity in refraction medium

  3. Reflection coefficientsqi 15 • very slight deviation from the normal-incidence case • For most seismic exploration purposes, qi 15 is a good assumption. • Therefore, normal-incidence RC is used in general.

  4. Reflection coefficientsqi> 15 • high deviation from the normal-incidence case • Therefore, normal-incidence is NOT a good assumption. • Full Zoeppritz equations have to be used. • Zoeppritz equations are very complicated algebraically. • If qi ≤ 30, approximations of Zoeppritz equations are used. • Studies involving amplitude variation with offset (AVO) use these approximations.

  5. Reflection coefficientsMagnitude • Rock-rock RC < |0.3| • Rock-soil RC ~ |0.7| • Rock-water RC ~ |0.7| • Rock-air RC ~ |1.0| • Water-deep-sea sediments RC ~ |0.3| • Water-air RC ~ |1.0|

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