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Multiple Attenuation Explained

Byadmin
 

Multiple Attenuation Explained

 

Introduction

Multiples are one of the most persistent challenges in seismic processing. These unwanted reflections obscure true geology, reduce interpretability, and distort amplitude‑based analysis. Multiple attenuation techniques aim to suppress these artifacts while preserving primary reflections.

This article explains what multiples are, why they occur, and how modern processing workflows remove them.

1. What Are Multiples?

Multiples are seismic reflections that bounce more than once before reaching the receiver. They include:

A. Surface‑Related Multiples

Reflections between the surface and subsurface.

B. Interbed Multiples

Reflections trapped between geological layers.

C. Peg‑Leg Multiples

Mixed‑path multiples involving multiple interfaces.

Multiples often mimic primary reflections, making them difficult to distinguish.

2. Why Multiples Are a Problem

Multiples can:

  • Mask true reflectors

  • Create false structures

  • Distort amplitudes

  • Reduce attribute reliability

  • Complicate AVO analysis

Removing them is essential for accurate imaging.

3. Multiple Attenuation Techniques

A. SRME (Surface‑Related Multiple Elimination)

Predicts multiples using the recorded wavefield. Pros: No subsurface model needed Cons: Sensitive to missing near offsets

B. Radon Transform Demultiple

Separates primaries and multiples based on moveout differences. Pros: Effective for simple geology Cons: Limited for complex structures

C. Model‑Based Demultiple

Uses velocity and structural models to predict multiples. Pros: High accuracy Cons: Requires good models

D. Wave‑Equation Demultiple

Advanced method using wave‑equation extrapolation. Pros: Excellent for complex geology Cons: Computationally expensive

4. Multiple Attenuation Workflow

  1. Data conditioning

  2. SRME prediction

  3. Adaptive subtraction

  4. Radon filtering

  5. Wave‑equation demultiple (optional)

  6. QC and validation

Each step must preserve primaries while removing multiples.

5. Challenges

  • Poor near‑offset coverage

  • Complex geology

  • Shallow‑water multiples

  • Amplitude leakage

  • Over‑subtraction

Conclusion

Multiple attenuation is essential for producing clean, interpretable seismic data. Modern workflows combine SRME, Radon, and wave‑equation methods to deliver high‑quality results that support accurate imaging and reservoir characterization.

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