AVO Modeller & Class Identifier

Calculate amplitude-versus-offset (AVO) reflectivity using Aki-Richards and Shuey approximations. Identify AVO classes (Rutherford & Williams, 1989) and visualize intercept-gradient crossplots for direct hydrocarbon indicators.

AVO Analysis Aki-Richards Shuey DHI

Input Parameters

Upper Layer (Shale/Seal)

m/s
Typical shale: 2500-3500 m/s
m/s
Typical Vp/Vs: 1.8-2.2
g/cm³
Typical shale: 2.2-2.5 g/cm³

Lower Layer (Reservoir)

m/s
Gas sand: 2500-3200 m/s
m/s
Maintain reasonable Vp/Vs
g/cm³
Gas sand: 2.0-2.3 g/cm³

Angle Range

degrees
Typical AVO analysis: 0-40°

Results

Theory & References

AVO Equations

Aki-Richards (3-term):

R(θ) = A + B·sin²(θ) + C·(tan²(θ) - sin²(θ))

Shuey (2-term):

R(θ) = R₀ + G·sin²(θ)

Where R₀ is the intercept (normal incidence) and G is the AVO gradient.

AVO Classification

  • Class 1: High impedance (R₀ > 0), dims with offset
  • Class 2: Near-zero impedance (|R₀| ≈ 0), brightens with offset
  • Class 2p: Polarity reversal (small R₀ > 0, G < 0)
  • Class 3: Low impedance (R₀ < 0), brightens with offset
  • Class 4: Low impedance (R₀ < 0), dims with offset