Shale Volume from Gamma Ray

Estimate shale volume (Vshale) from Gamma Ray logs using Linear and Larionov empirical relationships. Essential for net-to-gross calculations, porosity corrections, and reservoir quality assessment. Choose the appropriate method based on your geological setting.

Petrophysics Gamma Ray Shale Volume Larionov

Input Parameters

Gamma Ray Values

API
Current reading at depth of interest
API
Minimum GR in clean formation (no shale)
API
Maximum GR in pure shale zone

Geological Setting

Affects Larionov correction factor

Quick Presets

Results

Theory & References

Linear Method

IGR = (GR - GRclean) / (GRshale - GRclean)
Vshale = IGR

Characteristics:

  • Simplest method, widely used
  • Tends to overestimate shale volume
  • Best for preliminary screening
  • Not recommended for dispersed shale

Larionov Methods

Tertiary rocks:
Vshale = 0.083 × (23.7×IGR - 1)

Older rocks:
Vshale = 0.33 × (22×IGR - 1)

Advantages:

  • Non-linear correction for dispersed shale
  • Reduces over-estimation of Vshale
  • Empirically derived for different ages
  • More accurate for reservoir evaluation

Usage Guidelines

Selecting GR Baselines:

  • GRclean: Choose from cleanest sand/carbonate in section (histogram minimum)
  • GRshale: Choose from thickest shale bed (histogram maximum)
  • Verify with nearby wells if available
  • Check for hot shales or radioactive minerals

Method Selection:

  • Use Tertiary for young, unconsolidated rocks
  • Use Older for consolidated formations
  • Compare with other shale indicators (SP, Resistivity)