Vshale Calculator
Compute shale volume from gamma ray using five industry-standard methods. Compare Linear (IGR), Larionov Tertiary, Larionov Older Rocks, Steiber, and Clavier side-by-side.
Gamma Ray Inputs
IGR = (GR − GRclean) / (GRshale − GRclean)
Gamma Ray Index (IGR)
0.5500
Vshale Comparison
| Method | Formula | Vshale |
|---|
Vshale vs. IGR — All Methods
How this was calculated
Linear (IGR): Vsh = IGR. Simplest approach; tends to overestimate shale volume.
Larionov Tertiary: Vsh = 0.083 × (23.7×IGR − 1). Empirical correction for younger (Tertiary) rocks.
Larionov Older: Vsh = 0.33 × (22×IGR − 1). Empirical correction for older (pre-Tertiary) rocks.
Steiber: Vsh = IGR / (3 − 2×IGR). Reduces Vsh at high IGR values.
Clavier: Vsh = 1.7 − [3.38 − (IGR + 0.7)²]0.5. Non-linear empirical correction.
Assumptions: Single-mineral clean zone. GR response is linear with shale content. No uranium or other non-clay radioactive minerals.
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Book a free strategy call →Understanding Shale Volume from Gamma Ray Logs
Shale volume (Vshale) is one of the most critical petrophysical parameters in formation evaluation. It directly impacts porosity, water saturation, and permeability estimates. The gamma ray log is the most commonly used indicator of shale content, since clay minerals tend to concentrate naturally occurring radioactive elements (potassium, thorium, uranium).
The simplest approach is the linear or gamma ray index (IGR), which assumes a direct proportional relationship between the gamma ray response and shale content. However, this method consistently overestimates Vshale, particularly at intermediate values. Several non-linear empirical corrections have been developed to address this, including the Larionov (1969) equations for Tertiary and older rocks, the Steiber (1970) formula, and the Clavier (1971) method.
In practice, the choice of Vshale method depends on the geological setting, available calibration data (core, XRD), and the interpreter's experience. Using multiple methods and comparing results helps bracket the uncertainty in shale volume estimates.
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