Shale Index from Gamma Ray Spectrometry - Uranium-Free Gamma Formula
Shale Index from Gamma Ray Spectrometry - Uranium-Free Gamma calculates uranium-free gamma ray shale index for rock properties workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (G_Uf_log, G_Uf_min, G_Uf_sh) are known and the assumptions behind the cited rock properties relationship match the engineering case being checked.
Assumptions
- Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
- The declared units match the field-unit constants used in the formula.
- The cited formula applies to the selected petroleum engineering workflow.
Limitations
- The calculation does not replace a full engineering model or operating procedure.
- Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.
Common mistakes
- Mixing unit systems without converting the inputs.
- Using default example values as field recommendations.
- Applying the formula outside the source assumptions.
Default example
Using the default inputs, I_sh_Uf equals 0.4 dimensionless.
60
20
120
Inputs
G_Uf_log
API unitsUranium-Free Gamma Ray Response in Zone of Interest
G_Uf_min
API unitsUranium-Free Gamma Ray Response in Minimum-Radioactivity Zone
G_Uf_sh
API unitsUranium-Free Gamma Ray Response in Shale
Outputs
I_sh_Uf
Uranium-Free Gamma Ray Shale Index
G_Uf_log
Uranium-Free Gamma Ray Response in Zone of Interest
G_Uf_min
Uranium-Free Gamma Ray Response in Minimum-Radioactivity Zone
G_Uf_sh
Uranium-Free Gamma Ray Response in Shale
Source and review
reviewedTheory, Measurement, and Interpretation of Well Logs, Bassiouni, Z. (1994)
Bassiouni, Z. 1994. Theory, Measurement, and Interpretation of Well Logs. SPE Textbook Series Vol. 4, Chapter 7, Page 156.
Source