Shale Index from Gamma Ray Spectrometry - Thorium Formula
Shale Index from Gamma Ray Spectrometry - Thorium calculates thorium shale index for rock properties workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (C_Th_log, C_Th_min, C_Th_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_Th equals 0.375 dimensionless.
8
2
18
Inputs
C_Th_log
ppmThorium Curve Response in Zone of Interest
C_Th_min
ppmThorium Curve Response in Minimum-Radioactivity Zone
C_Th_sh
ppmThorium Curve Response in Shale
Outputs
I_sh_Th
Thorium Shale Index
C_Th_log
Thorium Curve Response in Zone of Interest
C_Th_min
Thorium Curve Response in Minimum-Radioactivity Zone
C_Th_sh
Thorium Curve 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