Vshale

Vsh or Vshale is the volume of shale in a given volume of rock. Usually synonymous with Vclay, though strictly speaking this should be measured at a different scale: Vclay pertains to a rock, whereas Vsh pertains to an interval of strata.

It is possible to calculate Vsh from spectral gamma-ray data. The equation is analogous to that used for gamma-ray, but uses the CGR curve:


 * $$x = \frac{\mathsf{CGR}_\mathrm{zone} - \mathsf{CGR}_\mathrm{clean}}{\mathsf{CGR}_\mathrm{shale} - \mathsf{CGR}_\mathrm{clean}}$$

In many circumstances, x can be used as Vsh. Alternatively, one of the following corrections can be optionally applied:


 * $$V_\mathrm{sh} = \frac{0.5x}{1.5-x}$$


 * $$V_\mathrm{sh} = 1.7 - \sqrt{3.38 - (x + 0.7)2}$$