(1) I_{GR} = \frac{GR_{log} - GR_m}{GR_{sh} - GR_m} where GR_{log}GR-tool readings GR_{log} GR_mthe reference values in clean rocks GR_m GR_{sh}the reference values in pure shales GR_{sh}
where
GR_{log}
GR-tool readings GR_{log}
GR_m
the reference values in clean rocks GR_m
GR_{sh}
the reference values in pure shales GR_{sh}