Petrophysics usually refers to the science of geophysical log data collection, processing, and analysis. More broadly, the term might include the specialist subject of rock physics.
Determination of Vsh from GR
Quantitative evaluation of shale content using gamma ray data assumes that radioactive minerals other than shales and clay are absent. The gamma ray shale index, is defined as
where is the log response in the zone of interest (API units), is the log response in a clean, shale free zone (API units), and is the log response in a shale bed (API units).
Determination of Vsh from SP
Equation, pitfalls, and considerations...