There is need for a term to express the physics of rocks. It should be related to petrology much as geophysics is related to geology. "Petrophysics" is suggested as the term pertaining to the physics of particular rock types, whereas geophysics pertains to the physics of larger rock systems composing the earth.

The petrophysics of reservoir rocks is discussed here. This subject is a study of the physical properties of rock which are related to the pore and fluid distribution. Over the past few years considerable study has been made of rock properties, such as porosity, permeability, capillary pressure, hydrocarbon saturation, fluid properties, electrical resistivity, self- or natural-potential, and radioactivity of different types of rocks. These properties have been investigated separately and in relation, one to another, particularly as they pertain to the detection and evaluation of hydrocarbon-bearing layers.