A subsurface formation petrophysical evaluation method including: determining formation porosity and permeability using a quantitative indication of formation composition; estimating water-filled formation resistivity using the formation porosity; associating differences between measured formation resistivity and estimated water saturated formation resistivity with the presence of subsurface hydrocarbons; and estimating irreducible formation water saturation using the formation porosity and the formation permeability. The invention further involves an apparatus adapted to carry out the inventive method. Other aspects of the invention involve making a plurality of different measurements of a subsurface formation, including measuring indicators of a plurality of absolute or relative formation elemental concentrations; processing the measurements to determine a plurality of parameters associated with the subsurface formation, and determining either net pay intervals or drilling parameters using these formation parameters and either interval acceptance criteria or desired wellbore criteria, respectively.