A process or procedure used to interpret petrophysical (usually wireline log) data. Usually representing a set of equations, algorithms or other mathematical processes, petrophysical models often have multiple routines. For example, a deterministic model might include routines that:

• calculate the shale volume
• calculate total porosity
• calculate effective porosity
• calculate water saturation
• calculate permeability.

Often, the model is calibrated using core, production, test and other data sets. Although many software packages contain ready-built petrophysical models or component routines that can be called upon, many log-analysis problems are unique and require that "built to purpose" models be constructed. Construction of new petrophysical models is normally driven by the data available and the nature of the problem to be solved.