Geothermal reservoirs models evolve along the reservoir life. They are enriched by the collected data and the knowledge of the geothermal system gained over time. The petrophysical values, such as porosity and permeability, used as inputs for modelling may change too. However, estimating the best values as early as possible contributes to the robustness of the models and improves the outcomes for the field management strategy. This paper presents a petrophysical characterisation technique based on rocks’ textural features or descriptors to provide estimates of petrophysical values. Four descriptors, consolidation, groundmass content, pore type, and pore-filling occurrence, are used as proxies of porosity and permeability. By combining these descriptors, rocks are classified into one of three rock types that have specific trends of porosity and permeability. Two examples of how these rock types are applied in the Tauhara Geothermal Field are presented. This approach encourages the collection of petrophysical data from the observation of rocks, provides estimated values of porosity and permeability when petrophysical tests are not available, and improves the communication of numerical inputs between geoscientists and engineers.