Abstract:
The proposed method allows rock samples to be classified into petrotypes within geothermal reservoirs. By studying twelve different textural descriptors observed on rock samples of two geothermal areas, Tauhara Geothermal Field, New Zealand, and Salak Geothermal Field, Indonesia, a selection of four relevant descriptors was made, consolidation degree, groundmass content, pore type, and occurrence of pore filling material. These four descriptors are used in a classification scheme that separates rocks according to their dominant permeability/porosity trend into petrotypes or petrophysical rock types. Once a rock is classified, if the porosity value is known, an estimation of permeability is possible by means of using a set of empirical equations provided. If no porosity estimate is available, a rock catalogue comprising representative samples studied in this project can be used as an analogue where visually similar rocks can be assigned the same petrophysical values. The proposed classification contributes to the modelling of geothermal reservoirs by developing alternative methods to estimate petrophysical properties. This is especially important if there are no adequate samples for laboratory testing or in the early phases of projects exploration when the available samples and data are limited. It is recommended to test the proposed classification as input in a numerical model. The numerical simulation was beyond the scope of this project. The characterisation of reservoir rocks helps in building robust numerical reservoir models, which are the most complete picture possible of a geothermal system at any time.