Rock typing in geothermal reservoirs: application of textural descriptors

Abstract

Geothermal energy is a key in the transition to 90% renewable electricity production by 2025, which is a target set by New Zealand government. 22% of the current national electricity generation comes from geothermal resources and it is expected to keep growing.
Geothermal systems can be represented at different space and time scales by reservoir models. A reservoir model provides useful information to make decisions and optimally manage these resources. For this purpose, robust models require coherent and realistic geoscientific and engineering input data, including physical properties of rocks. However, despite the fast development of tools to measure these properties, in many geothermal fields key petrophysical properties are not available at a scale appropriate to be used as input for reservoir modelling. This results in the need to explore alternative methods to determine such petrophysical properties.
This paper describes a rock typing method based on textural descriptors that are being adapted to volcanic rocks. It provides a classification method for rocks in geothermal fields based on their physical properties that govern the fluid flow. The geological implications of the rock typing system are discussed. Examples of potential applications of the method where the petrophysical data are limited are presented.