TRACKING MICRO-FRACTURE AND VOID CONNECTIVITY IN GEOTHERMAL HOST ROCKS USING SCANNING ELECTRON MICROSCOPY

Abstract

Scanning Electron Microscopy (SEM) was used to examine the characteristics of micro-fractures and voids, their dimensions, quantity and connectivity, in core recovered from two geothermal fields, referred to as A and B, located in the Taupo Volcanic Zone, New Zealand. SEM observations revealed significant variation in void structure exists between; (1) host rocks of the same lithologic unit, even over small depth intervals of <7 m, and (2) different lithologic units. In geothermal field A, void dimensions and micro-fracture connectivity increases with depth, while in geothermal field B, void dimensions and micro-fracture networks decrease with depth. The structure of voids control a rocks ability to transmit or store fluid, therefore it is important to understand site specific controls on permeability.