Abstract:
The dual techniques of Computerized Tomography (CT) and Scanning Electron Microscopy (SEM) reveal that significant subsurface processes are preserved in core from the Tauhara geothermal field, New Zealand. CT scans image the spatial distribution of density changes at 0.02 mm increments enabling 3D mapping of density variations within rocks. SEM images support the CT findings by documenting their associated subsurface processes. Dissolution, boiling of fluids, and thermal fluid flow resulting in silicification of the host rock, are three important subsurface processes documented in this study. In some cases, multiple events are recorded. The dimensions, structure and connectivity of voids and micro-fractures is also revealed. The cores examined show that some voids are connected with depth into the sample, while other areas reveal shallow disconnected voids. SEM observations on the same sample show the presence of both shallow and deep voids, confirming the CT scan findings. Micro-fracture orientations change with depth within individual samples. Some micro-fractures are infilled with crystals or clays reducing the potential permeability of these channels. The dual technique approach provides useful and significant information on the spatial distribution and timing of various subsurface processes.
