Fractures are important conduits for fluids in geothermal systems, and achieving and maintaining fracture permeability is a fundamental aspect of EGS (Engineered Geothermal System) development. Hydraulic or chemical stimulation techniques are often employed to achieve this. In the case of chemical stimulation, an understanding of the minerals present in the fractures themselves is desirable to better design a stimulation effort (i.e. which chemical to use and how much). Borehole televiewer surveys provide important information about regional and local stress regimes and fracture characteristics (e.g. aperture), and XRD is useful for examining bulk rock mineralogy, but neither technique is able to quantify the distribution of these minerals in fractures. QEMSCAN® is a fully-automated micro-analysis system that enables quantitative chemical analysis of materials and generation of high-resolution mineral maps and images as well as porosity structure. Initial applications of QEMSCAN® technology were predominantly in the minerals industry and application to geothermal problems has remained limited to date. In this pilot study, the application of QEMSCAN® technology to fracture characterization in geothermal systems was evaluated using samples from Newberry Volcano (Oregon) and Brady’s geothermal field (Nevada). QEMSCAN® results were compared with XRD and petrographic techniques. Nine samples were analyzed from each field, collected from the drill core in the 3400 – 4900 ft depth range in two shallow wells (GEO-N2 at Newberry Volcano and BCH-3 at Brady’s). The samples were prepared as polished thin sections for QEMSCAN® analysis. Results indicate that a sampling resolution of 10 µm is sufficient to resolve fracture morphology, mineral zonation (where multiple episodes of mineralization occurred), and elemental distribution, and enables relatively fast data acquisition (3 cm˛ can be analyzed in approximately 3 hours). Finer resolutions (down to 2.5 µm) take significantly longer, but can be used to provide additional spatial detail in areas of interest preceding a low resolution (10 µm) scan. Use of XRD and electron microprobe techniques in conjunction with QEMSCAN® data is sometimes needed to distinguish geothermal alteration minerals with similar chemical compositions (smectite clays and chlorite), however overall the technique appears to have excellent potential for geothermal applications.

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