Hyperspectral characterization of geothermal reservoirs in the Great Basin region

GBCGE project personnel: Kurt Kraal; Dr. Bridget Ayling

Project collaborators: TerraCore http://terracoregeo.com/     Ormat Technologies, Inc https://www.ormat.com/en/home/a/main/

Project duration: Ongoing

Project goal: Evaluate the utility of hyperspectral imaging of geothermal drill core and cuttings to shed insight into geothermal reservoirs in the Great Basin region. Using field sites in Nevada and the Great Basin, our research is exploring the relationship between hydrothermal alteration and other geothermal reservoir properties including the location of modern and fossil permeability, thermal regime, lithology, rock properties, stress regime and fracture distribution. Efforts to date have included work at the Fallon FORGE EGS site in the Carson Sink, and the Tungsten Mountain geothermal field operated by Ormat Technologies, Inc. (led by PhD student Kurt Kraal).

This figure shows six photographs of petrographic thin sections from the Fallon FORGE well 21-31 under the microscope.
Annotated photomicrographs of selected lithologies from pre-Miocene rocks encountered in Fallon FORGE well 21-31 (under plane-polarized light (PPL) and cross-polarized light (XPL)). Chl = chlorite, Plg = plagioclase feldspar, Qtz = quartz, Cal = calcite. See Supp. Fig. 2 for additional examples of alteration and veining. A: altered-basalt, 1860 m, PPL; B: Quartzite, 1902 m, XPL; C: Altered equi-granular felsic intrusive, 1984 m, XPL; D: quartzite, 2198 m, XPL; E: altered rhyolitic tuff (Tuff_B), 2461 m, XPL; F: Lithic-bearing volcaniclastic, 2301 m, XPL. Figure from Kraal et al., 2021.
Well log profile showing the variation in mineralogy in the Fallon FORGE well 21-31
Lithology, cuttings hyperspectral interpretation, side-wall core cuttings interpretation, spectral scalars, and XRD mineral percentage in the pre-Miocene section of Fallon FORGE well 21-31. For the SWIR and LWIR mineral logs, spectra from each sample interval were interpreted for dominant mineralogy, and plotted as a percent of the sample area with that mineral end-member spectra versus depth. Scalars were calculated on hull corrected data for the entire sample image, and the average value for each sample is plotted above. For “Illite Maturity”, shaded areas represent samples where the depth of the 2200 nm Al OH feature is greater than or equal to the depth of the 1900 nm H2O feature, meaning illite and/or muscovite likely predominate over smectite. For “Wavelength of 2200 nm feature”, shaded areas represent more phengitic illite/mica composition, and non-shaded regions represent more muscovitic compositions. “Depth of 1900 nm feature” is related to relative hydrated clay (such as smectite and illite) abundance. Figure from Kraal et al., 2021.

Publications to date (listed chronologically):

  • Kraal, K., Ayling, B. F., Calvin, W. M., Browning, D. (2018). Comparison of a Portable Field Spectrometer and Automated Imaging on Geothermal Drill Core: A Pilot Study, Geothermal Resources Council Transactions, Vol.42. https://www.geothermal-library.org/index.php?mode=pubs&action=view&record=1034001
  • Kraal, K., and Ayling, B.F., (2019). Hyperspectral Characterization of Fallon FORGE Well 21-31: New Data and Technology Applications. Proceedings of the 44th Workshop on Geothermal Reservoir Engineering, Stanford University, February 11-13th, 2019. SGP-TR-214. https://pangea.stanford.edu/ERE/pdf/IGAstandard/SGW/2019/Kraal.pdf
  • Kraal, K.O., Ayling, B.F., Blake, K., Hackett, L., Perdana, T.S.P., Stacey, R., (2020), Integration of Borehole Data for Hydrothermal Alteration, Natural Fracture, and Permeability Characterization at the Fallon FORGE EGS site, Nevada, USA. Transactions, Geothermal Resources Council annual meeting, October 19-23, 2020  https://www.geothermal-library.org/index.php?mode=pubs&action=view&record=1034321
  • Kraal, K.O., and Ayling, B.F., (2020), Spatial characterization of hydrothermal alteration in a fault-controlled amagmatic geothermal system at Tungsten Mountain, geothermal field, Nevada USA. Transactions, Geothermal Resources Council annual meeting, October 19-23, 2020. https://www.geothermal-library.org/index.php?mode=pubs&action=view&record=1034320
  • Kraal, K.O., Ayling, B.F., Blake, K., Hackett, L., Perdana, T.S.P., Stacey, R., (2021), Linkages between hydrothermal alteration, natural fractures, and permeability: Integration of borehole data for reservoir characterization at the Fallon FORGE EGS site, Nevada, USA. Geothermics, Vol. 89. https://doi.org/10.1016/j.geothermics.2020.101946
  • Kraal, K., Ayling, B. F., Calvin, W. M., (2021). Applications of Hyperspectral Imaging to Geothermal Drill Core and Cuttings: Case Studies from Nevada, Western USA. Proceedings, World Geothermal Congress, Reykjavik, Iceland

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