Nevada Petroleum and Geothermal Society
Topic: Linkages between Hydrothermal Alteration, Natural Fractures, and Permeability: Integration of Borehole Data for EGS Characterization at the Fallon FORGE Site, Nevada, USA
Abstract: Between 2016 and 2018, the Fallon FORGE EGS (Engineered Geothermal System) site in Churchill County, Nevada, USA, underwent detailed geoscientific characterization to evaluate its suitability to operate as a field demonstration site to test and develop EGS technologies. This included the compilation, synthesis and acquisition of varied datasets including geophysical, geological, geochemical, hydrological, and down-hole log and mineralogy datasets. The data collection culminated in the drilling of a 2481 m EGS observation well (21-31) to further verify the geology and properties of the proposed EGS reservoir. In this presentation, we analyze borehole data from well 21-31, including analysis of drill cuttings and sidewall cores (petrographic, XRD, hyperspectral) to interpret lithology and hydrothermal alteration, wireline geophysical logs (e.g. gamma, neutron porosity, resistivity, sonic scanner), borehole imagers (FMI, BHTV), and pressure and temperature logs. In addition, we present well testing data that was conducted to estimate permeability and injectivity of the formation to host the proposed EGS reservoir. We integrate these data to investigate the properties of natural fractures, stress state, and the type and location of hydrothermal alteration encountered in the borehole. We focus our investigation of the location of current and passed permeability encountered in the well, as well as linkages between the various data types. Our findings show that the majority of the well is low permeability (< 10-16 m), with some discrete, localized zones of relatively high permeability (~ 10 -12 m, less than 0.5 % of the pre-Miocene (deep) part of the well). Based on our analysis of the correspondence between drilling mudloss locations, sonic fracture analysis, and temperature logs, three distinct zones in the wellbore were identified as possibly hosting some of the permeability indicated by the well testing. We investigate the linkages between current permeability, past permeability (as indicated by hydrothermal alteration) and other datasets including fracture characteristics, and lithologic variability. Hydrothermal alteration and veining was found throughout the entire pre-Miocene interval, suggesting the presence of an active high-temperature convection-dominated hydrothermal system in the past, and therefore previously higher permeability. Lastly, we adapt our findings to update the conceptual model for proposed EGS development at the Fallon site, and explore implications for development in the Great Basin regionally.
Bio: Kurt is a 3rd year Geology Ph.D. student in the department of Geological Sciences and Engineering at the University of Nevada, Reno. His research at the Great Basin Center for Geothermal Energy focuses on characterizing known geothermal systems, both conventional (hydrothermal) geothermal systems and EGS in terms of reservoir properties, geology, and hydrothermal alteration. Kurt’s previous presentations at the Geothermal Resources Council (2018) and the Stanford Geothermal Workshop (2019) focused on applying infrared reflectance spectroscopy to characterize mineralogy observed in geothermal wells in Nevada. Field areas investigated include the Tungsten Mountain geothermal field, operated by Ormat Nevada, Inc., and the Fallon FORGE EGS site, both located in Churchill County, Nevada. Kurt’s future research plans include investigating the effects of hydrothermal alteration on the physical and mechanical properties of geothermal reservoirs in both Nevada and beyond. Kurt graduated from University of California, Davis with a B.S. in Geology in 2016.
The event details are as follows:
Organization: Nevada Petroleum and Geothermal Society (NPGS)
Event Name: February 2020 NPGS Meeting
Date(s): Feb 6, 2020, 06:30 PM to 09:30 PM
Cocktails, wine and beer will be served starting at 6:30 PM, and dinner is served at 7:15 PM.
Location: Tamarack Junction
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Cocktail Hosts: The dinner bar will be sponsored by Welsco Drilling Co., Please give them a BIG Thank You! Welsco Drilling Corporation began operation with an old cable tool back in 1972. The Corporation continued to drill water wells and provide pump services until the early 80s where work began with its first geothermal steam project. Since that time Welsco has honed its skills in the Geothermal Steam arena, has completed a multitude of water well projects and has added a 24-hour pump service. Our highly skilled and qualified team looks forward to providing you with our best.
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