Thermal modeling of the Clear Lake magmatic system, California: Implications for conventional and hot dry rock geothermal development

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The combination of recent volcanism, high heat flow ({ge} HFU or 167 mW/m{sup 2}), and high conductive geothermal gradient (up to 120{degree} C/km) makes the Clear Lake region of northern California one of the best prospects for hot dry rock (HDR) geothermal development in the US. The lack of permeability in exploration wells and lack of evidence for widespread geothermal reservoirs north of the Collayomi fault zone are not reassuring indications for conventional geothermal development. This report summarizes results of thermal modeling of the Clear Lake magmatic system, and discusses implications for HDR site selection in the region. The thermal ... continued below

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41 p.

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Stimac, J.; Goff, F. & Wohletz, K. June 1, 1997.

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Description

The combination of recent volcanism, high heat flow ({ge} HFU or 167 mW/m{sup 2}), and high conductive geothermal gradient (up to 120{degree} C/km) makes the Clear Lake region of northern California one of the best prospects for hot dry rock (HDR) geothermal development in the US. The lack of permeability in exploration wells and lack of evidence for widespread geothermal reservoirs north of the Collayomi fault zone are not reassuring indications for conventional geothermal development. This report summarizes results of thermal modeling of the Clear Lake magmatic system, and discusses implications for HDR site selection in the region. The thermal models incorporate a wide range of constraints including the distribution and nature of volcanism in time and space, water and gas geochemistry, well data, and geophysical surveys. The nature of upper crustal magma bodies at Clear Lake is inferred from studying sequences of related silicic lavas, which tell a story of multistage mixing of silicic and mafic magma in clusters of small upper crustal chambers. Thermobarometry on metamorphic xenoliths yield temperature and pressure estimates of {approximately}780--900 C and 4--6 kb respectively, indicating that at least a portion of the deep magma system resided at depths from 14 to 21 km (9 to 12 mi). The results of thermal modeling support previous assessments of the high HDR potential of the area, and suggest the possibility that granitic bodies similar to The Geysers felsite may underlie much of the Clear Lake region at depths as little as 3--6 km. This is significant because future HDR reservoirs could potentially be sited in relatively shallow granitoid plutons rather than in structurally complex Franciscan basement rocks.

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41 p.

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OSTI as DE97007850

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  • Other Information: PBD: Jun 1997

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  • Other: DE97007850
  • Report No.: LA--12778-MS
  • Grant Number: W-7405-ENG-36
  • DOI: 10.2172/505280 | External Link
  • Office of Scientific & Technical Information Report Number: 505280
  • Archival Resource Key: ark:/67531/metadc694259

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  • June 1, 1997

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  • Aug. 14, 2015, 8:43 a.m.

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  • Feb. 29, 2016, 7:52 p.m.

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Stimac, J.; Goff, F. & Wohletz, K. Thermal modeling of the Clear Lake magmatic system, California: Implications for conventional and hot dry rock geothermal development, report, June 1, 1997; New Mexico. (digital.library.unt.edu/ark:/67531/metadc694259/: accessed August 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.