Thermal and chemical evolution of The Geysers geothermal system, California

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Fluid inclusions and mineral assemblages provide a reward of the thermal and chemical changes that occurred during the evolution of The Geysers geothermal system. The data document the presence of an extensive liquid dominated geothermal system that developed in response to felsite intrusion and its evolution to a vapor-dominated regime. Temperatures within the early liquid-dominated system ranged from 175 C at a distance of 7200 feet from the felsite to more than 350 C near the contact while salinities varied from 5 equivalent weight percent NaCl (at a distance of 5500 feet) to more than 26 weight percent NaCl. As ... continued below

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121-126

Creation Information

Moore, J.N. January 1, 1992.

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Description

Fluid inclusions and mineral assemblages provide a reward of the thermal and chemical changes that occurred during the evolution of The Geysers geothermal system. The data document the presence of an extensive liquid dominated geothermal system that developed in response to felsite intrusion and its evolution to a vapor-dominated regime. Temperatures within the early liquid-dominated system ranged from 175 C at a distance of 7200 feet from the felsite to more than 350 C near the contact while salinities varied from 5 equivalent weight percent NaCl (at a distance of 5500 feet) to more than 26 weight percent NaCl. As temperatures around the felsite declined, the liquid-dominated system collapsed upon itself. Downward migration of the low salinity waters resulted in dilution of the fluids present in regions now occupied by the caprock and normal vapor-dominated reservoir. In contrast, dilution was minor in rocks now hosting the high-temperature vapor-dominated reservoir. This suggests that low permeabilities are the primary reason for the development of the high-temperature reservoir. Boiling within the caprock produced late-stage veins of calcite and quartz. As the fluid boiled off, condensate was trapped as low salinity fluid inclusions. Within the main body of the reservoir, a liquid phase with salinities of up to 7 equivalent weight percent NaCl persisted to temperatures between 250 and 270 C. However, except for the presence of vapor-rich inclusions, little evidence of boiling within the reservoir rocks was preserved.

Physical Description

121-126

Source

  • Seventeenth Workshop on Geothermal Reservoir Engineering: Proceedings, Stanford University, Stanford, CA, January 29-31, 1992

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  • Report No.: SGP-TR-141-18
  • Grant Number: None
  • Office of Scientific & Technical Information Report Number: 888671
  • Archival Resource Key: ark:/67531/metadc875961

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  • January 1, 1992

Added to The UNT Digital Library

  • Sept. 21, 2016, 2:29 a.m.

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  • Dec. 8, 2016, 11:49 p.m.

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Moore, J.N. Thermal and chemical evolution of The Geysers geothermal system, California, article, January 1, 1992; United States. (digital.library.unt.edu/ark:/67531/metadc875961/: accessed September 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.