Active magmatic degassing in the NW geysers high-temperature reservoir

Conference · Sat Oct 01 04:00:00 EDT 1994

OSTI ID:10120886

Kennedy, B. M. ^[1]; Truesdell, A. H. ^[2]

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1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2. Truesdell (Consultant), Menlo Park, CA (United States)

Noble gas isotope abundances in steam from selected wells of the Coldwater Creek field of the NW Geysers, California, show mixing between a nearly pure mid-ocean ridge basalt (MORB) type magmatic gas with high ³He/⁴He and low radiogenic Ar (R/Ra > 8.3 and ⁴⁰Ar/⁴He < 0.07), and a magmatic gas diluted with crustal gas (R/Ra < 6.6 and ⁴⁰Ar/⁴He > 0.25). Gases with the highest magmatic component are from wells producing entirely (or in large part) from the high-temperature reservoir (HTR), while gases with the most crustal dilution are generally produced from the overlying normal vapor-dominated reservoir. The MORB-type magmatic gas is interpreted to show (among other things) that (1) part of the high gas of the HTR in the NW Geysers is supplied by active degassing of an underlying magma body indicated by earlier geophysical studies; (2) the HTR was formed by rapid heating and boiling of existing reservoir liquid caused by injection of magma; and (3) the large-scale convection found in the south and central Geysers does not exist in the northwest part of the field.

• Research Organization: Lawrence Berkeley Lab., CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 10120886
• Report Number(s): LBL--36262; CONF-941043--8; ON: DE95006577
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150200
DEGASSING
ECOLOGICAL CONCENTRATION
GAS FLOW
GEOLOGY AND HYDROLOGY OF GEOTHERMAL SYSTEMS
GEOPHYSICS
GEYSERS GEOTHERMAL FIELD
MAGMA
RARE GASES