Reformulation and Performance Evaluation of the Sulfate-Water Oxygen Isotope Geothermometer

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Conference Paper: Reformulation and Performance Evaluation of the Sulfate-Water Oxygen Isotope Geothermometer

Abstract
Recent utilization of the dissolved sulfate–water oxygen isotope exchange geothermometer (δ18O SO4-H2O) to estimate geothermal fluid temperatures at depth appears infrequent, even with general literature support regarding its usefulness. Here, the authors provide support for continued use of this method through revision of the sulfate geothermometer equation and through analysis of publically available chemical and correlative wellbore temperature data. The utility of the δ18O SO4-H2O exchange reaction for calculating equilibration temperatures is based on a slow reaction exchange rate in pH neutral conditions: water-rock equilibration to 90% can take 500 years at 100°C and 2 years at 300°C. These high-temperature reaction rates, considered to be the slowest in the suite of established geothermometers, validate the use of the SO4-H2O geothermometer to help in estimating the temperatures of deep reservoir waters that have experienced long residence times. The reliability of this geothermometer can be affected by multiple processes that include geothermal and meteoric water mixing, δ18O fractionation of H2O during boiling, formation of SO4 by oxidation of H2S, influence by biologic activity, dissolution and precipitation of anhydrite, and an elevated exchange rate in acidic conditions. However, with the appropriate caveats applied and regard given to dissolved ion chemistry the δ18O SO4-H2O geothermometer can be a valuable tool.

Authors 
A.P.G. Fowler, L.B. Hackett and C.W. Klein






Conference 
GRC Annual Meeting; Las Vegas, NV; 2013/09/31


Published 
Geothermal Resources Council, 2013





DOI 
Not Provided
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Online 
Internet link for Reformulation and Performance Evaluation of the Sulfate-Water Oxygen Isotope Geothermometer

Citation

A.P.G. Fowler, L.B. Hackett, C.W. Klein. 2013. Reformulation and Performance Evaluation of the Sulfate-Water Oxygen Isotope Geothermometer. In: GRC Transactions. GRC Annual Meeting; 2013/09/31; Las Vegas, NV. Davis, CA: Geothermal Resources Council; p. 393-401