Development of the MultiGAS for determining fumarole gas chemistry in geothermal systems.


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Authors: Vigouroux, N.; Williams-Jones, G.; Hickson, C
Year: 2013
Journal: Transactions - Geothermal Resources Council 37: 1-14
Title: Development of the MultiGAS for determining fumarole gas chemistry in geothermal systems.
Abstract: Geothermal exploration relies in part on the gas geochemistry of fumaroles, bubbling springs and steaming ground to offer
insight into the nature of the fluids at depth, processes affecting them when rising to the surface, and provide estimates of the temperature of last equilibration of the gases within the reservoir.
Traditional measurements involve direct sampling of the gases
in pre-evacuated Giggenbach glass bottles before laboratory
chemical analysis. Gas component analysis, combined with the
isotope ratios of certain components (e.g., CO2, He), provides
insight into the proportion of magmatic, crustal, meteoric and
atmospheric components in the fluid, and the state of equilibrium
and temperature of these fluids at depth.
The Multi-component Gas Analyzing System (MultiGAS)
was developed by the volcanological community over 10 years
ago as a field-portable instrument for in-situ analysis of the major volcanic gas components in diffuse and dilute gas emissions. No two instruments are identical but all consist of various sensor
types now capable of simultaneously analyzing for H2O, CO2,
CO, SO2 and H2S.
In geothermal systems, surface manifestations are often comprised of gas emissions. In some cases, low temperatures and/or
low flow rates make traditional sampling of fumaroles difficult,
due to rapid vapor condensation (in water-rich fumaroles) and
atmospheric contamination. The MultiGAS is best suited to these
types of manifestations, providing a tool that can be used at a wide variety of locations with differing gas emission styles.
The MultiGAS has been field-tested in two very different
geothermal prospect areas: one characterized by cold, CO2-rich
gas seeps and bubbling springs, and the other characterized by
steaming ground and fumaroles with temperatures near the boiling
point of water. Results of the MultiGAS analysis are compared
with the equivalent ratios obtained from traditional sampling andanalytical procedures (where possible), in order to identify the advantages and disadvantages of this new technique. The MultiGAS allows for the rapid characterization of the gas geochemistry in the field, aids in mapping/targeting of fumaroles in a large field, and allows for the selection of the most ideal fumaroles to sample using the traditional Giggenbach method.
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