Title:

Soil Gas Flux Exploration at the Rotokawa Geothermal Field and White Island, New Zealand

Authors:

Simon BLOOMBERG, Clinton RISSMANN, Agnes MAZOT, Christopher OZE, Travis HORTON, Darren GRAVLEY, Ben KENNEDY, Cynthia WERNER, Bruce CHRISTENSON and Joanna PAWSON

Key Words:

soil gas flux, CO2 flux, Rotokawa, White Island, Taupo Volcanic Zone, steam and mass flow, heat flow, emissions

Geo Location:

White Island, New Zealand; Rotokawa, New Zealand; Taupo Volcanic Zone

Conference:

Stanford Geothermal Workshop

Year:

2012

Session:

Geochemistry

Language:

English

Paper Number:

Bloomberg

File Size:

1701 K

View File:

Abstract:

Soil Gas Flux Exploration at the Rotokawa Geothermal Field and White Island, New Zealand Simon Bloomberg, Clinton Rissmann, Agnes Mazot, Christopher Oze, Travis Horton, Darren Gravley, Ben Kennedy, Bridget Lynn, Amy Dougherty and Bruce Christensen A significant challenge to geothermal exploration is accurate quantification of the heat and mass flow between deep reservoir(s) and the surface. Here, we use high resolution carbon dioxide (CO2) flux at the surface to characterise the mass (CO2 and steam) and heat released from the geothermal reservoir. Complementary isotope tracer data provide insight into the origins of CO2 which in turn helps delineate the contribution of CO2 derived from the soil respired CO¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬2 and reduces the level of uncertainty when deriving mass (emissions) and heat flow estimates. Fumarole data can provide valuable geochemical data on the reservoir conditions in terms of molar gas ratios (H2O-CO2/H2S) which can be used in conjunction with CO2 emissions estimates to quantify the heat release from the deep reservoir. The results are of complementary soil gas surveys from two geothermal systems with markedly different soil respired CO2 components, White Island and Rotokawa. These results include over 3000 direct measurements of soil and fumarolic acid gases. Complementary stable isotopic analyses were performed in an effort to trace the source of the carbon phases. Current estimates of heat flow at Rotokawa are around 220MW, preliminary results which asses the heat flow prior to energy loss through steam condensing suggest a mass flow of 75MW, while the heat flow through soil is around 330MW. The total emissions rate sits around 6300td-1 CO2. Steam and heat flow values for White Island will be forthcoming once a fumarole sample has been taken, but heat flow through soil estimates put it at around 170MW. Previous soil gas surveys at white island have a total soil flux of 8.7td-1 whereas this surveys puts it between 110-210td-1 meaning that previous estimates of soil gas CO2 contribution to the total emission rate for the volcano are low. The plume produces around 2000 td-1 and previous estimates put soil gas flux contribution at


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