Applied CO2 flux to monitor natural emission from geothermal field, New Zealand

Abstract

Soil CO2 flux measurements could be used in geothermal areas to constrain surface CO2 emissions and to monitor degassing anomalies from volcanic, tectonic, or anthropogenic activities. However spatial and temporal variations in a utilised geothermal field are difficult to assess at a large scale due to the prerequisite of a lengthy CO2 flux survey and lack of monitoring data outside the power stations.
In this study, we analyse the temporal and spatial variations of soil CO2 flux and soil temperature in the Taupo region. Fortnightly monitoring between 2019 to 2022 at 8 stations across the Tauhara and Wairakei geothermal fields provide insight into changes of seasonal variations and geothermal activities. Carbon dioxide flux at 2 stations at Karapiti and 1 background site in the Wairakei geothermal field remain constant over the 2.5-year interval of monitoring. In contrast, CO2 flux at the 5 stations at Crown Park in the Tauhara geothermal field fluctuated synchronously.
To understand the broader distribution of natural degassing and to compare the CO2 flux over decades, we mapped the CO2 at Karapiti, Wairakei geothermal field (2021, 2003, 2018) (n=123), “Ring of Fire”, Tauhara geothermal field (2006, 2022) (n=646), and Rotokawa geothermal field (2003, 2011, 2022) (n=380). Differences in the CO2 flux distribution and total emission over a decade suggest possible changes to fluid pathways, permeability zones and/or reservoir conditions. The result gives important statistical insight into time constraints for future surface CO2 surveys and monitoring strategy in the geothermal field.