EGU2020-5735, updated on 10 Mar 2022
EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Variations of gas compositions during a drilling process: A key study on the Hartoušov Mofette, Czech Republic

Kyriaki Daskalopoulou1, Heiko Woith1, Martin Zimmer2, Samuel Niedermann2, Cemile D. Bağ1,3, Ralf Bauz1, Jakub Trubač4, and Tomáš Fischer5
Kyriaki Daskalopoulou et al.
  • 1Physics of Earthquakes and Volcanoes, German Research Centre for Geosciences-GFZ, Potsdam, Germany (
  • 2Inorganic and Isotope Geochemistry, German Research Centre for Geosciences-GFZ, Potsdam, Germany
  • 3Department of Geological Engineering, Middle East Technical University-METU, Çankaya, Turkey
  • 4Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University in Prague, Prague, Czechia
  • 5Institute of Hydrogeology, Engineering Geology and Applied Geophysics, Charles University in Prague, Prague, Czechia

The Eger Rift (Czech Republic) is an intraplate region without active volcanism but with emanations of magma-derived gases and the recurrence of mid-crustal earthquake swarms with small to intermediate magnitudes (ML < 5) in the Cheb Basin. To understand the anomalous earthquake activity and CO2 degassing, an interdisciplinary well-based observatory is built up for continuous fluid and earthquake monitoring at depth.

The fluid observatory is located at the Hartoušov Mofette (Cheb Basin), an area characterized by intense mantle degassing with a subcontinental lithospheric mantle (SCLM) contribution of He that increased from 38% in 1993 to 89% in 2016. Two drillings with depths of 30 and 108 m (F1 and F2, respectively) are being monitored since August 2019 for the composition of ascending fluids. Additionally, the environmental air composition is monitored. Gas concentrations were determined in-situ at 1-min intervals, while direct sampling campaigns took place periodically and samples were analyzed for their chemical and isotope composition. Samples of gases emerging in the mofette were also collected. During this period, a third borehole (F3) with a depth of 238 m was drilled.

At Hartoušov, carbon dioxide is the prevailing gas component (concentrations above 99.5%), with helium presenting a mantle origin (up to 90% considering a SCLM-type source). The atmospheric contribution is negligible, even though during drilling of F3 enrichments in atmospheric components such as Ar and N2 have been observed. An increase in both CH4 and He has been noticed in F2 (108 m borehole) at 40 m depth, whilst a decrease in He has been observed at 193 m depth in both F1 and the natural mofette. Enrichments in less soluble gases (eg. He and N2) at various depths accompanied by a minor CO2 decrease have also been noticed. Such variations may have been caused by the different solubilities of gases in aquatic environments. Moreover, a decrease in CO2 followed by a subsequent enrichment of CH4 and CxHy during the first days after the initial drilling could promote the hypothesis of the generation of microbialy derived CH4. Diurnal variations were observed for the majority of the gas components during the last phase of the F3 drilling, when the well reached a depth >200 m.

This research is a part of the MoRe - “Mofette Research” project, which is included in the ICDP project “Drilling the Eger Rift: Magmatic fluids driving the earthquake swarms and the deep biosphere”). This work was supported by the DFG grant# WO 855/4-1 and BA 2207/19-1.

How to cite: Daskalopoulou, K., Woith, H., Zimmer, M., Niedermann, S., Bağ, C. D., Bauz, R., Trubač, J., and Fischer, T.: Variations of gas compositions during a drilling process: A key study on the Hartoušov Mofette, Czech Republic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5735,, 2020.

This abstract will not be presented.