Articles | Volume 23
Sci. Dril., 23, 13–27, 2017
Sci. Dril., 23, 13–27, 2017

Science report 30 Nov 2017

Science report | 30 Nov 2017

Drilling into an active mofette: pilot-hole study of the impact of CO2-rich mantle-derived fluids on the geo–bio interaction in the western Eger Rift (Czech Republic)

Robert Bussert1, Horst Kämpf2, Christina Flechsig3, Katja Hesse4, Tobias Nickschick2,3, Qi Liu5, Josefine Umlauft3, Tomáš Vylita6, Dirk Wagner5, Thomas Wonik4, Hortencia Estrella Flores3, and Mashal Alawi5 Robert Bussert et al.
  • 1Institute of Applied Geosciences, Technische Universität Berlin, 13355 Berlin, Germany
  • 2GFZ German Research Centre for Geosciences, Section 3.2: Organic Geochemistry, 14473 Potsdam, Germany
  • 3Institute for Geophysics and Geology, University of Leipzig, 04103 Leipzig, Germany
  • 4Leibniz Institute for Applied Geophysics, 30655 Hannover, Germany
  • 5GFZ German Research Centre for Geosciences, Section 5.3: Geomicrobiology, 14473 Potsdam, Germany
  • 6Balneological Institute, 360 01 Karlovy Vary, Czech Republic

Abstract. Microbial life in the continental deep biosphere is closely linked to geodynamic processes, yet this interaction is poorly studied. The Cheb Basin in the western Eger Rift (Czech Republic) is an ideal place for such a study because it displays almost permanent seismic activity along active faults with earthquake swarms up to ML 4.5 and intense degassing of mantle-derived CO2 in conduits that show up at the surface in form of mofettes. We hypothesize that microbial life is significantly accelerated in active fault zones and in CO2 conduits, due to increased fluid and substrate flow. To test this hypothesis, pilot hole HJB-1 was drilled in spring 2016 at the major mofette of the Hartoušov mofette field, after extensive pre-drill surveys to optimize the well location. After drilling through a thin caprock-like structure at 78.5 m, a CO2 blowout occurred indicating a CO2 reservoir in the underlying sandy clay. A pumping test revealed the presence of mineral water dominated by Na+, Ca2+, HCO3, SO42− (Na-Ca-HCO3-SO4 type) having a temperature of 18.6 °C and a conductivity of 6760 µS cm−1. The high content of sulfate (1470 mg L−1) is typical of Carlsbad Spa mineral waters. The hole penetrated about 90 m of Cenozoic sediments and reached a final depth of 108.50 m in Palaeozoic schists. Core recovery was about 85 %. The cored sediments are mudstones with minor carbonates, sandstones and lignite coals that were deposited in a lacustrine environment. Deformation structures and alteration features are abundant in the core. Ongoing studies will show if they result from the flow of CO2-rich fluids or not.