Processes of hydrogen genesis during seismic cycles in active fault zones (ProHydroGen)
Mineralogy, Petrology and Geochemistry
Final Report Abstract
The ICDP-supported DSeis project (Drilling into Seismogenic zones in deep South African Gold Mines) drilled two boreholes (hole A 817m and hole B 700m long) at a 2.9 km deep mining level of the Moab Khotsong gold mine in order to penetrate into the aftershock plane of the M 5.5 Orkney earthquake that occurred in August 2014. Docked to this project, an automated gas analytical system was deployed, which was designed, developed and successfully used underground in the Moab Khotsong mine by the applicants within the framework of the DFG funded project ProHydrogen, to monitor the concentrations of specific gas released by the boreholes. The main components of the monitoring system include gas specific sensors for H2, CH4, CO2, O2, O3 (ozone), and 222Rn. The gases are monitored at one-minute intervals; the data is transmitted in real time to the surface. Generally, continuous gas data from hole A logged at minute intervals are available from 27th November 2018 to March 2021. Unfortunately, not all sensors lasted the entire period and broke. Therefore, large data gaps have arisen and the gas data of all sensors are only available for a few short time periods. Time series are available for O2, O3, CO2, H2, Rn, CH4 and for the pressure and temperature. The temperature and pressure are functions of the effectivity of the weathering in the tunnel. High temperatures were registered especially when the mine-weathering was switched off (in lock down periods) due to the reduced ventilation rates. O2 in the samples is a contamination and admixture of atmosphere to the wellbore gas phase as all gases, except O3, are negatively correlated with O2. O3 correlates positively with atmospheric O2, so that the radiolysis of atmospheric molecular O2 may be responsible for the formation of ozone. A correlation of CO2 with O3 is not visible, so that the radiolysis of CO2 is probably only a subordinate process in the rock formation. Hydrogen could be generated simultaneously with O3 by radiolysis. But as H2 does not correlate with O3, the radiolytic production of these gases is less likely. The reduction of water on transition metals/metal oxides and via FFT-reactions, that would only generate hydrogen, is therefore more likely. Also, other mechanisms of hydrogen generation (corrosion of the steel casing) may play a role for the hydrogen budget. To distinguish between corrosion H2 and other sources, D/H analyses are essential. Unfortunately, no isotopic analyses on H2 are available so that no further statements on the origin of H2 can be drawn. Gas samples collected from Hole A revealed CH4/[C2H6+C3H8] ratios between 10-11 and make a contribution of biogenic hydrocarbons less likely, which is typically 2-4 orders of magnitude higher for biogenic gas. The reverse carbon isotope values (δ13C) of C1-C4 hydrocarbons is atypical for thermogenic hydrocarbons but similar to an abiogenic source, e.g. by FTT reactions or serpentinization of ultramafic rocks. All noble gases are composed by a minor contribution of nuclides from nuclear processes, i.e. radiogenic 4He and 40Ar, nucleogenic 21Ne and 22Ne, and fossiogenic xenon isotopes. He and Ne isotopic analysis confirmed that there is no significant mantle-derived component associated with the Moab A borehole gas samples.
Publications
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2019 status report: Drilling into seismogenic zones of M2.0–M5.5 earthquakes in South African gold mines (DSeis project). Proceedings of the International Conference on Deep and High Stress Mining (2019), 375-384. The Southern Africa Institute of Mining and Metallurgy, Johannesburg.
Ogasawara, Hiroshi; Liebenberg, Bennie; Rickenbacher, M; Ziegler, Martin; van Esterhuizen, H; Onstott, Tullis; Durrheim, Raymond; Mngadi, Siyanda; Yabe, Yasuo; Ogasawara, Hiroshi; Kaneki, Shunya; Cason, Errol; Vermeulen, Jan-G; van Heerden, Esta; Wiersberg, Thomas; Zimmer, Martin; Kujawa, Christian; Conze, Ronald; van Aswegen, Gerhard; ... & Bucibo, Mavuso
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Briny SLiMEs in the subsurface of Earth and Mars [abstract 5025]. In Mars Extant Life: What’s Next? Conference Abstracts, Lunar and Planetary Institute, Houston. Available online
Onstott, T.C.; Rusley, C.; Liang, R.; Garvin, Z.; Nission, D.; Harris, R.; Higgins, J.; Slater, N.; Van Heerden, E.; Freese, B.; Leibenberg, B.; Ogasawara, H.; van Heerden, E.; Cason, E.; Vermeulen, J.; Sherwood L.B.; Kieft, T.; Wiersberg, T.; Zimmer, M.; Walters, C.; Freifeld, B. & Michalski, J.R.
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Investigations on fault zone gases in South African gold mines. Abstract EGU2019-5670,SSP1.2/CL1.32/EMRP3.11/GD2.9/GMPV1.7/NH5.12/ TS1.4, 7-12 April 2019, Vienna
Wiersberg, T.; Zimmer, M.; Kujawa, C.; Liebenberg, B.; Ogasawara, H.; Onstott, T.C.; Cason, E.; Vermeulen, Jan-G & van Heerden, E.
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The seismogenic zones of an M2.0-5.5 earthquakes successfully recovered in deep South African gold mines: the outcomes and the follow-up plan. American Geophysical Union (AGU).
Ogasawara Hiroshi, Liebenberg Bennie; Yabe Yasuo, Yokoyama Yuki; Hirono Tetsuro, Nisson Devan M.; Onstott Tullis C., Kieft Thomas L.; van Heerden Esta, Wiersberg Thomas; Noda Taku, Manzi Musa S.D.; Mngadi Siyanda B., Durrheim Raymond J.; Yamamaoto Yuhji, Ito Takatoshi; Funato Akio, Ziegler Martin; ... & Mori, James J.
