Quantification of gases released during seismic events: long-term, on-site borehole monitoring in deep active faults, South Africa
Zusammenfassung der Projektergebnisse
An on-site gas monitoring study has been conducted in the framework of an earthquake laboratory (the international NELSAM-DAFGAS projects) at the TauTona Gold mine, South Africa. Inside a 25 m² cubby five boreholes up to 60 m were drilled into the highly fractured Pretorius Fault zone at 3.54 km depth and instruments for chemical and seismic monitoring installed therein. Throughout four years sensitive gas monitoring devices have been continuously improved to enable the direct observation of geogas concentration variations in the DAFGAS borehole. The major gas concentrations are constant and air-like with about 78% N2, 21% O2, 1% Ar. The geogas components CO2, CH4, He and H2 show most interesting trends and variations on the minute-by-minute basis and significantly correlate with seismic data, while the 222Rn activity is constant throughout the years. This indicates that the geogases are released from existing gas reservoirs, not just recently released from freshly cracked rocks. Time series and cross correlation analysis allow the identification of different gas components (geogas and tunnel air) and the identification of two processes influencing the borehole gas composition: 1) pumping-induced tunnel air breakthrough through networks of initially water-saturated fault fractures; and 2) seismicity induced permeability enhancement of fault fractures to above ~5⋅10-10 m². The current set-up of the gas monitoring system is sensitive enough to quantify the resulting geogas transport during periods of intense blasting activities (including recorded blasts with seismic moment ≤ 1⋅109 Nm, located within 1000 m of the cubby) – and, we suggest, also during induced earthquakes – a final goal of the project. Regarding the DAFGAS project as one out of a group of interrelated, international projects contemporarily conducted by partners at same or very similar deep underground settings in South African mines drives us to jointly report on their overall coverage in the media: The earliest publication of the group was nicely covered in international and in German print and online media http://www.sueddeutsche.de/wissen/blick-in-die-erdgeschichte-die-unsichtbare-masse-1.912625 (Süddeutsche Zeitung, 12.12.2006), http://www.spiegel.de/wissenschaft/natur/0,1518,443617,00.html(Der Spiegel, 22.10.2006), http://idw-online.de/pages/de/news180707 (Informationsdienst Wissensschaft, 19.10.2006), as well as in broadcastings http://www.dradio.de/dlf/sendungen/forschak/555479/ (Deutschlandfunk, 22.10.2006). Continuous awareness allowed for combined reports also on the ongoing DAFGAS experiment: http://www.g-o.de/geounion-aws_basics-6439.html (Scinexx.de, 27.04.2007), and ZeitWissenMagazin (31.05.2011). Another, more recent publication on Neon gas identifying two billion year old water in the mines provoked an astonishing public awareness in online media (19.02.-25.02.2011): http://www.sciencedaily.com/releases/2011/02/110219202353.htm (ScienceDaily.com), http://www.spiegel.de/wissenschaft/natur/0,1518,746861,00.html (Spiegel Online), http://www.welt.de/wissenschaft/article12614106/Goldmine-birgt-zwei-Milliarden-Jahre-altes-Wasser.html (Welt.de), http://www.focus.de/wissen/wissenschaft/wissenschaft-zwei-milliarden-jahre-altes-wasser-entdeckt_aid_602414.html (Focus.de), http://www.wissenschaft.de/wissenschaft/news/313018 (Bild der Wissenschaft), http://derstandard.at/1297818676419/Fremdes-Leben-in-zwei-Milliarden-Jahre-altem-Grundwasser-entdeckt (DerStandard.at), http://www.taz.de/pt/2011/02/25/a0126.nf/text (Taz online), http://www.sz-online.de/nachrichten/artikel.asp?id=2694962 (SächsischeZeitung), http://www.big-screen.de/deutsch/pages/news/allgemeine-news/2011_02_23_5994_zwei-milliarden-jahre-altes-grundwasser-entdeckt.php (Big-screen.de), print media: Bildzeitung (22.02.2011), http://www.stadtwerkeitzehoe.de/fileadmin/documents/service/tana/2010/tana_4_2010/2010_04_s_6_9.pdf, and broadcastings: http://www.podcast.de/episode/2080759/Zwei+Milliarden+Jahre+altes+Wasser+entdeckt/ (SWR2 Impuls, 24.02.2011).
Projektbezogene Publikationen (Auswahl)
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(2005). Radiolytic H2 in the continental crust: Nuclear power for deep subsurface microbial communities. Geochemistry Geophysics Geosystems, 6(7), 1-13
Lin L.-H., Hall J., Lippmann-Pipke J., Ward J., DeFlaun M., Rothmel R., Moser D. P., Gihring Th. M., Sherwood Lollar B., Onstott T.C.
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(2006). 14C distribution in methane and DIC in South African gold mines: Implications to timing of methanogenesis. Geomicrobiol. J., 23, 453- 462
Slater G. F., Lippmann-Pipke J., Reddy C.M., Lacrampe-Couloume G., Onstott T.C., Sherwood Lollar B.
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(2006). Long term biosustainability in a high energy, low diversity crustal biome. Science, 314, 479-482
Lin L.-H., Wang P.-L., Rumble D., Lippmann-Pipke J., Boice E., Pratt L., Sherwood Lollar B., Brodie E., Hazen T, Andersen G, DeSantis T., Moser D.P., Kershaw D., and Onstott T.C.
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(2006). The origin and age of biogeochemical trends in deep fracture water of the Witwatersrand Basin, South Africa. Geomicrobiol. J., 23, 369-414
Onstott T.C., Lin L.-H., Davidson M., Mislowack B., Borcsik M., Hall J., Slater G., Ward J., Sherwood Lollar B., Lippmann-Pipke J., Boice E., Pratt L.M., Pfiffner S., Moser D., Gihring T., Kieft T.L., Phelps T.J., VanHerden E., Littaur D., DeFlaun M., Rothmel R. Wanger, G. and Southam, G
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(2011). Neon isotopes identifies two billion year old fluid component in KaapvaalCraton“. Chem. Geol., 283, 287-296
Lippmann-Pipke J., Sherwood Lollar, B., Niedermann S., Naumann R., Stroncik, N., van Heerden, E., Onstott T.C.
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Direct observation of blasting triggered geogas transport through an inactive fault system at 3.6km depth, Tautona gold mine, SA. Appl. Geochem., 26(12), 2134-2146
Lippmann-Pipke, J., Erzinger J., Zimmer M., Kujawa C., Heerden, E. van, Bester, A., Moeller, H., Boettcher, M., Reches, Z.
