Publication Date:
2017-04-04
Description:
Natural gas seeps in the Alpine region are poorly investigated. However, they can provide useful information
regarding the hydrocarbon potential of sedimentary Alpine units and related geofluid migration, typically controlled
by pressurized gas accumulations and tectonics. A gas seep located near Giswil, in the Swiss Northern
Alps, was investigated, for the first time, for molecular and isotopic gas composition, methane flux to the atmosphere,
and gas flux variations over time. The analyses indicated that the gas was thermogenic (CH4 〉 96%;
d13C1: )35.5& to )40.2&) and showed evidence of subsurface petroleum biodegradation (13C-enriched CO2,
and very low C3+ concentrations). The source rock in the region is marine Type II kerogen, which is likely the
same as that providing thermogenic gas in the nearby Wilen shallow well, close to Lake Sarnen. However, the
lack of d13CCO2 and d13C3 data for that well prevented us from determining whether the Wilen and Giswil seeps
are fed by the same reservoir and seepage system. Gas fluxes from the Giswil seep, measured using a closedchamber
system, were significant and mainly from two major vents. However, a substantial gas exhalation from
the soil occurs diffusely in an area of at least 115 m2, leading to a total CH4 output conservatively estimated to
be at least 16 tonnes per year. Gas flux variations, monitored over a 1-month period by a special tent and flowmeter,
showed not only daily meteorological oscillations, but also an intrinsic ‘pulsation’ with periods of enhanced
flux that lasted 2–6 h each, occurring every few days. The pulses are likely related to episodes of gas pressure
build-up and discharge along the seepage system. However, to date, no relationship to seismicity in the active
Sarnen strike-slip fault system has been established.
Description:
Published
Description:
476-485
Description:
4.5. Studi sul degassamento naturale e sui gas petroliferi
Description:
JCR Journal
Description:
restricted
Keywords:
Alps
;
isotopes
;
methane
;
organic geochemistry
;
seeps
;
Switzerland
;
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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