Ninth international conference on - Marum

Abstracts of posters 79
Preparative model-study for a CSEM-experiment at the North Alex mud volcano
S. Hölz 1 and M. Jegen 1
1 IFM-GEOMAR, CAU-Kiel, Wischhofstr. 1-3, 24148 Kiel
Marine controlled source electromagnetic (CSEM) has proven to be a feasible geophysical method for the
investigation of the subsurface's conductivity structure of the seafloor. The bulk conductivity of seafloor
sediments is mainly a function of porosity and connectivity of the pore fluid, i.e. seawater, and is decreased
where electrically insulating free gas and/or gas hydrates form in sufficient quantities.
We plan to use CSEM to image porosity and fluid and gas contents at the North Alex mud volcano located in the
outer reaches of the West-Nile-Delta. Due to the small scale of the mud volcano (1.5 km in diameter) and safety
consideration (seafloor communication cables) we have opted to develop a compact transmitter which is moved
along the seafloor by a ROV together with stationary electric field receivers on the seafloor. The design of the
CSEM receivers is based on the existing IFM-GEOMAR OBMT (ocean bottom magnetotelluric) stations.
We performed a straight forward 1D modeling study to derive specifications for the transmitter and to assess
necessary modifications for the receivers. Within the study, the achievable depth of penetration for various
measurement geometries (i.e. transmitter-receiver separations) was estimated by calculating the 1D sensitivity
for two and three layered models. Summarizing the results, it can be stated that a small transmitter system with a
dipole moment of approximately 200Am (20A output into a 10m dipole) is suitable to generate detectable
signals for transmitter-receiver separations of up to 250-350m. Depending on the separation, the resulting depth
of penetration is between a few meters up to approximately 100-200m.
The first deployment of the new CSEM-system is scheduled during the field experiment in the West-Nile-Delta
in November 2008. The CSEM-experiment will be complemented by a simultaneous MT- and MMRexperiment,
which cover the deeper conductivity structure of the North Alex.
Hydrocarbons of Lake Baikal (Eastern Siberia)
O. Khlystov 1
1 Limnological Institute, SB RAS, 664033 Irkutsk, Russian Federation
Lake Baikal is the largest and oldest water body on the globe. During its long geological development (>25 My),
more than 7 km of sediments saturated with organic matter accumulated. This matter was transformed with time
into hydrocarbons of different types. Natural gas in free, dissolved and solid (gas hydrates) state, as well as oil
are found in the lake sediments.
Gas and oil seeps in shallow water in Lake Baikal are known since its first descriptions in XVII-XVIIIth
centuries. First laboratory investigations in the last century showed that methane occurs more often than other
gases. The oil from Lake Baikal is heavily biodegraded, which makes it difficult to determine its age and
genesis. The idea on possible availability of gas hydrates in lake sediments was declared for the first time in
1980. In 1989, geophysical indications for gas hydrates (BSRs) were found. In 1997, first proofs of hydrate
occurrence were obtained by deep drilling at subbottom depths of >120 m. In 2000, first agglomerations of gas
hydrates were found in the near-bottom sediments (subbottom depth of