Ninth international conference on - Marum

32
Abstracts of oral presentations
Gas presence in the sediment pile – Black Sea case
G. Ion 1 , E. Ion 1 , F. Dutu 1 , A. Popa 1 , V. Radulescu 1
1 GeoEcoMar, 23-25 D. Onciul, 024053-Bucharest, Romania
Black Sea is one of the most researched areas in terms of gas presence, in the sediment pile. This is mainly due
to its very specific characteristics: an almost enclosed basin, 93% of its depth being anoxic and a geologic
history marked by successive states of fresh and saline waters. Large amounts of sediments have been
accumulated in some parts of the black sea (more than 12000 m in some areas).
The water level dynamics specific to the evolution of the Black Sea in glacial time, produced best environments
(deltas, marshes, migrating shoreline and river channels, etc.) for the production of important spots or even belts
of large amounts of organic matter that produced biogenic gas. Oil and gas proven provinces exists in the Black
Sea. Some methane originating from deep parts of the sediment pile ascends and reaches the shallow sediments
and even the water column. The fluids follow the most permeable structures and conduits, as tectonic features or
mud volcanoes.
Specific seismo-acoustic facies can be attached to characteristic geological structures. Contrasting facies are
specific for the presence of gas in the sediment pile (as wipe outs and acoustic turbid zones, etc) and a correct
geological interpretation requires great care and experience.
The mixing of biogenic and thermogenic methane can exist on all specific areas of the sea: continental shelf,
shelf break, continental slope and the deep sea. The possible bio-geochemical reworking of methane makes
difficult to distinguish between biogenic and thermogenic gas.
On the continental slope gas hydrate accumulations are present. Double BSR structures are quite common on the
western part of the continental slope and a unique and a strange feature made by four stacked BSRs has been
reported for the first time in the same area by Ion G. et. al., in 2002.
It is thought that Prokaryote organisms play a major role in mediating the methane production and consumption
in the sediment pile. In the last years Black Sea has been and still is a huge natural laboratory to study the
complex processes related to the microbiology and geology of the methane gas.
Mapping and main characteristics of multiple BSR reflectors in the Tuapse Trough (Black Sea)
M. Ivanov 1 , V Blinova 1, 2 , N. Malyshev 2 , R. Pevzner 3 , A. Volkonskaya 1 , S. Bouriak 3
1 UNESCO Centre for Marine Geology and Geophysics, Geological department, Moscow State University,
Moscow, Russia.
2 Corporate Research and Technology Centre, Rosneft oil company, Russia
3 Deco Geophysical, Moscow, Russia
Large numbers of the multichannel commercial 2D seismic records were analyzed to reveal a distribution of
BSR reflectors in sedimentary cover of the Tuapse Trough. Special set of seismic processing methods oriented
on detailed study of uppermost sedimentary section (until 500 m bsf) have been applied. It allows ensuring
maximum resolution and dynamic characteristics of seismic records at this depth interval.
BSR type reflectors have been detected in the most of seismic sections and map of gas hydrate bearing deposits
was created. Two areas of gas hydrate distribution: North-western and Central have been definitely identified. In
N-W area BSR reflector is very well traced in Quaternary deposits simulating complex relief of channel-levee
system. In Central area BSR reflectors are coincide with Maikopian folds. They are discontinuous and crossing
discordant with layers of different ages. Total area of BSR distribution in the Tuapse Trough is not less than
5100km 2 .
Maps of temperature gradients and heat flow were built on the base of BSR distribution map. They demonstrate
very high heat flow variations in this area ranges between 15 and 60 mW/m2, while highest values coincide with
outer, probably, most active folds. These data are in accord with direct measurements of heat flow at this area
and allow to give reasonable explanation for big variations of heat flow on relatively limited area.
Multiple BSR’s (from 2 to 4) have been revealed on several seismic lines. By simple modeling of P-T conditions
it was concluded that uppermost BSR in this vertical succession coincide with present-day bottom of gas hydrate
stability zone.
Comparison of these data with multiple BSR’s in N-W part of the Black Sea (Danube deep=sea fan) demonstrate
that they have similar nature and most probably reflect some local regional climatic changes influenced warming
of sea bottom water temperature in whole Black sea during last 10 m.y. due to opening of Bosporus Strait.