First Bulgarian gas hydrates: a BSR estimate
This article is a first attempt of gas hydrate study from probable bottom simulating reflectors (BSRs) for the Bulgarian part of the Black Sea. Eleven probable areas of GHs are found. The volumes of GH and methane in them are determined.The new results show the possibility of wide distribution of...
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Відділення морської геології та осадочного рудоутворення НАН України
2010
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irk-123456789-448452013-06-05T03:09:11Z First Bulgarian gas hydrates: a BSR estimate Vasilev, Atanas Газогидраты This article is a first attempt of gas hydrate study from probable bottom simulating reflectors (BSRs) for the Bulgarian part of the Black Sea. Eleven probable areas of GHs are found. The volumes of GH and methane in them are determined.The new results show the possibility of wide distribution of gas hydrates (GHs) in the area. Additionally the work introduces new challenging tasks concerning global warming impact on GHs and the role of main faults in forecasting oil and gas potential in the shelf areas. Стаття висвітлює першу для Болгарії спробу вивчення газогідратів (ГГ) з використанням BSR . Знайдено 11 вірогідних площ із ГГ, оцінено об’єм ГГ і вміщеного в них метану. Доведено можливість значного поширення ГГ у болгарській частині Чорного моря. Результати цінні для майбутніх досліджень означених площ і перспективних глибин. Робота привертає увагу до питання впливу зміни клімату на ГГ Чорного моря та ролі глибинних розломів у формуванні нафтогазоносності шельфу. Эта статья освещает первую для Болгарии попытку изучения газогидратов (ГГ) с использованием BSR. Открыты 11 вероятных площадей с ГГ, оценен объем ГГ и содержащегося в них метана. Доказана возможность значительного распространения ГГ в болгарской части Черного моря. Результаты ценны для будущих исследований в означенных районах на перспективных глубинах. Работа привлекает внимание к вопросу исследования влияния изменения климата на ГГ Черного моря и роли глубинных разломов в формировании нефтегазоносности шельфа. 2010 Article First Bulgarian gas hydrates: a BSR estimate / Atanas Vasilev // Геология и полезные ископаемые Мирового океана. — 2010. — № 2. — С. 22-26. — Бібліогр.: 13 назв. — англ. 1999-7566 http://dspace.nbuv.gov.ua/handle/123456789/44845 553.981 en Геология и полезные ископаемые Мирового океана Відділення морської геології та осадочного рудоутворення НАН України |
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Газогидраты Газогидраты |
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Газогидраты Газогидраты Vasilev, Atanas First Bulgarian gas hydrates: a BSR estimate Геология и полезные ископаемые Мирового океана |
| description |
This article is a first attempt of gas hydrate study from probable bottom
simulating reflectors (BSRs) for the Bulgarian part of the Black Sea. Eleven
probable areas of GHs are found. The volumes of GH and methane in them are
determined.The new results show the possibility of wide distribution of gas
hydrates (GHs) in the area. Additionally the work introduces new challenging
tasks concerning global warming impact on GHs and the role of main faults in
forecasting oil and gas potential in the shelf areas. |
| format |
Article |
| author |
Vasilev, Atanas |
| author_facet |
Vasilev, Atanas |
| author_sort |
Vasilev, Atanas |
| title |
First Bulgarian gas hydrates: a BSR estimate |
| title_short |
First Bulgarian gas hydrates: a BSR estimate |
| title_full |
First Bulgarian gas hydrates: a BSR estimate |
| title_fullStr |
First Bulgarian gas hydrates: a BSR estimate |
| title_full_unstemmed |
First Bulgarian gas hydrates: a BSR estimate |
| title_sort |
first bulgarian gas hydrates: a bsr estimate |
| publisher |
Відділення морської геології та осадочного рудоутворення НАН України |
| publishDate |
2010 |
| topic_facet |
Газогидраты |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/44845 |
| citation_txt |
First Bulgarian gas hydrates: a BSR estimate / Atanas Vasilev // Геология и полезные ископаемые Мирового океана. — 2010. — № 2. — С. 22-26. — Бібліогр.: 13 назв. — англ. |
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Геология и полезные ископаемые Мирового океана |
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AT vasilevatanas firstbulgariangashydratesabsrestimate |
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2025-07-04T03:24:55Z |
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2025-07-04T03:24:55Z |
| _version_ |
1836685193163833344 |
| fulltext |
VASILEV А.
22 ISSN 1999�7566. Геология и полезные ископаемые Мирового океана, 2010, №2
УДК 553.981
© Atanas Vasilev, 2010
Institute of Oceanology – Bulgarian Academy of Sciences, Varna, Bulgaria
FIRST BULGARIAN GAS HYDRATES:
ASSESSMENT FROM PROBABLE BSRS
This article is a first attempt of gas hydrate study from probable bottom
simulating reflectors (BSRs) for the Bulgarian part of the Black Sea. Eleven
probable areas of GHs are found. The volumes of GH and methane in them are
determined.The new results show the possibility of wide distribution of gas
hydrates (GHs) in the area. Additionally the work introduces new challenging
tasks concerning global warming impact on GHs and the role of main faults in
forecasting oil and gas potential in the shelf areas.
Introduction. The world resources of methane in gas hydrates exceed as
much as twice the total resources of traditional fossil fuels – coal, oil, gas and
peat [4]. They can solve not only the energy problem of mankind for centuries
but also are capable catastrophically to change the global climate. The present�
day great interest in gas hydrates resulted in intensive studies of their
reservoirs, development technologies of methane extraction from them and
special studies of their influence on the climate.
Method. There are many specific features on marine seismic records which
are related to the existence of GH in sediments. The most informative among
them are BSRs, which mark the thermobaric base of the gas stability zone
(BGHSZ) [5]. The reversed polarity of BSRs relative to the sea floor reflection
boundary resulted from a jump of acoustic impedance due to low velocity in
free gas�bearing layers beneath BGHSZ. The normal polarity is also registered
[9]. The free gas existence has confirmed by drilling [3, 7, 11]. Small horizontal
gradients of temperature control the geometry of reflections which follow that
of sea floor. These reflections are clearly observed on records from the
continental slope, where they intersect pinching out lithological�stratigraphic
boundaries.
Approach – weak and strong sides. The most appropriate first step after
model estimation is a visible determination of BSRs on archives seismic records.
The presented results are from transverse to the coast line seismic profiles of
Halliburton G.S. from 1992.
Weak points of the BSR approach are:
• BSRs don’t contain information on the concentration of GHs in sediments –
they are caused primarily by gas;
• The strongest BSRs don’t occur in reservoirs of quality sands but in shales;
• For BSRs identification geometry of sedimentary strata cant be not parallel
to the seafloor boundary;
• Not every GHs deposit shows BSR (free gas existence below a gas hydrate
saturated zone (GHSZ) is not compulsory). BSR can be a false positive
indicator of abundant hydrate, and its absence a false negative indicator.
FIRST BULGARIAN GAS HYDRATES: ASSESSMENT FROM PROBABLE BSRS
ISSN 1999�7566. Геология и полезные ископаемые Мирового океана, 2010, №2 23
• BSRs are not only associated with GHs. A transition of opal�A to opal�CT can
create a normal�polarity diagenesis related to BSRs [1, 2]. Detailed 3D seismic
interpretation including BSRs interpretation, velocity analysis and geological
information should be necessary for the evaluation of methane hydrates.
Strong points of the BSR approach are:
• BSRs define the phase boundary hydrate�free gas;
BSRs allows us to validate assumptions on geothermal gradient and gas
composition.
The approach of this work was to look for crossing reflections, starting
from the upper part of continental slope and continue in direction to the abyssal,
where the reflections became parallel, if there are continuous invisible
boundaries. Visual identification of probable BSRs, their coordinates and
thicknesses of layers with GHs on seismic records were determined with the
Landmark’s ProMAX software. Parameters registered are shot point numbers
(SPNs), two way travel times (TWTT, ms), all characteristic points of BSRs
and the upper boundary of GH spreading which are needed for a shape
description with straight lines, and UTM WGS84 coordinates of the above
points. Second (deeper) BSRs were also determined. Velocities from [6] were
used to determine 3 average velocities and to calculate depths in meters from
TWTT in ms. These velocities are 1500 m/s for water, 1800 m/s — for gas
hydrate saturated layers and 1625 m/s — for sediments between the seafloor
and layers with gas hydrates.
Results. According to the author’s model, the average thickness of the
GHSZ is 300 m and it appears at water depths 500–900 m in the Bulgarian
Fig. 1. Model of the Black Sea GHSZ base depth.
Light grey – registered BSRs; dark grey – faults; straight lines – seismic lines; stars –
potential and studied mud volcanoes; points – gas seepages; rectangular – study area of the
Bulgarian part of the Black Sea
•
VASILEV А.
24 ISSN 1999�7566. Геология и полезные ископаемые Мирового океана, 2010, №2
sector of the Black Sea (Fig. 1). In the Black Sea BSRs were discovered in 17
areas and 4 fields are outlined (Fig. 1). Eleven potential areas with GHs were
found in the northern deep water part of the Bulgarian economical zone (EZ)
(Fig. 2).
They are results of 21 groups/volumes with probable GHs determination
on seismic records. Three of them are not entirely bottom sub�parallel; 9 – have
one point which is out of the rest sub�parallel; 9 – are sub�parallel (maximum
difference between every depth and the average depth of the group is <10% of
the average). Only one area is located outside the GHSZ determined from the
model. Additional study is needed to prove if the reason is a wrong
interpretation, a relict GH deposit or there are GHs with “non�traditional”
gaseous content (a BSR area out of the GHSZ in the Turkish EZ is assumed to
present a deposit of H2S�hydrate (Fig. 1).
The three closest to the coast extend to the South�Moesian Fault which is
the Northern and Western boundary of the Kamchian Trough (paleo�Kamchia
river valley). The fault is main obstacle for hydrocarbons (HC) migration.
Gaseous flares, registered in expeditions of the IO�BAS (circles on Fig. 2) are
situated on the boundaries of these three areas. If the gas sources are related to
GHs these 3 areas can become a key target for the global warming study.
The largest area has a complex shape and a “peninsula of instability”,
reached the central part. Multiple BSRs are registered in 2 sub�areas. These
facts suggest a high oil and gas potential of the area and complex paths and
processes of HC distribution (Fig. 3). The most of relief of the probable BSR is
close to the relief of the model GHSZ base, but is shifted to the shallow waters
Fig. 2. Potential areas of GHs and their thicknesses on the map of model GHSZ.
Light grey contours –BSRs are registered during the EC 6FP project ASSEMBLAGE.
Isobaths – 100, 1000, 2000 m; light grey � faults; dark grey – GHSZ boundary; straight lines –
seismic lines; 0�500 m – depths of GHSZ & BSRs; stars – potential mud volcanoes; triangles–
heat flow stations; circles – gas seepages
FIRST BULGARIAN GAS HYDRATES: ASSESSMENT FROM PROBABLE BSRS
ISSN 1999�7566. Геология и полезные ископаемые Мирового океана, 2010, №2 25
and more wide. This is result from lack of geothermal station data (Fig. 2 –
filled triangles).
Four areas are longer than 10 km and one reaches 60 km. The total area
for which can be assumed existence of GHs is 2,600 км2. The determined
minimum, average and maximum thickness of the sediments with GHs are 8,
240 and 580 m respectively, and their total volume – 620 км3.
The volume porosity can be assumed as 55% from deep sea drilling and
the filling of the pore space with GH – 15±2% [6, 10]. Based on these
assumptions, the potential reserves of GHs are ~50 км3 and methane –
7,500 км3 in the GHSZ.
In the Dnieper paleo�delta area under the BSR one assumes the existence
of a zone with thickness of 100±5 m with free gas content of 1±0.1% [13]. In
this case the total methane reserves increase to ~7,800 км3 with an accuracy of
±25% (4±1 Gt or 4±1·10–3 Tt Carbon). The reliability of similar assessments
could be increased by special processing of digital records and additional
investigations, mainly geophysical.
Conclusions. This amount exceeds by six times the assessment of Lüdmann
for the paleo�Dnieper area and is 18% of the Black Sea reserves [12] or 0.04%
of the world total – 10 Tt [5].
The only for the present Bulgarian small marine gas field “Galata” has
reserves of 1.8 км3. The preliminary result shows that the maximum potential
reserves are equivalent to 4,300 such fields. In comparison with the world
largest gas field “Qatari North Field” the potential methane reserves are 30%
(45% from the area).
Let consider some additional information for comparison. Bulgarian annual
consumption of Russian gas is 3 км3 and transit gas transport is 16 км3. The
domestic market leader is “Bulgargaz” Ltd with a capacity of 7.8 км3 (2002).
The energy of 1 l benzene burning is equal to thus form 1.2 м3 SPT methane.
Fig. 3. Potential areas with GHs and BSRs depths on the model of the GHSZ base.
A. Only GHSZ base; B. Only pBSR
VASILEV А.
26 ISSN 1999�7566. Геология и полезные ископаемые Мирового океана, 2010, №2
Acknowledgements. This work could not be done without the kind help
of the state expert Valery Trendafilov from the Ministry of the Environment
and Waters, Bulgaria.
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Эта статья освещает первую для Болгарии попытку изучения газогидратов (ГГ)
с использованием BSR. Открыты 11 вероятных площадей с ГГ, оценен объем ГГ и со�
держащегося в них метана. Доказана возможность значительного распространения
ГГ в болгарской части Черного моря. Результаты ценны для будущих исследований в
означенных районах на перспективных глубинах. Работа привлекает внимание к
вопросу исследования влияния изменения климата на ГГ Черного моря и роли глубин�
ных разломов в формировании нефтегазоносности шельфа.
Стаття висвітлює першу для Болгарії спробу вивчення газогідратів (ГГ) з вико�
ристанням BSR . Знайдено 11 вірогідних площ із ГГ, оцінено об’єм ГГ і вміщеного в них
метану. Доведено можливість значного поширення ГГ у болгарській частині Чорного
моря. Результати цінні для майбутніх досліджень означених площ і перспективних
глибин. Робота привертає увагу до питання впливу зміни клімату на ГГ Чорного моря
та ролі глибинних розломів у формуванні нафтогазоносності шельфу.
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