GEOLOGY & GEOPHYSICS, 2003, V 44, N 7.
Special issue
PROCEEDINGS OF THE VI INTERNAIONAL CONFERENCE ON
"GAS IN MARINE SEDIMENTS"
PREFACE
581
GEOCHEMISTRY AND BIOGEOCHEMISTRY OF GASES IN WATERS
AND BOTTOM SEDIMENTS OF SEAS AND LAKES
UNDERPERMAFROST ACCUMULATIONS OF GAS IN THE UPPER PART OF THE
SEDIMENTARY COVER OF THE PECHORA SEA
V. N. Bondarev, S. I. Rokos, D. A. Kostin, A. G. Dlugach, and N. A. Polyakova
583
The State Unitary Enterprise for Arctic Sea Engineering-Geological Expeditions
(SEA ASIGE), Murmansk, carried out surveys in the northeastern Pechora Sea.
As a result, peculiar structures were revealed at the top of the sedimentary
cover and anomalous features in the bottom topography. The anomalous bottom
features are Pingo-like (Bulgunnyakh-like) rises with the base 20-60 to
100-130 m wide and with a relative altitude of 10-25 m. These rises are
drastically highlighted on the smooth gentle surface of the bottom.
They are made up of frozen ice-saturated deposits. On the domes of diapir-like
uplifts, the roof of frozen icy deposits occurs at a depth of less than 0.5 m
beneath the surface of the bottom, and their thickness reaches 100 m and more.
At the sites between these uplifts the roof of the frozen grounds lies at a
depth of about 15-20 m from the bottom surface with the thickness of the
frozen unit of about 30 m. One of the wells drilled between diapir-like
uplifts penetrated an overpressure gas accumulation at a depth
of 50 m below the bottom surface.
Shelf, permafrost, Quaternary deposits, biogenic gas,
seismoacoustic profiling, side-view hydrolocation
MAGIC: A GIS DATABASE OF MARINE GAS SEEPS AND SEEP INDICATORS
A. Judd, V. Jukes, and M. Leddra
595
A geographically related database called MAGIC has been developed,
using GIS (Geographic Information System) technology, for MArine Gas
seeps and seep IndiCators. A complementary bibliographic database
(GASREF) stores details of related publications. The databases include
data relating to natural seabed gas seeps and features such as pockmarks,
cold seep communities, and methane-derived carbonates which are known
to be found in association with seeps. The databases are compiled from
published reports (so far restricted to those written in English),
and users are able to interrogate the system for specified features
from user-defined areas.
Seeps, methane, marine sediments, Geographic Information Systems (GIS),
shallow gas
METHANE MONITORING IN WATERS OF THE EASTERN SHELF AND SLOPE OF SAKHALIN .
A. I. Obzhirov, O. F. Vereshchagina, V. A. Sosnin, R. B. Shakirov,
A. N. Salyuk, Sh. Lammers, E. Suss, N. Bibow, H. Winkler, and V. V. Druzhinin
601
Concentrations of water-dissolved methane were measured on the eastern
shelf and slope of Sakhalin. Seasonal variability of water structure
is chiefly responsible for seasonal differences in methane concentrations
in the water body. In the shelf zone the maximum flow of methane
to the atmosphere occurs in the cold season; in summer, it is much weaker.
The cold season is also the time when the methane-saturated shelf waters
reach intermediate depths on the continental slope. In summer, the shelf
waters stop sliding down the slope; therefore, no methane anomaly
is observed at intermediate depths. Methane concentrations at latitudinal
profiles vary from year to year, which is possibly due to variations
in seismotectonic activity of the region.
Our observations are important for calculation of the flow of methane
from the Earth's interior to water and from water to atmosphere in the western
Sea of Okhotsk. The available data show that there are natural sources
of methane supply to the atmosphere which depend on season and seismotectonic
activity of fault zones, generators and conduits of methane flows.
The methane flows in the Sea of Okhotsk participate in the global process
of its supply and increase in the atmosphere, which is, likely,
responsible for changes in climate (warming) and destruction of the ozone layer.
Methane monitoring, anomalous concentrations, water structure,
acoustic anomalies, gas hydrates
MODELING TRACE GASES IN HYDROCARBON SEEP BUBBLES. APPLICATION
TO MARINE HYDROCARBON SEEPS IN THE SANTA BARBARA CHANNEL
I. Leifer and J. Clark
609
Evaluating the importance of natural marine hydrocarbon seeps to global
methane budgets requires correctly predicting the gas fraction lost by
the seep bubbles during transit through the water column. In the Santa
Barbara Channel, California, three widely differing seeps
(depth, flux, oiliness) were visited and observations were made of seep
gas partial pressures, Pi, near the surface for alkanes to n = 5 (pentane)
as well as major atmospheric gases, and upwelling flows. It was found
that alkane Pi decreased exponentially with alkane diffusivity.
Seabed seep gas was available for one seep, and exhibited the same trend.
For alkanes heavier than methane, the ratio of the surface to sea floor
mole fraction showed a linear enhancement with increasing alkane number.
Methane behaved differently because the water column became saturated.
A numerical model was developed to study the sensitivity
to environmental parameters of the bubble transport of seep gas
to the surface. It was found that seep gas transport is highly sensitive
to both upwelling flows, dissolved gas concentrations, bubble surface
cleanliness, and bubble size. The model predicted that upwelling flows
increase bubble survivability and transport to the surface.
It also predicted that dissolved methane concentrations responsible
for pressure higher than 0.01 atm increase bubble survivability.
When applied to simulating alkanes, the studies showed that only
a narrow range in bub ble size could explain the observed alkane
enhancements. Thus model predictions were in agreement with
the observation that a wide size range of bubbles was
not observed at the sea surface.
Marine hydrocarbon seeps, gas bubble transit, mathematical modeling,
Santa Barbara Channel, California
APPLIED ASPECTS OF STUDY OF VOLATILE HYDROCARBONS IN SEA BASINS
Ch. S. Muradov
618
Under consideration are empirical aspects of the mode of hydrocarbon
gases in the Caspian Sea. This paper reports concentrations of gas
hydrocarbons in the sea water and bottom sediments of the Caspian
Sea and describes patterns of their distribution in the water and
sedimentary bodies of the region under study. The revealed regularities
served as a base for development of methodology, equipment, and approaches
to interpretation of data on gas geochemistry in searching for oil and
gas in water areas. In addition to solving the problems of search for
petroleum, the experimental study provided a possibility to use the results
obtained during gas surveys to solve engineering, ecological,
and other problems of national economy. The use of gas survey
in industry has been outlined in detail.
Gas hydrocarbons, sea, bottom sediments, water body, gas survey, ecology
GAS HYDRATES AND ESCAPES OF GASES IN LAKE BAIKAL
N.G. Granin and L.Z. Granina
625
In connection with the recent discovery of gas hydrates in Lake Baikal,
numerous published materials, which could contain any information on
the gas seepage from the bottom sediments, have been investigated.
We revealed that in the 1930s, both direct and indirect data showing
significant escapes of gases (presumably methane) in Lake Baikal
were obtained. Analysis of these materials indicates that the
dates of the ice steamthroughs opening are later and the intensity
of gas escapes from the ice steamthroughs is lower at present
as compared to the 1950s. The events of abundant death of pelagic
fish golomyanka (Comephorus baicalensis Pall.) as well as specific
forms of the ice cover caused by the methane escape, which used to
happen in the lake, has not been recorded in Baikal since the 1950s.
Thus, it seems that the intensity of gas escapes has significantly
decreased for the last 50-60 years. This may be due to lowering of
the number of catastrophic (M = 9-10) earthquakes in the Baikal region.
Gas escapes, gas hydrates, ice cover, ice steamthroughs,
published materials, Lake Baikal
NATURAL GASES OF BAIKAL
V. P. Isaev, N. G. Konovalova, and P. V. Mikheev
634
Natural gases emanating from the bottom of Baikal occur nearly
ubiquitously along the shore, but their maximum concentration
is observed at the front of the Selenga delta. In spring, the
gas outputs are visible in the form of openings in the Baikal ice.
Study was given to 54 openings. The gases are represented mainly
by methane (75 vol.% on average), but highly nitrogenous types
also occur (80 vol.% on average).
In addition to the explicit discharge of gases in the form of
openings, the implicit discharge of gases exists throughout the
Ust'-Selenga depression (USD). The chemical types of gases show
areal zoning: from nitrogen on the piedmont periphery of the
depression to methane in the near-shore band of the modern delta.
Joint analysis of geological, geophysical, and geochemical
information proves that the USD sediment is a powerful source
of generation of hydrocarbon gases and the similarity of its
geologic structure with the South Caspian depression suggests
the presence of "mud" volcanoes in Baikal.
A total of Cenozoic depressions of Baikal joint with its
sedimentary bed is a potentially gas-bearing basin. Hydrocarbons
are generated chiefly at the Baikal bottom, whereas the Selenga
delta and other depressions are zones of their transit and
accumulation. A regional cap for the natural reservoirs beneath
the Baikal bottom may be a gas hydrate layer. Oil fields are
hardly possible there, because all the studied gases are extremely
dry and the bitumen contents in the USD sediments and grounds
are very low. The reported facts and arguments permit
the Baikal geology to be considered anew.
Baikal, Selenga delta, Ust'-Selenga depression, gas shows,
openings in ice, mud volcanoes, gas hydrate layer, gas-bearing basin
BACTERIAL COMMUNITIES OF THE BOTTOM SEDIMENTS NEAR A HYDROTHERMAL
SOURCE IN FROLIKHA BAY, NORTHERN BAIKAL
B. B. Namsaraev, T. I. Zemskaya, O. P. Dagurova, L. Z. Granina,
L. P. Golobokova, and T. Ya. Sitnikova
640
Geological, microbiological, and isotopic investigations showed that
the bacterial communities form in surface sediments near a hydrothermal
source in Frolikha Bay, northern Baikal. The base of these communities
is colorless sulfur bacterium Thioploca. The bottom sediments in the
region are characterized by intensive processes of sulfate reduction
and methane genesis. Organic matter is used mostly for synthesis of
methane. Carbon isotope composition in sediments and fauna (to -68.3<)
suggests that the metabolism of the community of bottom sediments of
Frolikha Bay is based on biogenic methane utilized by methanotrophic
bacteria. The intensity of methane oxidation reaches high values:
1180.4 ..l CH4/kg<$Ecdot>day.
Outputs of underground waters, bacterial community, methane genesis,
methane oxidation, sulfate reduction, Lake Baikal
GAS HYDRATE
GLOBAL ASSESSMENT OF GAS AMOUNT IN SUBMARINE ACCUMULATIONS
OF GAS HYDRATES
V. A. Solov'ev
644
Based on the concepts of occurrence of submarine gas hydrates as
accumulations and on the general regularities of changes in their densities,
global assessment of gas amount in gas hydrates of the World ocean is given.
It is shown that the shape and the size of gas hydrate accumulations are
controlled either by a concentrated flow of gas-containing fluids through
the zone of gas hydrate stability and by parameters of their scattering halo
or by a dissipated flow of gas-saturated water depending on fluid guides
and lithologic peculiarities of the deposits. Geologo-geochemical and
geophysical data on 10 best studied accumulations of gas hydrates
were analyzed. The average specific (per unit area) content of gas
in studied gas hydrate accumulation has been obtained, ca. 6.5<$Ecdot>108 m3/km2.
The specific gas content in gas hydrates within all potential gas-hydrate-bearing
water areas is ca. 5<$Ecdot>106 m3/km2. According to data of performed mapping,
the total area of these water areas is about 35.7 mln km2, i.e., ca. 10%
of the area of the World ocean. The total amount of gas, mainly methane,
in the world's submarine gas hydrate accumulations is estimated
at ca. 2<$Ecdot>1014 m3.
Gas hydrates, methane, quantitative assessment, gas hydrate accumulations,
models for accumulation formation, potential gas-hydrate-bearing
water areas, World ocean
GEOLOGICAL CONTROL OVER GAS HYDRATE ACCUMULATION ON THE BLAKE OUTER RIDGE,
NORTHWESTERN ATLANTIC (from DSDP and ODP data)
T. V. Matveeva and V. A. Solov'ev
658
Results of geological investigation of gas hydrate accumulation within
the underwater sedimentary Blake Outer Ridge are presented. The study was
based on both published and new data that we obtained by processing 164 and
172 ODP leg observations. The geological control over the distribution
of gas hydrates is not quite clear despite the detailed seismic surveys
and drilling within the study area. The geologic, tectonic, and
hydrogeologic conditions in the Blake Outer Ridge area have been analyzed.
A radically new technical approach was used: The gas hydrate accumulation
was examined as a separate object with its specific characteristics.
It has been proved that the investigated gas hydrates formed under
the conditions of dissipated percolation of gas-containing fluids,
which controlled the shape and the size of the accumulation.
Based on geochemical, geophysical, and sedimentological data,
the regularities of gas hydrate distribution within the Blake Outer
Ridge have been established. The accumulation is controlled by
tectonic factors, is of filtration origin, and occurs mainly
in coarse-grained sediments.
Blake Outer Ridge, contourites, gas hydrates,
fluid migration, filtration
SPATIAL AND QUANTITATIVE EVALUATION OF THE BLACK SEA GAS HYDRATES
A. Vassilev and L. Dimitrov
668
The magnitude and spatial distribution of potential Black Sea methane
hydrate reservoirs has been estimated on the basis of
<$E6 prime^ times^ 6 prime > longitudeattitude data grid. The general
input includes bathymetry; bottom temperatures; heat flow (487 quoted
in situ measurements are considered); temperature gradients; thermal
conductivity of the sediments; pressure-temperature hydrate phase relations;
organic carbon content as a function of depth; sediment porosity-depth curves;
percentage of hydrate occupying the hydrate stability zone;
and volumetric gas expansion factor.
The estimations are based on the two main theories of gas hydrate
formation - in situ bacterial production and pore fluid expulsion models.
The spatial evaluation of the most probable gas hydrate distribution
is also discussed.
The calculations show that average water depth from which methane hydrate
starts to forms in the Black Sea runs from 620 to 700 m, embracing
a prone area of 288,100 km2, i.e., 91% of the deep Black Sea basin.
The average thickness of the MHSZ is 303 m with a bulk of sediment
running from 85,310 to 100,280 km3. The evaluations show the hydrate
content of 77-90 to 350<$Ecdot>109 m3, i.e., about 10 to 50<$Ecdot>1012 m3
of gas methane are trapped within the Black Sea sediments in the form of hydrate.
Gas hydrates, methane, thermal field, temperature gradients,
head flow, temperature, prone area, stability zone,
hydrate quantification, Black Sea
MEASURING HYDRATE PHASE BOUNDARY IN POROUS MEDIA
B. Tohidi, K. K. Ostergaard, R. W. Burgass, and M. Llamedo
681
There are massive quantities of gas hydrates in permafrost regions
and deep-sea sediments. The current estimates show that the amount
of energy in these gas hydrates is twice total fossil fuel reserves,
indicating a huge source of energy, which can be exploited in the right
economical conditions. Furthermore, these gas hydrates are a safety
hazard to drilling operation, as they could become unstable under
typical wellbore conditions and produce large quantities of gas.
The decomposition of natural gas hydrates in porous media could
also be responsible for subsea landslides and global weather changes.
Recent studies show that they might provide an opportunity for CO2 sequestering.
Hydrate phase boundary in porous media is known to be a function
of many factors, such as pore size, fluid saturation, in situ stresses,
and sediment mineralogy. Deviations, as great as 100 m, have been observed
between the measured and predicted thickness of hydrate stability
zones in marine sediments. Laboratory efforts in measuring gas hydrate
stability zone in porous media have concentrated on the effect of pore
size and fluid saturation. However, there are considerable deviations
and inconsistencies in the reported data.
This paper presents an experimental setup, test procedures, and some
of the results obtained on porous glass beads with 306
<$Eroman { A up 30 back 52 "-" } > and 158 <$Eroman { A up 30 back 52 "-" } >
pore sizes with using methane and CO2. The test procedure is based
on stepwise heating as compared to continuous heating used by many
laboratories. The results proved that stepwise heating technique
could provide reliable and consistent data on measuring hydrate
phase boundary in porous media, without compromising on the time
and cost of experiments. The data showed that there could be
a significant difference between the hydrate free zone of gas hydrates
in porous media and that of bulk conditions. These results are important
in estimating the hydrate stability zones in porous media,
as indicated by BSR in seismic surveys.
Gas hydrates, marine sediments, porous media, phase boundary,
experimental technique, methane, CO2
PHASE TRANSITIONS OF WATER IN GAS-SATURATED GROUNDS
E. M. Chuvilin, E. V. Perlova, N. A. Makhonina, and V. S. Yakushev
685
We have experimentally studied the peculiarities of water-gas hydrate
and water-ice phase transitions under gas pressure in dispersed
methane-saturated grounds on cyclic cooling-heating. Data on the conditions
of hydrate and ice formation in the ground pores have been obtained.
It is shown that on cooling of dispersed rocks, only part of the pore
water passes into hydrates; the rest (intimately bound with the particle surface)
transforms into ice on further cooling. Hydrate formation in the studied grounds,
compared with the system pure water-gas, occurs at higher pressures and
lower temperatures. It is demonstrated that the ground dispersion
and cooling-heating cycles affect the PT-conditions of formation and
decomposition of gas hydrates. Petrography of frozen artificially
hydrate-saturated rocks is studied.
Ice, gas hydrate, phase transitions, ground system, experimental modeling
GEOPHYSICAL METHODS OF STUDY OF GAS-SATURATED SEDIMENTS
GEOLOGICAL AND GEOPHYSICAL STUDIES OF EXHALATION IN NORTHWESTERN
BLACK SEA
R. I. Kutas, O. M. Rusakov, and V. P. Kobolev
694
Over 200 sites of exhalation (95-98% methane) have been discovered
through the past 15 years in the northwestern Black Sea. Fields of
exhalation are most often attributed to large fault zones.
Many sites are associated with carbonates.
Gas flame, methane, sediments, Black Sea
SHALLOW GAS: HAZARD TO PIPELINE ROUTING AND DETECTION TECHNIQUES
M. V. Kruglyakova, V. V. Kruglyakov, E. A. Lavrenova, and S. L. Maraev
702
Most typical examples of gas saturation images in acoustic fields
are presented based on data obtained using a MAK-1M acoustic complex
(designed at 'Yuzhmorgeologiya' Science Center) during research trips
in the Black Sea and northwestern Pacific.
Marine constructions, shallow gas cases,
gas-saturated sediments, acoustic images