Geologiya I Geofizika, 2002, V 43, N 7, July.

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 bubble 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

he 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 actors, 
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