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Natural oil and gas seeps on the Black Sea floor
Abstract
Migration of hydrocarbons to the seafloor in the Black Sea occurs via direct seepages, mud volcanoes, and development of fluidized sediment flows (e.g., diapers). Gas migration occurs on the shelf, continental slope, and abyssal plain. Gas hydrates are spatially related to gas accumulations and are present in shallow subsurface sediment layers. Their distribution is controlled by the activity of mud volcanoes. In regions of methane seepages, specific biogeochemical processes related to the activity of methane-oxidizing bacteria are evident. This activity results in the formation of diagenetic minerals (carbonates, sulfides, sulfates, phosphates and other minerals).
... Mud volcanoes are generally found along active plate boundaries and zones of compressional deformation, with more than 50 per cent of known mud volcanoes occurring along the Alpine-Himalayan active belt (Milkov 2000;Dimitrov 2002;Krastel et al. 2003;Yassir 2003). Some of the best studied mud volcanoes are located in the Mediterranean and Black Sea, and detailed analyses of their size, shape and fluid sources are given by Ivanov et al. (1996), Dimitrov (2002 and Kruglyakova et al. (2004). ...
... Mud volcanoes are a surface expression of overpressured sediments and Black Sea mud volcanoes have been extensively studied. The mud volcanoes can be found all along the continental shelf of the Black Sea (Kruglyakova et al. 2004) with a large concentration located in two specific areas: south of the Crimean Peninsula and within the Sorokin Trough (Ivanov et al. 1996;Dimitrov 2002;Krastel et al. 2003, Fig. 1). The volcanoes are distributed in water depths of 800-2200 m, are cone shaped and rise up to 120 m above the seafloor (Ivanov et al. 1996;Krastel et al. 2003). ...
... Positions of each OBS are shown as a white dot. Known locations of mud volcanoes are taken from Krastel et al. (2003), Ivanov et al. (1996) and Kruglyakova et al. (2004), and are shown as red dots. Other major features are also labelled and discussed further in the text. ...
... The presence of oil and gas in the Black Sea was verified as early as 1972. Currently, the Black Sea is considered to be one of the most important regions of hydrocarbon extraction, primarily of natural gas (Kruglyakova et al., 2004, 2009; Judd and Hovland, 2007). Since the midd1980s, an active search for natuu ral hydrocarbon sources and fields has been carrying out in different parts of the sea. ...
... However, crude oil seeps are not well studied. For example, based on the publications by Kruglyakova et al. (2004) (2011) and Judd and Hovland (2007), one of these seeps is located off the coast of Turkey (offshore the town of Rize), and some others are found in the Georgian secc tor of the Black Sea. The sedimentary cover in the eastern part of the continental slope and the Black Sea basin is composed of sedimentary rocks (Kruglyakova et al., 2009). ...
... The natural oil sources in the Georgian sector of the SE Black Sea, offshore Georgian town of Poti, have been known for a long time (Kruglyakova et al., 2004; Judd and Hovland, 2007). The latter cited work ...
One of the tasks being completed while oil pollution monitoring in the Black Sea, was a study of natural seepage. Two known oil seeps are located in the southeastern section, the Georgian sector, from which crude oil enters the marine environment. The archives of European Space Agency and ScanEx Research and Development Center have a considerable quantity of synthetic aperture radar (SAR) images acquired in 1993–2011 by the ERS-1/2, Envisat, and Radarsat-1 satellites, on which seep oil slicks are clearly visible in this region. Processing of the collected SAR images with detected slicks in combination with the geoinformation approach has revealed a link of these slicks with the bottom sources on the local sedimentary structure in the Southeast Black Sea; their analysis provides both new insight into this phenomenon and new information to help understand nature of these oil seeps. On the basis of an analysis of collected SAR images and detailed bathymetric data, information on the source positions on the bottom and estimates of oil volumes entering the sea surface are obtained.
... Mud volcanoes are generally found along active plate boundaries and zones of compressional deformation, with more than 50 per cent of known mud volcanoes occurring along the Alpine-Himalayan active belt (Milkov 2000;Dimitrov 2002;Krastel et al. 2003;Yassir 2003). Some of the best studied mud volcanoes are located in the Mediterranean and Black Sea, and detailed analyses of their size, shape and fluid sources are given by Ivanov et al. (1996), Dimitrov (2002 and Kruglyakova et al. (2004). ...
... Mud volcanoes are a surface expression of overpressured sediments and Black Sea mud volcanoes have been extensively studied. The mud volcanoes can be found all along the continental shelf of the Black Sea (Kruglyakova et al. 2004) with a large concentration located in two specific areas: south of the Crimean Peninsula and within the Sorokin Trough (Ivanov et al. 1996;Dimitrov 2002;Krastel et al. 2003, Fig. 1). The volcanoes are distributed in water depths of 800-2200 m, are cone shaped and rise up to 120 m above the seafloor (Ivanov et al. 1996;Krastel et al. 2003). ...
... Positions of each OBS are shown as a white dot. Known locations of mud volcanoes are taken from Krastel et al. (2003), Ivanov et al. (1996) and Kruglyakova et al. (2004), and are shown as red dots. Other major features are also labelled and discussed further in the text. ...
Mud volcanism associated with the degassing of deeply buried sediments has been identified in the Black Sea and Caspian Sea. Sampling of mud volcano breccia and seismic imaging of the "roots" suggest the origin lies in the Maykop formation, an organic-rich shale deposited in the Oligocene/Miocene that constitutes the major hydrocarbon source rock in the area. High sedimentation rates, leading to rapid burial and undercompaction, combined with hydrocarbon generation are possible mechanisms for generating overpressure in this layer. To our knowledge the magnitude of this overpressure in the Black Sea has not been quantified. The excess pore- pressure can be estimated from seismic velocities, however the Maykop formation is too deep (4 - 7 km below the seabed) for accurate velocities to be obtained from conventional multichannel seismic data. In spring 2005, four new wide-angle seismic reflection/refraction profiles were collected across the Eastern Black Sea Basin that provide better constraints on the sediment and crustal velocity structure. The data are of high quality allowing multiple sedimentary phases to be identified and linked with coincident reflection data. We have used the seismic tomography code JIVE, which performs simultaneous inversion of reflections and refractions from multiple layers. The model shows a thick sedimentary package, ~9 km in the centre of the basin. A low-velocity zone that may be associated with overpressure occurs near the base of the sediments. It is ~4 km thick in the centre of the basin, with anomalous velocities of ~2.6-3 kms-1 within the zone and ~3.6 kms-1 above and below. The low velocity zone is fairly continuous across the eastern basin and can also be identified on a profile that crosses the Mid-Black Sea High into the western basin. Overpressure can be expressed in terms of effective stress (lambda); the ratio of excess pore pressure to lithostatic pressure. Using our velocity model, we estimate values of lambda of approximately 0.77±0.02, corresponding to pore pressures of ~45 MPa within the low velocity zone. If overpressure exists throughout the Maykop formation, as suggested by our data, it may be one of the largest overpressured regions in the world.
... Mud volcanoes are generally found along active plate boundaries and zones of compressional deformation, with more than 50 per cent of known mud volcanoes occurring along the Alpine-Himalayan active belt (Milkov 2000;Dimitrov 2002;Krastel et al. 2003;Yassir 2003). Some of the best studied mud volcanoes are located in the Mediterranean and Black Sea, and detailed analyses of their size, shape and fluid sources are given by Ivanov et al. (1996), Dimitrov (2002 and Kruglyakova et al. (2004). ...
... Mud volcanoes are a surface expression of overpressured sediments and Black Sea mud volcanoes have been extensively studied. The mud volcanoes can be found all along the continental shelf of the Black Sea (Kruglyakova et al. 2004) with a large concentration located in two specific areas: south of the Crimean Peninsula and within the Sorokin Trough (Ivanov et al. 1996;Dimitrov 2002;Krastel et al. 2003, Fig. 1). The volcanoes are distributed in water depths of 800-2200 m, are cone shaped and rise up to 120 m above the seafloor (Ivanov et al. 1996;Krastel et al. 2003). ...
... Positions of each OBS are shown as a white dot. Known locations of mud volcanoes are taken from Krastel et al. (2003), Ivanov et al. (1996) and Kruglyakova et al. (2004), and are shown as red dots. Other major features are also labelled and discussed further in the text. ...
Although the Black Sea is one large depositional structure today, previous studies have shown that the basin can be divided into two sub-basins, which have different tectonic histories. There is a general consensus on the formation history of the Western Black Sea Basin but there is little agreement on the history of the Eastern Black Sea. In March 2005 we collected a series of onshore-offshore, wide-angle seismic refraction/reflection profiles throughout the basin to sample the crustal structure. Four lines were surveyed; Line 1 was a 470 km profile, shot along strike through the centre of the basin, Lines 3 and 4 were dip lines shot across the Mid-Black Sea High and one dip line (Line 2) was shot further to the east. Data quality is very good and deep arrivals can be typically detected to 100 km offset. These data will be combined with co-incident industry reflection profiles to constrain the extensional evolution of the Eastern Black Sea Basin. We present data from Line 1, which has been modelled to investigate the velocity structure of the basin. Line 1 has 34 ocean bottom seismometers, spaced at ~14 km, deployed along the profile with an additional seven seismometers deployed on land. The seismic source was an air-gun array with a total source volume of 3140 cu.in and the line was shot at a spacing of 60 s, equivalent to a spatial interval of about 120 m. A combination of ray-tracing and first-arrival seismic tomography has been used to create a 2D velocity model through the crust. The model shows that the basin has a thick sedimentary package (up to ~10 km thick) with velocities ranging from 1.6 - 4.2 km/s. These overlay a crystalline crust with velocities of 4.8 - 7.2 km/s, which thins to ~8 km thick in the deepest part of the basin. The model indicates the presence of a low velocity zone near the base of the sediment package. This anomalous layer stretches across most of the profile, with velocities as low as 3.1 +/- 0.12 km/s compared with sediment velocities of 3.9 km/s above. The most likely explanation for these low velocities is over pressurisation of pore-fluids leading to under-compaction of the sediments.
... Зразок білого мономінерального газогідрату (5-7 см) виявлено в колонці донних відкладів на глибині 2,85 м від поверхні дна на грязьовому вулкані в ме жах континентального схилу Гіресунської западини спільною експедицією НВО «Південморгеологія» та Британською нафтовою компанією в 1992 р. [48]. ...
... Згодом знахідки газогідратів неодноразово фіксувалися окремими міжна родними експедиціями НАН України, МДУ, НВО «Південморгеологія» та Гам бурзького університету на НДС «Професор Водяницький», «Метеор» та «Геленд жик» у межах грязьових вулканів у западині Сорокіна [4,20,25,45,48]. ...
Methane hydrates are one of the most powerful reserves of unconventional sources of hydrocarbons. This is clearly evidenced by the forecast estimates of world volumes of methane in the form of gas hydrates, which many times exceed the total resources of traditional natural gas. In the foreseeable future, natural methane hydrates should significantly increase the current energy balance of natural hydrocarbon fuel resources.
Progress in their study can be ensured by the dialectical unity of theoretical and experimental research, focused mainly on thermodynamics, kinetics and their physical properties, as well as on the development and testing of technologies for methane production from gas hydrate deposits. Existing methods of developing gas hydrates involve their preliminary dissociation into gas and water. At the same time, the deposit depressurization method is considered the most promising. However, there is still no commercially attractive technology for the development of gas hydrates.
The article presents an overview of gas hydrate research in the world, provides an analysis of prospective methods of their development, summarizes the advantages and disadvantages of current research and industrial attempts to extract methane from aqua deposits of gas hydrates, and evaluates the prospects of various technologies.
Currently known examples of research and industrial development of gas hydrate deposits have demonstrated a number of problems. However, encouraging results were obtained. The analysis of processes in the oil and gas production industry shows that profitable industrial production of natural gas from gas hydrate deposits will be possible after an effective breakthrough technology appears on the market.
... Note that several earthquakes were recorded in this area, especially from deeply rooted faults (Fig. 2, Table 1). The north-western Black Sea is also rich in hydrocarbon fields (oil, gas) (Kruglyakova et al., 2004;Georgiev, 2012), gas hydrates (Popescu et al., 2007;Merey and Sinayuc, 2016), and surficial gas systems with abundant gas seeps, pockmarks, and shallow gas fronts (e.g. Polikarpov et al., 1989;Egorov et al., 1998Egorov et al., , 2011Artemov et al., 2007;Naudts et al., 2008;Nikolovska et al., 2008;Greinert et al., 2010;Diaconu et al., 2020;Römer et al., 2020).. ...
... We show that the extent of the BSR, faulting patterns, and arrangement of architectural elements such as canyons, channel-levees, slide scars, and MTDs control the distribution of seal layers and sedimentary discontinuities and consequently gas-flare distribution. However, we cannot exclude that seepage may be primarily associated with tectonically driven flows through regional faults (Kruglyakova et al., 2004). Moreover, the release of seismic energy during earthquakes could cause slope failures and subsequent gas escape along slide scarps. ...
The upper continental slope offshore Romania is a complex area hosting turbidite deposits, multiple types and ages of deep-seated faults, gas hydrates, gas-escape features, and numerous Mass Transport Deposits (MTDs). Multi-scale seismic data sets (2D-high-resolution and near-bottom very high-resolution) were used to study the interaction between such disparate geological features and determine their impact on slope stability.
At least five main paleo-valleys have been identified in the north of the Viteaz (Danube) canyon/valley. The most recent channelized systems linked to these valleys formed over a basal layer of MTDs. These MTDs are associated with an unconformity corresponding to the Base Neoeuxinian Sequence Boundary formed during the last major sea-level fall. This erosional surface shows scarp alignments that coincide with underlying faults. We argue that gravity-driven fault reactivation, with possible upward gas/fluid migration along these faults, is a determinant factor controlling sedimentary instabilities. Numerous MTDs are also observed during channel-levees building and reveal local sediment instabilities related to localized erosional process in the canyon. Finally, MTDs recorded within the upper draping unit, suggest that sediment instability also occurred during recent sea level highstand. Sediment pulse, seismicity, and gas hydrate dynamics can also play a determinant role in sediment instability throughout the sediment record.
... Здесь неоднократно фиксировались находки газогидратов [2,10,22,48,59,60,63]. Образец белого мономинерального газогидрата (5-7 см) обнаружен в колонке донных отложений на глубине 2,85 м от поверхности дна на грязевом вулкане Гиресунской впадины [65]. ...
... [2,10,22,48,59,60,63]. Образец белого мономинерального газогидрата (5-7 см) обнаружен в колонке донных отложений на глубине 2,85 м от поверхности дна на грязевом вулкане Гиресунской впадины [65]. При этом следует отметить, что изучению фактически был доступен только трехметровый слой осадков, в раз ных интервалах которого попадались газогидратные новообразования. ...
... The Black Sea is the largest surface water reservoir of dissolved methane with a total methane concentration of 6 x 10 12 mol (Reeburgh et al., 1991). The shelves and continental slopes of the Black Sea are well known for gas saturated sediments and gas seeps (Kruglyakova et al., 2004;Greinert et al., 2006;Naudts et al., 2006). Kessler et al. (2006) estimate that the gas emissions from cold vents to the hydrosphere and atmosphere in the whole Black Sea comprise about 3.6-5.65 ...
... A thick sedimentary coverage and compressional deformation at the continental slopes of the Black Sea force over-pressured fluids and upward fluid migration along faults (Yun et al., 1999). Kruglyakova et al. (2004) suggest that gas seeps in the Black Sea are mainly related to tectonic faults, but Naudts et al. (2006) observed seeps controlled by stratigraphically controlled fluid migration in the Dnepr paleo-delta area. ...
Numerous gas seeps on the continental slope offshore Batumi (Georgia) occur in water depths at 850-1200 m on the top or flanks of ridge structures within the gas hydrate stability zone (GHSZ). High resolution multichannel seismic investigations carried out during the TTR-15 cruise (UNESCO Training Through Research Program) show that fluid migration towards the seafloor can be linked to the protrusion of buried diapiric structures, which controlled the development of the complex canyon-ridge system offshore Batumi. Depressions between growing diapirs guided the pathways for turbidity currents, primarily forming the canyon systems off Batumi by erosional processes. Over-steepening and faulting of canyon flanks due to diapiric uplift resulted in slope failures. Additionally, faults developed during the diapiric uplift particularly at the flanks and above the diapirs, as well as dipping reflectors at the steep flanks of the diapirs provide potential pathways for upward gas/fluid migration, which controls the distribution of the gas seeps off Batumi. A prominent gas seep of the survey area, the Batumi Seep, located on Kobuleti Ridge in the central study area, is characterized by high amplitude reflection patches beneath the seafloor, which indicate the presence of shallow gas hydrate and carbonate, most likely formed due to focused fluid flow. On several ridges additional potential seep sites were identified by acoustic disturbances in the strata. Although two diapiric mound structures have been identified, most seep sites offshore Batumi do not show upward material transport in diapirs. All seep sites are related to shallow gas accumulations, indicated by Bright Spots at different depths. Although gas hydrates have been sampled at different places, a bottom-simulating reflector (BSR) is limited to the Kobuleti Ridge, but Bright Spots at the depth of the BGHSZ (base of gas hydrate stability zone) might be related to the stability field of gas hydrate, generated where local fluid migration delivers sufficient gas to form gas hydrate. The depth of the BSR is located below the calculated theoretical depth of the BGHSZ for a methane-seawater system, which might be explained by low pore water salinity of 15‰.
... Mud volcanoes, the surface response of an overpressured layer (Dimitrov, 2002;Yassir et al., 2003), are found all along the continental shelf of the Black Sea (Kruglyakova et al., 2004), with the greatest density to the south of the Crimean Peninsula within the Sorokin Trough (Ivanov et al., 1996;Dimitrov, 2002) (Fig. 1). This location is experiencing compression, which squeezes the sediment laterally and generates overpressures in the low permeability sediments because the fluids cannot escape rapidly enough. ...
... However, due to the compressional tectonics affecting the margins of the EBSB, we can neither assume that the minimum principal effective stress is horizontal or that K 0 is equal to 0.6. The presence of mud volcanoes near the east coast of the EBSB (Kruglyakova et al., 2004) indicates the presence of hydraulic fracturing and so pore pressures greater than the minimum principal effective stress. Although the kà value in the centre of the EBSB exceeds 0.6, no mud volcanoes have been observed so far. ...
Locating and quantifying overpressures are essential to understand basin evolution and hydrocarbon migration in deep basins and thickly sedimented continental margins. Overpressures influence sediment cohesion and hence fault slip in seismically active areas or failure on steep slopes, and may drive catastrophic fluid expulsion. They also represent a significant drilling hazard. Here, we present a method to calculate the pore pressure due to disequilibrium compaction. Our method provides an estimate of the compaction factor, surface porosity and sedimentation rate of each layer in a sediment column using a decompaction model and the constraints imposed by seismic data and geological observations. For a range of surface porosities, an ad hoc iterative equation determines the compaction factor that gives a calculated layer thickness that matches the observed thickness within a tolerance. The surface porosity and compaction factor are then used to obtain a density profile and a corresponding estimate of P‐wave velocity (V p ). The selected parameters are those that give a good match with both the observed and calculated layer thicknesses and V p profiles. We apply our method to the centre of the Eastern Black Sea Basin (EBSB), where overpressures have been linked to a low‐velocity zone (LVZ) at ca. 5500–8500 m depth. These overpressures were generated by the relatively high sedimentation rate of ca. 0.28 m ka−1 of the low permeability organic‐rich Maikop formation at 33.9–20.5 Ma and an even higher sedimentation rate of ca. 0.85 m ka−1 at 13–11 Ma. We estimate a maximum pore pressure of ca. 138 MPa at ca. 8285 m depth, associated with a ratio of overpressure to vertical effective stress in hydrostatic conditions (λ*) of ca. 0.7. These values are lower than those presented in a previous study for the same area.
... Especially the eastern Black Sea basin is known for its oil potential (Robinson et al., 1996), yet few is known about oil occurrence in shallow sediments and oil seepage which is common in other hydrocarbon provinces, e.g. the Gulf of Mexico (Brooks et al., 1984;MacDonald et al., 1993). Several mud volcanoes emit mixtures of thermogenic hydrocarbons and biogenic LMWH (Blinova et al., 2003;Feseker et al., 2009;Kruglyakova et al., 2004;Stadnitskaia et al., 2008) but no oil seepage has been observed so far. A single site offshore Turkey was previously reported where oil reaches the sea surface (Kruglyakova et al., 2004;Robinson et al., 1996) but no detailed information has been presented. ...
... Several mud volcanoes emit mixtures of thermogenic hydrocarbons and biogenic LMWH (Blinova et al., 2003;Feseker et al., 2009;Kruglyakova et al., 2004;Stadnitskaia et al., 2008) but no oil seepage has been observed so far. A single site offshore Turkey was previously reported where oil reaches the sea surface (Kruglyakova et al., 2004;Robinson et al., 1996) but no detailed information has been presented. ...
Analysis of Advanced Synthetic Aperture Radar satellite images in combination with water column and seafloor investigations documented natural oil seepage from Pechori Mound and Colkheti Seep in 1,000 – 1,200 m water depth in the eastern Black Sea offshore Georgia. Hydroacoustic imaging of the water column using multibeam echosounder evidenced numerous gas emissions from both structures. Gas bubbles rose as high as 45 m below sea surface. It is proposed that oil coatings around gas bubbles hamper their dissolution allowing them to reach the sea surface where widespread oil slicks are formed. Slow rise velocities (14 ± 1 cm s-1) of bubbles with radii of 2.6 ± 0.3 mm (n = 101) derived from video data obtained with the remotely operated vehicle MARUM QUEST4000, corroborate the assumption that bubbles are oil-coated. High resolution seafloor mapping by autonomous underwater vehicle MARUM SEAL5000 at Colkheti Seep revealed a crater-strewn morphology whose formation is explained by frequent rafting of shallow gas hydrate deposits. Satellite imaging of oil slicks on the sea surface above both sites indicates that oil seepage is rather persistent since 2003. An order-of-magnitude estimation of minimum oil seepage rates suggests discharge rates of ∼40 liters per hour from both sites. The data presented are the first comprehensive description of oil seepage in the Black Sea.
... Ebrom et al. 2003;Kao 2010), gives similar overpressure. (Ivanov et al. 1996, Krastel et al. 2003Kruglyakova et al. 2004). Red squares indicate the location of industry and DSDP boreholes. ...
... Mud volcanoes are the surface response of an overpressured layer and they may indicate compressional deformation, since compression squeezes the sediment laterally and may generate overpressure in low permeability sediments if the fluids cannot escape rapidly enough. In the EBSB they are found along the continental shelf (Kruglyakova et al. 2004), with the largest density located in the compressional zone to the south of the Crimean Peninsula within the Sorokin Trough (Ivanov et al. 1996;Dimitrov 2002; Fig. 1). ...
Pore pressure above the hydrostatic (overpressure) is common in deep
basins. It plays an important role in pore fluid migration, represent a
significant drilling hazard, and is one of the factors controlling slope
stability and deformation in seismically active areas.
Here, we present an inverse model to calculate overpressure due to
disequilibrium compaction and aquathermal pressuring. We minimize a
function that contains the misfits between estimates from our forward
model and observed values using a non-linear least squares approach. The
inverse model allows the introduction of observed seismic and geological
constraints such as P-wave velocity (Vp) and density data,
and depth of the layer boundaries, for a better pore-pressure
prediction. The model output also provides estimates of: (1) surface
porosity, (2) compaction factor, (3) intrinsic permeability at surface
conditions, (4) a parameter controlling the evolution of the intrinsic
permeability with porosity, (5) the ratio between horizontal and
vertical permeability and (6) uncompacted thickness (so sedimentation
rate assuming known time intervals), for each sedimentary layer. We
apply our inverse approach to the centre of the Eastern Black Sea Basin
(EBSB) where the Vp structure has been inferred from
wide-angle seismic data. First, we present results from a 1-D inverse
model and an uncertainty analysis based on the Monte Carlo error
propagation technique. To represent the observed rapid change from low
Vp to normal Vp below the Maikop formation, we
impose a zero overpressure bottom boundary, and subdivide the layer
below the Maikop formation into two sublayers: an upper layer where the
rapid change is located and a lower layer where the Vp is
normal. Secondly, we present the results from a 2-D inverse model for
the same layers using two alternative bottom boundary conditions, zero
overpressure and zero flow. We are able to simulate the observed
Vp, suggesting that the low velocity zone (LVZ) at
˜3500-6500 m depth below the seabed (mbsf) can be explained by
overpressure generated due to disequilibrium compaction (>90 per
cent) and to aquathermal pressuring (<10 per cent). Our results
suggest that the upper sublayer, below the Maikop formation, behaves as
a seal due to its low permeability ˜0.3-2 × 10-14
m s-1. This seal layer does not allow the fluids to escape
downwards, and hence overpressure develops in the Maikop formation and
not in the layers below. This overpressure was mainly generated by the
relatively high sedimentation rate of ˜0.29 m ka-1 of
the Maikop formation at 33.9-20.5 Ma and an even higher sedimentation
rate of ˜0.93 m ka-1 at 13-11 Ma. We estimate a maximum
ratio of overpressure to vertical effective stress in hydrostatic
conditions (λ*) of ˜0.62 at ˜5200 mbsf associated
with an overpressure of ˜42 MPa.
... According to Riboulot et al. (2018), gas hydrates are currently stable in water depths larger than 660 m though this depth may increase to 720 m in the future (5000 years) due to salinization of sediments. Within the Black Sea, the existence of methane in the form of free gas or as solid methane hydrate has been documented by direct observations of methane seeps, gas flares, and mud volcanism (Limonov et al., 1997;Dimitrov, 2002;Greinert et al., 2006;Naudts et al., 2006;Nikolovska et al., 2008;Egorov et al., 2011) by acoustic investigations using side-scan sonar (Klaucke et al., 2006) and by direct sampling in gravity cores and drillings (Kruglyakova et al., 2004;Heeschen et al., 2011;Riedel et al., 2020). The latter yield direct information about the deeper structure of the seafloor down to 30 m in gravity cores (e.g. ...
The Black Sea is known to have extensive direct and indirect indicators of methane hydrates. Since the resistivity of the seafloor increases significantly in the presence of gas hydrates or free gas, marine controlled-source electromagnetics (CSEM) is a suitable method for the investigation of hydrates. We have collected CSEM data in a channel-levee system of the Danube paleo-delta (Bulgarian sector) at water depths of about 1500 m. The working area is within the gas hydrates stability zone and seismics suggests the presence of gas hydrates. The CSEM data were acquired with stationary receivers and a novel mobile, dual polarization transmitter system, and interpreted in terms of rotational invariants by means of 1-D inversions at common midpoints (CMP) to generate pseudo 2D resistivity sections. The inversion results reveal two resistive layers at shallow depths of 60–120 mbsf and greater depths of 270–400 mbsf. A comparison with seismics shows a good correlation of the shallow layer with high amplitude reflections and a velocity anomaly. The deeper layer can be tied to the current bottom simulating reflector (BSR). The comparison to a second CSEM experiment, which was conducted by the BGR (Federal Institute for Geosciences and Natural Resources, Germany) shows a good agreement of the derived sections down to a depth of about 350 m. Based on salinity and porosity models derived from boreholes in the Black Sea, we apply Archie's law to estimate potential gas hydrate saturations of up to 23% for the shallow resistor and up to 7% for the deeper layer. Differences are evident at depths greater than 450 m, where we see a conductive layer not evident in the BGR section. This deeper conductor could be evidence for increasing salinities of pore fluids at greater depths, which were previously found in DSDP drilling cores.
... At numerous sites, oil and gas migrate 85 towards the sediment surface and escape into the water body. Seafloor seepage of light hydrocarbons and partially of oil is widely distributed on Black Sea continental shelves and slopes (e.g., Artemov et al., 2007;Bohrmann et al., 2003Bohrmann et al., , 2007Bohrmann et al., , 2011Dembicki, 2020;Dimitrov, 2002;Greinert et al., 2006;Klaucke et al., 2006;Körber et al., 2014;Kruglyakova et al., 2004;Michaelis et al., 2002;Naudts et al., 2006;Nikolovska et al., 2008;Reitz et al., 90 2011;Riboulot et al., 2018;Römer et al., 2012Römer et al., , 2020Sahling et al., 2009;Schmale et al., 2005;Zander et al., 2020, this issue). At seepage sites located within the gas hydrate stability zone (GHSZ), which at current water salinities is located in waters deeper than about 720 m below sealevel (bsl) (Naudts et al., 2006;Pape et al., 2010), concentrations of methane and other light hydrocarbons exceeding solubility lead to gas hydrate formation in the sediment 95 (Vassilev and Dimitrov, 2002). ...
Numerous hydrocarbon seep sites at the continental shelf, slope, and in the deep water basin are known to feed the Black Sea water reservoir of dissolved methane. In this study, we identified the likely sources of gas and oil that are emitted at four sites located on the continental slope offshore Georgia in the Eastern Black Sea at 830 to 1,140 m water depth – an area with gas seepage only (Batumi seep area) and three areas of joint gas and oil seepage (Iberia Mound, Colkheti Seep, and Pechori Mound). The geochemistry of bulk parameters, organic fractions and individual hydrocarbon biomarkers in near-surface sediments and of gas/oil expelled from the seafloor was analyzed and jointly interpreted to assign most likely hydrocarbon source rocks in the studied region. Presence of oleanane in shallow oil-impregnated sediments and oil slicks attests that the source rock at all sites is younger than Mid Cretaceous in age. We conclude that hydrocarbons ascending at all the four seepage areas originate from the Eocene Kuma Formation and/or the Oligocene–Lower Miocene Maikop Group, which are considered the principal hydrocarbon sources in the Eastern Black Sea region. Distributions of crude oil biomarkers in shallow sediments suggests moderate to heavy biodegradation. C1/C2+ ratios (10 to 4,163) along with stable C and H isotopic ratios (δ¹³C-CH4 ‒46.3 to ‒53.1.3‰ V-PDB; δ²H-CH4 ‒159 to ‒178‰ SMOW) indicate gas mixtures of oil-associated thermogenic and secondary microbial light hydrocarbons that are discharged from the four seep sites. Light hydrocarbons discharged at the Batumi Seep area are characterized by significant enrichments of methane, but almost similar δ¹³C-CH4 values if compared to the other study sites. Such methane enrichments likely result from a comparably higher degree of petroleum degradation and associated formation of secondary microbial methane.
... A sample of white monomineral gas hydrate (5-7 cm) was recovered by a 3-m core within the Gerisunckiy Trough (Fig. 2) at a water depth 2850 m [25]. It is important that gas hydrates were present in different core intervals indicating the presence of gas hydrate deposition. ...
This paper discusses the formation of a special mud-volcanic type of gas hydrate accumulation in the deep-water part of the Black Sea. The main conclusions are based on the results of geological and geophysical studies of mud volcanoes carried out in the course of numerous scientific cruises between 1970-2015. Comparison of the Black Sea submarine mud volcanoes with their on-land analogues indicates the possible use of compensatory depressions, called “recessed synclines”, accompanying mud volcanoes, which is revealed in the course of prospecting and exploration of mineral deposits. In the sea they are represented by ring deposits of methane gas hydrates.
... Детальный анализ геологических особенностей площадок активных метановых газовыделений, выполненный в работе (Naudts et al., 2006), показал, что струйные газовыделения в палеодельте р. Днепр контролируются не системой разломов, как утверждают, например, авторы (Kruglyakova et al., 2004), а стратиграфическими и осадочными факторами. ...
Methane gas bubble emissions (seeps) are widespread phenomenon in the World Ocean, inter alia in Black Sea basin. The relevance of the research of methane seeps is due to their important role as a source of methane – greenhouse and environment-forming gas – for water column and atmosphere. The article presents a comparative analysis of the data from our biogeochemical 10-year studies of shallow gas seeps of the Crimean Peninsula and data on deep-sea gas seeps of the Black Sea. During 10-year period, apart from carrying out hydroacoustic research, the following parameters were determined: bubble gas component composition, methane carbon isotopic composition, microbial community structure of bacterial mats, covering gas bubble emission sites, and gas fluxes from separate seeps. During long-term monitoring, 14 separate gas bubble emission sites were detected and described in Crimean coastal areas; they were located from Cape Tarkhankut in the west of the peninsula to the Dvuyakornaya Bay in the southeast. Crimean coastal seeps were mostly of biogenic origin, with a seasonal nature of gas bubble emission. Laspi Bay seeps were classified as emissions of deep gas of thermocatalytic genesis. A significant variation was recorded in values of isotopic composition of methane carbon δ13C-CH4 of bubble gas in coastal shallow areas (−94…−34 ‰), which indicates different conditions for bubble gas generation and maturation in seabed sediments. Similar to deep-sea seeps, coastal gas bubble emissions were accompanied by bacterial mats of diverse structure, with different dominating species. As shown, formation of stable bacterial biomass, usually consisting of sulfide- and sulfur-oxidizing bacteria, requires a fluid flux of reduced dissolved gases, while pointwise bubble gas discharge does not provide sufficient concentration gradients and can mechanically disrupt community structure. Various methods were used to estimate the size spectra of bubbles, as well as fluxes from separate seeps. Gas flux values varied from 1.8 L·day−1 (the Martynova Bay) to 40 L·day−1 (the Laspi Bay). The environment-forming effects, related to gas bubble emission in coastal areas, are discussed: effect of seeps on oxygen conditions in seabed sediments and in water column above gas emission sites, vertical water mixing due to gas lift effect, and fluid discharge at gas emission sites.
... Îáðàçåц áåëîãî ìîíîìèíåðàëьíîãî ãàçîãèäðàòà (5-7 ñì) îáíàðóжåí â êîëîíêå äîííûх îòëîжåíèé íà ãëóáèíå 2,85 ì îò пîâåðхíîñòè äíà íà ãðÿçåâîì âóëêàíå â пðåäåëàх êîíòèíåíòàëьíîãî ñêëîíà Гèðåñóíñêîé âпàäèíû ñîâìåñòíîé эêñпåäèцèåé ÍПÎ «Южìîðãåîëîãèÿ» è Бðèòàíñêîé íåфòÿíîé êîìпàíèåé â 1992 ã. [61]. ...
... Orange line -the Euxinic Edge illustrating the border of Histria Depression -HB (after Pătruț et al., 1984 andAnton et al., 2019). Green dots and red triangles -gas seeps and mud volcanoes as identified by Egorov et al., 2011, Popescu et al., 2007and Kruglyakova et al., 2004. PCF -Peceneaga-Camena Fault. ...
Gas escape features are a common presence on any young sedimentary basins where large amounts of organic-rich sediments are deposited within a short time. The fast burial process conducts to maturation and carbonization of the sedimentary organic matter by bacterial and, later, by temperature transformations. The Black Sea is one such basin, where numerous shallow gas accumulation and gas escape features were observed and analyzed, ranging from gas hydrates, gas chimneys, flares, and mud volcanos. The study of such geological phenomena is important for identifying present seabed geohazards, and nonetheless for hydrocarbon exploration. Our study integrates newly acquired 2D high-resolution seismic lines, further used to correlate the gas escape features and their relationship with deep-seated faults, such as Peceneaga-Camena, and petroleum system of the Romanian Black Sea Shelf area. Our results show that in the studied area the gas escape features are confined into the Pliocene-Quaternary sequence, hence not related to Peceneaga-Camena Fault or to a deeper thermogenic petroleum system, and most probably, the gas is sourced from the shallower biogenic system.
... In many studies, hydrocarbon seeps in the onshore and offshore areas of Turkey have been cited. Geochemical characteristics of these seeps in some of these studies have been examined (TaĢman, 1950;Egeran, 1952;Erentöz and Ternek, 1959;Kurtman and Akkus, 1971;Coates, 1994;Alsharhan and Nairn, 2003;Kvenvolden and Cooper, 2003;Büyükutku, 2003;Çifçi et al., 2003;Garcı´a-Garcı´a et al., 2004;Demirel, 2004;Kruglyakova et al., 2004;Connan et al. , 2006;Gürgey et al., 2007;Bozcu and Poisson, 2008;Lykousis et al., 2008;HoĢgörmez et al., 2008;Garcia-Pineda et al., 2009;Çiftçi et al., 2010Çiftçi et al., Kavak et al. , 2010Starostenko et al., 2010;Chevalier et al., 2011;Dondurur et al., 2011;Önen, 2012;Tryon et al., 2012;Kara-Gülbay et al., 2012;Sen, 2013;Crémière et al. et al., 2013;Suresh et al., 2013;Kara-Gülbay and Korkmaz, 2013;Çukur et al., 2013;CoĢkun et al., 2016;D'Alessandro et al., 2017). In some studies, the oil and gas seeps in onshore Turkey have also been inspected in detail (TaĢman, 1950;Egeran, 1952;Erentöz and Ternek, 1959;Akarsu, 1972;Kavak et al., 2010). ...
The relationship between the hydrocarbon reservoirs and the seeps has been proved by multiple methods such as geochemical analyses and seismic measurements. Many giant oil and gas fields were discovered with oil wells drilled in the area close to the seeps. When looking at the discovery story of petroliferous basins of the world, oil and gas seeps have been proved to be the first clues about most of the oil and gas production basins/fields. In the literature, there are numerous studies showing the close relationship between oil and gas production basins/fields and hydrocarbon seeps. The relationships between types of hydrocarbon seeps and geological, tectonics, and petroleum geology characteristics of oil and gas production basin/fields have been examined in detail in those studies. One of the most critical parameters for the efficient exploration of hydrocarbon accumulations is to investigate the hydrocarbons seeps in detail. Numerous active or passive hydrocarbon seeps have been determined throughout Turkey so far. It was believed that destructions of oil and gas traps/structures in Turkey, where it is located in an active tectonic belt, caused this situation and also the seeps are the indicators of these destructions of the oil and gas traps/structures formed by various geological periods. This interpretation has been refuted by numerous previous studies that have proved a close relation between seeps and hydrocarbon production fields. Thus, numerous oil and gas seeps throughout the country show that Turkey, which is one of the most untouched countries of the world in terms of exploration activities, has a significant oil and gas potential.
Keywords: oil and gas seep, oil seepage, hydrocarbon seep, petroleum exploration, oil and gas potential of Turkey
... Many highly productive oil fields owe their existence to the discovery of oil and gas seeps; examples include the Syncrude oil field in Alberta (Canada), several oil and gas fields in the Gulf of Mexico, and the Karamay, Yanchang, and Shuanghe oil fields in China (Etiope, 2015;Liu, 1990;Pouderoux, Coderre, Pedersen, & Cronkwright, 2016;Ward, 2017;Zou et al., 2019). Oil and gas seeps are also useful in understanding the tectono-stratigraphic evolution of a basin (Burton, Moldowan, Magoon, Sykes, & Graham, 2019;Etiope, 2015;Kruglyakova, Byakov, Kruglyakova, Chalenko, & Shevtsova, 2004), hydrocarbon biodegradation (Teske, 2019), and the carbon cycle (Baciu, Ionescu, & Etiope, 2018;Berbesi, di Primio, Anka, Horsfield, & Wilkes, 2014;Lea-Smith et al., 2015). For these reasons, hydrocarbon seeps have been an active area of research for decades. ...
The southern Junggar Basin in NW China is a world‐class location for the study of oil and gas seeps, with widely distributed, highly variable oil and gas seeps including gaseous mud volcanoes, liquid oil seeps, and solid bitumen deposits. However, the sources and origins of these seeps are poorly understood, as there are many potential source sequences of Permian to Paleogene age. The uncertainty surrounding the seeps means that it has not been possible to address their significance for oil and gas exploration in the area, and they are not understood in the context of the tectono‐sedimentary evolution of the basin within the piedmont region of the northern Tian Shan Mountains (in the eastern part of the Central Asian Orogenic Belt, CAOB). In the present study, these issues were addressed using combined geological and geochemical methods. Results show that there are five main types of seeps in the region from west to east. Type A seeps originate from Jurassic source rocks and are best represented by the A'erqingou mud volcano. Type B seeps originate mainly from Paleogene source rocks but also contain a Jurassic‐sourced component; they are best represented by the Dushanzi mud volcano. Type C seeps originate from a Cretaceous source and are best represented by the South Anjihai and Horgos oil sands. Type D seeps originate mainly from Jurassic source rocks but also contain a Triassic‐sourced component; they are best represented by the Qigu oil seep. Type E seeps originate from Permian source rocks and are best represented by the Dalongkou bituminous deposit. The primary controls on seep distribution are both sedimentological (deposition of source rock) and tectonic (faulting). The position and burial history of sedimentary centres controlled the distribution and maturation of source rocks. Tectonic faults provided migration pathways and traps for the oil and gas. The results of this study will help to reduce uncertainty during exploration for oil and gas in the area. The findings also have general implications for petroleum systems and exploration in the piedmont areas of foreland basins worldwide.
... Traditional well drilling technologies, oriented at deep formations, do not assume determination of GH existence. At the same time, as a result of intended studies within other offshore areas of Russia and CIS, GH were detected in a number of zones of the Sea of Okhotsk, the Caspian Sea, the Black Sea and also on the bottom of the Baikal Lake [24,25,30,36]. ...
Gas hydrates (GH) are perspective energy sources, containing significantly more gas resources compared with conventional fields. At the same time, GH pose a danger for exploration and production of hydrocarbon fields. Methane release to the atmosphere is also a substantial factor of climate change. The objective of this research was the forecast of distribution of zones, favorable for GH existence in the Arctic Ocean and adjacent offshore areas, limited by the 45° latitude. For conducting research, existent data of National Oceanic and Atmospheric Administration (NOAA) on near-bottom water temperatures was analyzed. Using CSMHYD software, based on empirical equations of GH stability, minimal depths appropriate for methane hydrates formation at different temperatures were calculated. On the basis of obtained values, a cartographic scheme with a zone favorable for methane hydrates existence was created. The zone corresponded to distribution of BSRs defined in seismic sections, including those discovered for the first time on the continental slope of the Laptev Sea and in the TINRO Depression of the Sea of Okhotsk. Besides, the zone concurred with the results of other authors research, summarized in the geoinformation system “AWO” (The Arctic and the World Ocean), which could verify the validity of conducted forecast.
... Marine transportation of petroleum and routine maintenance of ships are reasons of the oil seeps. In Turkey, oil seeps are commonly seen in the Giresun Basin between Ordu and Trabzon [1]. ...
Turkey’s environmental pollution control strategies will contribute to the protection of the Black Sea water quality. Key pollution problems are eutrophication and non-point source (NPS) pollution. The Black Sea Trans boundary Analysis Project 2007 Report is the main source of this project in which the author of this paper was one of the contributors as expert. The aim is to analyze the current environmental situation in the provinces of Turkey that border the Black Sea and underline the most critical problems regarding pollution in the Black Sea. The results of this study show that the inadequate municipal discharge, lack of the treatment practices and poor wastewater infrastructure in Trabzon, Samsun, and Zonguldak provinces lead to eutrophication. NPS pollution is mostly due to agriculture and industry. The copper industry is the major industrial polluter in the region. Toxic chemical emission from industrial facilities is one of the leading environmental problems in the region.
... This unit forms the main source rock interval in producing fields in the adjacent South Caspian Basin, the north Caucasus foredeep and the Rioni Basin, Georgia (Inan et al. 1997;Katz et al. 2000;Bazhenova et al. 2002;Saint-Germes et al. 2002;Glumov et al. 2004;Isaksen et al. 2007). Basin modelling, together with evidence from the analysis of mud volcanoes and live oil seeps, indicate that the unit has achieved sufficient depth of burial and maturity level to generate hydrocarbons within the Black Sea region (Zabanbark & Konyukhov 1995;Geodekyan et al. 1996;Robinson et al. 1996;Glumov & Viginskiy 2000;Dimitrov 2002;Bohrmann et al. 2003;Kruglyakova et al. 2004;Andreev 2005;Afanasenkov et al. 2007;Wilson et al. 2007;Rainer et al. 2015). As a consequence, it is typically overpressured (Scott et al. 2009;Marín-Moreno et al. 2013). ...
This study comprises the source rock evaluation of 122 Late Middle Eocene-Early Miocene mudstones from the NE margin of the Black Sea. Samples are immature to early mature. The majority of samples have moderate to very good organic richness, poor to moderate source potential and a hydrogen-deficient to gas-prone source rock quality. However, a significant proportion of the samples have good to excellent organic richness and source potential, and an oil- and gas-prone quality derived from amorphous-rich kerogens. These samples would generate significant amounts of oil and associated gas where buried to peak maturity. They come from the lowermost (Rupelian) part of the Maykop Series and the late Bartonian-early Priabonian Kuma Suite or its stratigraphic equivalents. The Rupelian source-rock interval(s) in west Georgia is at least 60 m thick and potentially as much as 200 m thick. It has a source potential index (SPI) of 0.7-2.5 t HC m⁻². The thickness of the Kuma Suite-equivalent source rock interval south of the western Greater Caucasus is unconstrained. Maykop Series source rocks occur in the Black Sea Basin. Prospective Kuma Suite-equivalent samples on both the northern and southern margins of the Black Sea imply that similar sediments may also be present in the basin.
... It abundantly contains gas hydrates and H 2 S as CH 4 and hydrogen source, respectively (Demirbas, 2009;Dondurur and Cifci, 2009). CH 4 seepage is extremely intense on the shelf and on the slope of the Black Sea (Kruglyakova et al., 2004;Demirbas, 2009;Sozansky, 1997;Dimitrov, 2002;Heeschen et al., 2011;Xing, 2013;Küçük et al., 2015). ...
Many gas seepages, temperature, pressure, salinity, anoxic environment and high source gas potential of the Black Sea indicates that the Black Sea might have huge potentials for biogenic and thermogenic gas hydrates. However, the last important parameter to consider gas hydrate as an energy source is the type of sediments. Coarse marine sands are considered as good hydrate reservoirs because of high porosity and high permeability. Only very limited data is available related to the types of lithology of the Black Sea sediments. Hence, in this study, the literature data (especially the drilling and coring data of DSDP Leg 42B program) about gas seepages, temperature gradient, pressure gradient, salinity, anoxic environment and high source gas potential, and the types of the sediments in the Black Sea were investigated and analyzed. Although gas seepages, temperature gradient, pressure gradient, salinity, anoxic environment and high source gas potential of the Black Sea are appropriate for producible gas hydrate reservoirs, the sediments of the Black Sea appear to be generally fine grained with high clay content. Sandy-silt and silty sand layers in turbidites of the Black Sea might be potential producible hydrate reservoirs but these sediments are fine. As well as turbidites, separate thin sand layers might be potential gas hydrate reservoirs as an energy source in the Black Sea.
... Red areas represent regions of gas seepage and seabed pockmarks. Map is based on a data compilation from Kruglyakova et al. (2004) and Vassilev and Dimitrov (2002). on the atmospheric methane budget caused by massive methane inputs (e.g. ...
A steady state box model was developed to estimate the methane input into the Black Sea water column at various water depths. Our model results reveal a total input of methane of 4.7 Tg yr<sup>−1</sup>. The model predicts that the input of methane is largest at water depths between 600 and 700 m (7% of the total input), suggesting that the dissociation of methane gas hydrates at water depths equivalent to their upper stability limit may represent an important source of methane into the water column. In addition we discuss the effects of massive short-term methane inputs (e.g. through eruptions of deep-water mud volcanoes or submarine landslides at intermediate water depths) on the water column methane distribution and the resulting methane emission to the atmosphere. Our non-steady state simulations predict that these inputs will be effectively buffered by intense microbial methane consumption and that the upward flux of methane is strongly hampered by the pronounced density stratification of the Black Sea water column. For instance, an assumed input of methane of 179 Tg CH<sub>4</sub> d<sup>−1</sup> (equivalent to the amount of methane released by 1000 mud volcano eruptions) at a water depth of 700 m will only marginally influence the sea/air methane flux increasing it by only 3%.
... In the anoxic shelf of the north-western Black Sea numerous gas seeps are populated by methanotrophic microbial mats that can form tall reef-like structures [91]. The majority of gas seeps occur along the shelf break, especially where there are shallow subsurface faults [45]. Where gas seeps and mud volcanoes are known to occur within the boundaries of EU Member States, they should according to Annex I of the Habitats Directive be designated for conservation as Special Areas of Conservation (SAC), if they resemble the description under Code 1180 of Interpretation Manual of European Union Habitats -EUR28, April 2013. ...
The deep soft sediment Black Sea benthic community is dominated by cold seep habitats formed by the microbial breakdown of phytoplankton. The deep Black Sea benthic ecosystem is chemosynthetic with methanogenesis and the sulfate-driven anaerobic oxidation of methane acting as the primary metabolic pathways. Due to the depth and lack of metazoan life the deep Black Sea benthic ecosystem is generally regarded to be at low risk from anthropogenic impact and has little legislation pertaining directly to the preservation of the chemosynthetic habitats. The principal ecosystem services provided by the Black Sea include carbon sequestration and preservation of historical artefacts. Compared to other ecosystems, information on microbial biodiversity and ecosystem services in the deep Black Sea is lacking, and we highlight a need to plan and implement research programmes to address significant gaps and to enhance scientific understanding of this environment.
During the period from 2019 to 2021, complex studies of new shallow-water methane bubble gas emission sites were carried out in the coastal zone near Cape Fiolent (Southwest Coast of Crimea). The studies included determining the hydrocarbon and isotopic composition of bubble gas, measuring the concentration of methane and nutrients in the water in the areas of gas emissions, estimating the value of bubble flows, and measuring hydrophysical parameters over the sip sites compared to background areas. The seasonal type of Cape Fiolent methane seeps was noted, its active phases of gas emissions differed in duration in different years. The increased pore water silica concentration at the seep sites and their localization in the vicinity of freshwater slope springs may indicate its association with submarine freshwater discharge in the area. However, no significant desalination of both pore water and the bottom water layer above the siphons was recorded. Dissolved methane concentrations in pore water at seep sites were two orders of magnitude higher compared to background areas and reached 448 μmol/L. Also high values were obtained for surface water directly above the bubble gas emission points (maximum 353 nmol/L). Multi-hour monitoring of hydrophysical parameters above the active seeps showed a dissolved oxygen decrease compared to the background sites. The maximum difference in O2 concentrations was 3 mg/l. The carbon isotopic composition of bubble gas methane δ13C-CH4 (–62.84…38.27‰) and сarbon dioxide δ13C-CO2 (–16.83…–10.17‰) was corresponded to a mixture of isotopically heavy gas and near-surface isotopically light gas of microbial origin. The question remains open: what are the reasons for the change in the summer active and the cold season passive gas emission phases?
Long offset seismic reflection data reveal the presence of four Bottom Simulating Reflectors (BSR0-3) within folded sediments of the Tuapse Trough, along the NE margin of the Eastern Black Sea Basin (EBSB). Multiple BSRs are observed in other sites worldwide, however, their origin and formation mechanisms are still debated. Here, we investigate the formation mechanisms of the EBSB multiple BSRs based on their seismic character and on their physical properties derived from reflected and refracted arrival seismic velocities. Seismic reflection data are downward continued to enhance refracted arrivals. A 2D travel-time velocity model of the sub-seabed, using combined travel-times from non-downward-continued reflected and downward-continued refracted signals, shows variations in the physical properties at the BSRs and nearby sediments. The P-wave velocity (VP) increase of 1.55-1.72 km/s between the seafloor and BSR0 (258 mbsf) reflects normal compaction trends in sediments, whereas the VP of 1.75-1.83 km/s between BSR0 and BSR1 (360 mbsf) is higher than that expected for sediments at that depth. Beneath BSR1, a VP decrease from 1.83 km/s to 1.61 km/s occurs within a 70-80 m-thick layer including BSR2 (395 mbsf) and extending to BSR3 (438 mbsf). Beneath BSR3, VP increases. Based on an analytical model linking seismic velocity to physical properties, these VP trends can be explained by a gas hydrate saturation from 0 to 2% between the seafloor and BSR0, reaching 4 ± 2% just above BSR1. A free gas saturation of up to 20-25% is estimated within the low-velocity zone between BSR1 and BSR3. BSR1 likely represents the present-day base of the gas hydrate stability zone (BGHSZ), which aligns with the theoretical BGHSZ assuming a geothermal gradient of 26-30˚C/km. Based on seismic polarities and results from travel-time analysis and rock physics modelling, we suggest that hydrate dissociation and recycling processes may explain the negative polarity of BSR2 and BSR3, which are still visible due to the presence of relict gas, and inferred higher gas hydrate saturations close to the present-day base of the stability zone at BSR1. Also, structural and stratigraphic controls seem to have favoured focused free gas flow and hydrate formation at the top of an anticlinal structure, thus likely controlling multiple BSR generation in the EBSB.
At the end of the Eocene, the demise of the Tethys Ocean led to the formation of one of the largest anoxic seas in the last 50 million years of Earth history. This long-lived anoxic water body, named Paratethys, covered large parts of central Eurasia and functioned as a major carbon sink for 15-20 million years, characterised by the deposition of cherts, anoxic turbidites and black shales. The anoxic episode was followed by a phase of instable connectivity where full marine episodes alternated with evaporitic crises and lacustrine episodes, resulting in the deposition of marine molasses, evaporites and continental-lacustrine sediments. Finally, Paratethys transformed into a megalake that progressively filled with clastic sediments from the neighbouring mountain ranges.
Paratethys was tectonically fragmented in numerous sub-basins that spread W-E from the Alpine and Carpathian orogens to the East European Platform. Most Paratethyan stratigraphic records from Central and Eastern European tectonically-active regions are not complete and thus hamper paleogeographic and paleoenvironmental reconstructions. The only exception is the Outer Carpathian Basin, located in the external part of the Carpathian arc in Central Europe, that preserved a complete record of Tethys demise and the rise and fall of Paratethys. The Outer Carpathians sedimentary successions show various lithologies that reflect an interplay of interbasinal connectivity and water exchange with the global ocean.
Here we review the stratigraphic schemes of the different tectonic domains of the Outer Carpathians and describe the most complete records to produce a Carpathian-wide framework for the Eocene to Miocene evolution of Paratethys, the lost sea of Eurasia. Finally, we focus on the paleogeographic reconstructions of the interbasinal Paratethys connections and discuss how marine connectivity influenced anoxia and hypersalinity and impacted the Cenozoic depositional environments in central Europe.
This chapter explores how evidence of hydrocarbon seepage from charged petroleum reservoirs can be used in exploration. The discussion will cover microseepage onshore and macroseepage both onshore and offshore. Microseepage will focus on the direct hydrocarbon detection methods for soil gas and adsorber technologies. The macroseepage sections will concentrate on finding, sampling, analyzing, and interpreting data from seafloor seeps as part of a comprehensive offshore exploration program. It will also show how sea surface slicks can be used as more than just indicators of seafloor seeps in confirming the presence of petroleum systems.
This edited book, which is a piece of artwork prepared TUBA-Energy Working Group, brings a holistic approach to energy and covers all aspects of it, ranging from its history and importance to fundamental thermodynamic concepts and from the dimensions of energy systems to the role of innovation in these systems. The topics covered in the book are extensive and include basic thermodynamic concepts and methods, traditional fossil fuels, renewable energy resources, nuclear energy, biofuels, and alternative fuels, hydrogen energy, waste-to-energy, energy conservation and efficiency, energy storage, energy materials, smart grids, energy policies and strategies, economics and effectiveness of energy systems, energy- environment-sustainability as well as energy innovation.
Integrated interpretation of regional geochemical data and results of the numerical BM&PSM performed at the east part of the Sea of Azov and northeast part of the Black Sea reveal a correlation between the spatial distribution of light hydrocarbons in seabed sediments and investigated petroleum systems. The obtained results point out that the spatial distribution of gaseous hydrocarbons in marine sediments reflects the geological structure of sedimentary cover, and the maturity of petroleum systems, located within the basins. The origin of background levels and anomalies of light hydrocarbons was explained depending on the present-day petroleum system activity and the structure of overburden rocks.
Marine controlled source electromagnetic (CSEM) data have been analyzed as part of a larger interdisciplinary field study to reveal the distribution and concentration of gas hydrates and free gas in two working areas (WAs) in the offshore Danube fan in the western Black Sea. The areas are located in the Bulgarian sector in about 1500 m water depth (WA1) and in the Romanian sector in about 650 m water depth (WA2). Both areas are characterized by channel levee systems and wide spread occurrences of multiple bottom simulating reflections (BSRs) suggesting the presence of gas hydrates. Electrical resistivity models have been derived from two-dimensional (2D) inversions of inline CSEM data using a seafloor-towed electric dipole-dipole system. Comparing the resistivity models with coincident reflection seismic profiles reveals insight in the sediment stratigraphy of the gas hydrate stability zone (GHSZ). Gas hydrate and free gas saturation estimates have been derived with a stochastic approach of Archie's relationship considering uncertainties in the input parameters available from drilling with the MeBo-200 seafloor rig in WA2.
The resistivity models generally reflect the transition of marine to lacustrine conditions expressed by a sharp decay of pore water salinities in the top 30–40 m below seafloor caused by freshwater phases of the Black Sea due to sea level low stands in the past. In WA1, we derived saturation estimates of 10–20% within a 100 m thick layer at around 50 m depth below the channel which compares well with estimates from seismic P-wave velocities. The layer extends below the western levee with even higher saturations of 20–30%, but high gas hydrate saturations are unlikely within the fine grained, clayey sediment section, and the high resistivities may reflect different lithologies of lower permeability and porosity. The resistive layer terminates below the eastern levee where increasing resistivities at depth towards a stack of multiple BSRs indicate gas hydrate and free gas concentrations in the order of 10% to locally 30%. WA2 is characterized by a major slope failure at the landward edge of the gas hydrate stability field next to the channel. Gas hydrate saturation estimates within the slump area are close to zero within the GHSZ which is in agreement with coring results of the nearby MeBo drill sites. Elevated resistivities below the steeply upward bending BSR lead to saturation estimates less than 10% of free gas that may have accumulated.
In this chapter we discuss applications of satellite remote sensing for revealing and analyzing of spatial and temporal characteristics of sea surface oil slicks caused by hydrocarbon seeps on the seabed. Hydrocarbon seeps are natural leaks of liquid and gaseous hydrocarbons fed by underground deposits of oil and gas. Faults or fractures in the seabed serve as pathways through which gas bubbles coated with oil are released into the water column. The primary interest in the study of these phenomena is due to the probable existent link between the natural showings of hydrocarbons from the seabed and the presence of oil and gas fields in the area. On the other hand, the natural manifestations of hydrocarbons are permanent sources of pollution, which should be taken into account when assessing the ecological state of the aquatic areas and when studying the synoptic and climatic changes in the ocean.
Bu çalışmada, Türkiye denizlerinin hidrokarbon potansiyeli ve denizlerdeki geçmiş arama faaliyetleri değerlendirilmiştir. Akdeniz, Karadeniz ve Marmara Denizi’nde yapılan sondajlarda, bugüne kadar herhangi bir ekonomik hidrokarbon keşfi yapılamamıştır. Ancak, bu çalışmada sunulan ve yorumlanan jeolojik, jeokimyasal ve jeofizik veriler, söz konusu denizlerde belirlenmiş olan hedef alanlarda delinmesi için önerilen sondajlarla ekonomik petrol ve doğalgaz rezervlerinin bulunabileceğini göstermektedir.
Anahtar Kelimeler: Akdeniz, Karadeniz, Marmara Denizi, hidrokarbon potansiyeli, petrol ve gaz arama, arama hedefi, arama stratejisi, hidrokarbon emaresi, petrol jeolojisi
The Black Sea is one of the largest inland seas in the world and contains many geological occurrences such as numerous mud volcanoes, channels which played an active role in sediment transport, active faults, and methane leaks. In the wells drilled in the Exclusive Economic Zone (EEZ) of Turkey in the Black Sea, any long-term producible hydrocarbon discovery could not be made so far. The purpose of this paper is to determine hydrocarbon exploration targets in the EEZ of Turkey in the Black Sea based on the relations between the geological structures and hydrocarbon systems. Therefore, in the study, the suggestions have been made for hydrocarbon exploration targets and drilling locations to be drilled into these targets based on geological, geochemical, seismic, and gravity-magnetic measurements along with hydrocarbon discovery data from the previous studies. The geological and geophysical data presented in this investigation indicate that the oil and gas reservoirs may be discovered in the EEZ of Turkey in the Black Sea. Consequently, it is projected that the future hydrocarbon exploration activities to be conducted may contribute to the possible discovery prosperities if they are shifted to the target areas suggested in this study.
Keywords: Black Sea, hydrocarbon potential, petroleum systems, oil and gas exploration, exploration target, play types, petroleum geology
This chapter covers the entire catalogue of mud volcanoes known so far in the Black Sea region, in particular the Kerch and Taman peninsulas, the northwestern Caucasus, the Black Sea itself, and the southeastern part of the Sea of Azov.
Based on an analytical review of factual materials, the article discusses the peculiarities of the distribution of gas hydrates in the development zones of mud volcanism of the Mediterranean, Black and Caspian seas, which are direct indications of sedimentary gas complex. A comparative analysis of the composition of hydrate-forming fluids, sources and depths of gas hydrates distribution was performed. The article provides information on gas seeps and pokmarks. The presence of gas seepsand pokmarks in the water column and at the bottom of the Southern Caspian is assumed.
-NEHİRLERLE TAŞINAN PETROL YÜKLERİ VE ORTAMDAKİ PETROL KİRLİLİĞİ: KARADENİZ ÖRNEĞİ
-BARTIN-GÜNYE ORMAN İŞLETME ŞEFLİĞİ KARBON DEPOLAMA KAPASİTESİ
-BİYOYAKITLAR
-ATATÜRK ÜNİVERSİTESİ ÖĞRENCİLERİNİN KÜRESEL ISINMAYA YÖNELİK BİLGİ VE FARKINDALIK DÜZEYLERİNİN ARAŞTIRILMASI
-İN VİVO VE İN VİTRO EMBRİYO ÜRETİMİNE ETKİ EDEN FAKTÖRLER
-KIVIRCIK YAPRAK SALATANIN VERİM VE KALİTESİNE BAZI ORGANİK MATERYALLERİN ETKİSİ
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Fosil yakıtların çevre ve ekonomi üzerindeki olumsuz etkisi, toplumu yenilenebilir yakıt alternatifleri bulmaya yöneltmektedir. Yenilenebilir yakıtlar, biyoyakıtlar (örn., biyoetanol) gibi yenilenebilir kaynaklardan üretilen yakıtlardır. Bu, doğal gaz, petrol ve nükleer enerji gibi yenilenemeyen yakıtların tersidir. Bu kitap bölümü, biyoyakıtlar hakkında bazı bilgiler vermekte ve gerçekleri sentezlemektedir. Başlangıç olarak, biyoyakıtların üretiminden bahsedilmektedir. Daha sonra biyoyakıtların çevresel ve ekonomik yararları anlatılmakta ve son olarak da biyoyakıtın benzine olan üstünlüğü, kullanılabilirliği ile çevre ve ekonomi üzerindeki etkileri karşılaştırarak kanıtlanmaya çalışılmıştır.
Bu çalışmada, Türkiye’nin potansiyel petrol ve doğalgaz yatakları ile ilişkili iyotça zengin sularını belirlemek için yeni bir “ Petrol ve Doğalgaz Sahası Suyu Ayırma Grafiği ” geliştirilmiştir. Bu grafik yardımıyla ülke genelinde çok sayıda iyotça zengin su kaynağı bulunduğu tespit edilmiştir. Türkiye’deki yüzey ve yeraltısularındaki iyot zenginleşmesinin sebebi, derinlerdeki petrol ve doğalgaz yataklarından jeolojik olaylar (tektonizma, volkanizma vb.) etkisiyle yüzeye ve yüzeye yakın bölümlere göç eden hidrokarbonlarca ve iyotça zengin rezervuar sularıdır. Bu göçün en önemli kanıtı, iyotça zengin suların aynı zamanda olgun petrol hidrokarbonlarınca da zengin olmalarıdır. Çünkü, hem iyotça hem de olgun petrol hidrokarbonlarınca zengin sular, petrol ve doğalgaz sahası sularıdır. Çalışmada, oldukça yüksek iyot içerikli çok sayıda su kaynağı bulunması nedeniyle Batı ve Orta Anadolu bölgelerinin petrol ve doğalgaz potansiyelinin Güneydoğu Anadolu ve Trakya havzalarından daha yüksek olduğu belirlenmiştir. Dolayısıyla, birçok çalışmada öne sürülen görüşlerin aksine, bu çalışmada belirlenen iyotça zengin suların Batı ve Orta Anadolu bölgelerindeki özellikle çok sayıda diri fayın bulunduğu alanlarda yoğunlaşması, çeşitli jeolojik dönemlerde oluşmuş petrol ve doğalgaz yataklarının ülke genelinde genç jeodinamik olaylardan olumsuz etkilenmediğini göstermektedir. Bu çalışmanın diğer bir önemli sonucu da, aktif tektonik (dinamik olarak “hareketli”, “dengesiz”) ve jeolojik olarak karmaşık havzalar içeren Türkiye kara alanlarında yapılacak gelecek petrol ve doğalgaz aramaları için kaynak kaya hedefli organik kaya ve gaz jeokimyası yerine rezervuar hedefli organik hidrojeokimyasal yöntemlerin kullanılmasının daha uygun olduğunun belirlenmesidir. Çalışma ekinde verilen 76 ildeki 5189 adet su kaynağında, klasik petrol jeokimyası analizleri yapılarak bu su kaynaklarındaki iyot miktarlarının ve petrol hidrokarbonlarının jeokimyasal özelliklerinin tespit edilmesi, Türkiye kara alanlarının petrol ve doğalgaz potansiyelinin gerçek bir şekilde tanımlanmasını ve ülke genelinde yeni arama hedeflerinin belirlenmesini sağlayacaktır.
Anahtar Kelimeler: Türkiye’nin petrol ve doğalgaz potansiyeli, iyotça zengin sular, hidrojeokimya, yeraltısuyu kirliliği, petrol hidrojeolojisi, petrol arama
This chapter addresses two different awe-inspiring aspects primarily concerning the abyssal depths of the oceans; one (the Bermuda Triangle imbroglio) that is specific to the Atlantic Ocean, and the other (formation of polymetallic nodules (PMN)) that is common to the Pacific, Indian, and the Atlantic Oceans. The chapter begins with a brief general introduction, touching on both these diverse aspects. To meaningfully introduce the topic of the Bermuda Triangle imbroglio, some related aspects, such as the historical episode of fire breakout in the Japan Sea, and the trawler wreck in Witch’s Hole pockmark have been described. Subsequent discussion focus on other related aspects, including methane hydrate deposits in the seafloor sediment layer and their role in the Bermuda Triangle imbroglio, as well as the possible influence of the warm Gulf Stream in triggering methane gas emission, which, based on scientific evidence, is suspected to be the culprit in the sudden disappearances of ships and low-flying aircraft in the Bermuda Triangle region. The discussion is strengthened by invoking various scientific studies carried out to unlock the secret behind this dreaded story.
The second part of this chapter addresses another interesting aspect of the ocean floor, namely, the carpet of “dark gold” (PMN) having been paved over by nature over a period of billions of years’ utterly slow growth (at the rate of 1–3 mm/million years). The chapter attaches due importance to the devices used for collection of the dark gold from the abyssal ocean depths (paved on the ocean floor, as well as buried in thick sediments lying below the ocean floor’s water-sediment interface). Subsequent discussion on the dark nodules revolves around important aspects, such as their specialty and structure, factors influencing their formation, the role of nucleating materials, their shape and surface texture, internal features (thickness of oxide layer, internal microstructure), chemical composition, role of micro-organisms in their formation, and presence of rare earth elements. The chapter winds up with a discussion on the distribution of nodules in the world oceans.
Traditional energy generation technologies cause numerous environmental problems and consume non-renewable resources. Therefore, substitution of traditional energy generation technologies with modern sustainable methods is an important and promising issue.
Current distribution of energy production in Ukraine is: 40–50 % at the nuclear power plants (4 plants); ~40 % at the thermo power plants; ~6–10 % at the hydro power plants and less than 0.5 % at various sustainable power plants (wind power, small hydropower, PV, etc.).
Northern Near-Black Sea steppe region and Crimea possess considerable wind power generation potential. Total estimated wind power potential of the Southern Ukraine and Crimea is about 5,000 MW, which in the long-term outlook can cover about 20 % of the national energy consumption. The Crimean annual wind power energy production can reach about 10 billion kWt-h/year.
Besides, Northern Black Sea steppe is a region of very intense grain production, which produces high-tonnage by-products (hay, non-conditional grains, sunflower wastes, etc.). Most of them can be easily utilized in the biopower energy production (house and water heating, etc.). This would also decrease the need for electricity and other energy consumption required for these purposes.
Detailed estimation proves that total sustainable energy generation potential of the Northern Black Sea region and Crimea is quite considerable and can cover up to 30–40 % of its own energy need.
To understand the potential mechanism of marine extremophiles participating in the formation and the evolution of hydrocarbon resources in marine extreme environments, some typical kinds of extremophiles and their distributions in marine hydrothermal venting and cold venting are discussed and evaluated respectively. The potential relationship between extremophile activities and hydrocarbon resources in marine extreme environments are then discussed in details. It could be now preliminary concluded that archaea and bacteria are the two main kinds of extremophiles in marine extreme environments. The dominating microbial communities in hydrothermal venting are heterotrophic zymogens, sulphate reducers and methanogens, while the ANME-2 group (Methanosarcinales) surrounded by sulfate reducing bacteria and ANME-1 group are dominated in cold venting. Marine extremophiles would be able to use CH4 and H2S to synthesize energy for metabolism and to support food chains for other unique macrobiota nearby, which together present a high abundance but a low diversity with distinct characteristics of horizontal and vertical distributions. Marine extremophiles might play an important role either directly or indirectly in the processes of hydrocarbon formation and later alteration, and could indicate the evolution of hydrocarbon resources in marine extreme environments. Our research thus has a great significance both in theoretical approach of potential hydrocarbon resources formed by marine extremophile activities and in practical exploration of the potential hydrocarbon source sedimentary layers formed in the earth history or the potential strata in South China.
Gas Hydrate reservoir in the northeastern continental slope of South China Sea(SCS) have been confirmed by investigations and well drillings. Also, large amounts of methane-derived authigenic carbonates (MADC) were discovered in 2004 among this area. Based on sub-bottom profiles and seismic profiles, attributes and features associated with cold seepage system in the northeastern continental slope of SCS were analyzed. A seismic line cross the northeastern continental slope of SCS was used to show local sedimentary environment. Sub-bottom data were pieced together and denoised. Shallow gas, fluid migration and morphology features associated with cold seepage in processed sub-bottom profile were identified and discussed, with assistance of corresponding seismic lines and bathymetric charts. From observation of sub-bottom profiles and comparison with seismic and bathymetry data, cold seepage related features were listed as follow: (1) Acoustic plume (suspected of being cold seep) was found in a sub-bottom profile, with height of about 30 meters and width of 50 meters. (2) Mud volcanoes were found in this area, and caused discontinuity of Bottom Simulating Reflectors in seismic profiles. (3) Acoustic voids, the most frequent features in this region, had two types: “narrow” acoustic void and “broad” acoustic void. “narrow” acoustic void had width of 80~400 m and no layers information, “broad” acoustic void had width over 1000m and weak layers information. (4) The area of “narrow” acoustic void overlaid with mud volcanoes concentrated area, and the acoustic plume was located around “broad” acoustic voids. Cold seepage activities exist on the northeastern continental slope of SCS, both in history and in present. The results suggest that “narrow” acoustic voids on sub-bottom profiler correspond to fluid migration path, while “broad” acoustic voids possibly related with shallow gas accumulation along rock layers. The relationship between cold seepage system and gas hydrate in the northeastern continental slope of SCS worth further investigation.
Based on hydro-acoustic and geophysical observations, this paper presents an analysis of geomorphological and geological settings of gas methane occurrence on the NW shelf and upper continental slope, in the Sorokin trough and on the Kerch-Taman offshore, in the Black Sea. Gases are associated with seeps, mud volcanoes and gas hydrates. Evidence is given for the thermogenic nature of methane. The gas methane is of mostly abiogenic origin. Small gas releases may be produced by the decomposition of Quaternary organic material near the sea floor through the action of bacteria or biodegradation of redeposited thermogenic hydrocarbons. The origin of carbonate formations is related to degassing sedimentary layers. There is a possible role for deep faults in transporting gas to the sea floor. The gas hydrate stability zone in the Black Sea lies at minimum water depth of 600-650 m with its thickness up to 500 m.
The magnitude and spatial distribution of potential Black Sea methane hydrate reservoirs has been estimated on the basis of 6′ x 6′ longitude-lattitude data grid. The general input includes bathymetry; bottom temperatures; heat flow (487 quoted 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 350·109 m3, i.e., about 10 to 50·1012 m3 of gas methane are trapped within the Black Sea sediments in the form of hydrate.
Massive microbial mats covering up to 4-meter-high carbonate buildups prosper at methane seeps in anoxic waters of the northwestern Black Sea shelf. Strong 13C depletions indicate an incorporation of methane carbon into carbonates, bulk biomass,and specific lipids. The mats mainly consist of densely aggregated
archaea ( phylogenetic ANME-1 cluster) and sulfate-reducing bacteria (Desulfosarcina/Desulfococcus group). If incubated in vitro,these mats perform anaerobic oxidation of methane coupled to sulfate reduction. Obviously, anaerobic microbial consortia can generate both carbonate precipitation and substantial biomass accumulation,which has implications for our understanding of carbon cycling during earlier periods of Earth’s history.
sounder and shallow seismic data analyses of investigation s conducted before and after 1988, allow the main pockmark area to be enlarged and given more details. A total of 305 pockmarks have been located within an area of more than 100 km2 (2-5 km wide and 41 km long). The bottom of the area is covered with Holocene soft silty clay. The following trends are defined when moving from the northern part of the pockmark area to the southern part: 1) increase in seabed sediments thickness from 2.5 m to more than 3.2 m and decrease in mean sediment grain size; 2) increase in general water depth from 160-300 m to 230-340 m in areas where pockmarks occur; 3) increase in average individual pockmark size from 86 to 132 m in diameter and from 2 to 4 m in depth; 4) decrease of pockmark density from 8-9 p.m./knv2 to 3-4 p.m./km2. Similar trends are observed seaward where the pockmark profile shape changes from a smooth U-shaped to a sharp V-shaped form, with pockmark wall slope angle reaching more than 10°. A variety of acoustic anomalies such as acoustic turbidity, bright spots, enhanced reflections etc., are recorded in many places within the pockmark area, indicating the presence of gas in the sediments. Water column anomalies have also been recorded. The paper discusses the origin of the gas (most likely to be a mixture of thermogenic and biogenic gas) and die time of pockmark formation.
Massive microbial mats covering up to 4-meter-high carbonate buildups prosper at methane seeps in anoxic waters of the northwestern Black Sea shelf. Strong 13C depletions indicate an incorporation of methane carbon into carbonates, bulk biomass, and specific lipids. The mats mainly consist of densely aggregated archaea (phylogenetic ANME-1 cluster) and sulfate-reducing bacteria (Desulfosarcina/Desulfococcus group). If incubated in vitro, these mats perform anaerobic oxidation of methane coupled to sulfate reduction. Obviously, anaerobic microbial consortia can generate both carbonate precipitation and substantial biomass accumulation, which has implications for our understanding of carbon cycling during earlier periods of Earth's history.
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.
Over 200 gas seeps (95-98% methane) have been discovered through the past 15 years in the northwestern Black Sea, most often attributed to large fault zones. Many sites are associated with carbonates.
A regional estimation of the contribution to atmospheric methane by natural gas seepages on the UK continental shelf was undertaken by Judd et al. (Mar. Geol. 137(1/2) (1997) 165). This paper is the second in the series, and provides an estimation of the atmospheric methane flux from Bulgarian Black Sea continental shelf.Potential gas source rocks include Holocene gas-charged sediments, Quaternary peats and sapropels, and deep-lying Palaeocene and Neogene clays, Cretaceous coals, and other sediments of late Jurassic to early Cretaceous age. These cover almost the whole continental shelf and slope and, together with irregularly developed seal rocks and widespread active and conducting faults, provide good conditions for upward gas migration.A total of 5100 line kilometers of shallow seismic (boomer) and echo-sounder records acquired during the Institute of Oceanology's regional surveys, and several detailed side-scan sonar lines, have been reviewed for water column targets. Four hundred and eighty-two targets were assigned as gas seepage plumes. It is estimated that a total of 19,735 individual seeps exists on the open shelf. The number of seeps in coastal waters was estimated to be 6020; this is based on available public-domain data, specific research, and results of a specially made questionnaire which was distributed to a range of “seamen”.More than 150 measurements of the seabed flux rates were made in the “Golden sands” and “Zelenka” seepage areas between 1976 and 1991. Indirect estimations of flux rates from video and photo materials, and a review of published data have also been undertaken. Based on these data, three types of seepages were identified as the most representative of Bulgarian coastal waters. These have flux rates of 0.4, 1.8, and 3.5l/min.The contribution to atmospheric methane is calculated by multiplying the flux rates with the number of seepages, and entering corrections for methane concentration and the survival of gas bubbles as they ascend through seawater of the corresponding water depth. The estimation indicates that between 45,100,000 (0.03Tg) and 210,650,000m3 (0.15Tg)methaneyr−1 come from an area of 12,100km2.
The nature of hydrocarbons in the marine environment of the Black Sea is quite diverse: syngenetic biochemical gases, deep epigenetic gases and technogenic hydrocarbon components. The level and contribution of hydrocarbons from these sources to the marine environment are evaluated in this paper.Syngenetic hydrocarbon components are represented by biogenic methane. Methane concentrations reach their maximum in the hydrogen sulphide zone. It is established that there is a high rate of methane generation in seawater and seabed sediments. High gas saturations in seabed sediments produce acoustic anomalies (BSRs, bright spots, “boiling” sediment, griffons, etc.).Deep hydrocarbons are associated with gas evolution (seepage). To date more than 65 underwater mud volcanoes have been mapped in the Black Sea. Biogenic production of methane is higher than the flow from seeps by approximately 1.5 times. Considerable quantities of hydrocarbons are contained in accumulations near mud volcanoes; gas hydrates are also associated with them. Thus, it follows that hydrocarbons are natural components of the Black Sea, and they are the part of a single biogeochemical cycle of carbon in the marine environment.Technogenic hydrocarbon components are supplied to the sea from onshore by river catchments, industrial activity at oil-loading terminals, tanker transportation and marine navigation. Technogenic contamination is also noted in the coastal zone of the sea in general. Commensurate discharges to the marine environment of petroleum hydrocarbons of natural and technogenic origins can be recognized.
Marine gas hydrates of the Black Sea (MARGASCH). RV Meteor Cruise M52/1
- G Bohrmann
- Schenck
Marine gas hydrates of the Black Sea (MARGASCH) RV Meteor Cruise M52/1. Geomar Rep Surface geochemical exploration continues to progress global deepwater frontiers Gas hydrates in the Black Sea sedimentary thickness—hydrocarbonic raw materials for the future
- G Bohrmann
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- Jm
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- Je Zumberge
- Brown
Bohrmann G, Schenck S (eds) (2002) Marine gas hydrates of the Black Sea (MARGASCH). RV Meteor Cruise M52/1. Geomar Rep, Kiel Brooks JM, Bernard BB, Cameron NR, Zumberge JE, Brown S (2000) Surface geochemical exploration continues to progress global deepwater frontiers. http://TDI_Brooks_internet Byakov U, Kruglyakova R (2001) Gas hydrates in the Black Sea sedimentary thickness—hydrocarbonic raw materials for the future (in Russian). Razvedka okhrana nedr 8:13–19
Mud volcanoes in the Kerch-Taman region: atlas (in Russian) Naukova Dumka Zone of acoustic anomalies in the Black Sea near Sevastopol (in Rus-sian)
- E J Sobolevsky
- Gnatenko
E, Sobolevsky J, Gnatenko G (eds) (1986) Mud volcanoes in the Kerch-Taman region: atlas (in Russian). Naukova Dumka, Kiev Shnukov E, Mitin L, Kleshenko S, Grigorjev A (1993) Zone of acoustic anomalies in the Black Sea near Sevastopol (in Rus-sian). Geol Zhurnal 4:62–67
Gas vents on the bottom of the Black Sea (in Ukrainian) Nanu, Kiev Tugolesov D (ed) (1985) Tectonics of the Mezocainozoic sediments in the Black Sea Basin (in Russian) Spatial and quantitative evaluation of the Black Sea gas hydrates (in English and Russian)
- E A Pasnikov
- Kleshtenko
E, Pasnikov A, Kleshtenko S (1999) Gas vents on the bottom of the Black Sea (in Ukrainian). Nanu, Kiev Tugolesov D (ed) (1985) Tectonics of the Mezocainozoic sediments in the Black Sea Basin (in Russian). Nedra, Moscow Vassiliev A, Dimitrov L (2002) Spatial and quantitative evaluation of the Black Sea gas hydrates (in English and Russian). Sci J Geol Geofiz Siberian Branch Russian Acad Sci 43(7):672–685
Surface geochemical exploration continues to progress global deepwater frontiers
- Jm Brooks
- Bb Bernard
- Nr Cameron
- Je Zumberge
- S Brown
Gas hydrates in the Black Sea sedimentary thickness-hydrocarbonic raw materials for the future
- J M Brooks
- B B Bernard
- N R Cameron
- J E Zumberge
- S Brown
Brooks JM, Bernard BB, Cameron NR, Zumberge JE, Brown S
(2000) Surface geochemical exploration continues to progress
global deepwater frontiers. http://TDI_Brooks_internet
Byakov U, Kruglyakova R (2001) Gas hydrates in the Black Sea
sedimentary thickness-hydrocarbonic raw materials for the
future (in Russian). Razvedka okhrana nedr 8:13-19
Geological-geophysical investigations of the 57 cruise R/V ''Professor Vodyanitsky'' in the north-east Black Sea (in Russian). Tez dokl IV Mezhdynarod Konf Geodynamic and Oil Gaseous Systems of the Black Sea-Kaspian region
- S Dovgiy
- E Shnukov
- I Starostenko
- P Gozhik
- V Kobelev
- A Leibon
- V Radchuk
Dovgiy S, Shnukov E, Starostenko I, Gozhik P, Kobelev V, Leibon
A, Radchuk V (2002) Geological-geophysical investigations of
the 57 cruise R/V ''Professor Vodyanitsky'' in the north-east
Black Sea (in Russian). Tez dokl IV Mezhdynarod Konf Geodynamic and Oil Gaseous Systems of the Black Sea-Kaspian
region. Simferopol, pp 60-61
Heat flow, fault zones and gas seeps in the Black Sea
- R Kutas
Kutas R (2002) Heat flow, fault zones and gas seeps in the Black
Sea. In: Abstr Vol 7th Int Conf Gas in Marine Sediments, Nafta
Press, Baku, pp 111
The first results of search for submarine gas hydrates in the Black Sea (in Russian)
- A N Kremlev
- G D Ginsburg
Kremlev AN, Ginsburg GD (1989) The first results of search for
submarine gas hydrates in the Black Sea (in Russian). Geol
Geophyz 4:110-111
Black Sea sediment deformations as targets for fluid study
- L B Meisner
- D A Tugolesov
- Y A Byakov
Meisner LB, Tugolesov DA, Byakov YA (2001) Black Sea sediment deformations as targets for fluid study. Turkish Assoc
Petrol Geol Spec Publ 4:165-172
Gas vents on the bottom of the Black Sea
- E Shnukov
- A Pasnikov
- S Kleshtenko
Shnukov E, Pasnikov A, Kleshtenko S (1999) Gas vents on the
bottom of the Black Sea (in Ukrainian). Nanu, Kiev
Mud volcanoes in the Kerch-Taman region: atlas (in Russian)
- E Shnukov
- J Sobolevsky
- G Gnatenko
Shnukov E, Sobolevsky J, Gnatenko G (eds) (1986) Mud volcanoes
in the Kerch-Taman region: atlas (in Russian). Naukova
Dumka, Kiev
The West Black Sea mud volcano province (in Russian)
- L B Meisner
- D A Tugolesov
- E M Khakhalev
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