Satellite monitoring of oil slicks on the Black Sea surface

This paper summarizes the results of perennial combined satellite monitoring of the Black Sea conducted in order to detect sea-surface oil and oil-product pollution, as well as biogenic and anthropogenic surfactant films. A joint analysis of data obtained by various remote sensing techniques has been performed. The large amount of data has resulted in generalizations and reliable statistics on the spatial and temporal variability of different film manifestations in radar images of the sea surface. Regions most severely polluted by petroleum products have been identified. A hypothesis is suggested linking the surface manifestations of certain types of polluting films with natural gas and oil seeps and mud volcanism in the Black Sea. Improvements in the reliability of interpreting satellite data are discussed.     

Strong heat flow variability in an active shallow gas environment, Dnepr palaeo-delta, Black Sea

The Dnepr palaeo-delta on the north-western continental slope of the Black Sea is a prolific seepage zone characterised by a highly variable heat flow ranging from 24 to 88 mW/m². New thermal data were collected at 33 closely spaced stations in order to better understand the apparent relation between heat flow variability and seepage features. Strong relief gradients and associated landslide shaping may explain first-order heat flow variability but, locally, thermal parameters appear to be controlled by fluid and gas migrations. High heat flow anomalies are found at sites where faults and diapirs offer pathways for warm fluid flow from deeper sedimentary levels. Low heat flow is most strongly expressed at ridge crests near seepage sites but is also found where seeps are absent. Reduced heat flow and nonlinear temperature-depth variations are interpreted to result from natural or induced gas ebullition of saturated shallow gas covered by a thin, relatively impermeable sedimentary seal. The presence of sealed gas pockets, in particular at ridge crests, is supported by methane pore-water analysis and a shallow gas front widely observed in the study area.     

An enigmatic strong reflector on subbottom profiler records from the Black Sea—the top of shallow gas hydrate deposits

An anomalous strong, shallow reflector has been observed in several deep-tow subbottom profiler records in a region of the northern Black Sea characterised by seafloor fluid seeps, mud volcanoes, and the occurrence of gas hydrates. The digital data were processed using adapted seismic processing methods. Synthetic seismograms created to model representative traces from the observed profiles require anomalous alternations of acoustic properties in the upper sediments which can best be explained by interbedded layers of normal sediments and sediments with gas hydrates. The enigmatic strong reflector can be explained by constructive interference of reflections from five of these thin layers. It is proposed that the uppermost region of the gas hydrate stability zone here is represented by thinning layers of interbedded gas hydrates or layers with lower concentrations of gas hydrates.     

Possibility of Large Deposits of Gas Hydrates in Deeper Waters of India

The available geological and thermodynamic data, essential for the formation and accumulation of gas hydrates, have been integrated and broadly interpreted for the deeper waters of India. The preliminary studies indicate that, in all probability, vast gas hydrate resources exist in the shallow sediments under deep waters. The area of the Bay of Bengal and Arabian Sea, off the coast of India and Andaman Islands, have accumulated thick sediments, over 22 and 10 km, respec tively, during collision of the Indian Plate with the Tibetan Plate. Bottom Simulating Reflectors (BSRs), indicating the likely presence of gas hydrates, have been observed from multichannel and single-channel seismic reflec tion data west of the Andaman Islands and Kerala-Konkan offshore. The Indian continental shelf, slope, and rise areas have, at places, shown the presence of gas-charged sediments and gas seeps through faults. There are commercial oil and gas fields in the shallow waters of both the east and west coasts of India. These are indicative of generation of both biogenic as well as thermogenic gases in the offshore areas of India. For the first time, an attempt has been made to estimate in-place gas hydrate resources under deep waters of India beyond 600 m water depth to the legal continental shelf boundary, and to the Andaman Islands. The gas hydrate resources appear to be vast, and require extensive exploratory efforts for their precise mapping and quantitative assessment.     

Using iron speciation in authigenic carbonates from hydrocarbon seeps to trace variable redox conditions

Seepage of hydrocarbon-rich fluids out of the marine sedimentary column is characterized by temporal changes of flow intensity and resultant spatially variable redox conditions. Authigenic carbonates at marine hydrocarbon seeps provide excellent geological and geochemical archives that serve to explore seepage dynamics over time. In this study, we investigated the potential of Mössbuaer spectroscopy and Fe contents of seep-related authigenic carbonates from the Congo Fan, the Gulf of Mexico, and the Black Sea for reconstructing past redox conditions and fluid seepage activity at cold seeps. The Fe speciation observed by Mössbauer spectroscopy and Fe contents suggest that (1) the Congo Fan carbonates precipitated in a sulfidic environment, (2) the formation conditions of seep carbonates were variable at the Gulf of Mexico seep site, ranging from oxic to suboxic and anoxic and even spanning into the methanogenic zone, and (3) the stratified water column of the Black Sea or suboxic condition resulted in low Fe contents of Black Sea carbonates. The study reveals that Fe speciation can provide constraints on the wide range of redox conditions that imprinted seep carbonates during the life span of seepage. Similarly, Mössbauer spectroscopy – particularly when used in combination with the analysis of redox-sensitive elements – is a promising tool to trace variable redox conditions in marine paleoenvironments other than seeps.     

Distribution and expression of gas seeps in a gas hydrate province of the northeastern Sakhalin continental slope, Sea of Okhotsk

Multidisciplinary surveys were conducted to investigate gas seepage and gas hydrate accumulation on the northeastern Sakhalin continental slope (NESS), Sea of Okhotsk, during joint Korean–Russian–Japanese expeditions conducted from 2003 to 2007 (CHAOS and SSGH projects). One hundred sixty-one gas seeps were detected in a 2000 km² area of the NESS (between 53°45′N and 54°45′N). Active gas seeps in a gas hydrate province on the NESS were evident from features in the water column, on the seafloor, and in the subsurface: well-defined hydroacoustic anomalies (gas flares), side-scan sonar structures with high backscatter intensity (seepage structures), bathymetric structures (pockmarks and mounds), gas- and gas-hydrate-related seismic features (bottom-simulating reflectors, gas chimneys, high-amplitude reflectors, and acoustic blanking), high methane concentrations in seawater, and gas hydrates in sediment near the seafloor. These expressions were generally spatially related; a gas flare would be associated with a seepage structure (mound), below which a gas chimney was present. The spatial distribution of gas seeps on the NESS is controlled by four types of geological structures: faults, the shelf break, seafloor canyons, and submarine slides. Gas chimneys that produced enhanced reflection on high-resolution seismic profiles are interpreted as active pathways for upward gas migration to the seafloor. The chimneys and gas flares are good indicators of active seepage.     

Analysis of the Black Sea sediments by evaluating DSDP Leg 42B drilling data for gas hydrate potential

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.     

Oil seeps in the southeastern Black Sea studied using satellite synthetic aperture radar images

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.     

Geologic control of natural marine hydrocarbon seep emissions, Coal Oil Point seep field, California

High-resolution sonar surveys, and a detailed subsurface model constructed from 3D seismic and well data allowed investigation of the relationship between the subsurface geology and gas-phase (methane) seepage for the Coal Oil Point (COP) seep field, one of the world’s largest and best-studied marine oil and gas seep fields, located over a producing hydrocarbon reservoir near Santa Barbara, California. In general, the relationship between terrestrial gas seepage, migration pathways, and hydrocarbon reservoirs has been difficult to assess, in part because the detection and mapping of gas seepage is problematic. For marine seepage, sonar surveys are an effective tool for mapping seep gas bubbles, and thus spatial distributions. Seepage in the COP seep field occurs in an east–west-trending zone about 3–4 km offshore, and in another zone about 1–2 km from shore. The farthest offshore seeps are mostly located near the crest of a major fold, and also along the trend of major faults. Significantly, because faults observed to cut the fold do not account for all the observed seepage, seepage must occur through fracture and joint systems that are difficult to detect, including intersecting faults and fault damage zones. Inshore seeps are concentrated within the hanging wall of a major reverse fault. The subsurface model lacks the resolution to identify specific structural sources in that area. Although to first order the spatial distribution of seeps generally is related to the major structures, other factors must also control their distribution. The region is known to be critically stressed, which would enhance hydraulic conductivity of favorably oriented faults, joints, and bedding planes. We propose that this process explains much of the remaining spatial distribution.     

Hydraulic calculations of postglacial connections between the Mediterranean and the Black Sea

A series of simple hydraulic calculations has been performed to examine some of the questions associated with the reconnection of the Black Sea to the Mediterranean through the Turkish Strait System during the Holocene. Ryan et al.’s catastrophic flood scenario, whereby the erosive power of the marine in-fluxes, initiated after eustatic sea level reached the sill depth, opened up the Bosphorus, allowing saline water to pour into the Black Sea and filling it on a short time scale, is examined. The calculations show that although it might be possible to fill the palaeo-Black Sea within the order of a decade, a 1–2 year filling time scale is not physically possible. A hydraulic model is also used to examine the more traditional connection hypothesis of (near-)continuous freshwater outflow from the Black Sea, with a slowly increasing saline inflow from the Mediterranean beginning around 8–9 kyr BP. The model considers two forms for the structure of the Bosphorus: a shallow sill as seen today and a deep sill associated with no sediments filling the 100 m gorge above the bedrock in the strait. Sensitivity experiments with the hydraulic model show what possible strait geometric configurations may lead to the Black Sea reaching its present-day salinity of 18 psu. Salinity transients within the Black Sea are shown as a function of time, providing for values that can be validated against estimates from cores. To consider a deep, non-sediment-filled Bosphorus (100 m deep), the entry of Mediterranean water into the Sea of Marmara after 12.0 kyr BP is examined. A rapid entry of marine water into the Sea of Marmara is only consistent with small freshwater fluxes flowing through the Turkish Strait System, smaller than those of the present day by a factor of at least 4. Such a small freshwater flux would lead to the salinification of the Black Sea being complete by an early date of 10.2–9.6 kyr BP. Thus the possibility of a deep Bosphorus sill should be discounted.     

利用地热开采南海天然气水合物的技术研究

近年的研究表明南海北部陆坡区发育有底辟构造、海底滑坡以及活动断层带等有利于天然气水合物形成的地质构造环境.受深部地幔上隆的影响,南海整个海区热流背景值偏高,地热资源十分丰富,由此提出了利用地热加热海水,用热激发法分解天然气水合物的设想,并设计了初步的生产工艺.用传统热激发方法开采天然气水合物藏本身需要消耗大量能源,而且...     

A highly concentrated region of cold hydrocarbon seeps in the southeastern Mediterranean Sea

In July 1999, we conducted a side-scan sonar survey in the southeastern Mediterranean Sea, between 300- and 800-m water depths approximately 30 nautical miles from the Sinai Peninsula and Gaza Strip. Examination of the sonar imagery revealed numerous acoustic targets, each on the order of a few meters and surrounded by small depressions. Subsequent visual inspection of two of these targets by a remotely operated vehicle (ROV) revealed they were cold hydrocarbon seeps through which small bubbles of gas and shimmering fluids were emitted. Surrounding each cold seep were benthic communities of organisms. The ROV was used to gather video and still-camera imagery, map the surrounding microbathymetry, and collect samples of the seep structure and associated organisms. A sub-bottom profiler, which was attached to the ROV, was used to image the submerged structure of the second seep site. Further examination and analysis revealed that the seeps comprise hard deposits of calcium carbonate, and that the organisms are clams and polychaetes which are probably chemosymbiotic. The origin of the seep gas is hypothesized to be the natural decay of organic matter in the sapropel sediment, leading to the production of methane. Circulating fluids, which carry the dissolved gas through preferential pathways along small faults or bedding planes, percolate through the seafloor, precipitate calcium carbonate, release gas, and support the benthic organisms.     

南海西部海域新生代地质构造

南海西部海域地质构造复杂,以北东、北西和近南北向断裂构成区域性格架,重力异常和磁力异常具有明显方向性,地震剖面反映新生代地层可划分出上、中、下三套构造层,深部地壳结构变化较大,地壳强烈减薄,甚至出现了洋壳。此外,南海西部海域发育了一系列新生代沉积盆地,是南海地区一个重要的油气聚集带。本文通过收集多年来的地质一地球物理调查成果,从宏观上综合研究了这一地区的地球物理场和地质构造特征及地壳结构,为评价这一地区的油气资源潜力提供基础背景资料。     

浅剖资料在南海北部东沙西南海域水合物调查中的应用

南海北部东沙海域陆坡已经被证实为天然气水合物前景分布区,浅地层剖面数据以其高效率采集过程和浅表层高分辨率的特点被国内外学者应用到天然气水合物调查中并取得了很多成果。以南海北部东沙西南海域的两条浅剖测线为例,分析了该区浅表层沉积物的声学特征,并在浅剖剖面上发现了浅层含气带以及气体泄露现象,初步推测为深部的天然气水合物分解后通过断层运移到浅层中形成了浅层含气带,部分浅层气体还通过泄露点喷射到海水中从而形成了剖面中的气体泄露现象。最后,进一步通过对研究区域的沉积及气源条件、温压条件、地质及生物证据的讨论,证实该区具有天然气水合物发育的基本条件,因此,可以证实上述浅剖资料解释中关于天然气水合物的推测。     

Evidence of NW extension of the North Anatolian Fault Zone in the Marmara Sea: a new interpretation of the Marmara Sea (Izmit) earthquake on 17 August 1999

Active faults aligning in NW–SE direction and forming flower structures of strike-slip faults were observed in shallow seismic data from the shelf offshore of Avcılar in the northern Marmara Sea. By following the parallel drainage pattern and scarps, these faults were traced as NW–SE-directed lineaments in the morphology of the northern onshore sector of the Marmara Sea (eastern Thrace Peninsula). Right-lateral displacements in two watersheds of drainage and on the coast of the Marmara Sea and Black Sea are associated with these lineaments. This right-lateral displacement along the course of these faults suggests a new, active strike-slip fault zone located at the NW extension of the northern boundary fault of the ?ınarcık Basin in the Marmara Sea. This new fault zone is interpreted as the NW extension of the northern branch of the North Anatolian Fault Zone (NAFZ), extending from the ?ınarcık Basin of the Marmara Sea to the Black Sea coast of the Thrace Peninsula, and passing through B üy ük ?ekmece and K ü ? ük ?ekmece lagoons. These data suggest that the rupture of the 17 August 1999 earthquake in the NAFZ may have extended through Avcılar. Indeed, Avcılar and İzmit, both located on the Marmara Sea coast along the rupture route, were strongly struck by the earthquake whereas the settlements between Avcılar and İzmit were much less affected. Therefore, this interpretation can explain the extraordinary damage in Avcılar, based on the newly discovered rupture of the NAFZ in the Marmara Sea. However, this suggestion needs to be confirmed by further seismological studies.     

Evidence of NW extension of the North Anatolian Fault Zone in the Marmara Sea: a new interpretation of the Marmara Sea (İzmit) earthquake on 17 August 1999

Active faults aligning in NW–SE direction and forming flower structures of strike-slip faults were observed in shallow seismic data from the shelf offshore of Avc?lar in the northern Marmara Sea. By following the parallel drainage pattern and scarps, these faults were traced as NW–SE-directed lineaments in the morphology of the northern onshore sector of the Marmara Sea (eastern Thrace Peninsula). Right-lateral displacements in two watersheds of drainage and on the coast of the Marmara Sea and Black Sea are associated with these lineaments. This right-lateral displacement along the course of these faults suggests a new, active strike-slip fault zone located at the NW extension of the northern boundary fault of the Ç?narc?k Basin in the Marmara Sea. This new fault zone is interpreted as the NW extension of the northern branch of the North Anatolian Fault Zone (NAFZ), extending from the Ç?narc?k Basin of the Marmara Sea to the Black Sea coast of the Thrace Peninsula, and passing through B üy ük çekmece and K ü ç ük çekmece lagoons. These data suggest that the rupture of the 17 August 1999 earthquake in the NAFZ may have extended through Avc?lar. Indeed, Avc?lar and ?zmit, both located on the Marmara Sea coast along the rupture route, were strongly struck by the earthquake whereas the settlements between Avc?lar and ?zmit were much less affected. Therefore, this interpretation can explain the extraordinary damage in Avc?lar, based on the newly discovered rupture of the NAFZ in the Marmara Sea. However, this suggestion needs to be confirmed by further seismological studies.     

Seismic evidence for gas accumulation related to the area of mud volcanism in the deep Black Sea

 Bright spots were observed on seismic time sections acquired in 1991 and 1993 during cruises carried out within the UNESCO-ESF Training-through-Research (TTR) program in the deep Black Sea mud volcanic area. We demonstrate the results of detailed study of the anomalous reflections, which indicate that gas is responsible for the bright spots in the study area. Most of the bright spots are characterized by inverted polarity and enlarged elastic energy attenuation.     

Authigenic carbonates from the eastern Black Sea as an archive for shallow gas hydrate dynamics – Results from the combination of CT imaging with mineralogical and stable isotope analyses

Authigenic carbonates associated with cold seeps provide valuable archives of changes in the long-term seepage activity. To investigate the role of shallow-buried hydrates on the seepage strength and fluid composition we analysed methane-derived carbonate precipitates from a high-flux hydrocarbon seepage area (“Batumi seep area”) located on the south-eastern Black Sea slope in ca. 850 m. In a novel approach, we combined computerized X-ray tomography (CT) with mineralogical and isotope geochemical methods to get additional insights into the three-dimensional internal structure of the carbonate build-ups.     

Deep structure and selected aspects of the oil and gas potential of the southern seas of Russia

Regional deep seismic sounding—refracted wave seismic profiles across the Sea of Azov, the Caspian, and the Black seas carried out by the Shirshov Institute of Oceanology, Russian Academy of Sciences, in 1957–2002 with the use ocean bottom seismographs—provided information on the deep structure of the regions studied. Multichannel seismic profiling helped to refine the structure of the sedimentary cover. A combined interpretation of the reflection and refraction data allowed us to construct structural-lithological models of the southern seas of Russia and to estimate their oil and gas potential.     

Multi-beam and seismic investigations of the active Haima cold seeps,northwestern South China Sea

To confirm the seabed fluid flow at the Haima cold seeps, an integrated study of multi-beam and seismic data reveals the morphology and fate of four bubble plumes and investigates the detailed subsurface structure of the active seepage area. The shapes of bubble plumes are not constant and influenced by the northeastward bottom currents, but the water depth where these bubble plumes disappear (630–650 m below the sea level) (mbsl) is very close to the upper limit of the gas hydrate stability zone in the water column (620 m below the sea level), as calculated from the CTD data within the study area, supporting the “hydrate skin” hypothesis. Gas chimneys directly below the bottom simulating reflectors, found at most sites, are speculated as essential pathways for both thermogenic gas and biogenic gas migrating from deep formations to the gas hydrate stability zone. The fracture network on the top of the basement uplift may be heavily gas-charged, which accounts for the chimney with several kilometers in diameter (beneath Plumes B and C). The much smaller gas chimney (beneath Plume D) may stem from gas saturated localized strong permeability zone. High-resolution seismic profiles reveal pipe-like structures, characterized by stacked localized amplitude anomalies, just beneath all the plumes, which act as the fluid conduits conveying gas from the gas hydrate-bearing sediments to the seafloor, feeding the gas plumes. The differences between these pipe-like structures indicate the dynamic process of gas seepage, which may be controlled by the build-up and dissipation of pore pressure. The 3D seismic data show high saturated gas hydrates with high RMS amplitude tend to cluster on the periphery of the gas chimney. Understanding the fluid migration and hydrate accumulation pattern of the Haima cold seeps can aid in the further exploration and study on the dynamic gas hydrate system in the South China Sea.