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Anomalously intensive gas seeps on the sea surface due to damage to the Nord Stream 1 and Nord Stream 2 subsea gas pipelines in the Baltic Sea have been analyzed using optical (Kanopus-V and Sentinel-2B) and radar (Sentinel-1A) satellite images. Positive contrasts of NRCS (up to 7.5 dB) registered by Sentinel-1A radar and of spectral reflectance (up to 0.73 units) registered by Kanopus-V and Sentinel-2B optical sensors have been detected in the area of the gas seeps. Specific features of the seeps were revealed on the sea surface in the form of dome-shaped swells, fountains, vortices, foam, wave breaking, disturbance of the surface wave structure, and wind shadows. Taking into consideration the volume and density of gas located in the damaged gas pipelines, it was shown that the total volume of methane emission was no more than ~0.51 Tg, i.e., less than 0.1% of the annual global methane emissions into the atmosphere. [ABSTRACT FROM AUTHOR]

A wide range of geological and geophysical methods was carried out on the Yamal Peninsula in the Arctic in the period 2014–2022. The results were analyzed together with data from remote sensing of the Earth. Fundamentally new data on the gas-dynamic mechanisms of dangerous processes in permafrost have been obtained. These data included catastrophic gas blowouts and explosions with the formation of giant craters. More than three thousand zones of powerful gas blowouts with the formation of craters at the bottom of thermokarst lakes, rivers, and the coast of the Kara Sea have been discovered. According to data on remote sensing of the Earth, large mud volcanic structures, located at the bottom of the Labvarto and Yambuto thermokarst lakes, were discovered on the Yamal Peninsula in 2022–2023 for the first time. Monitoring of their state with the use of retrospective satellite images showed the presence of periodic release of underground fluids, including gas. A conclusion was made about the discovery of active mud volcanoes on the Yamal Peninsula. [ABSTRACT FROM AUTHOR]

The Russian sector of the arctic shelf is the longest in the world. Quite a lot of places of massive discharge of bubble methane from the seabed into the water column and further into the atmosphere were found there. This natural phenomenon requires an extensive complex of geological, biological, geophysical, and chemical studies. This article is devoted to aspects of the use of a complex of marine geophysical equipment applied in the Russian sector of the arctic shelf for the detection and study of areas of the water and sedimentary strata with increased saturation with natural gases, as well as a description of some of the results obtained. This complex contains a single-beam scientific high-frequency echo sounder and multibeam system, a sub-bottom profiler, ocean-bottom seismographs, and equipment for continuous seismoacoustic profiling and electrical exploration. The experience of using the above equipment and the examples of the results obtained in the Laptev Sea have shown that these marine geophysical methods are effective and of particular importance for solving most problems related to the detection, mapping, quantification, and monitoring of underwater gas release from the bottom sediments of the shelf zone of the arctic seas, as well as the study of upper and deeper geological roots of gas emission and their relationship with tectonic processes. Geophysical surveys have a significant performance advantage compared to any contact methods. The large-scale application of a wide range of marine geophysical methods is essential for a comprehensive study of the geohazards of vast shelf zones, which have significant potential for economic use. [ABSTRACT FROM AUTHOR]

The distribution map of submarine landslides in the Sea of Okhotsk based on compilation of available data is presented in this work for the first time. This map is indicative of environments and trigger mechanisms of landsliding. All gravitational processes studied in this work occurred in the environments of an open continental slope and submarine canyons. The most obvious trigger mechanisms of landslides on the Eastern Sakhalin slope are seismic activity and gas seeping. The main trigger mechanism of landslides on the northern slope of the Kuril Basin and in the back-arc basin of the Kuril island arc is seismic activity. [ABSTRACT FROM AUTHOR]

The Russian sector of the arctic shelf is the longest in the world. Quite a lot of places of massive discharge of bubble methane from the seabed into the water column and further into the atmosphere were found there. This natural phenomenon requires an extensive complex of geological, biological, geophysical, and chemical studies. This article is devoted to aspects of the use of a complex of marine geophysical equipment applied in the Russian sector of the arctic shelf for the detection and study of areas of the water and sedimentary strata with increased saturation with natural gases, as well as a description of some of the results obtained. This complex contains a single-beam scientific high-frequency echo sounder and multibeam system, a sub-bottom profiler, ocean-bottom seismographs, and equipment for continuous seismoacoustic profiling and electrical exploration. The experience of using the above equipment and the examples of the results obtained in the Laptev Sea have shown that these marine geophysical methods are effective and of particular importance for solving most problems related to the detection, mapping, quantification, and monitoring of underwater gas release from the bottom sediments of the shelf zone of the arctic seas, as well as the study of upper and deeper geological roots of gas emission and their relationship with tectonic processes. Geophysical surveys have a significant performance advantage compared to any contact methods. The large-scale application of a wide range of marine geophysical methods is essential for a comprehensive study of the geohazards of vast shelf zones, which have significant potential for economic use.

The highest concentration of cold seep sites worldwide has been observed along convergent margins, where fluid migration through sedimentary sequences is enhanced by tectonic deformation and dewatering of marine sediments. In these regions, gas seeps support thriving chemosynthetic ecosystems increasing productivity and biodiversity along the margin. In this paper, we combine seismic reflection, multibeam and split-beam hydroacoustic data to identify, map and characterize five known sites of active gas seepage. The study area, on the southern Hikurangi Margin off the North Island of Aotearoa/New Zealand, is a well-established gas hydrate province and has widespread evidence for methane seepage. The combination of seismic and hydroacoustic data enable us to investigate the geological structures underlying the seep sites, the origin of the gas in the subsurface and the associated distribution of gas flares emanating from the seabed. Using multi-frequency split-beam echosounder (EK60) data we constrain the volume of gas released at the targeted seep sites that lie between 1,110 and 2,060 m deep. We estimate the total deep-water seeps in the study area emission between 8.66 and 27.21 × 106 kg of methane gas per year. Moreover, we extrpolate methane fluxes for the whole Hikurangi Margin based on an existing gas seep database, that range between 2.77 × 108 and 9.32 × 108 kg of methane released each year. These estimates can result in a potential decrease of regional pH of 0.015–0.166 relative to the background value of 7.962. This study provides the most quantitative assessment to date of total methane release on the Hikurangi Margin. The results have implications for understanding what drives variation in seafloor biological communities and ocean biogeochemistry in subduction margin cold seep sites.

The purpose of this work was to analyze the causes of intensive gas emission in the central part of the Laptev Sea. On the basis of a seismic survey of the JSC Marine Arctic Geological Expedition, the wave fields have been studied on 28 profiles with a total length of 5930 km. Zones with refracted waves from the high-velocity horizons, associated with frozen sediments and possible occurrence of gas hydrates, have been revealed. For the first time for the region, a cartographic scheme of change in the refracted wave propagation velocity and physical state of bottom sediments (frozen or thaw) has been created. The absence of permafrost and gas hydrates in the area of active gas emission was proved, and the deep origin of gas and its migration along tectonic faults were grounded. [ABSTRACT FROM AUTHOR]

High-resolution marine seismic reflection studies on the eastern shelf of the Saros Gulf have revealed the presence of gascharged sediments across a narrow submarine valley incised by the Ganos Fault along the North Anatolian Fault system. Quaternary sediments, accumulated during glacial and interglacial periods through transgressional and progradational units, were controlled by glacio-eustatic sea-level fluctuations and tectonic deformation. The transgressional units made of upward-fining deposits created seals at their tops to form gas accumulation pockets. Conversely, the progradational units appear heavily eroded at their top, which is unfavorable for gas accumulation. The sediment's gas accumulation features include enhanced reflections, acoustic blanking (or blanket), acoustic turbidity, acoustic curtain, and acoustic columns. In contrast, the gas escape features consist of acoustic plumes, cloudy turbidity, domes, and pockmarks. Their concentration along the Ganos Fault indicates that active deformation, punctuated by large magnitude earthquakes, has played an essential role in their formation, storage, and seep. Understanding these interactions may provide valuable contributions to hydrocarbon explorations and early-warning strategies against earthquake risk. [ABSTRACT FROM AUTHOR]

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.

Among the 26 nature reserves established in the Transylvanian Basin, 13 have the status of geological reserves, and four of them are represented by mud volcanoes. Active volcanoes currently occur only in the area of Băile Homorod. The other three reserves, Filiaş, Monor and Hăşag, represent mud volcanoes in their late stage of development. Assessment of these four reserves indicate that they show scientific importance, but only those from Homorod present interesting feature of active mud volcanoes as well as a high scientific value. Educational and touristic values of the three reserves with inactive mud volcanoes are rather limited, especially that they are remotely situated and they are more difficult to find, as there are no signs for location or explanatory panels. Also, the risk of degradation of the three inactive mud volcano fields are greater, due to cessation of their activity, possibly caused by exhaustion of gases generating them, or drying of the groundwater level crossed by the gases in their way to the surface. [ABSTRACT FROM AUTHOR]

The presence of gas hydrates (GHs) increases the stiffness and strength of marine sediments. In elasto‐plastic constitutive models, it is common to consider GH saturation (Sh) as key internal variable for defining the contribution of GHs to composite soil mechanical behavior. However, the stress‐strain behavior of GH‐bearing sediments (GHBS) also depends on the microscale distribution of GH and on GH‐sediment fabrics. A thorough analysis of GHBS is difficult, because there is no unique relation between Sh and GH morphology. To improve the understanding of stress‐strain behavior of GHBS in terms of established soil models, this study summarizes results from triaxial compression tests with different Sh, pore fluids, effective confining stresses, and strain histories. Our data indicate that the mechanical behavior of GHBS strongly depends on Sh and GH morphology, and also on the strain‐induced alteration of GH‐sediment fabrics. Hardening‐softening characteristics of GHBS are strain rate‐dependent, which suggests that GH‐sediment fabrics dynamically rearrange during plastic yielding events. We hypothesize that rearrangement of GH‐sediment fabrics, through viscous deformation or transient dissociation and reformation of GHs, results in kinematic hardening, suppressed softening, and secondary strength recovery, which could potentially mitigate or counteract large‐strain failure events. For constitutive modeling approaches, we suggest that strain rate‐dependent micromechanical effects from alterations of the GH‐sediment fabrics can be lumped into a nonconstant residual friction parameter. We propose simple empirical evolution functions for the mechanical properties and calibrate the model parameters against the experimental data. Plain Language Summary: Gas hydrates (GHs) are crystalline‐like solids, which are formed from natural gas molecules and water at high pressure and low temperature. GHs, and particularly methane hydrates, are naturally abundant in marine sediments. It is known that the presence of GH increases the mechanical stiffness and strength of sediments, and there is strong effort in analyzing and quantifying these effects in order to understand potential risks of sediment destabilization or slope failure. Based on our experimental results from high‐pressure geotechnical studies, we show that not only the initial amount and distribution of GH are important for the increased strength of GH‐bearing sediments but also the dynamic rearrangement of GH‐sediment fabrics during deformation characterizes the stress‐strain response and enables strength recovery after failure. We propose that different microstructural mechanisms contribute to this rearrangement and strength recovery of GH sediment. However, we consider these complicated processes in a simplified manner in an improved numerical model, which can be applied for geotechnical risk assessment on larger scales. Key Points: The mechanical properties and hardening‐softening characteristics of gas hydrate‐bearing sediments are dependent on strain ratesHardening‐softening behavior and strength evolution depend on structural alterations and dynamic rearrangement of gas hydrate‐sediment fabricsThe effects of strain rate‐dependent structural alterations can be conceptualized as a nonconstant residual friction term in soil mechanical modeling [ABSTRACT FROM AUTHOR]

Hydrogen gas is seeping from the sedimentary basin of São Franciso, Brazil. The seepages of H2 are accompanied by helium, whose isotopes reveal a strong crustal signature. Geophysical data indicates that this intra-cratonic basin is characterized by (i) a relatively high geothermal gradient, (ii) deep faults delineating a horst and graben structure and affecting the entire sedimentary sequence, (iii) archean to paleoproterozoïc basements enriched in radiogenic elements and displaying mafic and ultramafic units, and (iv) a possible karstic reservoir located 400 m below the surface. The high geothermal gradient could be due to a thin lithosphere enriched in radiogenic elements, which can also contribute to a massive radiolysis process of water at depth, releasing a significant amount of H2. Alternatively, ultramafic rocks that may have generated H2 during their serpentinization are also documented in the basement. The seismic profiles show that the faults seen at the surface are deeply rooted in the basement, and can drain deep fluids to shallow depths in a short time scale. The carbonate reservoirs within the Bambuí group which forms the main part of the sedimentary layers, are crossed by the fault system and represent good candidates for temporary H2 accumulation zones. The formation by chemical dissolution of sinkholes located at 400 m depth might explain the presence of sub-circular depressions seen at the surface. These sinkholes might control the migration of gas from temporary storage reservoirs in the upper layer of the Bambuí formation to the surface. The fluxes of H2 escaping out of these structures, which have been recently documented, are discussed in light of the newly developed H2 production model in the Precambrian continental crust.

The aim of Stage 1 of the FNI project GEOHydrate is to prove the hypothesis that gas hydrates deposits (GHDs) create measurable temperature and heat flow (T&HF) anomalies on the seafloor. We use a PetroMod™ model for 98 Ma basin analysis of the Western Black Sea basin, developed in GEOMAR, FRG. The model was run 2 times - with and without GH formation. The resultant difference of the heat flows on the seabed shows average heat flow anomaly above GHDs of 7 mW/m² and a maximum of 15 mW/m². [ABSTRACT FROM AUTHOR]

The aim of this work is to reconstruct the variations of the total gas hydrate (GH) masses of the Danube deep-sea fan after 0.265 Ma BP. The PetroMod™ model developed in GEOMAR, Germany is for basin analysis of the Western Black Sea for 98 Ma. Geological structure is from 2D seismic of the Black Sea consortium "Geology without limits". Results show a trend for total GH masses decrease after Middle Pleistocene and the role of the GHs as sink and source of methane. [ABSTRACT FROM AUTHOR]

Methane emissions out of the seabed could seriously affect Earth's climate and are usually associated with the dissociation of gas hydrates stored in marine sediments on the continental margins. Spatially, gas emissions out of the seafloor are not evenly distributed in continental margins. Gas emissions out of the seabed generally occur through submarine mud volcanoes and gas seeps. To understand the seabed gas emissions off SW Taiwan, we investigate the distributions of active submarine mud volcanoes, gas seeps, and gas plumes off SW Taiwan. We examine all of the available sub-bottom profiler and EK echo sounder data. We identified 19 submarine mud volcanoes, 220 gas seeps, and 295 gas plumes. The gas emissions are generally distributed at the crests of mud diapiric ridges. Most of the active mud volcanoes and gas seeps cluster at the KASMVG (Kaoping submarine mud volcanoes group) area. We speculate that the intensive mud volcanism and gas seepage at the KASMVG area are ascribed to submarine channel erosion along the continental slope base. The erosion causes a deep V-shaped channel and a steep BSR (Bottom-Simulating Reflector) slope curve across the continental margin. The upward migration rate of free gas beneath the BSR is thus increased and intensifies mud volcanism and gas seepage at the KASMVG area. The gas seeps can reduce the slope stability and generate small-scale slides. The development of mud volcanoes in an area could effectively disturb the seabed morphology so that large-scale submarine landslides cannot easily happen. [ABSTRACT FROM AUTHOR]

Gas hydrate provinces occur in two sedimentary basins along Brazil’s continental margin: (1) The Rio Grande Cone in the southeast, and (2) the Amazon deep-sea fan in the equatorial region. The occurrence of gas hydrates in these depocenters was first detected geophysically and has recently been proven by seafloor sampling of gas vents, detected as water column acoustic anomalies rising from seafloor depressions (pockmarks) and/or mounds, many associated with seafloor faults formed by the gravitational collapse of both depocenters. The gas vents include typical features of cold seep systems, including shallow sulphate reduction depths (

This study investigated the zones associated with the potential distribution and absence of frozen ground and gas hydrates on the East Siberian Arctic Shelf in the Laptev and East Siberian seas. The investigation was based on an analysis of velocities of refracted waves registered as first breaks from common-shot gathers along 71 common depth point seismic lines with a total length of 15 630 km acquired by JSC MAGE in 2007–2016. Consequently, essentially new data that illustrate the state of the cryolithozone on the East Siberian Arctic Shelf were obtained. In particular, this study confirmed a significant decrease in the area of possible existence of frozen ground and methane hydrates in the postglacial period. Based on an extensive analysis of subsea frozen ground degradation zones on the shelves of the Laptev, East Siberian, Chukchi, and Beaufort seas (∼57% of the total area), it can be concluded that there is a low probability of considerable contribution of methane, being released from the dissociating gas hydrates, to climate change. • Seismic refracted wave velocities in shallow subsurface were analyzed for seismic lines with total length of 15630 km. • Large decrease of the area with possible frozen ground and gas hydrate existence was substantiated for the shelf. • Frozen ground has degraded in most part of the shallow water area of the Laptev, East Siberian, Chukchi and Beaufort seas. • Gas hydrate dissociation in shallow water areas of the Arctic seas must not contribute significantly to climate change. [ABSTRACT FROM AUTHOR]

Seismic resolution and illumination issues are sources of challenges in the detailed imaging and detection of subsurface fault architecture and fluid migration. Improved constraints on resolution can provide input into monitoring requirements and detectability of CO 2 leakage, and fault-sealing properties during subsurface visualization of migration pathways. This study explores detection and resolution thresholds via synthetic seismic imaging of a detailed shallow normal fault model with realistic fault architecture including sub-seismic structures of damage zones. The base fault model is built from interpretations of high-resolution P-Cable seismic data and is further developed and conditioned by outcrop-based observations and empirical laws for fracture and deformation band distribution. Damage zones of sandstone layers host deformation bands contrary to shale layers with fractures, while mixed lithologies (shaley sandstone and sandy shale) are subjected to a combination of the two deformation mechanisms. We utilize a 2D point-spread function based convolution seismic modelling to produce the synthetic seismic images. Test scenarios include one baseline fault model without a damage zone (M1), and five more advanced/detailed fault models incorporating features known from outcrops (M2-M6; damage zones, an isolated fracture corridor, and gas seeps (CO 2) along damage zones of faults and in the fracture corridor). Furthermore, sensitivity analyses on two selected models test the effect of changing the illumination angle and wavelet. The results show that: (1) faults with damage zones have larger disturbances in seismic signals than faults without damage zones, (2) stronger amplitudes are distinguished for models with CO 2 -filled fractures, (3) a fracture corridor (5 m at it widest) is clearly visible where it crosses horizons bounding horizontal layers, (4) sensitivity tests show good imaging for illumination ≥45°, which is the average dip of the main fault segment, and (5) learnings from fault modelling offer guidance for seismic monitoring. • Seismic imaging and detection of faults in seismic data with different resolutions. • Building realistic fault models with damage zones and an isolated fracture corridor. • Exploring fault models by seismic modelling to address resolution and illumination limitations in seismic data. • Testing effects of gas (CO 2) in the fault damage zone and fracture corridor. [ABSTRACT FROM AUTHOR]

Experiments on bubble formation from a granular medium are presented. The granular medium consisted of immersed stones giving a sediment bed thickness of 10 cm. High speed photographic and acoustic passive wireless techniques were employed to obtain the bubble size. The power spectra of the acoustic data for bubble production of 0.5 bubbles/s showed the existence of two principal peaks which are correlated with two discrete events. Firstly, a signal peak at 0.497 kHz, representing asymmetric bubble detachment, and secondly, a peak at 2.070 kHz, which corresponded to interactions of the granular media as inter-particle gaps advance, representing elastic resistance to orifice creation. Provided the signals were windowed to the bubble-detachment event only, the classical bubble-acoustical Minnaert relation for the bubble size agreed with optical data within about 10%. Since seepage generates discrete bubble pulses, appropriate acoustic analyses could both count and size the bubbles formed. The results of this study lead to the proposition that underwater acoustic sensors could warn of critical changes in bubble-seep behavior over time. This could lead to the possibility of remote early warnings, because shifts in production-rate regimes from seeps may herald alterations in the progression of global warming, or impending earthquakes and tsunamis. [ABSTRACT FROM AUTHOR]

Alunite minerals occur as white powdery lumps and laminated coloured deposits within cavity and solution channel infill of the palaeokarst zone of the Upper Eocene Dammam Formation. This formation is exposed in a quarry located on the Al Ahmadi ridge within the Greater Burgan oil field in southern Kuwait. Field occurrences and sedimentary structures of the alunite deposits were described. Collected samples were petrographically described, and their mineralogy and geochemistry were determined using X-ray diffraction and X-ray fluorescence, respectively. Microfabrics were investigated using SEM, revealing that they are primarily composed of fibrous alunogen (hydrous aluminium sulphate) and pseudo-cubical K-alunite (hydrous potassium aluminium sulphate). Their mode of occurrence suggests a hypogenetic origin, where sulphide gases associated with hydrocarbon gases reacted with an Al-rich solution leached from clay minerals and feldspars of the cavity-fill muddy sand sediments. The hydrocarbon gases may have seeped from sub-surface petroliferous formations within the Greater Burgan oil field along vertical fractures. This study suggests that these acidic seeps may have played a role in the development of the palaeokarst zone of the Dammam Formation. [ABSTRACT FROM AUTHOR]

The continental slope of the Canadian Beaufort Sea presents an exceptional opportunity to study the relationship between the fluid venting and the formation of mass-transport deposits. The continental shelf was emergent and partially ice-free during the last glaciation and is underlain by widespread permafrost. Water-column backscatter has shown the locations of more than 40 active gas vents along seaward margin of the subsea permafrost at the shelf break and upper slope. New multibeam bathymetry and subbottom profiler data show shallow potentially late Holocene failures and mass-transport deposits on the upper slope. Upslope from a prominent headscarp, undulating seabed with apparent growth faults overlies an acoustically incoherent to stratified horizon at 50 m sub-bottom interpreted as a decollement surface over which progressive creep has occurred. Similar creep is present in places on the upper slope and in places seems to have evolved into small translational slides, involving more compacted sediment buried > 25 m, or into muddy debris flows where sediments buried < 25 m have failed. Much of the slope failed during a regional retrogressive event, the Ikit slump, likely initiated on steep channel walls on the lower slope. Characteristic ridge and trough morphology resulting from retrogressive spreading or rotational slumping are preserved on gradients < 2° on the upper slope, but appear to have been completely evacuated on gradients of 3° on the mid slope, where muddy debris-flow deposits are found. Correlations between radiocarbon dated cores and sub-bottom profiles show that the retrogressive failure occurred in the last 1000 years. This study implies that Holocene shelf break and upper slope stability in the Beaufort Sea are strongly linked to the dynamics of the permafrost and the presence of weak, gas-rich sediments. It demonstrates that creep deformation evolves into either muddy debris flows or translational slides, dependent on sediment strength. [ABSTRACT FROM AUTHOR]

Abstract: Considerable seepage of natural gas occurs throughout the Katakolo Bay, both at sea and on land, along the Ionian coast of Peloponnesus (Western Greece). Explosive levels of CH4 and toxic concentrations of H2S accumulating in the ground, pose a severe hazard for humans and tourist infrastructures. A wide offshore and onshore gas survey, including marine remote sensing, underwater exploration by a towed instrumented system, compositional and isotopic analyses, and flux measurements of gas, allowed us to assess that: (a) gas seepage takes place along two main normal faults; (b) offshore side-scan sonographs recorded at least 823 gas bubble plumes over an area of 94,200m2, at depths ranging from 5.5 to 16m; (c) offshore and onshore seeps release the same type of thermogenic gas (δ 13CCH4 ~−34 to −36‰); (d) offshore gas showed increased stable carbon isotopic ratio of CO2 and propane, which suggests enhanced biodegradation of hydrocarbons; (e) isotopic data combined with thermogenic gas generation modeling and maturity plots, suggest that the gas is related to a deep Petroleum System with Jurassic carbonate reservoirs, Triassic source rocks, and Triassic evaporites; (f) H2S (δ 34S: +2.4‰) is produced by thermochemical sulfate reduction in deep anhydrites, in contact with hydrocarbon-rich carbonates; (g) due to the shallow depth, more than 90% of CH4 released at the seabed enters the atmosphere, consistent with theoretical bubble dissolution models, with a mean plume output of 0.12kgd−1; total offshore CH4 output was estimated in the range of 33 to 120ty−1; and (h) in the onshore area at least 50 gas vents in the harbor and a large seep on the adjacent Faros hill, emit in total about 89tCH4 y−1. Katakolo results to be one of the biggest thermogenic gas seepage zones in Europe. [Copyright &y& Elsevier]

Abstract: The UK’s first well to encounter shale gas was drilled into the Upper Jurassic Kimmeridge Clay in 1875, but its significance was not realised at the time. 25 years ago research at Imperial College applied the US shale gas paradigm to evaluate the UK’s shale gas potential. Shale sequences with potential for gas production were identified in Carboniferous strata in the Midlands, and in Jurassic strata, particularly in the Weald. Without encouragement from Her Majesty’s Government no exploration resulted from this initial research. Publication of the results of the project was rejected by many UK journals. It was finally published in the USA in 1987. Subsequent evaluations of UK petroleum resources by the Department of Energy and its descendants published in 2001 and 2003 omitted any mention of shale gas resources. Recent timely re-evaluations of the UK’s shale gas potential have been carried out by the British Geological Survey and the Department for Energy & Climate Change. In 2008 the 13th Round of Onshore Licensing resulted in the award of several blocks for shale gas exploration, though bids were often based on a quest for both shale gas and conventional prospects. Cuadrilla Resource’s Preese Hall No. 1 well drilled in 2010 was the first well drilled to specifically test for UK shale gas. The same drilling and fracturing techniques that led to the shale gas renaissance in the USA are now being applied to extracting oil from organic-rich shales that are currently in the oil window. It is interesting to speculate that oil may be produced by such techniques from the thermally mature Jurassic shales in the Wessex and Weald basins in the southern UK. [Copyright &y& Elsevier]

This review describes methodology and software developments for acoustic data acquisition and determining parameters of gas bubble streams; shows geographical distribution of more than 3000 seeps in the Black Sea; presents data on methane fluxes from the deep-sea mud volcanoes; gives a model for evaluation of gas exchange in the water environment and methane emission from gas seeps to water column and atmosphere; explains modern views on the impact of cold seeps on the hydrochemical characteristics of the marine environment, the vertical water exchange, methanotrophic chemosynthesis and trophic structure of water; reveals a new form of life in the anoxic water column of the Black Sea, which is represented by a symbiotic community of anaerobic archaea and methane oxidizing and sulfate-reducing bacteria; contains estimates of potential environmental hazards due to methane discharge from the bottom of the Black Sea, and outlooks the possible use of cold seeps as a resource factors because they can be indications for shallow or deep hydrocarbon accumulations. [ABSTRACT FROM AUTHOR]

Abstract: Multi-scale gravitational instabilities are widespread in the Coastal Ranges of the North Island of New Zealand. We document here a detailed analysis of the Waitawhiti landslide complex, located in the core of the Tawhero syncline, and investigate the potential landslides triggering factors in the area. Four contiguous large slides form the Waitawhiti complex. These slides involve fine-grained Miocene sandstones and massive fractured siltstones. Sliding occurs mostly along nearly horizontal strata. All slides are bounded laterally and/or distally by deep-incised valleys. Three gas seeps evidencing thermogenic gas release have been discovered in the vicinity of the slides. We propose that river incision, continuously removing distal buttresses, is the main destabilizing factor in the area. However, additional factors, such as tectonic activity and intense rainfall, cannot be excluded. We also propose that fluid overpressure, reducing the effective shear strength at the base of low-permeability layers, may have influenced the triggering of landslides in the Waitawhiti area. [Copyright &y& Elsevier]

Meiobenthos densities and higher taxon composition were studied in an active gas seepage area at depths from 182 to 252 m in the submarine Dnieper Canyon located in the northwestern part of the Black Sea. The meiobenthos was represented by Ciliata, Foraminifera, Nematoda, Polychaeta, Bivalvia, Gastropoda, Amphipoda, and Acarina. Also present in the sediment samples were juvenile stages of Copepoda and Cladocera which may be of planktonic origin. Nematoda and Foraminifera were the dominant groups. The abundance of the meiobenthos varied between 2397 and 52,593 ind.·m−2. Maximum densities of Nematoda and Foraminifera were recorded in the upper sediment layer of a permanent H2S zone at depths from 220 to 250 m. This dense concentration of meiobenthos was found in an area where intense methane seeps were covered by methane-oxidizing microbial mats. Results suggest that methane and its microbial oxidation products are the factors responsible for the presence of a highly sulfidic and biologically productive zone characterized by specially adapted benthic groups. At the same time, an inverse correlation was found between meiofauna densities and methane concentrations in the uppermost sediment layers. The hypothesis is that the concentration of Nematoda and Foraminifera within the areas enriched with methane is an ecological compromise between the food requirements of these organisms and their adaptations to the toxic H2S. [ABSTRACT FROM AUTHOR]

Abstract: Expressions of gas seepage observable within North Sea seismic and acoustic data include seabed pockmarks, seepage plumes in the water column, acoustic blanking, shallow enhanced reflectors, and shallow seismic chimneys. Three areas were selected for a marine survey in which 60 vibrocores were taken. Gas content of the seabed sediment samples (methane and ethane concentrations of 2 to10,395vppm and 0.5 to 2.2vppm respectively were observed in the headspace gas) and carbon stable isotope ratios of methane (−88.3 to −30.5‰) were determined, in order to examine if geochemical anomalies confirm the interpretation of geophysical anomalies. In a few cases they did, whereas in other cases it was questionable whether only slightly elevated concentrations may be considered as a confirmation of the interpretation of geophysical anomalies. In the case of a seabed pockmark methane concentrations in headspace gas were elevated (122.6vppm) in the samples taken from the centre of the pockmark compared with 5–10vppm background values away from the pockmark. Very high concentrations of methane (up to 10,395vppm) were found near an active vent, which had previously been identified via a seepage plume in the water column. Shallow enhanced reflectors in a 2D seismic profile confirm the presence of gas in the subsurface at this site. The methane concentrations (5 to 172vppm) and carbon isotope ratios ranging from −88.9 to −30.5‰ found in samples taken above a Jurassic condensate field provide indications for leakage of a mixture of thermogenic and biogenic hydrocarbons to the seabed. [Copyright &y& Elsevier]

Microbial and thermogenic methane migrates towards the seabed where some is utilised during microbially-mediated anaerobic oxidation. Excess methane escapes as gas seeps, which occur in a variety of geological contexts in every sea and ocean, from inter-tidal zones to deep ocean trenches. Some seeps are localised, gentle emanations; others are vigorous covering areas of>1 km2; the most prolific seeps reported (offshore Georgia) produce ~40 t CH4 per year. Gas bubbles lose methane to the water as they rise, so deep water seeps are unlikely to contribute to the atmosphere. However, bubbles break the surface above some shallow water seeps. Estimates of the total methane contribution to the atmosphere are poorly constrained, largely because the data set is so small. 20 Tg yr-1 is considered a realistic first approximation. This is a significant contribution to the global budget, particularly as methane from seeps is14C-depleted. A seep measurement programme is urgently required. [ABSTRACT FROM AUTHOR]

Extensive deposits of methane hydrate characterize Hydrate Ridge in the Cascadia margin accretionary complex. The ridge has a northern peak at a depth of about 600 m, which is covered by extensive carbonate deposits, and an 800 m deep southern peak that is predominantly sediment covered. Samples collected with benthic instrumentation and from Alvin push cores reveal a complex hydrogeologic system where fluid and methane fluxes from the seafloor vary by several orders of magnitude at sites separated by distances of only a few meters. We identified three distinct active fluid regimes at Hydrate Ridge. The first province is represented by discrete sites of methane gas ebullition, where the bulk of the flow occurs through channels in which gas velocities reach 1 m s−1. At the northern summit of the ridge the gas discharge appears to be driven by pressure changes on a deep gas reservoir, and it is released episodically at a rate of ∼6×104 mol day−1 following tidal periodicity. Qualitative observations at the southern peak suggest that the gas discharge there is driven by more localized phenomena, possibly associated with destabilization of massive gas hydrate deposits at the seafloor. The second province is characterized by the presence of extensive bacterial mats that overlay sediments capped with methane hydrate crusts, both at the northern and southern summits. Here fluid typically flows out of the sediments at rates ranging from 30 to 100 cm yr−1. The third province is represented by sites colonized by vesicomyid clams, where bottom seawater flows into the sediments for at least some fraction of the time. Away from the active gas release sites, fluid flows calculated from pore water models are in agreement with estimates using published flowmeter data and numerical model calculations. Methane fluxes out of mat-covered sites range from 30 to 90 mmol m−2 day−1, whereas at clam sites the methane flux is less than 1 mmol m−2 day−1. [Copyright &y& Elsevier]

Hydrogen gas is seeping from the sedimentary basin of São Franciso, Brazil. The seepages of H2 are accompanied by helium, whose isotopes reveal a strong crustal signature. Geophysical data indicates that this intra-cratonic basin is characterized by (i) a relatively high geothermal gradient, (ii) deep faults delineating a horst and graben structure and affecting the entire sedimentary sequence, (iii) archean to paleoproterozoïc basements enriched in radiogenic elements and displaying mafic and ultramafic units, and (iv) a possible karstic reservoir located 400 m below the surface. The high geothermal gradient could be due to a thin lithosphere enriched in radiogenic elements, which can also contribute to a massive radiolysis process of water at depth, releasing a significant amount of H2. Alternatively, ultramafic rocks that may have generated H2 during their serpentinization are also documented in the basement. The seismic profiles show that the faults seen at the surface are deeply rooted in the basement, and can drain deep fluids to shallow depths in a short time scale. The carbonate reservoirs within the Bambuí group which forms the main part of the sedimentary layers, are crossed by the fault system and represent good candidates for temporary H2 accumulation zones. The formation by chemical dissolution of sinkholes located at 400 m depth might explain the presence of sub-circular depressions seen at the surface. These sinkholes might control the migration of gas from temporary storage reservoirs in the upper layer of the Bambuí formation to the surface. The fluxes of H2 escaping out of these structures, which have been recently documented, are discussed in light of the newly developed H2 production model in the Precambrian continental crust. [ABSTRACT FROM AUTHOR]

Using an interdisciplinary approach, this paper reviews current knowledge in the field of natural hydrogen. For the first time, it combines perspectives on hydrogen from the literature of the former Eastern bloc with that of the West, including rare hardcopies and recent studies. Data are summarized and classified in three main sections: hydrogen as a free gas in different environments, as inclusions in various rock types, and as dissolved gas in ground water. This review conclusively demonstrates that molecular hydrogen is much more widespread in nature than was previously thought. Hydrogen has been detected at high concentrations, often as the major gas, in all types of geologic environment. A critical evaluation of all the proposed mechanisms regarding the origin of natural hydrogen shows that a deep-seated origin is potentially the most likely explanation for its abundance in nature. By combining available data, an estimate of 23 Tg/year for the total annual flow of hydrogen from geologic sources is proposed. This value is an order of magnitude greater than previous estimate but most likely still not large enough to account for recently discovered worldwide diffusive seepages. Hydrogen could play a critical role in mechanisms taking place in both the shallow and deep geospheres and it can influence a very wide range of natural phenomena. Hydrogen is an essential energy source for many microorganisms. Sampling for hydrogen can be a useful tool in studying natural environments, geologic mapping, monitoring of earthquakes, plotting fault traces and resource exploration. Hydrogen of geologic origin has the potential to become the renewable energy source of the future, with exploratory projects ongoing at the present time. The topic of natural hydrogen is therefore relevant from many different perspectives. [ABSTRACT FROM AUTHOR]

We analyse an area of high density submarine methane gas seeps situated on the shelf to slope transition (130–420 m water depth) on the northern region of New Zealand's Hikurangi margin, off Poverty Bay. Multibeam and singlebeam echo sounder data collected in 2014 and 2015 revealed >600 seeps, at much greater density than any previously mapped areas of seepage on the Hikurangi margin. To broadly constrain the output of methane from these seeps, we have estimated the flow of methane at individual seeps, utilising perspective-measurements applied to still frames from a deep towed camera system to measure the dimensions of rising bubbles. We combine bubble size and rise-rate distributions with singlebeam acoustic data to estimate gas flow rates at six selected seeps sites. Our results predict a wide range (3.0–2249 mL/min) of methane release into the water column. If we assume that the six seeps we analysed are representative of the entire seep population, and that gas flow is constant, we can extrapolate across the seep field and infer a gas release of 30 to 2415 t of methane per year into the ocean. • We report on methane seeps found at shallow depths on New Zealand's Hikurangi Margin. • Tools have been applied to measure bubble characteristics from video footage and to estimate the gas flow rate using acoustic data. • We estimate that the entire Tuaheni seep field produces somewhere in the range of 30–2415 t of methane per year. • The density of seeps at this location is far greater than anything else observed on the Hikurangi Margin. [ABSTRACT FROM AUTHOR]

Gas hydrate provinces occur in two sedimentary basins along Brazil's continental margin: (1) The Rio Grande Cone in the southeast, and (2) the Amazon deep-sea fan in the equatorial region. The occurrence of gas hydrates in these depocenters was first detected geophysically and has recently been proven by seafloor sampling of gas vents, detected as water column acoustic anomalies rising from seafloor depressions (pockmarks) and/or mounds, many associated with seafloor faults formed by the gravitational collapse of both depocenters. The gas vents include typical features of cold seep systems, including shallow sulphate reduction depths (<4 m), authigenic carbonate pavements, and chemosynthetic ecosystems. In both areas, gas sampled in hydrate and in sediments is dominantly formed by biogenic methane. Calculation of the methane hydrate stability zone for water temperatures in the two areas shows that gas vents occur along its feather edge (water depths between 510 and 760 m in the Rio Grande Cone and between 500 and 670 m in the Amazon deep-sea fan), but also in deeper waters within the stability zone. Gas venting along the feather edge of the stability zone could reflect gas hydrate dissociation and release to the oceans, as inferred on other continental margins, or upward fluid flow through the stability zone facilitated by tectonic structures recording the gravitational collapse of both depocenters. The potential quantity of venting gas on the Brazilian margin under different scenarios of natural or anthropogenic change requires further investigation. The studied areas provide natural laboratories where these critical processes can be analyzed and quantified. [ABSTRACT FROM AUTHOR]