Submarine Gas Research Articles

The Effects of Controlling Gas Escape and Bottom Current Activity on the Evolution of Pockmarks in the Northwest of the Xisha Uplift, South China Sea

Submarine pockmarks are typical indicators of submarine gas escape activity. The deep strata of the Xisha Uplift are rich in biogenic and thermogenic gas, accompanied by strong bottom current activity. Investigating the effects of controlling submarine gas escape and bottom current activity on the formation and development of pockmarks in the Xisha Uplift is significant for understanding the evolution of submarine topography and geomorphology. This study utilized high-resolution multibeam data to identify 261 submarine pockmarks in the northwest of the Xisha Uplift. These pockmarks were categorized based on their morphology into circular, elliptical, elongated, crescent-shaped, and irregular types. The diameters of pockmarks in the study area range from 0.21 to 4.96 km, with maximum depths reaching 30.88 m. Using high-resolution multi-channel seismic data, we conducted a detailed analysis of the subsurface strata characteristics of the pockmarks, identifying chaotic weak reflections, bright spots, and high-angle reflectors. We believe that deep gas in the northwest of the Xisha Uplift escapes to the seafloor through migration pathways, such as faults, fractures, and gas chimneys, resulting in the formation of submarine pockmarks. Bottom current activity has a significant impact on already-formed pockmarks. Crescent-shaped and elongated pockmarks in the Xisha Uplift are largely the result of bottom current modifications of pre-existing pockmarks.

Exploring ophiolitic deposits offshore Scoglio d’Affrica islet (northern Tyrrhenian Sea): A comprehensive geophysical model of the shallow crustal dynamics

The islet of Scoglio d’Affrica (Tuscany Archipelago, northern Tyrrhenian Sea) is an emerging segment of the Elba-Pianosa Ridge. This ridge is a major tectonic-structural high formed by Eocene-Early Miocene clastic succession which separates the Tuscany shelf from the Corsica basin. The distinctive structural setting of the Scoglio d’Affrica region is a result of crustal fragmentation during the extensional tectonic regime of the northern Tyrrhenian Sea. Along the Elba Pianosa Ridge, a complex interplay between Miocene magmatism, active submarine gas emissions and mud volcanism has been observed. Currently, the Scoglio d’Affrica region experiences active mud volcanism, accompanied by diffuse seafloor gas leakages and sporadic violent mud-water mixed eruptions, as exemplified by the most recent event in 2017.In this study, we present a comprehensive analysis of shipborne magnetic data, swath bathymetry, single and multichannel seismic profiles of Scoglio d’Affrica region focalized to provide a comprehensive geophysical model of shallow crustal dynamics.Forward and inverse magnetic models reveal the presence of a continuous high magnetic susceptibility body running along a NNW-SSE direction, parallel to the main tectonic lineaments. This high magnetic source is interpreted as an ophiolite/high grade serpentinite deposit embedded in Eocene siliciclastic layers resulting from the disrupting of the Corsica Alpine basement. This deposits are related to sedimentary gravity processes originated from peripheral highs and accumulated in intra-wedge basins subsequently deformed during the Oligocene. Our reconstruction provides previously unknown details about geometry and distribution of shallow ophiolite-like deposits thereby improving the comprehension the intricate structural evolution of Elba-Pianosa Ridge featured by a multiphase tectonic deformation and shallow manifestations of fluid/gas circulation.

Multi-Factor Coupling Analysis of Porous Leakage in Underwater Gas Pipelines

Natural gas pipeline leaks under the sea will have a significant negative effect on the marine ecosystem, result in significant financial losses, and possibly even harm marine floating objects. The VOF (Volume of Fluid) multi-phase flow model is used to numerically simulate and study the diffusion process of porous leakage in submarine gas pipelines. Experiments confirmed the model’s correctness and dependability. Based on this, the coupling effect and the porous effect of the leakage velocity, the size of the leaked pore, and water velocity of the natural gas pipelines on the diffusion of porous leakage in the submarine gas pipelines are analyzed with the test scheme designed by the orthogonal test method. The similarity principle is used to connect the leakage model with the actual application. The results show that three factors, namely, the leakage velocity, the size of leaked pore, and the water velocity, influence the shape of the air mass, the time when the gas reaches the sea surface, and the diffusion range. The size of the leakage hole and the leakage velocity have a substantial impact on the form of the air mass and the amount of time it takes for the gas to reach the sea surface, while the water velocity has no effect. Additionally, while there is essentially little impact from the leakage velocity, the size of the leaky pore and the water velocity have a significant impact on the diffusion range. Furthermore, the porous effect between leaky pores has a significant impact on the gas diffusion range. This study can serve as a guide for risk assessment and emergency decision-making regarding a submarine gas pipeline leak.

Seismic evidence of extensive microbial gas migration and trapping in submarine gas hydrates (Rakhine Basin, Bay of Bengal)

Submarine methane-rich gas hydrates in ocean sediments are a potential atmospheric greenhouse gas and energy source. It is considered that microbial methane is generally autochthonous, produced in situ within the gas hydrate stability zone with low gas flux and pressure, while thermogenic gas is allochthonous, migrated from a deeper petroleum system, with higher gas flux and pressure and therefore potentially higher energy resource and environmental impact. Here, we report on the allochthonous nature of large microbial gas hydrate deposits in the Rakhine Basin, Bay of Bengal. An innovative and automatic tool, developed to analyze high-resolution three-dimensional seismic data, allowed to detect hundreds of thousands gas occurrences throughout a 2 km thick Pliocene-Pleistocene sedimentary sequence extending below the gas hydrate stability zone. A supercharged section matching the present-day optimum temperature for microbial methanogenesis was identified. Combining seismic and geochemical data of the Rakhine Basin gas system points to a dominant microbial nature of the gas. Stacked amplitude anomalies and vertical anomaly clusters demonstrate active free-phase gas migration towards the shallow gas hydrate stability zone. The Rakhine Basin gas hydrates are the ultimate seal for the entire petroleum system and represent a case of “frozen seepage” of microbial gas with relatively high flux and pressure.

Subsurface heat and salts cause exceptionally limited methane hydrate stability in the Mediterranean Basin

Abstract Knowledge of the global reservoir of submarine gas hydrates is of great relevance for understanding global climate dynamics, submarine geohazards, and unconventional hydrocarbon energy resources. Despite the expected presence of gas hydrates from modeling studies, the land-locked Mediterranean Basin displays a lack of evidence of extensive gas hydrate presence from samples and seismic data. We modeled the theoretical Mediterranean distribution of methane hydrate below the seafloor and in the water column using available geological information provided by 44 Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) boreholes, measured geothermal gradients, and thermohaline characteristics of the water masses. We find that the pervasive presence of high-salinity waters in sediments, coupled with the unique warm and salty water column, limit the thickness of the theoretical methane hydrate stability zone in the subsurface and deepen its top surface to 1163–1391 m water depth. The theoretical distribution of methane hydrates coincides well with the distribution of shallow, low-permeability Messinian salt deposits, further limiting the formation of pervasive gas hydrate fronts and controlling their or distribution due to the prevention of upward hydrocarbon gas migration. We conclude that the Mediterranean Basin, hosting the youngest salt giant on Earth, is not prone to the widespread formation and preservation of gas hydrates in the subsurface and that the gas hydrate potential of salt-bearing rifted continental margins may be considerably decreased by the presence of subsurface brines.

Evaluation of Natural Gas Hydrate Fault System: A Case from a Sag in Deep-Water Slope Area of the Northern South China Sea

AbstractThe fault system is one of the structural carrier systems of gas hydrate accumulation, which plays a vital role in controlling the distribution of natural gas hydrate (NGH) accumulation. The previous studies mainly focus on summarizing the vertical migration mode of high flux fluid along the fault with obvious geophysical response characteristics on the seismic profile, such as “fault with gas chimney,” “fault with mud diapir,” and “fault with submarine collapse”, but lack of evaluation methods for the fault carrier system. We use the X sag in the deep-water continental margin slope area of the northern South China Sea as an example to study the fault systems closely related to NGH. This paper puts to use attribute technologies, such as coherence, curvature, and fusion, to analyze the characteristics and combination of the fault systems. We discussed migration patterns and evaluation methods of dominant fault carrier systems. This research proves that the strike-slip fault system in the platform area can directly connect the gas source bed with high-quality hydrocarbon generation to the gas hydrate stability zone (GHSZ). The activity of this fault system is more conducive to the accumulation of hydrocarbon in the GHSZ. This area has a good site for pore-filling gas hydrate prospecting and a preferential favorable fault carrier system. The composite fault system, consisting of a normal dip-slip fault system and a polygonal fault system, in the slope area can jointly communicate the biogenic gas-rich reservoir. Its activity and well-migration performance are the main reasons for the submarine gas leakage and collapse. It is a secondary favorable fault carrier system in the study area. There may be massive and vein natural gas hydrate formation in fractures in the leakage passage, and pore-filled gas hydrate may exist in the submarine nonleakage area. In this work, a three-factor evaluation method of the fault carrier system is proposed for the first time. This method is of great significance for the evaluation and exploration of NGH reservoirs in the continental margin slope area of the northern South China Sea.

КЛИМАТООБРАЗУЮЩАЯ РОЛЬ ЭМИССИИ МЕТАНА НА ШЕЛЬФЕ МОРЕЙ ВОСТОЧНОЙ АРКТИКИ

Satellite data on tropospheric methane and dynamical permafrost model simulations were used to analyze the methane emission in the subaquatic permafrost on the East Siberian Arctic shelf. The hypothesis of potential methane release from the dissociation of submarine gas hydrates was studied. It was demonstrated that the methane emission on the Arctic shelf is governed mainly by geological factors and is not related to contemporary climate change. Numerical experiments with the INM-CM48 Earth system model showed that there is no feedback between the methane emission on the shelf and global air temperature. A conceptual model of methane emission on the East Siberian Arctic shelf was developed.

Extraction of Submarine Gas Plume Based on Multibeam Water Column Point Cloud Model

The gas plume is a direct manifestation of sea cold seep and one of the most significant symbol indicators of the presence of gas hydrate reservoirs. The multibeam water column (MWC) data can be used to extract and identify the gas plume efficiently and accurately. The current research methods mostly start from the perspective of image theory, which cannot identify the three-dimensional (3D) spatial structure features of gas plumes, reducing the efficiency and accuracy of detection. Therefore, this paper proposes a method for identifying and extracting the gas plume based on an MWC point cloud model, which calculates the spatially resolved homing of MWC data and constructs a 3D point cloud model of MWC containing acoustic reflection intensity information. It first performs noise suppression of the 3D point cloud of the MWC based on the symmetric subtraction and Otsu algorithm by leveraging the noise distribution of the MWC and the reflection intensity characteristics of the gas plume. Then, it extracts the point cloud clusters containing the gas plume based on Density-Based Spatial Clustering of Applications with Noise (DBSCAN) according to the density difference between the gas plume point cloud and the background MWC point cloud and next identifies the point cloud clusters by feature matching based on fast point feature histograms (FPFHs). Finally, it extracts the gas plume point cloud set in the MWC. As evidenced by the MWC data collected from gas hydrate enrichment zones in the Gulf of Mexico, the location of gas plume extracted by this method is highly consistent with that of gas leakage points measured during the cruise. Using this method, we obtained the point cloud data set of gas plume for the first time and accurately characterized the 3D spatial morphology of the subsea gas plume, providing technical support for gas hydrate exploration, subsea gas seepage area delineation, and subsea seepage gas flux estimation.

Monitoring and Research on Submarine Hydrate Mound: Review and Future Perspective

Abstract Submarine hydrate mounds are important indicators of submarine methane seepages, hydrocarbon reservoirs, and seabed instability. In order to fully understand the formation of hydrate mounds, here, we review the study of hydrate mounds, in which the morphology, the formation mechanism, as well as the research techniques are introduced. The formation mechanism of hydrate mounds can be classified into: (1) The sediment volume expands due to the formation and accumulation of shallow hydrates; (2) unconsolidated shallow sediment layers respond mechanically to increasing pore pressure caused by shallow gas accumulation; (3) materials extrude from submarine layers driven by the over-pressure caused by shallow gas accumulation; and (4) the interaction of multiple factors. Most hydrate mounds occur in submarine gas hydrate occurrence areas. Active hydrate mounds are circular or ellipse well-rounded shaped, with gas seepages and abundant organisms, whereas inactive hydrate mounds are rough or uneven irregular shaped, with low flux of fluid in the migration channel. Due to the limitation of long-term in-situ observation technology, the existing observation method makes it possible to provide basic morphology features, stratigraphic structures, and fluid migration channels of the hydrate mound. Future research should be focused on the long-term in-situ monitoring technology, the formation mechanism of the hydrate mounds, and the role of gas hydrates in the seafloor evolution. In addition, the features of hydrate mounds (e.g., gas chimneys and fluid migration conduits) and the relationship between hydrate mounds and pockmarks could be further studied to clarify the influence of methane release from hydrate mounds on biogeochemical processes and the atmospheric carbon contents.

Saturation sensitivity and influencing factors of marine DC resistivity inversion to submarine gas hydrate

The submarine gas hydrate usually exists in the sediment on the continental slope. The bottom simulating reflector on the reflected seismic was identified as the bottom of the hydrate stability zone. However, many BSRs may not find the hydrate’s effective storage and its underlying free gas in many places. It is essential to identify the saturation of the hydrate. The resistivity can be used to evaluate the hydrate’s porosity and saturation. The hydrate boasts a high resistance to the surrounding sediments. The sensitivity of the marine Direct Current resistivity method (DCR) to the high resistance of the sediment can be used to evaluate the saturation of the hydrate. We have assessed the sensitivity of various DCR array arrangements, towed depths, hydrate thicknesses, and saturation. These influencing factors for improving recognition ability were also systematically analyzed. We have compared the inversion results of various DCR array arrangements, as well as different depths, thicknesses, and hydrate saturation, and calculated the saturation. We suggest using the corrected saturation equation to analyze the DCR results, which can improve the ability of hydrate identification. Evaluating these parameters will help develop or select DCR instruments for detecting the submarine gas hydrate.

Hydrodynamic characteristics and wake evolution of a submarine pipe with the presence of gas leakage at a low Reynolds number of 160

Hydrodynamic characteristics and wake structures of a submarine gas transmission pipe with the presence of gas leakage are of significance from a scientific and practical viewpoint. In this paper, we present a numerical investigation of flow past a leaking pipe at a low Reynolds number of 160 using the Eulerian–Eulerian multi-fluid volume of fluid model. The focus is on the effects of gas buoyancy and the location of the leak hole on the wake flow structures, bubble–vortex interference, and hydrodynamic forces. The variation of drag and lift coefficients is highly associated with the evolution of gas bubbles and the interaction between the bubble-induced vortices and the shear layers. When the gas buoyancy is ignored, the alterations of the main vortex structure and hydrodynamic forces are not sensitive to the location of the leak hole. The bubble-induced vortices are encompassed by the two shear layers and quickly dissolved in the main vortices. Finally, the released gas bubbles are locked in the center of main vortices and convected downstream with them. In contrast, when the buoyancy is considered, the gas bubbles line up in the upper shear layer, strongly interfering with the formation of the upper main vortex. Each gas bubble introduces a pair of small vortices that experience complicated merging or splitting during the migration. Consequently, the upper main vortex is suppressed at θ = 90° and vanished at θ = 180° and θ = 270° (θ is measured clockwise from the forward stagnation point), leading to the negative time-averaged lift force and the same-frequency oscillation of drag and lift coefficients. Due to the upward migration of gas bubbles from both front and rear surfaces at θ = 270°, the evolution of bubble-induced vortices is more complicated and the oscillation of hydrodynamic forces is significantly enhanced in comparison with other cases.

Analysis of Engineering and Geological Conditions of International Submarine Optical Fiber Cable Routing in the East China Sea Section

The East China Sea section of the Chinese international submarine optical fiber cable generally starts from the Shanghai coast, crosses the East China Sea shelf and continental slope to the east, and intersects with the international optical fiber cable system in Okinawa Trough. In this paper, the regional tectonic, seismic, and other environmental conditions of the East China Sea section of the international submarine optical cable are briefly described based on the previous data. Additionally, the geological engineering conditions of the international optical cable routing in the East China Sea area will be analyzed based on the field investigation data such as multibeam, side-scan sonar, shallow stratigraphic profile, sediment sampling, and cone penetration test (CPT). It is found that the main geological factors in the East China Sea shelf area are submarine scouring, sandwave, shallow gas, and hard seabed; in the land slope area are steep slope, submarine valley, rock, landslide, and shallow gas (pockmark); and in the Okinawa Trough area are gully, sea mound/seamount, rock, shallow gas, fault, and hard strata outcrop. This paper briefly analyzes the impact of each geological disaster factor on the submarine cable project and proposes solutions for providing essential information and some scientific basis for designing, constructing, operating, and maintaining international submarine optical fiber cables in the East China Sea area.

Very-Short-Term Variations of Sea Surface and Atmospheric Parameters Before the Ms 6.2 Zhangbei (China) Earthquake in 1998

The Ms 6.2 Zhangbei earthquake occurred at 3:53 (UTC) on 10 January 1998, with its epicenter located at about 150 km northwest of Beijing, China. Over the past 2 decades, many studies have reported that there was a positive thermal infrared (TIR) anomaly appearing along the direction from the Bohai Sea to Zhangbei within 2–3 days preceding the earthquake, which was considered to be caused by the activity of the great Zhangbei-Bohai fault (ZBF) extending across the Bohai Sea to the southeast, while neither the TIR anomaly is convinced nor the mechanism is clear. A collaborative analysis of the atmospheric disturbances several days before, during, and after the earthquake was conducted by using satellite observations and reanalysis datasets with multiple parameters, including sea surface roughness, evaporation rate, atmospheric CO concentration, atmospheric sea salt concentration, and cloud base height above the sea surface, as well as satellite infrared cloud images. Through individual analysis of the change of each parameter and synergic analysis of multiple parameters, particular atmospheric disturbances, including the formation of strip-shaped clouds on January 7 and 9, were revealed over the ZBF and another great fault named Tancheng-Lujiang fault (TLF), which extends across the Bohai Sea to the northeast. After careful investigation and attribution analysis of the spatio-temporal evolutions of the atmospheric disturbances every hour above and around the Bohai Sea from January 7 to 12, we came to the conclusion that the particular strip-shaped clouds were low-level clouds caused by the seismic activity and submarine gas release from TLF but not ZBF and was forced by particular wind field and lowering boundary layer. As an aftereffect of the gas release from TLF and the formation of the localized low-level clouds of higher brightness temperature than that of the land surface, a positive TIR anomaly, thus, appeared above TLF and by chance along ZBF, preceding the Zhangbei earthquake.

Clumped methane isotopologue-based temperature estimates for sources of methane in marine gas hydrates and associated vent gases

Gas hydrates stored in the continental margins of the world’s oceans represent the largest global reservoirs of methane. Determining the source and history of methane from gas hydrate deposits informs the viability of sites as energy resources, and potential hazards from hydrate dissociation or intense methane degassing from ocean warming. Stable isotope ratios of methane (13C/12C, D/H) and the molecular ratio of methane over ethane plus propane (C1/C2+3) have traditionally been applied to infer methane sources, but often yield ambiguous results when two or more sources are mixed, or when compositions were altered by physical (e.g., diffusion) or microbial (e.g., methanotrophy) processes.We measured the abundance of clumped methane isotopologue (13CH3D) alongside 13C/12C and D/H of methane, and C1/C2+3 for 46 submarine gas hydrate specimens and associated vent gases from 11 regions of the world’s oceans. These samples are associated with different seafloor seepage features (oil seeps, pockmarks, mud volcanoes, and other cold seeps). The average apparent equilibration temperatures of methane from the Δ13CH3D (the excess abundance of 13CH3D relative to the stochastic distribution) geothermometer increase from cold seeps (15–65 °C) and pockmarks (36–54 °C), to oil-associated gas hydrates (48–120 °C). These apparent temperatures are consistent with, or a few tens of degrees higher than, the temperature expected for putative microbial methane sources. Apparent methane generation depths were derived for cold seep, pockmark, and oil seep methane from isotopologue-based temperatures and the local geothermal gradients. Estimated methane generation depths ranged from 0.2 to 5.3 kmbsf, and are largely consistent with source rock information, and other chemical geothermometers based on clay mineralogy and fluid chemistry (e.g., Cl, B, and Li).Methane associated with mud volcanoes yielded a wide range of apparent temperatures (15–313 °C). Gas hydrates from mud volcanoes the Kumano Basin and Mediterranean Sea yielded δ13C-CH4 values from −36.9 to −51.0‰, typical for thermogenic sources. Δ13CH3D values (3.8–6.0‰) from these sites, however, are consistent with prevailing microbial sources. These mud volcanoes are located at active convergent plate margins, where hydrogen may be supplied from basement rocks, and fuel methanogenesis to the point of substrate depletion. In contrast, gas hydrate from mud volcanoes located on km-thick sediments in tectonically less active or passive settings (Black Sea, North Atlantic) yielded microbial-like δ13C-CH4 and C1/C2+3 values, and low Δ13CH3D values (1.6–3.3‰), which may be due to kinetic isotope effects. Additionally, using samples from two sites, we found that Δ13CH3D values of hydrate-bound gas and vent gas agree within measurement error. This study is the first to document the link between methane isotopologue-based temperature estimates and key submarine gas hydrate seepage features, and validate previous models about their geologic driving forces.

THE LEARNING OF THERMOBARIC REGIME FEATURES OF SUBSEA GAS PIPELINE IN THE CASPIAN SEA

The article provides information on temperature and pressure regimes in submarine gas pipelines, their study, as well as a brief analysis of the difficulties encountered during transportation and various methods for their prevention. The introduction section provides general information on gas-condensate fields, their characteristics and difficulties in operation, as well as temperature and pressure regimes during the transportation of the product from the DSF in the pipeline. As objective of the problem is the complexity of the product composition and the formation of a new mixture by mixing products from different fields during transportation, also the difficulties created by this mixture during transportation are noted. Keywords: “DSF”– Deep Sea Foundations, hydrate, crystallization centers, turbulence, corrosion.

LAYING OF PIPELINES IN SUBSEA TAKING INTO ACCOUNT THE PROTECTION OF THE ENVIRONMENT

This article is devoted to the construction of offshore pipelines, taking into account the protection of the environment. Initially, information was provided on the conditions of the pipelines. Then there was a discussion about the methods of laying pipelines, their pros and cons, and therefore the choice of method, which is economically viable and takes into account the environment. We know that the main factor in choosing any method of laying a submarine pipeline is economic and environmental factors. Underwater pipelines are invaluable for offshore oil and gas transportation and water supply to the islands. The construction method is very important for the installation of an expensive and time-consuming offshore pipeline and should be selected after a general consideration of equipment, capital and time. In addition, the environmental impact and safety of construction and its impact on surrounding marine operations are also determining factors. Decks, pipelines and cables, valves and switches, pumps, cleaning and all equipment must work without hindrance and must be tested repeatedly to avoid endangering people and the environment. At present, submarine gas pipelines continue to develop, accounting for 45% of natural gas exports to the west. Therefore, before the submarine is laid, the entire route along the seabed must be carefully studied, and all potential obstacles, including the sunken ship, large rocks must be identified, eliminated or bypassed. Subsea pipelines are the safest, most cost-effective, and most environmentally friendly route. Keywords: subsea pipelines, construction technologies, submarine pipeline installation, environment supervision, management and control of industrial waste, prevention of pollution, pipeline laying.

Acoustic Observation, Identification, and Scattering Intensity Measurement of Cold Seep Based on Bubble Resonance

The active “ cold seep “ is indisputable evidence to identify the existence of submarine gas hydrate. Due to the difference in acoustic properties between cold seep bubbles and surrounding seawater, measuring scattering intensity is a new means to detect active cold seep. Cold seep bubbles are the main cause of acoustic scattering, and the scattering ability is closely related to the frequency of the incident sound wave, the radius of the bubble, and the depth of the bubble. The paper introduces a ship-borne cold seep sonar system, which uses the resonance principle of bubbles to measure the scattering intensity at various depths underwater and display it with an intuitive acoustic image. Through the investigation and measurement of the cold seep located in the South China Sea, it is proved that the cold seep sonar system can well identify the submarine cold seep. The measured data are consistent with the theoretical simulation results, confirming that the cold seep bubbles have frequency-selective characteristics for incident sound waves. Compared with other detection methods, it has the characteristics of lossless, fast, and high efficiency.

Methane flux and gas hydrate accumulations in the Sea of Okhotsk and their ecological aspects

Methane is one of the important representatives of the organic substances in the atmosphere (for example, an increase of methane content in the atmosphere can affect enhancing the greenhouse effect). Gas hydrates are an essential part of links in the methane cycle and the accompanying fluxes of other gases. The research object in this paper is the Sea of Okhotsk, where gas hydrate fields and active submarine gas discharge areas were found. The study of methane fluxes is relevant both for the Sea of Okhotsk and the World Ocean. From 1984 to 2015, the background and anomalous methane fields were explored in the Sea of Okhotsk as a result of gas geochemical research carried out by scientists of the Gasgeochemistry Laboratory (POI FEB RAS). The flux of natural gas became stronger from the sources to the seafloor, from the seafloor to the water, and, finally, to the atmosphere due to renew of fault zones. Moreover, the amount of methane vents on the Sakhalin slope has increased from 2-3 vents to more than 400. The most representative hydroacoustic anomalies “flares” mapped direct methods study methane hydrates. The received outcomes indicate the urgency of the study of methane fluxes and the formation-dissociation mechanism of gas hydrates, and the influence of natural gas from hydrocarbon sources on the environment.

Optimal substitution rate analysis of submarine natural gas hydrates considering geological and hydrological conditions

In order to improve the ability of data mining and information scheduling for the best replacement rate of seabed natural gas hydrate under geological and hydrological conditions, an optimization algorithm for estimating the best replacement rate of seabed natural gas hydrate is proposed. By using piecewise linear estimation method, the characteristic data of submarine gas hydrate database are grouped and reconstructed, and the optimal replacement rate of submarine gas hydrate in the database is fused with related information. According to the spatial distribution of geological and hydrological conditions, the optimal replacement rate of submarine gas hydrate is adaptively dispatched. The optimal replacement rate of submarine gas hydrate is extracted by frequent item mining method, and the extracted optimal replacement rate of submarine gas hydrate is processed in turn. Finally, the unbiased estimation of the optimal replacement rate of submarine gas hydrate is realized by using regularized power spectrum estimation method. The experimental results show that the design method has small deviation and high accuracy in estimating the best substitution rate of submarine natural gas hydrate.

Impact of tides and sea-level on deep-sea Arctic methane emissions

Sub-sea Arctic methane and gas hydrate reservoirs are expected to be severely impacted by ocean temperature increase and sea-level rise. Our understanding of the gas emission phenomenon in the Arctic is however partial, especially in deep environments where the access is difficult and hydro-acoustic surveys are sporadic. Here, we report on the first continuous pore-pressure and temperature measurements over 4 days in shallow sediments along the west-Svalbard margin. Our data from sites where gas emissions have not been previously identified in hydro-acoustic profiles show that tides significantly affect the intensity and periodicity of gas emissions. These observations imply that the quantification of present-day gas emissions in the Arctic may be underestimated. High tides, however, seem to influence gas emissions by reducing their height and volume. Hence, the question remains as to whether sea-level rise may partially counterbalance the potential threat of submarine gas emissions caused by a warmer Arctic Ocean.