Natural gas hydrate is ice‐like mixture of gas (mostly methane) and water that is widely found in sediments along the world's continental margins and within and beneath permafrost and glaciers in a near‐surface depth interval where the pressure is sufficiently high and temperature sufficiently low for gas hydrate to be stable. We categorize the myriad of geological gas hydrate deposits into five characteristic types. We then review the multiple quantitative models that have proposed to describe the genesis of these deposits and describe how each may have formed. We emphasize the importance of coupling multiphase flow (free gas and liquid water) and multicomponent reactive transport with geological history to describe the dynamical processes of gas hydrate formation and evolution in geological systems. A better insight into the kinetics of methane formation from microbial biogenesis and the processes of multiphase flow at the pore scale will advance our knowledge of how these systems form. By understanding the generation and evolution of gas hydrate through time, we will better decipher the role of gas hydrate in the carbon cycle, its potential to contribute to climate change and geohazards, and how to design optimal strategies for gas production from hydrate reservoirs.

AbstractMethane hydrates are ice‐like compounds made of gas methane and water. Hydrates are stable under low‐temperature and high‐pressure conditions constraining their occurrence in sediments to marine and permafrost settings. A shift from the stability condition triggers an endothermic hydrate dissociation with the associated release of gas and water, impacting (among others) on sediment pore pressure, temperature, and deformations. Therefore, the behavior of hydrate‐bearing sediments (HBS) is controlled by strongly coupled thermo‐hydro‐chemo‐mechanical actions. The analysis of available data from past field and laboratory experiments and the optimization of future field production studies require a formal and robust numerical framework able to capture the complex behavior of this type of soil. In this paper we used a fully coupled thermo‐hydro‐mechanical framework to study different problems involving HBS, from laboratory experiments involving natural hydrate samples to gas production tests. We also develop an analytical solution for the case of gas production via radial depressurization from a confined HBS reservoir. The analyses show the complexity of the thermo‐hydro‐mechanical phenomena associated with this type of system and contribute to better understand the behavior of HBS.

Gas hydrate is an ice‐like form of water and low molecular weight gas stable at temperatures of roughly −10°C to 25°C and pressures of ~3 to 30 MPa in geologic systems. Natural gas hydrates sequester an estimated one sixth of Earth's methane and are found primarily in deepwater marine sediments on continental margins, but also in permafrost areas and under continental ice sheets. When gas hydrate is removed from its stability field, its breakdown has implications for the global carbon cycle, ocean chemistry, marine geohazards, and interactions between the geosphere and the ocean‐atmosphere system. Gas hydrate breakdown can also be artificially driven as a component of studies assessing the resource potential of these deposits. Furthermore, geologic processes and perturbations to the ocean‐atmosphere system (e.g., warming temperatures) can cause not only dissociation, but also more widespread dissolution of hydrate or even formation of new hydrate in reservoirs. Linkages between gas hydrate and disparate aspects of Earth's near‐surface physical, chemical, and biological systems render an assessment of the rates and processes affecting the persistence of gas hydrate an appropriate Centennial Grand Challenge. This paper reviews the thermodynamic controls on methane hydrate stability and then describes the relative importance of kinetic, mass transfer, and heat transfer processes in the formation and breakdown (dissociation and dissolution) of gas hydrate. Results from numerical modeling, laboratory, and some field studies are used to summarize the rates of hydrate formation and breakdown, followed by an extensive treatment of hydrate dynamics in marine and cryospheric gas hydrate systems.

AbstractThe concentration of methane in air bubbles within permafrost was sampled from both alluvial deposits and ice wedges in Eastern Siberia. The values of methane concentration were as high as 6000 ppmv in both frozen soil and ice wedges. The anti‐proportional relationship between methane and carbon dioxide concentration values in permafrost was examined. Values of methane concentration in ice wedges are smaller than those in frozen soils. Values of total volumetric air content, water content and density were obtained by on‐the‐spot investigation. Increases of methane and carbon dioxide concentrations were detected in accordance with increases of water content of frozen soil. Geologically older permafrost contained higher values of methane concentration than younger permafrost. Samples of frozen soils were incubated at temperature −5°C in order to study possible methane production. A slow production in different soils was observed, although the experiments took a long time before measurable changes of methane content could be found. The rate of methane production decreases in time; therefore, long‐term forecasts of methane content in frozen soils are still problematical. Copyright © 2002 John Wiley & Sons, Ltd.

Favorable thermobaric conditions of hydrate formation and the significant accumulation of methane, ice, and actual data on the presence of gas hydrates in permafrost suggest the possibility of their formation in the pore space of frozen soils at negative temperatures. In addition, today there are several geological models that involve the formation of gas hydrate accumulations in permafrost. To confirm the literature data, the formation of gas hydrates in permafrost saturated with methane has been studied experimentally using natural artificially frozen in the laboratory sand and silt samples, on a specially designed system at temperatures from 0 to −8 °C. The experimental results confirm that pore methane hydrates can form in gas-bearing frozen soils. The kinetics of gas hydrate accumulation in frozen soils was investigated in terms of dependence on the temperature, excess pressure, initial ice content, salinity, and type of soil. The process of hydrate formation in soil samples in time with falling temperature from +2 °C to −8 °C slows down. The fraction of pore ice converted to hydrate increased as the gas pressure exceeded the equilibrium. The optimal ice saturation values (45−65%) at which hydrate accumulation in the porous media is highest were found. The hydrate accumulation is slower in finer-grained sediments and saline soils. The several geological models are presented to substantiate the processes of natural hydrate formation in permafrost at negative temperatures.

Abstract The presence of hydrates has primarily been a nuisance or a well control issue when drilling for conventional oil and gas offshore and in onshore permafrost regions. However, methane hydrates could very well become the new source of clean and affordable gas supplies in the United States by 2030. For example, if several large "sweet spots" of hydrates could be defined and developed in U.S. waters, the ultimate recoverable hydrate resource could range from 1,500 to 2,000 Tcf of gas. This is close to the current U.S. domestic natural gas recoverable resource, yet it may be less than 1% of the total in-place methane hydrate resources of the U.S. To achieve the long term goals of the Federal Government in regard to energy supplies for the U.S.A., the Department of Energy is committed to developing the knowledge and technology base to allow commercial production of methane from domestic hydrate deposits by the year 2015. Hydrates or clathrates are a crystalline lattice material consisting of molecules of water that have formed an open, cage-like solid lattice that encloses molecules of methane. Hydrates of a given composition exist under particular pressure-temperature conditions caused by geological conditions. The variability of the pressure-temperature phase diagrams for hydrates is caused by changes in geological conditions during hydrate evolution and by the chemical composition of the hydrate, which may have been enriched with ethane. Under changing geological condit

percentage of clathrates deposits may provide an economically viable resource. Methane clathrates in continental rocks are trapped in beds of sandstone Methane clathrate (CH4·5.75H2O) or (4CH4·23H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, methane gas, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer reg Methane clathrate (CH4·5.75H2O) or (4CH4·23H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, methane gas, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth (around 1100 m below the sea surface). Methane hydrate is formed when hydrogen-bonded water and methane gas come into contact at high pressures and low temperatures in oceans. Methane clathrates are common constituents of the shallow marine geosphere and they occur in deep sedimentary structures and form outcrops on the ocean floor. Methane hydrates are believed to form by the precipitation or crystallisation of methane migrating from deep along geological faults. Precipitation occurs when the methane comes in contact with water within the sea bed subject to temperature and pressure. In 2008, research on Antarctic Vostok Station and EPICA Dome C ice cores revealed that methane clathrates were also present in deep Antarctic ice cores and record a history of atmospheric methane concentrations, dating to 800,000 years ago. The ice-core methane clathrate record is a primary source of data for global warming research, along with oxygen and carbon dioxide. Methane clathrates used to be considered as a potential source of abrupt climate change, following the clathrate gun hypothesis. In this scenario, heating causes catastrophic melting and breakdown of primarily undersea hydrates, leading to a massive release of methane and accelerating warming. A 2020 review of the climate tipping points research concludes that for methane hydrate release the "likelihood of occurrence remains unclear". The tipping point cascades (such as Arctic ice loss causing further warming and a release of methane from hydrates) have only been studied starting from 2018. The IPCC Sixth Assessment Report ignores the…

Clathrates have been found to occur naturally in large quantities. Around 6.4 trillion (6.4×1012) tonnes of methane is trapped in deposits of methane Clathrate hydrates, or gas hydrates, clathrates, or hydrates, are crystalline water-based solids physically resembling ice, in which small non-polar molecules (typically gases) or polar molecules with large hydrophobic moieties are trapped inside "cages" of hydrogen-bonded, frozen water molecules. In other words, clathrate hydrates are clathrate compounds in which the host molecule is water and th Natural…