Methane Hydrate Deposits Research Articles

Methane Hydrates: An Abundance of Clean Energy?

The discovery that gas hydrates (also called clathrate hydrates) can crystallize (Figure 1) as a solid by the combination of water and several types of gases exposed to low temperatures and elevated pressure goes back to the 1800s. French researchers were the frst to report the formation of methane, ethane, and propane hydrates.1 Results of these studies remained as scientifc novelties until the mid-1930s, when it was discovered in Germany that gas hydrates forming as solids above 0°C in gas pipelines blocked the fow of natural gas.2 This observation initiated a furry of activities both in Europe and in the United States to fnd various inhibitors to prevent hydrate formation in gas transmission lines. During the mid-1960s, it was recognized that nature, over millions of years, has deposited vast amounts of methane hydrates along most of the continental margins in the ocean sediments, as well as along the permafrost regions in Alaska, Canada, and Russia.3 Figure 2 shows the presence of methane hydrate deposits in the ocean sediments and in the permafrost regions of the world. These deposits are byproducts of microbial decomposition of organic matter or of Earth's geothermal heating distributed worldwide where temperature and pressure are suitable for hydrate formation. The distribution of organic carbon in Earth's crust as methane

メタンハイドレート層における深部地球熱を用いた熱刺激法の評価

Thermal stimulation method is one of the prospective methods for gas production from methane hydrate (MH) deposits. In the thermal stimulation method, MH is dissolved to methane gas and water either by injecting heated water into the MH deposits or by circulating heated water in production wells. In this paper, the feasibility of heated water injection using the ground heat in the deep formation was investigated with numerical simulations. A co-axial ground heat exchanger (GHE) is designed to be drilled below MH deposits to produce the heated water. Numerical simulations showed that a GHE of 2000m deep can extract a geothermal heat over 200kW. On the basis of the estimated heat supply, numerical reservoir simulations were carried out to optimize the strategy of water injection in terms of gas production rates. The simulations showed that water injection should be commenced after a gas production with depressurization for 3 years since the timing maximized the cumulative gas recovery; the optimum injection rate was estimated 250L/min. The use of seawater as water source was also examined to demonstrate that the inhibitor effect of seawater, which lowers the dissociation temperature of MH, can accelerate the dissolution of MH. Assuming a production life of 20 years, the cumulative gas production, when using a GHE of 2000m deep and seawater as water source, was estimated 48.9% larger than the cumulative gas production without heated water injection.

Subseafloor Microbial Communities in Methane Hydrate-Bearing Sediment at Two Distinct Locations (ODP Leg204) in the Cascadia Margin

The prokaryotic communities in deep subseafloor sediment collected during Ocean Drilling Program (ODP) Leg 204 from the South Hydrate Ridge (SHR) on the Cascadia Margin were analyzed by 16S rRNA gene clone sequencing and a fluorescent quantitative PCR technique. The microbial communities came from sites with contrasting geological characteristics on the SHR: sites 1244 and 1245 (located on the flank of the ridge, hydrate-rich sediment) and site 1251 (located on the slope basin of SHR, hydrate-poor sediment). The overall copy numbers of the 16S rRNA gene, and the proportion of archaeal 16S rRNA gene in all 16S rRNA gene community in sediment were larger on the slope basin than on the flank of the SHR. Archaeal community structure around the sulfate-methane transition zone at site 1251 (4.5 mbsf) was intensively investigated using two different PCR primer sets. A relatively abundant distribution of the 16S rRNA gene sequences related to mesophilic methanogen of the genus Methanoculleus was identified at a depth of 43.2 mbsf, and suggested that the methanogens occur in relatively shallow zones of sediment. This study demonstrated that the subseafloor microbial communities shown by 16S rRNA gene clone analyses were not directly associated with subseafloor methane hydrate deposits.

Oceanic gas hydrate instability and dissociation under climate change scenarios

Global oceanic deposits of methane gas hydrate (clathrate) have been implicated as the main culprit for a repeated, remarkably rapid sequence of global warming effects that occurred during the late Quaternary period. However, the behavior of contemporary oceanic methane hydrate deposits subjected to rapid temperature changes, like those predicted under future climate change scenarios, is poorly understood, and existing studies focus on deep hydrate deposits under equilibrium conditions. In this study, we simulate the dynamic response of several types of oceanic gas hydrate accumulations to temperature changes at the seafloor and assess the potential for methane release into the ecosystem. The results suggest that while many deep hydrate deposits are indeed stable under the influence of rapid seafloor temperature variations, shallow deposits, such as those found in arctic regions or in the Gulf of Mexico, can undergo rapid dissociation and produce significant carbon fluxes over a period of decades.

얼음 물질을 이용한 미래 에너지와 지구 온난화 처리 방안

낮은 온도와 높은 압력에서 저분자량의 가스가 물분자들에 의해 만들어지는 격자 속으로 포집되면서 형성되는 가스하이드레이트에 대한 존재가 알려진 것은 비교적 오래 되었으나, 물과 가스에 의해 형성되어 진다는 점에서 최근 관심이 증가되고 있다. 포집되는 가스의 종류에 따라 독특한 특성을 가지고 각각의 구조 결정을 형성하는 하이드레이트는 최근 지구 온난화가스인 이산화탄소 문제와 다양한 에너지원, 특히 천연가스와 수소 에너지에 대한 연구로 크게 주목받고 있다. 따라서 본 고에서는 가스 하이드레이트 활용 분야 중에서 활발히 진행되고 있는 분야, 즉 대표적 지구온난화 가스인 이산화탄소의 심해저장과 동시에 메탄 하이드레이트 층으로부터의 천연 가스의 포집연구와 수소 저장량을 극대화시킨 수소하이드레이트에 관한 전반적인 연구동향을 소개하도록 한다. Gas hydrates are known to form by physical interactions between host water and guest gas molecules and thus can be treated as a special type of icy materials. The gas hydrates are recently highlighted because of their use to future energy source even though they were discovered naturally in the deep-sea marine sediments a long time ago. However, the present and future urgent task is to develop the efficient and safe production technology for recovering methane from gas hydrates. Here, we propose one of potential recovery processes using swapping phenomenon occurring between gaseous carbon dioxide and methane hydrate deposits. Such a swapping process provide several technological and economical advantages over conventional processes. The carbon dioxide can be directly sequestered into methane hydrate layer and simultaneously methane can be produced with a high recovery rate more than 90%. In addition, the icy powders can be effectively used as a new medium for storing hydrogen. To increase hydrogen storage capacity the icy hydrate networks need to be redesigned to create the more empty cages in which hydrogen gas can be enclathrated. Functionalized icy materials might be used in a variety of energy and environmental fields.

Complex gas hydrate from the Cascadia margin

Natural gas hydrates are a potential source of energy and may play a role in climate change and geological hazards. Most natural gas hydrate appears to be in the form of 'structure I', with methane as the trapped guest molecule, although 'structure II' hydrate has also been identified, with guest molecules such as isobutane and propane, as well as lighter hydrocarbons. A third hydrate structure, 'structure H', which is capable of trapping larger guest molecules, has been produced in the laboratory, but it has not been confirmed that it occurs in the natural environment. Here we characterize the structure, gas content and composition, and distribution of guest molecules in a complex natural hydrate sample recovered from Barkley canyon, on the northern Cascadia margin. We show that the sample contains structure H hydrate, and thus provides direct evidence for the natural occurrence of this hydrate structure. The structure H hydrate is intimately associated with structure II hydrate, and the two structures contain more than 13 different hydrocarbon guest molecules. We also demonstrate that the stability field of the complex gas hydrate lies between those of structure II and structure H hydrates, indicating that this form of hydrate is more stable than structure I and may thus potentially be found in a wider pressure-temperature regime than can methane hydrate deposits.

Seismic investigation of natural methane hydrate deposits

The world’s continental margins are home to the very high pressures and low temperatures where methane combines with water to form the ice‐like methane hydrate. Only in the last couple of decades has it been discovered that methane hydrate is distributed over virtually every continental margin, as well as Arctic and Antarctic regions, and as such, may play a significant role as a future energy source, an agent of global climate change, or a factor in marine slope stability. Because the acoustic impedance of gas phase methane is significantly less than sediment, water, or methane hydrate, the phase boundary between gas and gas hydrate is frequently quite strong, and easily discernible in seismic sections. Further, because pressure variations in this part of the seafloor are typically small, the phase boundary can be used to determine sediment temperature. In certain circumstances, lateral variations in the depth to this phase boundary can be used to constrain the flux of heat, pore‐water, and methane responsible for concentrated methane hydrate deposits and chemosynthetic communities found at seafloor seeps.

Methane Hydrate: Little Known Energy Resource of the Future

Methane hydrate was discovered only a few decades ago and little research has been done on it until recently. However, the immense volumes of gas and the richness of the deposits may make methane hydrates a strong candidate for development as an energy resource. By some estimates, the energy locked up in methane hydrate deposits is more than twice the global reserves of all conventional gas, oil and coal deposits combined. The present paper briefly updates some of the issues related to methane hydrates with respect to its origin, occurrence, structure and properties, energy potential and extraction.

Diversity of Archaea in Marine Sediments from Skan Bay, Alaska, Including Cultivated Methanogens, and Description of Methanogenium boonei sp. nov

Methanogenesis in cold marine sediments is a globally important process leading to methane hydrate deposits, cold seeps, physical instability of sediment, and atmospheric methane emissions. We employed a multidisciplinary approach that combined culture-dependent and -independent analyses with geochemical measurements in the sediments of Skan Bay, Alaska (53 degrees N, 167 degrees W), to investigate methanogenesis there. Cultivation-independent analyses of the archaeal community revealed that uncultivated microbes of the kingdoms Euryarchaeota and Crenarchaeota are present at Skan Bay and that methanogens constituted a small proportion of the archaeal community. Methanogens were cultivated from depths of 0 to 60 cm in the sediments, and several strains related to the orders Methanomicrobiales and Methanosarcinales were isolated. Isolates were psychrotolerant marine-adapted strains and included an aceticlastic methanogen, strain AK-6, as well as three strains of CO(2)-reducing methanogens: AK-3, AK7, and AK-8. The phylogenetic positions and physiological characteristics of these strains are described. We propose a new species, Methanogenium boonei, with strain AK-7 as the type strain.

Methane hydrate deposit found off California

Methane hydrate deposit found off California

A movable trigger: Fossil fuel CO2 and the onset of the next glaciation

The initiation of northern hemisphere ice sheets in the last 800 kyr appears to be closely controlled by minima in summer insolation forcing at 65°N. Beginning from an initial typical interglacial pCO2 of 280 ppm, the CLIMBER‐2 model initiates an ice sheet in the Northern Hemisphere when insolation drops 0.7 σ (standard deviation) or 15 W/m2 below the mean. This same value is required to explain the history of climate using an orbitally driven conceptual model based on insolation and ice volume thresholds (Paillard, 1998). When the initial baseline pCO2 is raised in CLIMBER‐2, a deeper minimum in summertime insolation is required to nucleate an ice sheet. Carbon cycle models indicate that ∼25% of CO2 from fossil fuel combustion will remain in the atmosphere for thousands of years, and ∼7% will remain beyond one hundred thousand years (Archer, 2005). We predict that a carbon release from fossil fuels or methane hydrate deposits of 5000 Gton C could prevent glaciation for the next 500,000 years, until after not one but two 400 kyr cycle eccentricity minima. The duration and intensity of the projected interglacial period are longer than have been seen in the last 2.6 million years.

Global warming and the mining of oceanic methane hydrate

The impacts of global warming on the environment, economy and society are presently receiving much attention by the international community. However, the extent to which anthropogenic factors are the main cause of global warming is still being debated. There are obviously large stakes associated with the validity of any theory since that will indicate what actions need to be taken to protect the human race’s only home—Earth. Most studies of global warming have investigated the rates and quantities of carbon dioxide emitted into the atmosphere since the beginning of the industrial revolution. In this paper, we focus on the earth’s carbon budget and the associated energy transfer between various components of the climate system. This research invokes some new concepts: (i) certain biochemical processes which strongly interact with geophysical processes in climate system; (ii) a hypothesis that internal processes in the oceans rather than in the atmosphere are at the center of global warming; (iii) chemical energy stored in biochemical processes can significantly affect ocean dynamics and therefore the climate system. Based on those concepts, we propose a new hypothesis for global warming. We also propose a revolutionary strategy to deal with global climate change and provide domestic energy security at the same time. Recent ocean exploration indicates that huge deposits of oceanic methane hydrate deposits exist on the seafloor on continental margins. Methane hydrate transforms into water and methane gas when it dissociates. So, this potentially could provide the United States with energy security if the technology for mining in the 200-mile EEZ is developed and is economically viable. Furthermore, methane hydrate is a relatively environmentally benign, clean fuel. Such technology would help industry reduce carbon dioxide emissions to the atmosphere, and thus reduce global warming by harnessing the energy from the deep sea.

An improved fluorescence in situ hybridization protocol for the identification of bacteria and archaea in marine sediments

In situ identification of prokaryotic cells in subsurface sediments is hampered by the low cellular rRNA contents of the target organisms. Fluorescence in situ hybridization with catalyzed reporter deposition (CARD–FISH) has the potential to overcome this limitation, and was therefore optimized for a 40 cm deep sediment core sampled from a tidal sandy flat of the German Wadden Sea. Treatment with methanol and H 2O 2 inactivated endogenous peroxidases and effectively reduced the background signal. Percentage of DAPI stained cells detected with the probe combination EUB(I-III), targeting nearly all the Bacteria, were comparable for CARD–FISH with a horseradish peroxidase (HRP)-labeled probe and FISH with a fluorescently monolabeled probe in the 2–3 cm depth interval (92% and 82%, respectively), but significantly higher with the HRP-labeled probe at 35–40 cm, the deepest layer sampled (63% with HRP vs. 26% with monolabeled probe). With CARD–FISH Alphaproteobacteria and the Desulfobulbaceae group of sulfate-reducing bacteria were detected only in the upper layers. In contrast, Desulfosarcinales, the Bacteroidetes group, Planctomycetes, Betaproteobacteria, and Gammaproteobacteria were found at all depths. Archaea were detectable with ARCH915-HRP after achromopeptidase treatment. Surprisingly, aggregates of Bacteria and Archaea were found, below 12 cm depth, that strongly resemble consortia involved in anoxic oxidation of methane that have previously been found in sediments near methane hydrate deposits. With the optimized CARD–FISH protocol, microbial populations could also be detected in deeper sediment horizons. Furthermore, the intensity of the CARD–FISH signals improved detection of rare organisms such as Archaea.

Proposed System for Hydrogen Production from Methane Hydrate with Sequestering of Carbon Dioxide Hydrate

Methane hydrate exists in huge amounts in certain locations, in sea sediments and the geological structures below them, at low temperature and high pressure. Production methods are in development to produce the methane to a floating platform. There it can be reformed to produce hydrogen and carbon dioxide, in an endothermic process. Some of the methane can be burned to provide heat energy to develop all needed power on the platform and to support the reforming process. After separation, the hydrogen is the valuable and transportable product. All carbon dioxide produced on the platform can be separated from other gases and then sequestered in the sea as carbon dioxide hydrate. In this way, hydrogen is made available without the release of carbon dioxide to the atmosphere, and the hydrogen could be an enabling step toward a world hydrogen economy.

Geochemical constraints for coexisting CO 2 gas hydrate and calcite: implications for sheet cracks, stromatactis, zebra and tepee-like structures

The Ordovician Meiklejohn Peak mud-mound in western Nevada contains sedimentary structures (e.g., stromatactis and “zebra-rock”) that resemble features found in modern methane hydrate deposits. However, the δ 13C of the mud-mound carbonates (−1 to 1‰ PDB) does not suggest interaction with δ 13C-depleted methane. Consequently, Krause (Sedimentary Geology 145 (2001) 189) proposed that the Meiklejohn structures might have been produced by the formation and dissociation of CO 2 gas hydrate rather than methane gas hydrate. Structures in Neoproterozoic cap carbonates, sheet cracks and tepee-like structures have also been suggested to represent gas hydrate interaction with carbonate sediments (Geology 29 (2001) 443), but, similarly, δ 13C values do not suggest direct interaction with methane. The objective of this contribution is to see if the presence of CO 2 gas hydrate is plausible for either setting. To test the feasibility of CO 2 gas hydrate involvement in the formation of these structures, necessary concentrations of TCO 2 were calculated based on required phase equilibria using the quadruple points Q1 (−1.73 °C, 10.2 atm) and Q2 (10.2 °C, 44.5 atm) from the phase diagram for CO 2 gas hydrate (Miller, S.L., 1974. The Nature and Occurrence of Clathrate Hydrates. In: Kaplan, I.R. (Ed.), Natural Gases in Marine Sediments. Plenum, New York, NY, pp. 151–178). A limit for Ca +2 was established based on the lack of evidence for gypsum formation in this environment and the assumption that sulfate was up to 100% of its present oceanic value; the calculated TCO 2 concentration, however, is relatively insensitive to the concentration of SO 4 −2 used. The lowest permissible value of pCO 2 and TCO 2 were found at Q1, where TCO 2 must be at least 300 times the present value. These conditions are implausible for the formation of the Meiklejohn Peak mud-mound. Although some models for Neoproterozoic “Snowball Earth” require highly elevated atmospheric CO 2, these models predict pCO 2 that is still too low to permit the formation of CO 2 gas hydrates in carbonate sediments. In addition, if the required conditions could be achieved during “Snowball Earth”, one would expect to find the associated structures only at the base of the section, while they are commonly observed meters to tens of meters above the base. Therefore, we conclude that it is unlikely these structures were produced by the formation and dissociation of CO 2 gas hydrate.

Potential impact on climate of the exploitation of methane hydrate deposits offshore

Considerable attention has focussed on methane hydrates as a potential energy resource but much less on the potential environmental problems of exploiting these deposits. In fact, methane hydrate deposits represent a dynamic system formed as a result of the continuous migration of methane gas along fracture systems. Any exploitation of methane hydrates offshore will perforce take place in these unstable systems and could lead to the large-scale release of CH 4 under unfavourable circumstances. However, most of this CH 4 would be oxidized to CO 2 within the water column under steady-state conditions. Only under exceptional circumstances would large-scale release of CH 4 into the atmosphere take place. The impact of exploiting these deposits offshore on global climate may therefore be limited provided serious efforts are made to minimize environmental impacts. At present, prospects for the commercial exploitation of methane hydrates are in their infancy. Considerable ingenuity will be required to satisfy the requirements of safe operating conditions, mitigation of environmental hazards and commercial viability. The need to exercise caution before attempting to exploit these deposits is emphasized.

海域メタンハイドレートガス開発の経済性及びＣＯ２排出量評価

海域メタンハイドレートガス開発の経済性及びＣＯ２排出量評価

Clathrate nucleation and inhibition from a molecular perspective

Identifying the molecular processes that lead to clathrate-hydrate nucleation has been an active area of research for more than a decade. The question has a number of important ramifications, spanning applications in geology (formation and stability of natural methane-hydrate deposits), environmental science (CO2 sequestration), and industry (prevention of hydrate blockages). The drive to develop more active and robust hydrate inhibitors for the oil industry that work at very low dosages, in particular, has been slowed down because our understanding of the molecular mechanisms by which such inhibitors work is still largely conjectural. In this paper, we present results from the first direct molecular-dynamics simulations of the inhibition of nucleation in methane hydrate. Molecular-dynamics simulations have been used to simulate the behaviour of a thin film of water under a methane atmosphere with and without poly(vinylpyrrolidone) (PVP). Simulations in the absence of PVP show clear evidence of the nucleation and growth of methane hydrate; this behaviour is completely suppressed, however, when PVP is included in the simulation. We conclude that these simulations provide an excellent basis for understanding the way in which PVP inhibits hydrate nucleation. PACS Nos.: 81.10Aj, 81.10Dn, 81.10Fq

Decreased stability of methane hydrates in marine sediments owing to phase-boundary roughness.

Below water depths of about 300 metres, pressure and temperature conditions cause methane to form ice-like crystals of methane hydrate. Marine deposits of methane hydrate are estimated to be large, amassing about 10,000 gigatonnes of carbon, and are thought to be important to global change and seafloor stability, as well as representing a potentially exploitable energy resource. The extent of these deposits can usually be inferred from seismic imaging, in which the base of the methane hydrate stability zone is frequently identifiable as a smooth reflector that runs parallel to the sea floor. Here, using high-resolution seismic sections of seafloor sediments in the Cascadia margin off the coast of Vancouver Island, Canada, we observe lateral variations in the base of the hydrate stability zone, including gas-rich vertical intrusions into the hydrate stability zone. We suggest that these vertical intrusions are associated with upward flow of warmer fluids. Therefore, where seafloor fluid expulsion and methane hydrate deposits coincide, the base of the hydrate stability zone might exhibit significant roughness and increased surface area. Increased area implies that significantly more methane hydrate lies close to being unstable and hence closer to dissociation in the event of a lowering of pressure due to sea-level fall.

2-15.海域メタンハイドレートガス開発の経済性・CO_2排出量評価と補助金導入の検討((4)資源・輸送,Session 2 天然ガス・メタンハイドレート等)

2-15.海域メタンハイドレートガス開発の経済性・CO_2排出量評価と補助金導入の検討((4)資源・輸送,Session 2 天然ガス・メタンハイドレート等)