Gas Hydrate Research Papers - Academia.edu (original) (raw)

Estimating the amount of gas-hydrate and freegas is difficult in deep seas even with scientific coring and downhole measurements. Well data may be incompatible between holes of a site as well as with depth in the same hole. In this paper, we demonstrate an approach to estimate saturation of gas-hydrate from seismic velocities at any site where data set is limited. The study is carried out in the outer Blake Ridge, which is one of the most intensively studied regions of natural gas-hydrate occurrences and a very distinctive example of studying geophysical signatures of gas-hydrate and free-gas in deep marine sediments. Although, downhole measurements from both vertical seismic profiles (VSPs) and sonic logs provide the most accurate and direct measurements of velocity, only VSP velocities at Ocean Drilling Program (ODP) Sites 994, 995, and 997 on the Blake Ridge are used to estimate the saturation of gas-hydrate and free-gas as sonic logs at ODP sites are not reliable. Here we derive a general trend of the background velocity with depth using the porosity and mineralogy from coring at discrete depth intervals. Saturations of gas-hydrate and free-gas are then estimated from this background velocity using the effective medium modeling. The porosity and mineralogical compositions are taken from four different depths at Site 995, as data quality is the best in this hole. Average saturations of gas-hydrate and free-gas at three holes are estimated as 10-14 and 2-3%, respectively.

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- Geophysics, Oceanography, Gas Hydrate, Natural Gas

We recorded high-resolution seismic-reflection data in the northern Gulf of Mexico to study gas and gas-hydrate distribution and their relation to seafloor slides. Gas hydrate is widely reported near the seafloor, but is described at only one deep drill site. Our data show highreflectivity zones (HRZs) near faults, diapirs, and gas vents and interbedded within sedimentary sections at shallow depth (, 1 km). The HRZs lie below the gas-hydrate-stability zone (GHSZ) as well as within the zone (less common), and they coincide with zones of shallow water-flows. Bottom simulating reflections are rare in the Gulf, and not documented in our data. We infer HRZs result largely from free gas in sandy beds, with gas hydrate within the GHSZ. Our estimates for the base BHSZ correlate reasonably with the top of HRZs in some thick well-layered basin sections, but poorly where shallow sediments are thin and strongly deformed. The equivocal correlation results from large natural variability of parameters that are used to calculate the base of the GHSZ. The HRZs may, however, be potential indicators of nearby gas hydrate. The HRZs also lie at the base of at least two large seafloor slides (e.g. up to 250 km 2) that may be actively moving along decollement faults that sole within the GHSZ or close to the estimated base of the GHSZ. We suspect that water/gas flow along these and other faults such as 'chimney' features provide gas to permit crystallization of gas hydrate in the GHSZ. Such flows weaken sediment that slide down salt-oversteepened slopes when triggered by earthquakes. Published by Elsevier Science Ltd.

- by Patrick Hart
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- Geology, Geophysics, Gas Hydrate, Salt diapir

Gas hydrate formation and decomposition on water droplets using an 89.4% methane-10.6% ethane mixture, and a 90.1% methane-9.9% propane mixture were carried out in a new apparatus suitable for morphology studies. As expected the induction time was found to be much shorter when the water had hydrate memory. All droplets nucleated simultaneously and the droplet size and shape had no noticeable effect on induction time and macroscopic crystal growth morphology for hydrates from the methane-ethane mixture. However, the surface of the hydrate crystals from methane-propane had a "hairy-like" appearance which changed to a smooth surface over time. Moreover, the smaller droplets during hydrate reformation showed an extensive hydrate growth and looked like snow-flakes. Sequential pictures generated by time-lapse videos showed that the time required for hydrate to cover the water droplet surface ranged from 10 to 23 s and was shorter when there was gas-phase agitation (mixing). The growth is postulated to occur in two stages. The first stage lasts about 10-23 s and growth takes place laterally. Growth takes place at the hydrate/gas and the hydrate/water interfaces during the second stage. The implication of the findings for process design of hydrate formation vessels is also discussed.

- by Peter Englezos
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- Mechanical Engineering, Chemical Engineering, Design, Crystal Growth
- by Hitoshi Koide
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- Carbon Sequestration, Gas Hydrate, Deep Carbon Cycle, CO2 capture and storage

A phase-field theory is applied to model the growth of carbon dioxide hydrate and methane hydrate from a supersaturated solution in water. Temperature-and pressure-dependent thermodynamics for the two systems are accounted for. Simulations of the growth of a planar hydrate film and a circular hydrate nucleus are presented and the interface velocity has been extrapolated from the results to experimental time scales. We discuss how pressure and temperature affects the growth rate and argue that the governing process for the dynamics is the chemical diffusion of the guest molecule in the aqueous solution. We also present results from anisotropic simulations and outline how this will affect the growth. r

- by László Gránásy and +1
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- Thermodynamics, Crystal Growth, Carbon Dioxide, Gas Hydrate

In the last years, the interest of the scientific community about gas hydrates has increased from many points of view. In addition, the oil companies are strongly interested about the gas hydrate hazard for human offshore manufactures. In this context, it is very important to improve the knowledge about the relationship between hydrate stability and overpressure condition below the bottom simulating reflector (BSR). Theoretical studies suggest that the base of the hydrate stability is affected by overpressure condition, water depth and geothermal gradient. The results of this study can be used to re-interpret the considerations of previous studies about the disagreement between the theoretical and seismic BSR depth. Finally, an accurate analysis of the BSR nature and pore pressure condition is required to improve the reliability of the gas-phase estimation for gas hydrate and free gas exploitation.

- by Umberta Tinivella
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- Earth Sciences, Modeling, Gas Hydrate, Overpressure

Landslides at continental margins are natural hazards for submarine installations and coastal regions. The occurrence of gas hydrates at continental margins is thought to be one major cause for these slides. It is assumed that the decomposition of gas hydrates increases the water content of the host sediment and thus lowers the strength of the soil. In order to predict

- by Serge KREITER
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- Geology, Soil Mechanics, Slope Stability, Finite element method

Networked Experiments) will be an innovative network of many sub-sea observatories linked by about 3,000 km of powered, electro-optic cable covering most of the Juan de Fuca Plate (200,000 sq km), North-East Pacific, with shore stations at Port Alberni, BC and probably Nedonna Beach, OR (www.neptunecanada.ca, www.orionprogram.org, www.neptune.washington.edu). Each observatory will host and power many scientific instruments on the surrounding seafloor, in boreholes in the seafloor, and buoyed into the water column. Remotely operated and autonomous vehicles will reside at depth, powered or recharged at observatories and directed from distant labs. Continuous near-real-time multidisciplinary measurement series will extend over 25 years. Major research themes include: structure and seismic behavior of the ocean crust; dynamics of hot and cold fluids and gas hydrates in the upper ocean crust and overlying sediments; ocean/climate change and effects on ocean biota/fisheries at all depths; deep-sea sedimentation, ecosystem dynamics and biodiversity; and engineering and computational systems research. These involve interacting processes, long-term changes, and chaotic, episodic events difficult to study and quantify by traditional means.

- by Benoît Pirenne
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- Climate Change, Gas Hydrate, Autonomous Vehicle, Innovation Network

Understanding the upward motion of CO 2 droplets or CH 4 bubbles in oceanic waters is prerequisite to predict the vertical distribution of the two most important greenhouse gases in the water column after these have been released from the seabed. One of the key parameters governing the fate of droplets or bubbles dissolving into the surrounding seawater as they rise, is the terminal velocity, u T. The latter is strongly influenced by the ability of both compounds to form skins of gas hydrate, if pressure and temperature satisfy thermodynamic framework conditions. Experimental efforts aiming to elucidate the rise properties of CO 2 droplets and CH 4 bubbles and specifically the influence of hydrate skins open the possibility to obtain a parameterization of u T applicable to both hydrate-coated and pure fluid particles of CH 4 and CO 2. With the present study, we report on experimentally determined terminal velocities of single CH 4 bubbles released to pressurized and temperature-regulated seawater. Hydrate skins were identified by high bubble sphericities and changed motion characteristics. Based on these experiments as well as published data on the rise of hydrate-coated and pure liquid CO 2 droplets and physical principles previously successfully used for clean bubbles near atmospheric pressures, a new parameterization of u T is proposed. Model predictions show a good agreement with the data base established from the laboratory-based measurements.

- by Nikolaus K Bigalke
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- Geochemistry, Oceanography, Thermodynamics, Gas Hydrate

In this paper we present 2 years of data obtained during the late summer period (September 2003 and September 2004) for the East Siberian Arctic shelf (ESAS). According to our data, the surface layer of shelf water was supersaturated up to 2500% relative to the present average atmospheric methane content of 1.85 ppm, pointing to the rivers as a strong source of dissolved methane which comes from watersheds which are underlain with permafrost. Anomalously high concentrations (up to 154 nM or 4400% supersaturation) of dissolved methane in the bottom layer of shelf water at a few sites suggest that the bottom layer is somehow affected by near-bottom sources. The net flux of methane from this area of the East Siberian Arctic shelf can reach up to 13.7 × 10 4 g CH 4 km − 2 from plume areas during the period of ice free water, and thus is in the upper range of the estimated global marine methane release. Ongoing environmental change might affect the methane marine cycle since significant changes in the thermal regime of bottom sediments within a few sites were registered. Correlation between calculated methane storage within the water column and both integrated salinity values (r = 0.61) and integrated values of dissolved inorganic carbon (DIC) (r = 0.62) suggest that higher concentrations of dissolved methane were mostly derived from the marine environment, likely due to in-situ production or release from decaying submarine gas hydrates deposits. The calculated late summer potential methane emissions tend to vary from year to year, reflecting most likely the effect of changing hydrological and meteorological conditions (temperature, wind) on the ESAS rather than riverine export of dissolved methane. We point out additional sources of methane in this region such as submarine taliks, ice complex retreat, submarine permafrost itself and decaying gas hydrates deposits.

- by Natalia Shakhova
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- Oceanography, Gas Hydrate, Environmental Change, Methane

Potential application of gas hydrate-based desalination was suggested with a novel apparatus design. The equipment continuously produces and pelletizes CO 2 hydrates by a squeezing operation of a dual cylinder unit, which is able to extract hydrate pellets from the reactor containing hydrate slurries. Removal efficiencies for each dissolved mineral from seawater samples was also tested by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) analysis. In a single-stage hydrate process, 72-80% of each dissolved mineral was removed in the following order: K + N Na + N Mg 2+ N B 3+ N Ca 2+ . Our results also showed that ion rejection by the hydrate process strongly depends on the ionic size and charge. This study illustrates that the suggested method and apparatus may solve the separation difficulty between hydrate crystals and concentrated brine solutions, thus it can be applied for more effective desalination processes.

- by Sang Yeon Hong
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- Engineering, Gas Hydrate, Desalination, CHEMICAL SCIENCES

The list of known and inferred submarine mud volcanoes is presented in this paper. They occur worldwide on shelves, continental and insular slopes and in the abyssal parts of inland seas. Submarine mud volcanoes are distributed on the Earth more extensively than their subaerial analogs. The estimated total number of known and inferred deep-water mud volcanoes is 10 3 -10 5 . There are two key reasons for the formation of submarine mud volcanoes-high sedimentation rate and lateral tectonic compression. Submarine mud volcanoes form by two basic mechanisms: (1) formation on the top of a seafloor-piercing shale diapir; (2) formation due to the rise of fluidized sediments along faults. Fluid migration is critical to the formation of a mud volcano. Gas hydrates are often associated with deep-water mud volcanoes and have many common features from one accumulation to another. Gas hydrates form by conventional low-temperature hydrothermal process around the central part of a mud volcano and by metasomatic processes at its periphery. A preliminary global estimate of methane accumulated in gas hydrates associated with mud volcanoes is about 10 10 -10 12 m 3 at standard temperature and pressure. ᭧ (A.V. Milkov). a SESS-subcircular elevated seafloor structures; SPD-seafloor-piercing diapirs; FE-fluids expulsions above elevated seafloor structures; MI-transient mud islands; GB-gas bubbles at the surface of water.

- by Alexei Milkov
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- Earth Sciences, Marine Geology, Gas Hydrate, Mud volcanoes

There has been a dramatic increase in gas hydrate research over the last decade. Interestingly, the research has not focussed on only the inhibition of gas hydrate formation, which is of particular relevance to the petroleum industry, but has evolved into investigations on the promotion of hydrate formation as a potential novel separation technology. Gas hydrate formation as a separation technology shows tremendous potential, both from a physical feasibility (in terms of effecting difficult separations) as well as an envisaged lower energy utilization criterion. It is therefore a technology that should be considered as a future sustainable technology and will find wide application, possibly replacing a number of current commercial separation processes. In this article, we focus on presenting a brief description of the positive applications of clathrate hydrates and a comprehensive survey of experimental studies performed on separation processes using gas hydrate formation technology. Although many investigations have been undertaken on the positive application of gas hydrates to date, there is a need to perform more theoretical, experimental, and economic studies to clarify various aspects of separation processes using clathrate/semi-clathrate hydrate formation phenomena, and to conclusively prove its sustainability.

- by Dominique Richon
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- Carbon Dioxide, Chemical thermodynamics, Gas Hydrate, Experimental Study

At the summit of Hydrate Ridge (ODP Sites 1249 and 1250), pore fluids are highly enriched in dissolved chloride (up to 1370 mM) in a zone that extends from near the sediment surface (~1 mbsf) to depths of 25F5 mbsf. Below this depth, brines give way to chloride values approaching seawater concentrations with lower chloride anomalies superimposed on baseline values. We developed a one dimensional, non-steady state, transport reaction model to simulate the observed chloride enrichment at Site 1249. Our model shows that in order to reach the observed high chloride values, methane must be transported in the gas phase from the depth of the BSR to the seafloor. Methane transport exclusively in the dissolved phase is not enough to form methane hydrate at the rates needed to generate the observed chloride enrichment. Methane transport in the gas phase is consistent with geophysical and logging data, estimates of gas pressure beneath the BSR, and observations of bubble plumes at the seafloor.

- by Gerhard Bohrmann
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- Earth Sciences, Kinetics, Gas Hydrate, Physical sciences

The accuracy of the focused beam reflectance measurement (FBRM) probe, which measures a chord length distribution, from Mettler-Toledo Lasentec ᭨ has been explored. A particle video microscope (PVM) probe, which provides in situ digital images, was used as a direct visual method to test the reliability of the FBRM results. These probes can provide in situ particle characterization at high pressures. The FBRM has been used to study emulsions and ice and clathrate hydrate formation. The ability of the FBRM to accurately characterize unimodal and bimodal distributions of particles and droplets and to measure agglomeration events was investigated. It was found that while the FBRM can successfully identify system changes, certain inaccuracies exist in the chord length distributions. Particularly, the FBRM was found to oversize unimodal distributions of glass beads, but undersize droplets in an emulsion and was unable to measure full agglomerate sizes. The onset of ice and hydrate nucleation and growth were successfully detected by the FBRM, but quantitative analysis of the particle and agglomerate sizes required simultaneous PVM measurements to be performed.

- by Alberto Montesi and +1
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- Mechanical Engineering, Chemical Engineering, High Pressure, Gas Hydrate

One of the objectives of the Gulf of Mexico Gas Hydrate Joint Industry Project Leg II (GOM JIP Leg II) was the collection of a comprehensive suite of logging-while-drilling (LWD) data within gas-hydrate-bearing sand reservoirs in order to make accurate estimates of the concentration of gas hydrates under various geologic conditions and to understand the geologic controls on the occurrence of gas hydrate at each of the sites drilled during this expedition. The LWD sensors just above the drill bit provided important information on the nature of the sediments and the occurrence of gas hydrate. There has been significant advancements in the use of downhole well-logging tools to acquire detailed information on the occurrence of gas hydrate in nature: From using electrical resistivity and acoustic logs to identify gas hydrate occurrences in wells to where wireline and advanced logging-while-drilling tools are routinely used to examine the petrophysical nature of gas hydrate reservoirs and the distribution and concentration of gas hydrates within various complex reservoir systems. Recent integrated sediment coring and well-log studies have confirmed that electrical resistivity and acoustic velocity data can yield accurate gas hydrate saturations in sediment grain supported (isotropic) systems such as sand reservoirs, but more advanced log analysis models are required to characterize gas hydrate in fractured (anisotropic) reservoir systems. In support of the GOM JIP Leg II effort, well-log data montages have been compiled and presented in this report which includes downhole logs obtained from all seven wells drilled during this expedition with a focus on identifying and characterizing the potential gas-hydrate-bearing sedimentary section in each of the wells. Also presented and reviewed in this report are the gas-hydrate saturation and sediment porosity logs for each of the wells as calculated from available downhole well logs.

- by William Shedd and +1
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- Geology, Geophysics, Gas Hydrate, Data acquisition
- by Ralph Stephen
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- Earth Sciences, Gas Hydrate, Layer, Tethys Oceanic Crust

The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the different slope failures events from different parts of the Costa target areas, which reflect diverse triggering mechanisms. The aim of the first part of this study was to identify the geotechnical response of the sediment to different external mechanisms (earthquake, rapid sedimentation and gas hydrate melting). We have focused on the relation between external mechanisms and the consequence change in the in-situ stress state and the physical, mechanical, and elastic properties of the sediment. In the second part of the paper, the geotechnical properties of the sediment from different Costa areas are presented. Comparison between observed geotechnical properties and the theoretical behaviour was done in order to improve our understanding of the origin of the different observed slides.

- by Miquel Canals
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- Earth Sciences, Marine Geology, Gas Hydrate, Mass Transport

An overview is provided of time-independent physical/chemical properties as related to crystal structures. The following two points are illustrated in this review: (1) Physical and chemical properties of structure I (sI) and structure II (sII) hydrates are well-defined; measurements have begun on sH. Properties of sI and sII are determined by the molecular structures, described by three heuristics: (i) Mechanical properties approximate those of ice, perhaps because hydrates are 85 mol % water. Yet each volume of hydrate may contain as much as 180 volumes (STP) of the hydrate-forming species. (ii) Phase equilibrium is set by the size ratio of guest molecules within host cages, and three-phase (L w -H-V) equilibrium pressure depends exponentially upon temperature. (iii) Heats of formation are set by the hydrogen-bonded crystals and are reasonably constant within a range of guest sizes. (2) Fundamental research challenges are (a) to routinely measure the hydrate phase (via diffraction, NMR, Raman, etc.), and (b) to formulate an acceptable model for hydrate formation kinetics. The reader may wish to investigate details of this review further, via references contained in several recent monographs.

- by dendy II
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- Engineering, Gas Hydrate, CHEMICAL SCIENCES, Chemical Properties

[1] Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current understanding of phenomena involved in... more

- by Jaewon Jang and +1
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- Engineering, Earth Sciences, Carbon Dioxide, Slope Stability

The economic potential of well-studied offshore gas hydrate accumulations and provinces is assessed qualitatively based on consideration of geological, technological, and economic factors. Three types of gas hydrate accumulations are suggested. Structural accumulations occur where thermogenic, bacterial, or mixed gases are rapidly transported from the subsurface petroleum system to the gas hydrate stability zone along faults, mud volcanoes, and other structures (e.g. northwestern Gulf of Mexico, Hydrate Ridge, and Haakon Mosby mud volcano). These accumulations are generally characterized by high gas hydrate concentration in sediment, high resource density, high recovery factors, as well as low development and production costs. It is likely that structural accumulations provide marginal or economic gas hydrate reserves if they represent signi®cant volumes of hydrate-bound gas. Stratigraphic accumulations occur in relatively permeable sediments and form largely from bacterial methane generated in situ or slowly migrated from depth in the section (e.g. Blake Ridge, Gulf of Mexico minibasins). These accumulations are generally characterized by low gas hydrate concentration in sediments and low recovery factor, as well as high development and production costs. Stratigraphic accumulations mainly provide a subeconomic gas hydrate resource. However, in cases such as the Nankai Trough province, high gas hydrate concentration occurs in permeable sand layers and may represent a viable exploration and exploitation target. Less geological data are available on the combination gas hydrate accumulations controlled both by structures and stratigraphy. On the global scale, gas hydrate reserves are likely to represent only a small fraction of the gas hydrate resource because the largest volume of gas hydrate is in subeconomic stratigraphic accumulations. However, some concentrated gas hydrate accumulations may be exploited pro®tably, and those should be subjected to detailed quantitative economic analysis. q (A.V. Milkov).

- by Alexei Milkov
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- Geology, Geophysics, Economic Geology, Gas Hydrate

A synthesis of backscatter imagery coupled with a large 3D seismic dataset in the Lower Congo 18 Basin (LCB) reveals a patchy distribution of features interpreted to be associated with fluid seepage from 19 300 m to 2500 m water depth. With the exception of one region of anomalous backscatter positive relief 20 mounds, all inferred seep sites occur in negative relief pockmarks. The extensive 3D seismic dataset in the 21 LCB offers a unique opportunity to study the plumbing system that is feeding surface cold seep systems, and 22

- by Michel Lopez
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- Earth Sciences, Marine Geology, Gas Hydrate, Gas Hydrates

Holocene and slightly pre-Holocene submarine landslide are found both in high-latitude glacial-dominated margins and in lower latitude, river-dominated margins. This paper constitutes a major assessment on some of the best-studied submarine instabilities in the world. We review and update from original data and literature reports the current state of knowledge of Storegga, Traenadjupet and Finneidfjord slides from the mid-Norwegian margin, Afen Slide from the Faeroe-Shetland Channel,

- by Miquel Canals
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- Earth Sciences, Marine Geology, Gas Hydrate, Mediterranean Sea

Heat capacities of the rocks within a sedimentary basin can significantly influence geothermal gradients if sedimentation or erosion is rapid. This paper provides data on specific heat capacities of minerals and nonporous rocks at 20 • C, derives equations for calculating specific heat capacities of minerals and nonporous rocks at temperatures between 0 • C and 1200 • C, and shows that pressure effects on heat capacities of solids can be neglected. It derives an equation for estimating specific heat capacity of any mineral or nonporous rock as a function of density. Finally, it shows how to calculate the specific heat capacity of any mixture of solid materials. A companion paper discusses specific heat capacities of the fluids in pore spaces of rocks and of fluid-filled porous rocks. The data for minerals and rocks provided herein can be incorporated directly into existing modeling software by users. However, the temperature-dependent equations would have to be incorporated by software developers.

- by Douglas Waples
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- Natural Resources, Software Development, Density, Gas Hydrate
- by Rhonald López González
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- Software Engineering, Gas Hydrate, Cape Open

In the present study the effect of three commercially available anionic surfactants on the hydrate growth from a gas mixture of 90.5 mol% methane/9.5 mol% propane mixture was investigated. The surfactants used were sodium dodecyl sulfate (SDS), sodium tetradecyl sulfate (STS), and sodium hexadecyl sulfate (SHS). The morphology of the growing crystals and the gas consumption were observed during the experiments. The results showed that in the presence of surfactants, branches of porous fibre-like crystals were formed instead of dendritic crystals formed in the absence of any additive. In addition, extensive hydrate crystal growth on the crystallizer walls and a ''mushy'' hydrate layer instead of a thin crystal film appeared at the gas/water interface. Finally, the addition of SDS with concentration range between 242 and 2200 ppm (DT¼ 13.1 K) was found to increase the mole consumption for hydrate formation by approximately 14 times compared to pure water. This increase is related to the change in hydrate morphology, whereby a more porous hydrate forms with enhanced water/gas contacts.

- by Praveen Linga
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- Crystal Growth, Gas Hydrate, Porous Materials, Thin Films
- by William Waite
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- Acoustics, Gas Hydrate, Stability, Multidisciplinary

Por supuesto que puede ser utilizado en forma autónoma por quién tenga que realizar un contrato. Pero la función principal con la que pensamos este instrumento, es la de ser una apoyo material, que se completa con el diskette, y con la... more

- by David Aguilera
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- Earth Sciences, Kinetics, Gas Hydrate, Growth Kinetics

High-resolution δ 13C and δ 18O curves, calibrated against planktonic foraminiferal and calcareous nannofossil biostratigraphy, are provided for the upper Aptian–lower Cenomanian pelagic succession of the Gargano Promontory (Coppa della Nuvola section, southern Italy). The succession consists of two superimposed formations: the Marne a Fucoidi and the Scaglia (lower portion only). According to our integrated biostratigraphy, the entire succession spans

- by Miriam Cobianchi and +1
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- Geology, Carbon Dioxide, Gas Hydrate, Planktonic Foraminifera

Accurate knowledge of hydrate phase equilibrium in the presence of inhibitors is crucial to avoid gas hydrate formation problems and to design/optimize production, transportation and processing facilities. In this communication, we report new experimental dissociation data for various systems consisting of methane/water/ethylene glycol and natural gas/water/ethylene glycol. A statistical thermodynamic approach, with the Cubic-Plus-Association equation of state, is employed to model the phase equilibria. The hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw. The thermodynamic model was used to predict the hydrate dissociation conditions of methane and natural gases in the presence of distilled water or ethylene glycol aqueous solutions. Predictions of the developed model are validated against independent experimental data and the data generated in this work. A good agreement between predictions and experimental data is observed, supporting the reliability of the developed model.

- by Bahman Tohidi
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- Chemical Engineering, Thermodynamics, Gas Hydrate, Natural Gas

Virtually all gas hydrate models use a statistical thermodynamic approach to describe solid phase gas hydrates. An alternative to this model is a "solid solution" model based on classical thermodynamics. Various models are used to describe associated gas phase and aqueous electrolyte properties. None of the electrolyte models, however, are state-of-the-art with respect to gas/electrolyte interactions. The objectives of this work were to (1) develop a classical thermodynamic approach for gas hydrate equilibria, (2) incorporate these hydrate chemistries into a state-of-the-art electrolyte model, and (3) validate the gas hydrate/electrolyte model.

- by Ulrich Wortmann
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- Earth Sciences, Gas Hydrate
- by Win Bin Cheng
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- Geophysics, Oceanography, Gas Hydrate, Seismic Tomography

Elliott-Suresh-Donohue (ESD) equation of state (EOS) which is based on thermodynamic perturbation theory and uses the Wertheim association contribution to account for association interactions, is applied to predict hydrate formation conditions in the presence and absence of thermodynamic inhibitors. The ESD EOS is coupled with the van der Waals-Platteuw model. Methane, ethane, propane, nitrogen, carbon dioxide, n-butane and isobutane are considered as gas components and methanol, ethanol, and mono-ethylene glycol (MEG) are thermodynamic inhibitors considered to be present in the aqueous phase. Different cases of single gas and gas mixtures in pure water and in a solution of water and an inhibitor are considered. To achieve more accurate results, binary interaction coefficients are adjusted as a linear function of temperature. Generally, with regard to the results obtained in various cases, it is shown that the application of the ESD EOS in predicting hydrate formation conditions leads to accurate and acceptable results.

- by Amir H Mohammadi
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- Chemical Engineering, Thermodynamics, Carbon Dioxide, Gas Hydrate

Bulk sedimentary nitrogen isotope (d15Ntot) data have been generated from Lower Jurassic black, carbon-rich shales in the British Isles and northern Italy deposited during the early Toarcian oceanic anoxic event. A pronounced positive d15Ntot excursion through the exaratum Subzone of the falciferum Zone (defined by characteristic ammonites in the British Isles) broadly correlates with a relative maximum in weight percent total organic carbon and, in some sections, with a negative d13Corg excursion. Upwelling of a deoxygenated water mass that had undergone partial denitrification is the likely explanation for relative enrichment of d15Ntot, and parallels may be drawn with Quaternary sediments of the Arabian Sea, Gulf of California, and northwest Mexican margin. The development of Early Toarcian suboxic water masses and consequent partial denitrification is attributed to increases in organic productivity. Approximately coincident phenomena include the following: a relative climatic optimum, realignment of major oceanic current systems, and a possible release of methane gas hydrates from continental margin sediments early in the history of the oceanic anoxic event.

Natural-gas hydrates have been encountered beneath the permafrost and considered a nuisance by the oil and gas industry for years. Engineers working in Russia, Canada and the U.S have documented numerous drilling problems, including kicks and uncontrolled gas releases, in arctic regions. Information has been generated in laboratory studies pertaining to the extent, volume, chemistry and phase behavior of gas hydrates. Scientists studying hydrate potential agree that the potential is great -on the North Slope of Alaska alone, it has been estimated at 590 TCF. However, little information has been obtained on physical samples taken from actual rock containing hydrates.

- by Carl Sondergeld
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- Geology, Geophysics, Chemistry, Production

... regional multi-channel 2D-seismic lines are used to complement the 3D-seismic interpretation (Fig. ... 3) illustrates the major stratigraphic units and geological structures of the subsurface in the ... The main structural and... more

- by Hervé Nouzé
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- Earth Sciences, Marine Geology, Gas Hydrate, Methane

- by Farzad Alavi and +1
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- Thermodynamics, Carbon Dioxide, Equations of State, Gas Hydrate

Potential accumulations of gas hydrates in Alaminos Canyon Block 21 (AC21) in the Gulf of Mexico are thought to occur in a shallow sand-rich interval, stratigraphically separated from sources of free gas below the base of the gas hydrate stability zone (BGHSZ), by an intervening thick layer of clay-and siltrich sediments. Availability of sufficient gas charge from depth, in addition to local biogenic sourcing is considered key to the formation of gas hydrates in the GHSZ. Implicitly, a detailed understanding of geometries associated with fault and fracture networks in relation to potential gas migration pathways can provide additional confidence that seismic amplitude anomalies are related to gas hydrate accumulations. Delineation of fault and fracture systems from high resolution seismic data in and below the gas hydrates stability zone (GHSZ) was performed using an automated algorithmdAnt Tracking. The capturing of small-scale detail has particular significance at AC21, revealing a pervasive network of typically small-extent discontinuities, indicative of fracturing, throughout this intervening clay-and siltrich layer of mass-transport deposits (MTDs). Ant Tracking features appear to correlate, to some extent, with potential gas hydrate accumulations, supporting the concept that fracturing possibly provides migration pathways albeit via a tortuous, complex path. This study demonstrates that the Ant Tracking attribute, in conjunction with detailed seismic interpretation and analysis, can provide valuable evidence of potential gas migration pathways.

- by Sushmita Dasgupta
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- Geology, Geophysics, Fault Detection, Gas Hydrate

Four seep sites located within an $20 km 2 area offshore Georgia (Batumi seep area, Pechori Mound, Iberia Mound, and Colkheti Seep) show characteristic differences with respect to element concentrations, and oxygen, hydrogen, strontium, and chlorine isotope signatures in pore waters, as well as impregnation of sediments with petroleum and hydrocarbon potential. All seep sites have active gas seepage, near surface authigenic carbonates and gas hydrates. Cokheti Seep, Iberia Mound, and Pechori Mound are characterized by oil-stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release. Pechori Mound is further characterized by deep fluid advection of lower salinity pore fluids. The Pechori Mound pore fluids are altered by mineral/water reactions at elevated temperatures (between 60 and 110°C) indicated by heavier oxygen and lighter chlorine isotope values, distinct Li and B enrichment, and K depletion. Strontium isotope ratios indicate that fluids originate from late Oligocene strata. This finding is supported by the occurrence of hydrocarbon impregnations within the sediments. Furthermore, light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at Pechori Mound, Iberia Mound, and Colkheti Seep. C 15+ hydrocarbons at the oil seeps are allochtonous, whereas those at the Batumi seep area are autochthonous. The presence of oleanane, an angiosperm biomarker, suggests that the hydrocarbon source rocks belong to the Maikopian Formation. In summary, all investigated seep sites show a high hydrocarbon potential and hydrocarbons of Iberia Mound, Colkheti Seep, and Pechori Mound are predominantly of thermogenic origin. However, only at the latter seep site advection of deep pore fluids is indicated.

- by Mark Schmidt and +1
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- Geology, Geochemistry, Gas Hydrate, Cold Seep

Multidisciplinary study of seep-related structures on Southern Vøring Plateau has been performed during several UNESCO/IOC TTR cruises on R/V Professor Logachev. High-resolution sidescan sonar and subbottom profiler data suggest that most of the studied fluid discharge structures have a positive relief at their central part surrounded by depression. Our data shows that the present day fluid activity is concentrated on the top of these “seep mounds”. Number of high hydrocarbon (HC) gas saturated sediment cores and 5 cores with gas hydrate presence have been recovered from these structures. δ13C of methane (between −68 and −94.6‰ VPDB) and dry composition of the gas points to its biogenic origin. The sulfate depletion generally occurs within the upper 30–200 cm bsf and usually coincides with an increase of methane concentration. Pore water δ18O ranges from 0.29 to 1.14‰ showing an overall gradual increase from bottom water values (δ18O ∼ 0.35‰). Although no obvious evidence of fluid s...

- by Adriano Mazzini
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- Geology, Geophysics, Gas Hydrate, Methane

Analysis of multi-channel seismic reflection data from the Ulleung Basin, East Sea (Japan Sea), reveals various seismic indicators of gas hydrate and associated gas, including the bottom-simulating reflector (BSR), enhanced reflections below the BSR, and seismic chimneys. The recent recovery of massive gas hydrate by drilling, together with these seismic indicators, strongly suggests favorable conditions for the formation of gas hydrate in the area. The BSR is most common and of a wide range of amplitude and continuity. Seismic chimneys, characterized by columnar zones of amplitude reduction, terminate mostly within the gas hydrate stability zone (GHSZ), but a few extend to pockmarks or mounds on the seafloor. Seismic chimneys with seafloor expressions probably represent vertical vents for gas originating from below the GHSZ. The increase in the degree of amplitude reduction in seismic chimneys with increasing seismic frequency may be due to seismic attenuation by gas bubbles trapped in hydrate-filled/coated fractures in the GHSZ. BSR-derived heat flows range from about 65 to over 115 mW/m 2 , comparable to those from direct measurements. Heat flows in the northern part of the study area are very high for the age of the basin, suggesting hotter than normal mantle temperature. The area of high (N 105 mW/m 2 ) heat flows also coincides largely with the distribution of the presumed incipient oceanic crust, formed during the earliest stage of seafloor spreading.

- by Han Kim
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- Earth Sciences, Marine Geology, Gas Hydrate, Heat Flow

It is generally assumed that oceanic gas hydrates contain a huge volume of natural gases, mainly methane. The most widely cited estimate of global hydrate-bound gas is 21 Â 10 15 m 3 of methane at STP (or f 10,000 Gt of methane carbon), which is proposed as a ''consensus value'' from several independent estimations. This large gas hydrate reservoir is further suggested as an important component of the global carbon cycle and as a future energy source. Here, I present a revised and updated set of well-justified global estimates and discuss how and why they changed over time. It appears that the global estimates of hydratebound gas decreased by at least one order of magnitude from 1970s -early 1980s (estimates on the order of 10 17 -10 18 m 3 ) to late 1980s -early 1990s (10 16 m 3 ) to late 1990s -present (10 14 -10 15 m 3 ). The decrease of estimates is a result of growing knowledge of the distribution and concentration of gas hydrates in marine sediments and ongoing efforts to better constrain the volume of hydrate-bearing sediments and their gas yield. These parameters appear to be relatively well constrained at present through DSDP/ODP drilling and direct measurements of gas concentrations in sediments. The global estimate of hydrate-bound gas that best reflects the current knowledge of submarine gas hydrate is in the range (1 -5) Â 10 15 m 3 ( f 500 -2500 Gt of methane carbon). A significantly smaller global gas hydrate inventory implies that the role of gas hydrates in the global carbon cycle may not be as significant as speculated previously. Gas hydrate may be considered a future energy source not because the global volume of hydrate-bound gas is large, but because some individual gas hydrate accumulations may contain significant and concentrated resources that may be profitably recovered in the future. D

- by Alexei Milkov
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- Earth Sciences, Carbon Cycle, Gas Hydrate, Global Carbon Cycle

Several gas seeps and near-surface gas hydrate deposits have been identified in 850-900-m water depth on the continental slope offshore Batumi, Georgia (eastern Black Sea) using deep-towed high-resolution sidescan sonar data. The seeps are located on a ridge named Kobuleti Ridge separating two canyons: the Supsa canyon north of the ridge and the deeply incised central canyon south of it. The southern wall of this canyon shows signs for additional gas seeps. Gas seeps are shown by acoustic anomalies in the water column on raw sonar records and as high backscatter intensity areas on processed data.

- by Gerhard Bohrmann
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- Earth Sciences, Marine Geology, Gas Hydrate, Methane
- by Cristina Amon
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- Environmental Science, Applied Research, Science and Technology, Gas Hydrate

U . S . D e p a r t m e n t o f E n e r g y • O f fi c e o f F o s s i l E n e r g y • N a t i o n a l E n e r g y T e c h n o l o g y L a b o r a t o r y CONTaCT Ray Boswell Technology Manager-Methane Hydrates, Strategic Center for... more

U . S . D e p a r t m e n t o f E n e r g y • O f fi c e o f F o s s i l E n e r g y • N a t i o n a l E n e r g y T e c h n o l o g y L a b o r a t o r y CONTaCT Ray Boswell Technology Manager-Methane Hydrates, Strategic Center for Natural Gas & Oil 304-285-4541 ray.boswell@netl.doe.gov Methane Hydrate Newsletter Reprinted from the Fall 2006

- by Thomas Collett
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- Gas Hydrate

Gas hydrates are increasingly considered a potential energy resource. Various methods of exploiting gas hydrates (thermal stimulation, depressurization, inhibitor injection, etc.) have been proposed so far, but each of them has some drawbacks. To overcome some of these drawbacks, we propose a new technology for producing methane from gas hydrates. The method uses in situ thermal stimulation by introducing a specially designed hydrate heating apparatus into a horizontal borehole drilled into a gas hydrate zone (GHZ). Instead of using water or other hot fluid injected from the surface or another location away from the GHZ, an air/gas fuel mixture is introduced into a combustion vessel from the surface via a fuel injection tubing string directly into GHZ. Burning the fuel mixture results in the heat necessary to dissociate gas hydrate. The freed natural gas is then conveyed to the surface via a casing that is lining the wellbore. This technology has the advantage of permitting the dissociated gas to be produced through the same wellbore through which the air/gas fuel mixture is injected, thereby avoiding the need of using two wells (injection and exploitation). An estimated energy gain efficiency of the proposed method shows that only about 1.1 to 1.7% of gas produced will have to be burned to decompose hydrates. Previous estimates of other thermal decomposition methods, for example steam injection, show that about 50% of gas produced will have to be burned just to decompose hydrates. An added advantage is that the produced natural gas is not mixed with the combustion gases, thus avoiding the problem of the resulting gas having a BTU content that is too low.

- by Constantin Cranganu
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- Chemistry, Gas Hydrate, Energy efficiency, Natural Gas
- by Herman Karl
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- Geology, Gas Hydrate, Geophysical Survey, Natural Gas

The Nyegga region, located at water depths of about 600–800 m on the NW European continental margin, contains more than 200 pockmarks. Recently collected TOPAS seismic profiles and EM1002 bathymetric records now provide high-resolution information on their seabed and shallow sub-seabed geological setting. The identified pockmarks are up to 15 m deep, between 30 m and 600 m across and reach a maximum area of ca. 315,000 m2. The pockmarks are sediment-empty features. They do not have any preferred direction of orientation and show large variations in their shape. The pockmarks are restricted to a <16.2 cal. ka old sediment unit. This unit comprises sandy mud and is characterised by sedimentation rates of ca. 1 mm/year. The pockmarks are localised over a thick late Plio-Pleistocene prograding sediment package and a polygonal faulted Miocene-Oligocene ooze-rich unit. The late Plio-Plistocene deposits host bottom simulating reflectors, indicative of gas hydrate-bearing sediments. Inspection of the newly collected high-resolution dataset, combined with previously analysed sediment cores and 2D multichannel seismic profiles, reveals that the Nyegga pockmark field does not show any strong relationship between seabed features, sub-seabed structures and the sedimentary setting. This suggests a more complex evolution history of the Nyegga pockmark field then previously thought.

- by Atle Nygård
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- Geophysics, Oceanography, Structural Control, Gas Hydrate

Keywords: mass-transport deposit turbidite earthquake subduction erosion seismic cycle Investigations of Mass-Transport Deposits (MTDs) and turbidite deposition in the confined North Ecuador subduction trench provide access to paleoseismic information and insights into long-term mechanisms for frontal tectonic erosion at a convergent margin. The studied trench has been the site of four great subduction earthquakes (7.7 ≤ Mw ≤ 8.8) during the 20th century. The trench is isolated from major continental sediment input, so that investigated MTDs and turbidites are considered of local origin. Swath bathymetry, seismic reflection and Chirp data, together with sedimentary cores and 14 C dating revealed that seven MTDs were emplaced in distinct trench sub-basins since ∼ 23 kyr, and 27 turbidites deposited in the southernmost trench sub-basin since ∼ 4.9 kyr. Our analysis shows that six MTDs were derived from the margin, while a single one stemmed from the outer trench wall. Temporal correlations between MTDs emplaced within trench sub-basins separated by a structural saddle, indicate that the seven MTDs were emplaced during five main events. Three were triggered locally and tentatively dated 5.8, 1.6 kyr and Recent, whereas four were emplaced in distinct trench sub-basins as a result of two regional events at 22.6 and 15.4 kyr. None of the MTDs occurred during the fast stage of the last sea-level rise (∼ 13 to 8 kyr). However, dissociation of gas hydrates during the last 8 kyr-stage of slow sea-level rise might have contributed to trigger the three youngest MTDs. The large 1.5-13.5 kyr return time of the MTDs contrasts with that of 189 yr of the turbidites. The later is consistent with the 73 yr return time of two local Mw ≥ 8.2 earthquakes, implying that turbidites might have been triggered by large earthquakes. The very large MTDs return time is attributed to long-term deformation processes and mechanical weakening of the margin outer wedge, in response to repeated variations in basal friction, pore pressure and margin extensional/contraction strain over multiple earthquake cycles. This process contributes to short-term frontal erosion, the rate of which is estimated to be 8.6 · 10 − 3 km 3 /kyr/km, since at least 15.4 kyr.

- by m sosson
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- Earth Sciences, Gas Hydrate, Erosion, Physical sciences