The inter-conversion of methane-ethane hydrate from metastable to stable structures was studied using Raman spectroscopy. To investigate factors controlling the inter-conversion, the rate of structural transition was measured at 59% and 93% methane in ethane. The observed slower structural conversion rate in the lower methane concentration atmosphere can be explained in terms of the differences in kinetics (mass transfer of gas and water rearrangement). Also, the effect of kinetic hydrate inhibitors, poly-N-vinylpyrrolidone (PVP) and polyethylene-oxide (PEO), on the hydrate metastability was investigated at 65% and 93% methane in ethane. PVP increased the conversion rate at 65% methane in ethane (sI is thermodynamically stable), but retarded the rate at 93% methane in ethane (sII is thermodynamically stable), indicating that the function of PVP depends on hydrate structure. PEO did not affect the structural transition considerably for either methane-ethane compositions.

Gas Hydrates Markup Language (GHML) has been under development since 2003 by the CODATA Task Group “Data for Natural Gas Hydrates” as an international standard for data storage and transfer in the gas hydrates community. We describe the development of this evolving communication protocol and show examples of its implementation. In describing this protocol, we concentrate on the most recent updates that have enabled us to include ThermoML, the widely used IUPAC XML communication standard for thermodynamic data, into the GHML schema for the representation of all gas hydrate thermodynamic data. In addition, a new GHML element for the description of crystal structures is described. We then demonstrate a new tool - Guided Data Capture for Gas Hydrates - for the rapid capture of large amounts of data into GHML format. This tool is freely available and publicly licensed for use by any gas hydrate data producer or collector interested in using the GHML format. An effort will be made to achieve a consensus between scientific journals publishing thermophysical and structural data for gas hydrates to recommend their authors use this new software tool in order to generate GHML data files at the time of the submission of scientific articles. Finally, we will demonstrate how this format can be used to advantage when accessing data from a web-based resource by showing on-line access to GHML files for gas hydrates through a web service.

The chloride anion is known to be the most abundant salt ion in sea water. At the regions such as ODP Sites 1249 and 1250 the highly enriched chloride concentration is observed in a zone extended from near the sediment surface (~1 mbsf) to depths about 25 mbsf. Here, we designed the in-situ electric circuit system for measuring chloride concentration within reliable accuracy. In the cylindrical cell the 5-10 tubes having holes on the wall and electrodes were equipped around clay mixture. The open holes were made to regulate to a certain degree the interface area between methane gas and clay sample. As may be anticipated, the chloride concentration abnormally increased under fast rate condition for forming methane hydrate, but no noticeable concentration change was detected under relatively low rate. In fact, the present experiment seems to be a lot deficient to investigate the ion diffusion and moreover does not fully reflect the real deep-sea floor condition, but the meaningful results for describing the abnormal salinity enrichment might be drawn. The physical effects of chloride anions on surface morphologies of methane hydrate formed in the sediments were additionally examined with the Field Emission-Scanning Electronic Microscope (FE-SEM).

Remote determination of the hydrate content of marine sediments remains a challenging problem. In the absence of boreholes, the most commonly used approach involves the measurement of Pwave velocities from seismic experiments. A range of seismic effective medium methods has been developed to interpret these velocities in terms of hydrate content, but uncertainties about the pore-scale distribution of hydrate can lead to large uncertainties in this interpretation. Where borehole geophysical measurements are available, electrical resistivity is widely used as a proxy for hydrate content, and the measurement of resistivity using controlled source electromagnetic methods shows considerable promise. However, resistivity is commonly related to hydrate content using Archie’s law, an empirical relationship with no physical basis that has been shown to fail for hydrate-bearing sediments. We have developed an electrical effective medium method appropriate to hydrate-bearing sediments based on the application of a geometric correction to the Hashin-Shrikman conductive bound, and tested this method by making resistivity measurements on artificial sediments of known porosity. We have adapted our method to deal with anisotropic grains such as clay particles, and combined it with a well-established seismic effective medium method to develop a strategy for estimating the hydrate content of marine sediments based on a combination of seismic and electrical methods. We have applied our approach to borehole geophysical data from Integrated Ocean Drilling Program Expedition 311 on the Vancouver Island margin. Hydrate saturations were determined from resistivity logs by adjusting the geometric factor in areas of the log where hydrate was not present. This value was then used over the entire resistivity log. Hydrate saturations determined using this method match well those determined from direct measurements of the methane content of pressurized cores.

Potential applications of gas hydrates, including carbon dioxide sequestration in the deep ocean, coal bed methane–produced water treatment, storage and transportation of natural gas, and gas separations, are based on continuous, large-scale production of gas hydrates. A novel three-phase injector/reactor was developed at Oak Ridge National Laboratory for the continuous synthesis of gas hydrates. The reactor receives water and a hydrate-forming species and rapidly forms hydrate with a residence time of a few seconds. The reactor was designed to maximize interfacial area between reactants, thus minimizing mass transfer barriers and thermal effects that negatively affect conversion of reactants into hydrate. The cohesiveness and the density of the hydrate product desired for specific applications can be controlled by slight variations in the geometry of an exchangeable internal piece of the reactor, the choice of the guest gas, and by the regulation of operating parameters such as pressure, temperature, reactant ratios, and degree of emulsification. In general, spraying one reactant into the other, within the jet-break up regime, results in the highest conversions. The reactor has been field tested for ocean carbon sequestration and in the laboratory for coal-bed methane produced-water treatment using liquid carbon dioxide. In this paper, the application of the reactor for ocean carbon sequestration will be discussed.

Modeling of the onset of permafrost formation and succeeding gas hydrate formation in the changing surface temperature environment has been done for the Beaufort-Mackenzie Basin (BMB). Numerical 1D modeling is constrained by deep heat flow from deep well bottom hole temperatures, deep conductivity, present permafrost thickness and thickness of Type I gas hydrates. Latent heat effects were applied to the model for the entire ice bearing permafrost and Type I hydrate intervals. Modeling for a set of surface temperature forcing during the glacial-interglacial history including the last 14 Myr, the detailed Holocene temperature history and a consideration of future warming due to a doubling of atmospheric CO2 was performed. Two scenarios of gas formation were considered; case 1: formation of gas hydrate from gas entrapped under deep geological seals and case 2: formation of gas hydrate from gas in a free pore space simultaneously with permafrost formation. In case 1, gas hydrates could have formed at a depth of about 0.9 km only some 1 Myr ago. In case 2, the first gas hydrate formed in the depth range of 290 – 300 m shortly after 6 Myr ago when the GST dropped from -4.5 °C to -5.5. °C. The gas hydrate layer started to expand both downward and upward subsequently. More detailed modeling of the more recent glacial–interglacial history and extending into the future was done for both BMB onshore and offshore models. These models show that the gas hydrate zone, while thinning will persist under the thick body of BMB permafrost through the current interglacial warming and into the future even with a doubling of atmospheric CO2.

In this paper we will discuss the first successful molecular simulation studies exploring the statesteady crystal growth of sI and sII methane hydrates. Since the molecular modeling of the crystal growth of gas hydrates has proven in the past to be very challenging, we will provide a brief overview of the simulation framework we have utilized to achieve heterogeneous growth within timescales accessible to simulation. We will probe key issues concerning the nature of the solid/liquid interface for a variety of methane hydrate systems and will make important comparisons between various properties. For example, the interface demonstrates a strong affinity for methane molecules and we find a strong tendency for water molecules to organize into cages around methane at the growing interface. The dynamical nature of the interface and its microfaceted features will be shown to be crucial in the characterization of the interface. In addition to the small and large cages characteristic of sI and sII hydrates, water cages with a 51263 arrangement were identified during the heterogeneous growth of both sI and sII methane hydrate and their potential role in cross-nucleation of methane hydrate structures will be discussed. We will describe a previously unidentified structure of methane hydrates, designate structure sK, consisting of only 51263 and 512 cages, and will also show that a polycrystalline hydrate structure consisting of sequences of sI, sII and sK elements can be obtained. In this paper we will also detail a variety of host defects observed within the grown crystals. These defects include vacant cages, multiple methane molecules trapped in large cages, as well as one or more water molecules trapped in small and large cages. Finally, preliminary results obtains for THF and CO2 hydrates will be presented and their behaviour contrasted to that of methane hydrate.

In February 2007, the U.S. Department of Energy, BP Exploration (Alaska), Inc., and the U.S. Geological Survey conducted an extensive data collection effort at the "Mount Elbert #1" gas hydrates stratigraphic test well on the Alaska North Slope (ANS). The 22-day field program acquired significant gas hydrate-bearing reservoir data, including a full suite of open-hole well logs, over 500 feet of continuous core, and open-hole formation pressure response tests. Hole conditions, and therefore log data quality, were excellent due largely to the use of chilled oilbased drilling fluids. The logging program confirmed the existence of approximately 30 m of gashydrate saturated, fine-grained sand reservoir. Gas hydrate saturations were observed to range from 60% to 75% largely as a function of reservoir quality. Continuous wire-line coring operations (the first conducted on the ANS) achieved 85% recovery through 153 meters of section, providing more than 250 subsamples for analysis. The "Mount Elbert" data collection program culminated with open-hole tests of reservoir flow and pressure responses, as well as gas and water sample collection, using Schlumberger's Modular Formation Dynamics Tester (MDT) wireline tool. Four such tests, ranging from six to twelve hours duration, were conducted. This field program demonstrated the ability to safely and efficiently conduct a research-level openhole data acquisition program in shallow, sub-permafrost sediments. The program also demonstrated the soundness of the program's pre-drill gas hydrate characterization methods and increased confidence in gas hydrate resource assessment methodologies for the ANS.

Nucleation is a stochastic process, most accurately represented by a probability distribution. Obtaining sufficient data to define this probability distribution is a laborious process. Here, we describe a novel instrument capable of the automated determination of hydrate nucleation probability under non-equilibrium conditions for a range of natural gas mixtures at pressures up to 10MPa. The instrument is based on the automated lag time apparatus (ALTA) which was developed to study the stochastic nature of nucleation in ambient pressure systems [1].We demonstrate that the probability distribution represents a robust and reproducible tool for the quantitative evaluation of hydrate formation risk under pseudo-realistic pressure conditions.

Two internationally-partnered research well programs, in 1998 and 2002, studied the Mallik gas hydrate accumulation in the Mackenzie Delta, Canada. Gas hydrate bearing intervals were cored, logged and production tested thus establishing Mallik as an excellent site for testing geophysical imaging techniques. Here, we apply a model-based acoustic impedance inversion technique to 3D seismic reflection data acquired over the Mallik area to characterize gas hydrate occurrences and to help define their spatial extent away from well control. Sonic logs in Mallik research wells show that P-wave velocity of sediments increases with hydrate saturation, enough to produce detectable reflections for the lower two of three known gas hydrate zones. The inversion method converts these reflections into acoustic impedances from which velocity and hydrate saturation can be estimated. Acoustic impedance inversion results indicate that the deepest gas hydrate zone covers an area of approximately 900,000 m2. With some assumptions on the lateral continuity of gas hydrate saturation, porosity and thickness measured at the wells, we estimate that this zone contains approximately 771x106 m3 of gas at standard atmospheric pressure. At a regional scale, results allowed the detection of a high-velocity area near the A-06 well, about 6 km south-east of 5L-38. We infer that the high velocity area corresponds to a gas hydrate accumulation. Logging data in A-06 indicate the presence of gas hydrates in this area and support our interpretation.