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FIRST-PRINCIPLES STUDY ON MECHANICAL PROPERTIES OF CH4 HYDRATEMiranda, Caetano R., Matsuoka, Toshifumi 07 1900 (has links)
The structural and mechanical properties of s-I methane hydrate have been investigated by first
principles calculations. For the first time, the fully elastic constant tensor of s-I methane hydrate
is obtained entirely ab-initio. The calculated lattice parameter, bulk modulus, and elastic
constants were found to be in good agreement with experimental data at ambient pressure. The
Young modulus, Poisson ratio and bulk sound velocities are estimated from the calculated
elastic constants and compared with wave speed measurements available.
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AB INITIO STRUCTURE DETERMINATION OF GAS HYDRATES AND REFINEMENT OF GUEST MOLECULE POSITIONS BY POWDER X-RAY DIFFRACTIONTakeya, Satoshi, Udachin, Konstantin A., Ripmeester, John A. 07 1900 (has links)
Structure determination of powdered crystals is still not a trivial task. For gas hydrates, the difficulty lies in how to determine the rotational disorder and cage occupancies of the guest molecules without other supporting information or constraints because the complexity of the problem for the powder diffraction technique generally depends on the number of atoms to be located in the asymmetric unit. Here, the crystal structures of gas hydrates of CO2, C2H6, C3H8, and Methylcyclohexane/CH4, as determined by the direct-space and Rietveld techniques are reported. The resultant structures and cage occupancies were consistent with results found from conventional experimental methods using single crystal x-ray diffraction or solid-state 13C-NMR. It was shown that the procedures reported in this study make it possible to determine guest disorder and absolute cage occupancy of gas hydrates even from powder crystal.
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EXPERIMENTAL STUDIES OF THE SATURATION LEVEL OF METHANE HYDRATE IN THE EASTERN NANKAI TROUGH SEDIMENTSKawasaki, Tatsuji, Fujii, Tetsuya, Nakamizu, Masaru, Lu, Hailong, Ripmeester, John A. 07 1900 (has links)
The pore saturation of natural gas hydrate in sediments is a key parameter for estimating hydrate resources in a reservoir. For a better understanding of gas hydrate distribution, the experimental study of the pore saturation of methane hydrate in sediments from a hydrate reservoir in the Eastern Nankai Trough have been carried out. In total, eleven samples, comprising sand, silty sand, silt, and representative of the main sediment types identified in the Eastern Nankai trough, were tested. The results obtained clearly indicate a particle size and clay content dependent trend: almost 100% of pores were saturated with methane hydrate in sand when little silt and clay were present, decreasing to ~ 13% in silty sand (sand 54%, silt 41% and clay 5%), and ~ 4% in clayey silt. These results are generally consistent with NMR logging results for high-saturation samples, but somewhat different for samples with medium or low saturation levels.
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THE SEARCH FOR “GREEN INHIBITORS:” PERTURBING HYDRATE GROWTH WITH BUGSHuva, Emily I., Gordienko, Raimond V., Ripmeester, John A., Zeng, Huang, Walker, Virginia K. 07 1900 (has links)
Certain organisms, including some bugs (both insects and microbes) are able to survive low
temperatures by the production of either ice nucleating proteins (INPs) or antifreeze proteins
(AFPs). INPs direct crystal growth by inducing rapid ice formation whereas AFPs adsorb to ice
embryos and decrease the temperature at which the ice grows. We have also shown that certain
AFPs can inhibit the crystallization of clathrate hydrates and eliminate more rapid
recrystallization or “memory effect”. Here we examine several bacterial species with iceassociating
properties for their effect on tetrahydrofuran (THF) hydrate crystallization. The
bacteria Chryseobacterium sp. C14, which shares the ice recrystallization inhibition ability of
AFPs, increased induction time to THF hydrate crystallization in isothermal experiments. In an
effort to understand the association between AFPs and THF hydrate we have produced
bacterially-expressed AFPs as probes for hydrate binding. Although the structure of hydrates is
clearly distinct from ice, the apparent potential for these products to perturb clathrate hydrate
growth compels us to explore new techniques to uncover “green inhibitors” for hydrate binding.
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NATURAL GAS HYDRATES UP CLOSE: A COMPARISON OF GRAIN CHARACTERISTICS OF SAMPLES FROM MARINE AND PERMAFROST ENVIRONMENTS AS REVEALED BY CRYOGENIC SEMStern, Laura A., Kirby, Stephen H. 07 1900 (has links)
Using cryogenic SEM, we investigated the physical states of gas-hydrate-bearing samples
recovered by drill core from several localities including the SE India margin (NGHP Expedition
01), Cascadia margin (IODP Leg 311), Gulf of Mexico (RV Marion Dufresne 2002), and
Mackenzie River Delta (Mallik site, well 5L-38). Core material with a significant fraction of
preserved hydrate has only been obtained for cryogenic SEM investigation from relatively few
sites worldwide to date, yet certain consistent textural characteristics, as well as some clear
differences between sites have been observed. Gas hydrate in cores recovered from Cascadia,
Gulf of Mexico, and Mallik often occurs as a dense substrate with typical grain size of 30 to as
large as 200 μm. The hydrate often contains a significant fraction of isolated macropores that are
typically 5–100 μm in diameter and occupy 10-30 vol. % of the domain. In fine-grained sediment
sections of marine samples, gas hydrate commonly forms small pods or lenses with clay platelets
oriented sub-parallel around them, or as thin veins 50 to several hundred microns in thickness. In
some sections, hydrate grains are delineated by a NaCl-bearing selvage that forms thin rinds
along hydrate grain exteriors, presumably produced by salt exclusion during original hydrate
formation. Preliminary assessment of India NGHP-01 samples shows some regions consistent
with the observations described above, as well as other regions dominated by highly faceted
crystals that line the walls or interior of cavities where the hydrate grows unimpeded. Here, we
focus on gas hydrate grain morphology and microstructures, pore characteristics and distribution,
and the nature of the hydrate/sediment grain contacts of the recovered samples, comparing them
to each other and to laboratory-produced gas hydrates grown under known conditions.
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MICROMECHANICAL ADHESION FORCE MEASUREMENTS BETWEEN CYCLOPENTANE HYDRATE PARTICLESDieker, Laura E., Taylor, Craig J., Koh, Carolyn A., Sloan, E. Dendy 07 1900 (has links)
Cyclopentane hydrate interparticle adhesion force measurements were performed in pure cyclopentane liquid using a micromechanical force apparatus. Cyclopentane hydrate adhesion force measurements were compared to those of cyclic ethers, tetrahydrofuran and ethylene oxide, which were suspected to be cyclic ether-lean and thus contain a second ice phase. This additional ice phase led to an over-prediction of the hydrate interparticle forces by the capillary bridge theory. The adhesion forces obtained for cyclopentane hydrate at atmospheric pressure over a temperature range from 274-279 K were lower than those obtained for the cyclic ethers at similar subcoolings from the formation temperature of the hydrate. The measured cyclopentane interparticle adhesion forces increased linearly with increasing temperature, and are on the same order of magnitude as those predicted by the Camargo and Palermo rheology model.
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PRELIMINARY DISCUSSION ON GAS HYDRATE RESERVOIR SYSTEM OF SHENHU AREA, NORTH SLOPE OF SOUTH CHINA SEAWu, Nengyou, Yang, Shengxiong, Zhang, Haiqi, Liang, Jinqiang, Wang, Hongbin, Su, Xin, Fu, Shaoying 07 1900 (has links)
Gas hydrate is a very complicated reservoir system characterized of temperature, pressure, gas composition, pore-water geochemical features, and gas sources, gas hydrate distribution within the gas hydrate stability zone. Temperature, pressure and the gas composition of the sediments were suitable for gas hydrate formation in the gas hydrate reservoir system of Shenhu Area, north slope of South China Sea. The high-resolution seismic data and the gas hydrate drilling getting high concentrations of hydrate (>40%) in a disseminated form in foram-rich clay sediment showed that gas hydrate is distributed heterogeneously at all spatial scales in all drill holes, and the hydrate-bearing sediments ranged several ten meters in thickness are located in the lower part of gas hydrate stability zone (GHSZ), just above the bottom of gas hydrate stability zone (BGHSZ). It is likely seem that the methane to crystallize gas hydrate is from in-situ microbial methane.
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OBSERVED GAS HYDRATE MORPHOLOGIES IN MARINE SEDIMENTSHolland, Melanie, Schultheiss, Peter, Roberts, John, Druce, Matthew 07 1900 (has links)
Small-scale morphology of gas hydrate is important for understanding the formation of gas
hydrate deposits, for estimating the concentrations of gas hydrate from geophysical data, and for
predicting their response to climate change or commercial production. The recent use of borehole
pressure coring tools has allowed marine gas-hydrate-bearing sediments to be recovered with
centimeter to sub-millimeter gas hydrate structures preserved in their in situ condition. Once
these sediment samples are recovered at in situ temperature and pressure, nondestructive
analyses, including gamma density, P-wave velocity, and X-ray imaging, are used to examine the
character of the gas hydrate relative to the structure of the surrounding sediment. Gas hydrate
morphology from pressure core data is summarized from the recent national gas hydrate
expeditions of India, China, and Korea, as well as from Ocean Drilling Program Leg 204,
Integrated Ocean Drilling Program Expedition 311, and the Gulf of Mexico Chevron-Texaco
Joint Industry Project. The most striking result is the variability of gas hydrate morphology in
clay, ranging from complex vein structures to an invisible pore-filling matrix. Both of these
morphologies have been observed in clay sediments at gas hydrate saturations equivalent to
30-40% of pore volume. A clear knowledge of detailed gas hydrate morphology will provide
important data to help determine the mechanisms of gas hydrate deposit formation and also
provide crucial data for modeling the kinetics of deposit dissociation, from both natural and
artificial causes. The morphology also has large effects on sedimentary physical properties, from
seismic velocities on a large scale to borehole electrical resistivities on a smaller scale, and gas
hydrate morphology will therefore impact estimation of gas hydrate saturation from geophysical
data. The detailed morphology of gas hydrate is an essential component for a full understanding
of the past, present, and future of any gas hydrate environment.
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PETROLEUM HYDRATE DEPOSITION MECHANISMS: THE INFLUENCE OF PIPELINE WETTABILITYAspenes, Guro, Høiland, Sylvi, Barth, Tanja, Askvik, Kjell Magne, Kini, Ramesh A., Larsen, Roar 07 1900 (has links)
The mechanisms by which hydrates deposit in a petroleum production-line are likely to be related
to pipeline surface properties, e.g. pipeline material, surface energy and roughness. In this work,
the wettability alteration of pipeline surfaces from contact with oil, as well as the adhesion energy
between water and solid in the presence of oil is investigated. Contact angles are determined as a
function of solid material and oil composition, for both model oils and crude oils. Although contact
angles in oil/brine/solid systems have been extensively reported in the literature, the variety of solids
that may mimic a pipeline is limited. In this study, we include various metal surfaces in addition to
glass and a coating. Initial results from using near infrared imaging for collecting contact angle data
in non-translucent systems are also presented.
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CRITICAL DESCRIPTORS FOR HYDRATE PROPERTIES OF OILS: COMPOSITIONAL FEATURESBorgund, Anna E., Høiland, Sylvi, Barth, Tanja, Fotland, Per, Kini, Ramesh A., Larsen, Roar 07 1900 (has links)
In petroleum production systems, hydrate morphology is observed to be influenced by the crude
oil composition. This work is aimed at identifying which crude oil compositional parameters that
need to be determined in order to evaluate natural anti-agglomerating properties of crude oils, i.e. the
critical compositional descriptors. The compositional features of 22 crude oils have been studied,
and multivariate data analysis has been used to investigate the possibility for correlations between
several crude oil properties. The results show that biodegradation together with a relatively large
amount of acids are characteristic for non-plugging crude oils, while excess of basic compounds is
characteristic for plugging crude oils. The multivariate data analysis shows a division of the nonbiodegraded
oils, which are all plugging, and the biodegraded oils. In addition, the biodegraded
oils seem to be divided into two groups, one with plugging oils and one with mostly non-plugging
oils. The results show that the wettability can be predicted from the variables biodegradation level,
density, asphaltene content and TAN.
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