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[en] Highlights: ► Scaling criteria is derived for gas hydrate production by depressurization. ► Sensitivity factor is defined to evaluate dominance degree of scaling criteria. ► Dominance degree is quantitatively evaluated by proposed numerical method. - Abstract: A numerical approach of sensitivity analysis of dimensionless parameters in gas hydrate reservoir physical simulation is proposed by analyzing the sensitivity factor defined as the relative variation ration of a target function with respect to the relative variation of dimensionless parameter. With this approach, the dominance degree of all the dimensionless parameters can be quantitatively evaluated and the dominant ones can be singled out conveniently. Taking a 1-D experiment of gas production from hydrate reservoir by depressurization as an example, we find that the order of sensitivity factors ranges from 10−5 to 100. The most dominant dimensionless parameter is the dimensionless initial temperature of hydrate reservoir and the dimensionless phase equilibrium pressure of gas hydrate, which just reflects that the consumed energy for hydrate dissociation comes from the energy contained in formation and the driving force for hydrate dissociation is very important in hydrate dissociation by depressurization
[en] Highlights: • Water-saturated hydrate dissociation by Huff and Puff method are studied. • It is hard to dissociate water-saturated hydrate by H&P above the equilibrium pressure. • Hydrate can be dissociated completely by H&P below the equilibrium pressure. - Abstract: The world has huge reserves of gas hydrates which are considered to be a potential energy resource. Therefore, developing methods for commercial gas production from hydrate reservoirs are attracting extensive attention. In order to mimic the geological condition of the practical oceanic hydrate reservoir, water-saturated hydrate sample with low gas saturation (8.27%) was obtained by the formation process of multi-step water injection. The huff and puff (H&P) method (above or below the equilibrium pressure for hydrate dissociation) was applied for hydrate dissociation. Results show that the system pressure rises with the increase of the H&P cycle for the H&P method above the equilibrium pressure. Furthermore, the dissociated hydrate in the injection period can be reformed in the soaking and production periods, and hydrate saturation increases mildly after each cycle of H&P. Hence, the H&P method above the equilibrium pressure is unpractical for hydrate dissociation with low gas saturation. However, the hydrate in the reservoir can be completely dissociated by the H&P method below the equilibrium pressure. Therefore, in the water-saturated hydrate reservoir, the regular H&P method is not suitable. The regular H&P should combine with depressurization method for gas recovery from the water-saturated hydrate reservoir.
[en] Marine landslide due to gas hydrate dissociation is a kind of potential heavy hazards. Numerical simulation was processed to investigate the deformation, landslide and effects of main factors on the critical scale of dissociation zone to induce marine landslides during/after dissociation of gas hydrate. A simple method for analyzing the critical scale was presented based on the limit equilibrium method. It is shown that the maximum settlement is located near the upper side of the dissociation zone. The soil near the lower side of the dissociation zone uplifts. There is a critical scale of dissociation zone over which landslide will occur under given conditions. Expansion modes of the dissociation zone have obvious effects on the critical scale.
[en] Ways of determining Langmuir constants are evaluated to improve the accuracy of calculating the parameters of hydrate processes. An indirect approach is used in the evaluation that consists of calculating the hydrate number using the Langmuir constants and comparing it to known values. The criterion of evaluation is the minimum deviation between these values. The selection of the best way of calculating the Langmuir constants is validated.
[en] Broad developments in experimental NMR techniques have opened new and exciting opportunities for application of solid state nuclear magnetic resonance (SS NMR) in studies of gas hydrates and inclusion compounds in general. Perhaps the most important advance of the last 10 years was the extension into very high magnetic fields beyond 20 T. This progress is especially significant in studies concerned with low-γ, low natural abundance, and quadrupolar nuclei. This work reports our recent exploration of clathrate hydrates and other inclusion compounds (β-quinol, tert-Bu-Calix, and dodecasil-3C) with SS NMR of nuclei that were not so long ago completely out of reach for NMR, namely 131Xe, 83Kr, and 33S. Although 129Xe is a widely used NMR probe, applications of the low-γ isotope 131Xe were very scarce. Being a quadrupolar spin 3/2 nucleus, 131Xe provides an additional probe for sampling the electric field gradients in inclusion compounds. Another nucleus that has been seriously under-explored is 83Kr, with its very low γ being the main obstacle, and along with quadrupolar coupling we report the first detection of the chemical shift anisotropy in krypton. The relative values of the Sternheimer antishielding factors for 131Xe and 83Kr, obtained by comparison of the spectra of the two in identical cage environments, are also discussed. Though 33S NMR of solids is notoriously difficult due to its low γ, low natural abundance, and relatively large quadrupolar moment, working at the field of 21.1 T it was possible to acquire, in a reasonable time, natural abundance 33S SS NMR spectra of various H2S and SO2 gas hydrates and inclusion compounds. In most cases the spectra are dominated by the quadrupolar interactions, providing information on the symmetry of the cages encapsulating the guest molecules, and also show the effects of very rapid reorientation of the encaged H2S and SO2. The impact of the introduction of new NMR nuclei on hydrate research is discussed. (author)
[en] This paper deals with the principle of determining the rate of guest-gas uptake into a clathrate hydrate being formed in a semibatch-type isobaric reactor or a batch-type closed reactor on the basis of experimental data for the guest-gas supply into the reactor or the pressure change inside the reactor. The specific issue considered here is the possible necessity of taking into account the effect of the change in the total volume of the condensed (liquid + hydrate) phases inside the reactor during each hydrate-forming operation. General schemes for evaluating this effect in semibatch and batch operations are formulated and applied to some specific hydrate-forming operations to evaluate the effect on estimating the guest-gas uptake into the hydrate
[en] Complete text of publication follows. Seabed resources like submarine hydrothermal deposits and methane hydrate have lately become a subject of special interest as potential alternative resources for the future. It is, however, difficult to estimate the accurate abundance of those resources. One of the reasons is considered that effective methods for such exploration have not been well-established. On the other hand, undersea technology and exploration techniques on land have recently achieved remarkable development. Thus appropriate exploration near the sea floor must advance great development of the deep-sea resources. From this point of view, we started a project to develop new deep-sea exploration tools for seabed resources by electrical and magnetic methods with financial support of MEXT (Ministry of Education, Culture, Sports, Science and Technology - Japan). In this project, we are working on research and development regarding measurement of the magnetic field with high resolution and high sampling rate, electrical exploration with accurately controlled source signals, electrical exploration tools for shallow and deep targets, versatile instruments of electrical and magnetic explorations with multi-platforms (deep-tow system, ROV (Remotely Operated Vehicle), and AUV (Automated Underwater Vehicle)), comprehensive analyses of electrical, magnetic, acoustic and thermal data, and so on. We will introduce the outline and the current state of the project (including sea trial of deep-sea magnetometer) in this presentation.
[en] Highlights: • The effect of liquid phase compositions when modeling gas hydrate systems was demonstrated. • VLE predictions were found to be greatly dependent on liquid phase compositions for two and three component systems. • Liquid composition predictions were found to be highly dependent on interaction parameters compared to gas compositions. • When interaction parameters are optimized based on vapor data only, liquid compositions of H-Lw-V systems are inadequate. -- Abstract: Liquid compositions obtained through vapor + liquid + hydrate equilibrium modeling are often neglected and not reported in literature. This work demonstrates the sensitivity and importance of the liquid phase compositions on selected models and parameters. The equations of state used to model two-phase systems are the Soave–Redlich–Kwong, the Valderrama–Patel–Teja and the Trebble–Bishnoi equations of state. The modeling analysis for three-phase systems is based on the Trebble–Bishnoi equation of state along with the model by van der Waals and Platteeuw. The vapor + liquid equilibrium model predictions at gas hydrate formation conditions were found to be greatly dependant on the liquid phase compositions. At the three-phase equilibrium, small modifications in the equation of state’s interaction parameters significantly affected the liquid composition predictions while leaving the vapor compositions mostly unchanged. Lastly, the interaction parameters were optimized for the two phases separately using vapor + liquid equilibrium data. When optimized only for liquid, vapor and liquid compositions were predicted correctly. However, when optimized only for vapor, liquid compositions failed to fit experimental data
[en] A model for the behavior of oil and gas spills at deepwater locations was presented. Such spills are subjected to pressures and temperatures that can convert gases to gas hydrates which are lighter than water. Knowing the state of gases as they rise with the plume is important in predicting the fate of an oil or gas plume released in deepwater. The objective of this paper was to develop a comprehensive jet/plume model which includes computational modules that simulate the gas hydrate formation/decomposition of gas bubbles. This newly developed model is based on the kinetics of hydrate formation and decomposition coupled with mass and heat transfer phenomena. The numerical model was successfully tested using results of experimental data from the Gulf of Mexico. Hydrate formation and decomposition are integrated with an earlier model by Yapa and Zheng for underwater oil or gas jets and plumes. The effects of hydrate on the behavior of an oil or gas plume was simulated to demonstrate the models capabilities. The model results indicate that in addition to thermodynamics, the kinetics of hydrate formation/decomposition should be considered when studying the behavior of oil and gas spills. It was shown that plume behavior changes significantly depending on whether or not the local conditions force the gases to form hydrates. 25 refs., 4 tabs., 12 figs
[en] The tundra biome has an important direct influence on the global climate through its exchange of radiatively active 'greenhouse gases', carbon dioxide and methane. A number of suggestions have been raised as to how a changing climate may alter the natural state of this exchange causing significant feedback effects in a changing climate. This paper provides a brief discussion of three different issues relating to the interaction between tundra and climate. It is concluded that release of methane hydrates, permafrost degradation and major biome changes are processes which in the long term may have important effects on further development of the global climate. (au) 32 refs