Methane hydrate formation and dissociation in synthetic seawater

The formation and dissociation of methane gas hydrate at an interface between synthetic seawater （SSW） and methane gas have been experimentally investigated in the present work. The amount of gas consumed during hydrate formation has been calculated using the real gas equation. Induction time for the formation of hydrate is found to depend on the degree of subcooling. All the experiments were conducted in quiescent system with initial cell pressure of 11.14 MPa. Salinity effects on the onset pressure and temperature of hydrate formation are also observed. The dissociation enthalpies of methane hydrate in synthetic seawater were determined by Clausius-Clapeyron equation based on the measured phase equilibrium data. The dissociation data have been analyzed by existing models and compared with the reported data.

Water transfer characteristics during methane hydrate formation and dissociation processes inside saturated sand

Gas hydrates formation and dissociation processes inside porous media are always accompanied by water transfer behavior, which is similar to the water behavior of ice freezing and thawing processes. These processes have been studied by many researchers, but all the studies are so far on the water transfer characteristics outside porous media and the water transfer characteristics inside porous media have been little known. In this study, in order to study the water transfer characteristics inside porous media during methane hydrate formation and dissociation processes, a novel apparatus with three pF-meter sensors which can detect water content changes inside porous media was applied. It was experimentally observed that methane hydrate formation processes were accompanied by water transfer from bottom to top inside porous media, however, the water behavior during hydrate dissociation processes was abnormal, for which more studies are needed to find out the real reason in our future work.

Comparison of the water change characteristics between the formation and dissociation of methane hydrate and the freezing and thawing of ice in sand

Hydrate formation and dissociation processes are always accompanied by water migration in porous media, which is similar to the ice. In our study, a novel pF-meter sensor which could detect the changes of water content inside sand was first applied to hydrate formation and dissociation processes. It also can study the water change characteristics in the core scale of a partially saturated silica sand sample and compare the differences of water changes between the processes of formation and dissociation of methane hydrate and freezing and thawing of ice. The experimental results showed that the water changes in the processes of formation and dissociation of methane hydrate were basically similar to that of the freezing and thawing of ice in sand. When methane hydrate or ice was formed, water changes showed the decrease in water content on the whole and the pF values rose following the formation processes. However, there were very obvious differences between the ice thawing and hydrate dissociation.

Water transfer characteristics in the vertical direction during methane hydrate formation and dissociation processes inside non-saturated media

In order to study water transfer characteristics inside non-saturated media during methane hydrate formation and dissociation processes,water changes on the top,middle and bottom locations of experimental media during the reaction processes were continuously followed with a novel apparatus with three pF-meter sensors.Coarse sand,fine sand and loess were chosen as experimental media.It was experimentally observed that methane hydrate was easier formed inside coarse sand and fine sand than inside loess.Methane hydrate formation configuration and water transfer characteristics during methane hydrate formation processes were very different among the different non-saturated media,which were important for understanding methane hydrate formation and dissociation mechanism inside sediments in nature.

Nuclear magnetic resonance study of the formation and dissociation process of nature gas hydrate in sandstone

In this work,the authors monitored the formation and dissociation process of methane hydrate in four different rock core samples through nuclear magnetic resonance(NMR)relaxation time(T_(2))and 2D imaging measurement.The result shows that the intensity of T_(2) spectra and magnetic resonance imaging(MRI)signals gradually decreases in the hydrate formation process,and at the same time,the T_(2) spectra move toward the left domain as the growth of hydrate in the pores of the sample accelerates the decay rate.The hydrate grows and dissociates preferentially in the purer sandstone samples with larger pore size and higher porosity.Significantly,for the sample with lower porosity and higher argillaceous content,the intensity of the T_(2) spectra also shows a trend of a great decrease in the hydrate formation process,which means that high-saturation gas hydrate can also be formed in the sample with higher argillaceous content.The changes in MRI of the sample in the process show that the formation and dissociation of methane hydrate can reshape the distribution of water in the pores.

A comprehensive analysis of formation conditions,intrinsic properties,and mechanical responses of gas hydrate-bearing sediments

Natural gas hydrates(NGH)stored in submarine deposits are a promising energy resource,Yet,the deterioration in sediment strength can trigger geological disasters due to drilling-induced hydrate dissociation.Hence,an in-depth investigation on geo physical-mechanical performance of gas hydrate-bearing sediments(GHBS)is crucial for recovery hydrates safely and efficiently.This paper provides a comprehensive assessment of the research progress on formation conditions,intrinsic properties,and mechanical responses of GHBS.The key findings have been presented:gas composition,inhibitors and promoters alter hydrate formation by modifying the thermodynamic equilibrium of temperature and pressure.Also,we identified the key determinants of porosity of GHBS and revealed the correlation between permeability,hydrate saturation,and hydrate morphology.Moreover,we highlighted the differences in mechanical behavior between hydrate-free sediments and GHBS along with their underlying mechanisms.Furthermore,we examined the methods for GHBS preparation as well as the employed test apparatuses,providing critical insights into the limitations and recommendations.By synthe-sizing data from existing literature,we conducted a comprehensive analysis of the dependence of mechanical parameters of GHBS on factors such as hydrate saturation,effective confining stress,and temperature,and dis-cussed the mechanical responses subjected to various hydrate dissociation methods.Finally,we offer a perspective for future research to focus on the micro-scale aspects,heterogeneous distribution,and long-term stability of GHBS.The discerned patterns and mechanical mechanisms are expected to guide the improvement of predictive model for geo physical-mechanical behavior of GHBS and establish a reference for developing effective strategies for recovery hydrates.

Some Recent Progress on Quark Pairings in Dense Quark and Nuclear Matter

In this review article we give a brief overview on some recent progress in quark pairings in dense quark/nuclear matter mostly developed in the past five years.We focus on following aspects in particular:the BCS-BEC crossover in the CSC phase,the baryon formation and dissociation in dense quark/nuclear matter,the Ginzburg-Landau theory for three-flavor dense matter with UA(1) anomaly,and the collective and Nambu-Goldstone modes for the spin-one CSC.