Thermal Properties Response And Thermal Analysis Technique Application Of Natural Gas Hydrates During The Dynamic Formation And Dissociation Process In Porous Media

Recently, natural gas hydrates are explored from both frozon area and seafloor ofChina, it is said that the hydrates resources are abundant in our country, and it is a keyway to solve the enery problem if the commercial exploitation program have beencarried out. Besides, the gas hydrates technique is also useful in some industryapplications such as hydrate transportation and energy supply systems. Unlike thecommon resource, gas hydrate stability need special high pressure and lowtemperature conditons, and the processes of formation and dissociation usuallyaccompanied with obviously themal exchange phenomenon. Therefore, in this papergas hydrates are selected as the target, and the thermal properties of hydrates arediscussed under the hydrates formation and dissociation process. Based on theexperiment method and analysis techniques established during the research, somethermal property related problems and applications are studied as well.In these experiments different compositions and ratios of the liquid phase, gasphase and solid phase are selected as the research conditions. High pressuredifferential scanning calorimetry and raman spectrum technique are used to measurethe hydrates mole dissociation heat; the self designed apparatus are used to study therelationship between the thermal conductivities of sediment and saturation of gashydrates, as well as hydrater thermal diffusion characteristics under different heatdistance, heating time and so on.Based on these researches, the method of high pressure differential scanningcalorimetry is set up especially on the heat flow analysis, thermal conductivitycalculation and thermal stimulation dissocaiton experiment procedures. Together withthe theoretical models of thermal dynamic and kinetics, some thermal relatedproblems are studied such as hydrate phase equilibrium in complex conditions,metastability characteristics of hydrate preservation, mass transfer feature during hydrate formation and the energy efficiency of thermal stimulated exploitation.Based on the research, some important findings are acquired, including:(1) aseries data of themal physical properties of hydrates are collected such as dissociationheat, thermal conductivity, thermal diffusive characteristic and phase equilibriumpoint, and the variation pattern effected by hydrates saturation are discussed;(2) thehydrate metastablility phenomenon is confirmed, ice plays an important role in thisprocess but it is not the necessary condition for hydrate meatstability;(3) the masstransfer pattern is studied through experimental method, and it is said that thepredominant way of mass transfer during hydrate formation is gas supply to thehydrate film;(4) according to the results of hydrate formation and dissociation underdifferent conditions, it is inferred that subcooling and sub excess pressure playsdifferent roles on hydrates formation, subcooling prefers to determin the length ofinduction time and excess pressure decides the saturation of gas hydrates.