HR: 16:45h
AN: OS34B-04    [Abstracts]
TI: Systematic Specification of Thermodynamic State and Phase Transition Processes of Natural Gas Hydrate Systems
AU: * Xu, W
EM: wenyue.xu@eas.gatech.edu
AF: School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 United States
AB: Natural gas hydrate systems, either in permafrost areas or under the seafloor, consist of water, salts, gases, and their combinations in various phases, reside in and interact with host sediments, and constantly undergo dynamic evolution and interact with environmental changes. Dynamic processes within these systems are further complicated by numerous feedback mechanisms involved. Modeling and simulation are therefore one of the indispensable approaches in studying natural gas hydrate systems. Specification of thermodynamic state and phase transition processes, and mathematical description of conservation laws are the two essential tasks that need to be done before carrying out any successful numerical simulation work. According to the state postulate in thermodynamics, the total number of components (water, salts, gases and their compounds) of a natural gas hydrate system determines the number of the independent parameters required to specify the thermodynamic state of the system. The maximum number of properties that are homogeneous to all phases of a system in thermodynamic equilibrium, such as pressure, temperature and chemical potentials, that may be used together as the independent thermodynamic parameters is limited by the Gibbs phase rule. Therefore, it is critically important to first carefully choose the number and proper types of independent properties to specify the thermodynamic state of and phase transition processes involved in the system. Pressure and temperature are usually not appropriate to be used together as two of the independent thermodynamic parameters since they are dependent to each other along the gas hydrate stability boundary. Consequently, models using both pressure and temperature as independent thermodynamic parameters are not able to quantify phase transition processes along the gas hydrate stability boundary. A non-homogeneous thermodynamic property should be chosen to replace a non-independent homogeneous property. Examples will be discussed for systems of water-gas and water-gas-salt, and systems containing multiple gases.
DE: 3919 Equations of state
DE: 3939 Physical thermodynamics
DE: 3022 Marine sediments--processes and transport
DE: 3210 Modeling
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting