HR: 0800h
AN: T21C-0518    [Abstracts]
TI: Thermodynamically Sufficient Models of Multicomponent Multiphase Fluid Flow, Transport and Phase Transformation in Geological Environments
AU: Wu, X
EM: wux@mail.c-geos.ac.cn
AF: Institute of Geology and Geophysics, Chinese Academy of Science, Beijing, 100029 China
AU: * Xu, W
EM: wenyue.xu@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 United States
AB: Various geodynamic processes involving fluids of multiple chemical components in multiple phases. Examples include those of partial melt in the mantle, mid-ocean ridge hydrothermal systems, natural gas hydrate systems, oil/gas reservoirs, etc. Understanding phase transformation, flow and transport processes of geofluids is of great interest to many in the geoscience society. Models have been developed to quantify dynamic processes involved in these geosystems and most of them are successful to certain degree. However, many of them are not developed to sufficiently model one or more important features and need to be either modified or completely rewritten. Yet in other cases, it may not even become immediately clear how a model may be modified or what a thermodynamically sufficient model is for a particular problem. Since most geodynamic processes operate in large time scales and may be viewed as taking place under conditions fairly close to thermodynamic equilibrium, we propose to use the Gibbs phase rule or its extended version to guide us in developing thermodynamically sufficient models. In principle, the behavior of a geodynamic system can be sufficiently described as long as the thermodynamic state everywhere in the system is known. A certain number of independent thermodynamic properties are needed to specify the state. These parameters can be obtained by solving governing equations constructed according to the relevant conservation laws. This has been the normal practice of the modelers of many geodynamic processes. However, questions such as (1) how many independent thermodynamic properties and (2) which thermodynamic properties are independent to each other confuse many of us from time to time. According to the extended Gibbs phase rule, for a system consisting of NC chemical components, the number of independent thermodynamic properties that are required to specify the state is NC+1. For the purpose of this study, thermodynamic properties may be classified into two types ­C homogeneous and nonhomogeneous. We call those having the same value in coexistent phases, such as pressure, temperature and chemical potentials, as homogeneous and the rest nonhomogeneous. The original Gibbs phase rule tells us that, for a system consisting of NC chemical components and NP coexistent phases, the number of the homogeneous properties that are independent to each other is NC-NP+2. Hydrothermal systems and gas hydrate systems will be used as examples to demonstrate what we have learned from this study. We will show whether and why they are either thermodynamically sufficient or not in modeling geodynamic systems. Finally, a formalized set of governing equations and constitutive equations of phase partition is presented for modeling geodynamic systems consisting of multiple chemical components and coexistent phases.
DE: 1000 GEOCHEMISTRY
DE: 3200 MATHEMATICAL GEOPHYSICS (0500, 4400, 7833)
DE: 4465 Phase transitions
DE: 8100 TECTONOPHYSICS
DE: 8400 VOLCANOLOGY
SC: Tectonophysics [T]
MN: Fall Meeting 2005