Title page for ETD etd-10062005-222419


Type of Document Dissertation
Author Lin, Fang
Author's Email Address flin@vt.edu
URN etd-10062005-222419
Title Experimental Study of the PVTX Properties of the System H2O-CH4
Degree PhD
Department Geosciences
Advisory Committee
Advisor Name Title
Bodnar, Robert J. Committee Chair
Dove, Patricia M. Committee Member
Read, James Fredrick Committee Member
Schreiber, Madeline E. Committee Member
Sum, Amadeu K. Committee Member
Keywords
  • synthetic fluid inclusions
  • Raman spectroscopy
  • methane hydrate
  • H2O-CH4 system
  • PVTX properties
  • phase equilibria
Date of Defense 2005-09-23
Availability unrestricted
Abstract
The system H2O-CH4 is found in a variety of geological environments in the earth's crust,

from sedimentary basins to low grade metamorphic terrains. Knowledge of the Pressure-

Volume-Temperature-Composition (PVTX) properties of the H2O-CH4 system is

necessary to understand the role that these fluids play in different geological

environments. In this study the properties of the H2O-CH4 fluid system at elevated

temperatures and pressures has been investigated experimentally to determine the PVTX

properties of H2O-CH4 fluids in the P-T range equivalent to late diagenetic to low grade

metamorphic environments, and CH4 mole fraction less than and equal to 4mol%. A study has also been conducted to

determine methane hydrate stability over the temperature range of -40~20 degree Celsius. Synthetic

fluid inclusions were employed in both studies as miniature autoclaves.

Experimental data for the PVTX properties of H2O-CH4 fluids under late

diagenetic to low grade metamorphic conditions was used to calculate the slopes of iso-

Th lines (the line connecting the P-T conditions of the inclusions at formation and at

homogenization) at different PTX conditions. An empirical equation to describe the slope

of iso-Th line as a function of homogenization temperature and fluid composition was

developed. The equation is applicable to natural H2O-CH4 fluid inclusions up to 500 degree Celsius

and 3 kilobars, for fluid compositions less than and equal to 4 mol% CH4.

The Raman peak position of CH4 gas is a function of the pressure and temperature.

This relationship was used to determine the pressure along the methane hydrate stability

curve in the H2O-CH4 system. The combined synthetic fluid inclusion, microthermometry

and Raman spectroscopy method is a novel experimental approach to determine the P-T

stability conditions of methane hydrates. The method is fast compared to conventional

methods, and has the potential to be applied to study other gas hydrate systems.

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