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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