Experimental study of the PVTX properties of the system water-methane

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 XCH4≤4mol%. A study has also been conducted to determine methane hydrate stability over the temperature range of -40∼20°C. 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-T h line as a function of homogenization temperature and fluid composition was developed. The equation is applicable to natural H2O-CH 4 fluid inclusions up to 500°C and 3 kilobars, for fluid compositions ≤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-CH 4 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.