title: Thermodynamic calculations in the system CH4-H2O and methane hydrate phase equilibria.
abstract: Using the Gibbs function of reaction, equilibrium pressure, temperature conditions for the formation of methane clathrate hydrate have been calculated from the thermodynamic properties of phases in the system CH4-H2O. The thermodynamic model accurately reproduces the published phase-equilibria data to within +/-2 K of the observed equilibrium boundaries in the range 0.08-117 MPa and 190-307 K. The model also provides an estimate of the third-law entropy of methane hydrate at 273.15 K, 0.1 MPa of 56.2 J mol(-1) K(-1) for 1/nCH4.H2O, where n is the hydrate number. Agreement between the calculated and published phase-equilibria data is optimized when the hydrate composition is fixed and independent of the pressure and temperature for the conditions modeled.
authors.affiliation: U.S. Geological Survey, 345 Middlefield Rd. MS 977, Menlo Park, California 94025, USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Circone
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Kirby
authors.forename: Laura A
authors.initials: LA
authors.lastname: Stern