Natural gas hydrates are solid, non-stoichiometric compounds of small gas molecules and water. They form when the constituents come into contact at low temperature and high pressure. The physical properties of these compounds, most notably that they are non-flowing crystalline solids that are denser than typical fluid hydrocarbons and that the gas molecules they contain are effectively compressed, give rise to numerous applications in the broad areas of energy and climate effects. In particular, they have an important bearing on flow assurance and safety issues in oil and gas pipelines, they offer a largely unexploited means of energy recovery and transportation, and they could play a significant role in past and future climate change.

Fundamental principles and applications of natural gas hydrates

Structure and nanostructure in ionic liquids.

Pore fluids strongly influence the seismic properties of rocks. The densities, bulk moduli, velocities, and viscosities of common pore fluids are usually oversimplified in geophysics. We use a combination of thermodynamic relationships, empirical trends, and new and published data to examine the effects of pressure, temperature, and composition on these important seismic properties of hydrocarbon gases and oils and of brines. Estimates of in-situ conditions and pore fluid composition yield more accurate values of these fluid properties than are typically assumed. Simplified expressions are developed to facilitate the use of realistic fluid properties in rock models. Pore fluids have properties that vary substantially, but systematically, with composition, pressure, and temperature. Gas and oil density and modulus, as well as oil viscosity, increase with molecular weight and pressure, and decrease with temperature. Gas viscosity has a similar behavior, except at higher temperatures and lower pressures, where the viscosity will increase slightly with increasing temperature. Large amounts of gas can go into solution in lighter oils and substantially lower the modulus and viscosity. Brine modulus, density, and viscosities increase with increasing salt content and pressure. Brine is peculiar because the modulus reaches a maximum at a temperature from 40 to 80°C. Far less gas can be absorbed by brines than by light oils. As a result, gas in solution in oils can drive their modulus so far below that of brines that seismic reflection bright spots may develop from the interface between oil saturated and brine saturated rocks.

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Seismic properties of pore fluids

The volumetric and thermodynamic functions correlated by Pitzer and co-workers analytically represented with improved accuracy by a modified BWR equation of state. The representation provides a smooth transition between the original tables of Pitzer et al. and more recent extensions to lower temperatures. It is in a form particularly convenient for computer use.

A generalized thermodynamic correlation based on three‐parameter corresponding states

High-pressure adsorption of methane, carbon dioxide, and nitrogen on zeolite 13X was measured in the pressure range (0 to 5) MPa at (298, 308, and 323) K and fitted with the Toth and multisite Langmuir models. Isosteric heats of adsorption were (12.8, 15.3, and 37.2) kJ/mol for nitrogen, methane, and carbon dioxide respectively, which indicate a very strong adsorption of carbon dioxide. The preferential adsorption capacity of CO2 on zeolite 13X was much higher than for the other gases, indicating that zeolite 13X can be used for methane purification from natural gas or for carbon dioxide sequestration from flue gas.

Adsorption Equilibrium of Methane, Carbon Dioxide, and Nitrogen on Zeolite 13X at High Pressures

Effect of high pressure on gas hydrate equilibrium curve determined experimentally for methane, argon and nitrogen hydrates

Hydrates at high pressures: Part I. Methane‐water, argon‐water, and nitrogen‐water systems

Physicochemical measurements by gas chromatography

Vapor-Liquid Equilibria For Binary Hydrocarbon-Water Systems

Viscosity of Hydrocarbon Gases Under Pressure

Measurements of the bubble-point compositions are reported and combined with dew-point data to give K-values for the methane--n-butane system at 40/sup 0/, 0/sup 0/, -20/sup 0/, -40/sup 0/, -60/sup 0/, -80/sup 0/, -100/sup 0/, -116.6/sup 0/, -120/sup 0/, -140/sup 0/, -160/sup 0/, -180/sup 0/, and -200/sup 0/F from the vapor pressure of n-butane up to critical point of the vapor pressure of methane. Experimental conditions were selected so that direct isobaric observations were also possible. Results showed significant deviations in the low-temperature range of the NGPSA critical loci as based on the experimental results of J. J. McKetta et al. from +40/sup 0/F to -140/sup 0/F. Data, however, are consistent in the high-temperature range as based on the data of B. H. Sage et al. from 70/sup 0/F to 250/sup 0/F. The 13 isotherms shown are constructed from data obtained from both experimental procedures.

Riki Kobayashi

Papers

Hydrates at high pressures: Part I. Methane‐water, argon‐water, and nitrogen‐water systems

Physicochemical measurements by gas chromatography

Vapor-Liquid Equilibria For Binary Hydrocarbon-Water Systems

Viscosity of Hydrocarbon Gases Under Pressure

Vapor-liquid equilibrium of methane-n-pentane system at low temperatures and high pressures