Natural Gas Hydrates

Abstract

Natural gases under pressure form crystalline hydrates with water.Experimental data are reported on four-phase equilibrium for themethane-propane-water, methane-pentane-water, and methane-hexane-water systems.Temperatures and pressures for equilibrium between gas, water-rich liquid, hydrocarbon-rich liquid, and hydrate were measured, as well as the percentagesof methane and propane in the hydrate. The data indicate that natural gashydrate behaves as a solid solution and that pentanes and heavier hydrocarbonsdo not enter into the solid phase. Vapor-solid equilibrium constants arepresented that permit the approximation of the conditions for hydrateformation, from the composition of a gas. Introduction Natural gas hydrates have been the object of considerable research in recentyears, because of the trouble they have caused in the natural-gas andnatural-gasoline industries. Natural gas hydrates are white crystallinecompounds of water and gas, which, under pressure, exist at temperaturesconsiderably above the freezing point of water. Because of the relatively hightemperatures at which the hydrates exist, they become a nuisance inhigh-pressure gas operations where water is present, since their formationcauses partial or complete plugging of valves and pipes. From a practicalstandpoint, the trouble incident to hydrate formation has been solved bydehydration of the gas before it enters the plant or pipe line, or by otherremedial measures. Extensive work on gas hydrates in the latter part of the nineteenth century, by Villard and others, gave data on methane hydrate and on ethane hydrate.Schroeder summarized these theoretical studies, Hammerschmidt introduced theinformation on gas hydrates to the gas industry, and Deaton and Frost gathereda considerable number of data on the behavior of natural gas hydrates. Recentpapers have extended both the data and the theory of these hydrates. At present, data are available on temperatures and pressures of hydrateformation for pure methane, ethane, propane, n-butane, methane-ethane mixtures, methane-propane mixtures, methane-butane mixtures, and some 15 natural gases, all in the presence of excess water. However, up to the present time no methodhas been available for predicting the temperature at given pressures or thepressure at given temperatures at which natural gases will form hydrates ifsaturated with water. T.P. 1371