The influence of porous medium and temperature regime on the formation and gas composition in hydrates of multicomponent gas mixtures

Abstract

The relevance of the study of multicomponent gas mixtures hydrate formation in porous media is due to the widespread occurrence of gas hydrates on the shelf of seas and continents, which requires experimental work to study the effect of a porous medium on the distribution of natural gas components between the gas and hydrate phases in order to understand the processes of hydrate deposit formation. Natural gas from the Srednevilyui field was used to obtain hydrates, in which the sum of C2-C4 homologues is 7.08 mol%. The object of the study was hydrates of this gas obtained in bidispersed quartz sand with a humidity of 15%. Phase transitions during cooling and heating of the «natural gas - sand – water» system were studied by differential thermal analysis. The experiments were conducted in two modes of system cooling: the first mode up to 270.5 K, the second mode up to 279 K. Analysis of the gas composition in the hydrate was determined by gas adsorption chromatography. It was found that in a porous medium natural gas forms a mixture of hydrates with cubic structure sI (methane hydrate) and sII (gas hydrate with a higher content of hydrocarbons C2-C4 (18.73 mol.)), and, as experiments have shown, this mixture can be thermodynamically separated. Based on the conducted study, it was concluded that when gas migrates through the thickness of sedimentary rocks in the area of high temperatures at depth, a deposit of hydrates with a high content of hydrocarbons C2-C4 can be formed, and closer to the surface, where the temperature of the rock decreases, methane hydrate can accumulate.