Hydrate Formation in Natural Gas

In compounds with water, many of the constituents of natural gas (methane, ethane, propane, isobutane, carbon dioxide, nitrogen, and hydrogen sulfide) form so-called gas hydrates, which are solid crystalline compounds that resemble compressed snow and exist above 0° C at high pressures.

Structurally, gas hydrates are inclusion compounds (clathrates) formed by trapping of gas molecules (M) in the voids of crystalline structures consisting of H₂O molecules. Gas hydrates have the general formula M · nH₂O, with n varying from 5.75 to 17 depending on gas composition and conditions under which the hydrates are formed.

During the extraction of gas, hydrates may form in the shafts of boreholes, industrial supply lines, and gas mains. The hydrates, which form on the walls of tubes, greatly reduce the tubes’ transmission capacity. To combat hydrates in gas fields, various inhibitors are introduced into the boreholes and pipelines (methanol, glycols, 30-percent CaCl₂ solution), or the temperature of the gas flow is maintained above the temperature of hydrate formation by means of heaters, insulated pipelines, or the choice of operating conditions to give maximum gas-flow temperature. Drying is the most effective way of preventing hydrate formation in gas mains.

Hydrate formation is used for the desalinization of sea-water. A number of methods for storing natural and inert gases (argon, krypton, and xenon) as hydrates have also been patented. In 1970, Soviet scientists demonstrated the basic possibility of the existence of natural-gas deposits of gas hydrates in regions of permafrost. The creation of effective methods of prospecting for and exploitation of such deposits will considerably increase gas resources.