Earth’s Cryosphere, 2024, Vol. XXVIII, No. 4, p. 33-43.

GASES AND GAS HYDRATES IN THE EARTH’S CRYOSPHERE

METHOD OF RAPID ESTIMATION OF THE EFFECT OF THE HYDRATE-FORMING GAS PRESSURE ON NONCLATHRATED WATER CONTENT IN SOILS

V.A. Istomin1,2,*, D.V. Sergeeva2, E.M. Chuvilin2, B.A. Bukhanov2, N.S. Sokolova2

1 Gazprom VNIIGAZ LLC, Malokhtinsky prosp. 45A, St. Petersburg, 195112 Russia
2 Center for Petroleum Science and Engineering, Skolkovo Institute of Science and Technology, Bolshoi Boulevard 30/1, Moscow, 121205 Russia
*Corresponding author; e-mail: vlistomin@yandex.ru

Natural gas hydrates exist in porous media at high pressure and low temperature, including permafrost. The development of express methods for calculating hydrate phase equilibria in soils and sediments, including the equilibrium content of nonclathrated water, i.e., the pore water, which is in equilibrium with hydrate and hydrate-forming gas under given thermobaric conditions, is of special interest in the study of natural hydrates. Nonclathrated water is similar to unfrozen water in frozen soils. The current study covers thermodynamic relationships for calculating nonclathrated water content in soil under certain thermobaric conditions on the basis of experimental data of pore water activity and soil water content. It is shown that at a fixed temperature the nonclathrated water content sharply decreases according to a power law during an increase in gas pressure. The results of thermodynamic calculation are in agreement with direct measurements of nonclathrated water in soil systems using the contact method. Thus, at temperatures below 0°C, the content of nonclathrated water in kaolinite clay and in sandy clayey soils decreases by more than two times with an increase in methane pressure from 2.3 to 11 MPa. The obtained relationships allow us to recalculate the nonclathrated water content upon transition from one hydrate-forming gas to another, as well as calculate nonclathrated water content using the unfrozen water content curve at different temperatures. The developed thermodynamic approach can be applied to various hydrate-forming gases and their mixtures.

Keywords: gas hydrates, sediments, pore water, phase equilibria, nonclathrated water, unfrozen water, ice, thermodynamic calculations.

Recommended citation: Istomin V.A., Sergeeva D.V., Chuvilin E.M., Bukhanov B.A., Sokolova N.S., 2024. Method of rapid estimation of the effect of the hydrate-forming gas pressure on nonclathrated water content in soils. Earth’s Cryosphere XXVIII (4), 33–43.

Received January 30, 2024
Revised May 27, 2024
Accepted June 23, 2024
Translated by E.S. Shelekhova