Sergey Grebenkin

1. Natural gas in the shallow crust can exist in either free or hydrate (clathrate) form. Gas hydrates are ice-like, crystalline water-based solids that form under specific temperature and pressure...

Recent global warming trends are degrading Arctic permafrost, posing risks to the construction of facilities and leading to increased emission of greenhouse gases. Methane emitted from thawing permafrost may be released by dissociation of intrapermafrost gas hydrates. Northern West Siberian permafrost contains two hydrate-bearing layers: the present zone of gas hydrate stability below 200 m depth and a shallow metastable hydrate zone (150–200 m) preserved from past geological conditions due to the self-preservation effect. Original laboratory tests on the kinetics of phase transitions revealed considerable differences in thermal responses of hydrate-bearing sediments under different pressures and temperatures close to in situ permafrost conditions. According to the experimental results, stable pore gas hydrates are resistant to warming and dissociate only within the range of positive temperatures determined by the equilibrium gas pressure. On the contrary, metastable pore gas hydrates are highly sensitive to thermal effects and prone to rapid dissociation, as they dissociate at some critical temperatures ∼1.0°С–1.5°С below the thawing point for non-saline sand. In this respect, the geotechnical and environmental risks associated with gas production from high-latitude West Siberian reservoirs can be reduced by incorporating the empirical temperature of pore gas hydrate dissociation into the design, in addition to the permafrost thawing temperature.

In the unique and highly variable territories of the Arctic, average annual air temperatures have been rising over the past few decades, which affects the increase in the depth of seasonal thawing of permafrost, activates thermokarst processes, and leads to changes in the bearing capacity of soils. As a result, the tasks of developing technical solutions for the therm stabilization of foundations, geocryological and geotechnical monitoring, and engineering-geocryological forecasting of territories come to the forefront. One of the main methods for observing the temperature regime of soils is the establishment of permanent thermometric boreholes, which allow for the assessment of both annual and multi-year temperature fluctuations. Based on this principle, the State Background Monitoring System is being created in Russia. However, the state of the temperature regime of the upper layers of the cryolithozone can also be assessed through numerous temperature measurements in boreholes during engineering surveys. The presence of hundreds of measured boreholes allows for the elimination of erroneous values using statistical methods and obtaining a distribution of values across the entire studied area. The article describes methodological approaches to creating a digital model of the upper layers of the cryolithozone in Western Yamal, based on the method of matrix zoning using statistical data processing methods and regression-correlation analysis to identify dependencies between the parameters of relief, landscapes, and the geological environment. The model is based on data from engineering surveys as well as data from remote sensing methods. The proposed approach allows for a comprehensive analysis and monitoring of the state of frozen layers in the territory, as well as the identification of technological and economic complexities during the design and operation of structures. Based on the obtained data, patterns were established for the interpolation and extrapolation of engineering-geocryological conditions in areas with insufficient degrees of study. As a result, a model database was formed with characteristics necessary for conducting thermal engineering forecasts using numerical methods, on the basis of which a dynamic geoinformation model of permafrost conditions was created. The practical significance of the developed approaches lies in their versatility for application in planning activities in the cryolithozone. They can be effectively used in engineering surveys for the development of project documentation, conducting thermal engineering forecasts of soil temperatures at the design stage, as well as within the framework of geotechnical monitoring during the operation of facilities.