The Principles of Complex Geocryological Geophysical Analysis for Studying Permafrost and Gas Hydrates on the Arctic Shelf of Russia

Abstract

The active development of the Russian Arctic in the last 10 years requires relevant data on the bearing capacity of rocks on the Arctic shelf of the Russian Federation. To assess the bearing capacity of soils, knowledge of the distribution and state of permafrost on the Arctic shelf is needed. This article discusses the rationale and possibilities of the proposed integrated geocryological and geophysical analysis. The technique of the research includes sea electroprospecting works, drilling on the shelf, thermometric observations in the drilled wells, bench tests of soils, and modeling of electromagnetic and thermal fields on the shelf. It is shown that the most informative geophysical method for studying of permafrost on the shelf is electromagnetic sounding by the TEM method. The most informative geophysical method for studying of permafrost in the “land–shelf” transit zone is frequency electromagnetic (FS) sounding. In this article there are examples of the standard interpretation of geophysical data and inversion of geophysical data in the mode of the fixed model of specific electrical resistivity. Using the example of the Yamal shelf it is shown that the standard interpretation does not allow an unambiguous solution of geocryologic tasks on the shelf. Specific electric results of determination of electric properties of soils in laboratory are necessary in the case of the inversion of geophysical data in the mode of thickly stratified models and the fixed model. An important component of the proposed complex is boring and thermometric research, which provide validation of the results of geophysical inversion. Measurement of the temperatures of soils in the wells is especially important under the conditions of the Arctic shelf. Calculations for thermal models complete the complex of research. The collateral analysis of geoelectric and thermal models allows one to estimate the depth to the bottom of permafrost, as well as the thickness of gas hydrate strata. Use of the developed complex of studies on the shelf of the Pechora, Karsky, Laptev, and Chukchi Seas made it possible to obtain new ideas about the distribution permafrost rocks and the development of gas hydrates on the shelf of the seas of the Russian Arctic.