Thawing of permafrost rocks when exploiting geothermal wells in Eastern Siberia

Abstract

Relevance. Ensured by well-known theses about energy security and transition to alternative energy sources, reducing environmental emissions and energy saving in various industries through the use of geothermal energy. The study of the thermal regimes of deposits of geothermal energy sources located in zones of permafrost is of particular interest. The operation of geothermal wells in permafrost is associated not only with the danger of collapses in the wellhead zone, but also with the destruction of well structures with the withdrawal of their operation for long periods of time. Aim. Numerical analysis of heat transfer in the area where geothermal wells are located, taking into account the real characteristics of a typical geological section to predict the thawing of permafrost in Eastern Siberia. Object. Typical geothermal well design, the main elements of which (columns, conductor and directions) are made of cement. Methods. The simple iteration cycle was used in conjunction with the methods of two fractional steps according to the splitting scheme and the sweep method to solve the problem by the finite difference method. At nodal points belonging to several areas, the thermophysical characteristics were calculated as arithmetic averages. The adequacy of the results of the numerical analysis is confirmed by varying the grid parameters, the energy balance at the boundaries of the calculation area, and comparing the research results with literature data. Results. The authors have carried out the analysis of heat transfer during the operation of geothermal wells in Eastern Siberia, taking into account the actual characteristics of permafrost rocks that vary with depth. It was revealed that the radii of thawing of permafrost for the conditions of Eastern Siberia are 12–17 meters. The feasibility of taking into account the dependence of the thermophysical characteristics of rocks/soils in accordance with the parameters of the geological section during the design, construction and operation of objects using geothermal energy is shown.