PENETRATION OF HEAT INTO PERMAFROST DURING SEALING WELLS WITH DIFFERENT THERMAL CONDUCTIVITY CEMENTING MATERIALS

Permafrost rocks are widespread on the globe. Problems arise at all stages of well con-struction, when we are drilling wells in these regions. In the process of drilling the well, it is possible to formation of cavities and increase the diameter of the well. At the stage of cementing wells, problems arise due to a sharp slowing down of the hydration of bind-ers when the temperature is lowered. Lower temperatures significantly increase the wait-ing time for the solidification of cement, which is necessary for the cement slurryto obtain the required strength, at which further work is possible. Therefore, in order to reduce the intensity of the thermal interaction in the «well-ground» system, it is important to estimate the probability of thawing the near-wellbore zone thaw-ing during its operation. In the process of the analytical solution a vertical well passing through the thickness of the permafrost was considered. In the examined well the rocks are homogeneous and isotropic, the density of the frozen rock is equal to the thawing density, heat is transferred only due to thermal conductivity, and when the front of phase transitions in the permafrost is moving, mass transfer of liquid fluids does not take place. The temperature across the thickness of each casing was assumed unchanged, because the coefficient of thermal conductivity of casing steel is several tens of times higherthan the thermal conductivity of cement stone. In the problem, a mathematical model of a vertical well having a four-layer support con-sisting of casing columns and cement casings with different thermal conductivity is considered. In this case, numerical estimates of the temperature change in the multilayer support were obtained by using different sealing materials. The results of the calculations showed that even using of cementing materials with low thermal conductivity leads to thawing of the near-wellbore zone of the permafrost, and the question is only the timing of the thawing of the rocks around the well and the time of their loss of stability.