On the base of a mathematical model of thermal field in a nonuniform frozen soil from a heat source located on the surface of the ground, a vertical flare system used to gas flaring in northern oil and gas fields is simulated. Long-time forecasts of permafrost degradation around this system is obtained for different operations, including emergencies, due to which there is a short-term heat flow increasing near the surface of the ground, leading to a further increasing of the soil temperature. Computations were carried out for different scenarios, regular operation of the flare system and different versions of insulation surface (riprap) of the permafrost soil for the purpose of making recommendations on the optimal choice of the structure of heat-insulating riprap layers to reduce the thermal effects on the permafrost. By computer simulation an acceptable depth is determined, which may be used for heat insulating materials with limited operating temperature range (e.g., for penoplex the temperature has to be no greater than 70оC). Also the features of thermal field propagation in the soil are considered in detail, taking into account different physical and climatic factors. In particular, it was found that the emergency temperature increasing near the ground surface within fifteen days, after six months the temperature of the surface soil layer is not more than 1оC in compare with regular operation. The results of numerical simulation transferred to practical use for one of the northern Russian oil and gas fields.