The formation of plugs in pipelines and well shafts caused by deposition of paraffins, resins, or gas hydrates often complicates oil and gas production. In the process of exploitation of wells, asphalt-resin-paraffin deposits are formed on the surfaces of tubing strings as a result of decreases in temperature and pressure. In some cases, they completely clog the space between pipes, which stops production from a well. The results of laboratory investigations and industrial tests show that one promising method of controling the formation of plugs is the use of high-frequency electromagnetic heating [1][2][3].From the point of view of radio engineering, the internal space of a well equipped with a tubing string is a coaxial transmission line along which electromagnetic radiation with a frequency of up to .~ 10 l~ Hz (the frequency is not limited from below) and power P ..~ 10-20 kW can be directed. Meeting a plug, the electromagnetic radiation heats it to the melting point or decomposition temperature and thereby eliminates the obstacle. The advantages of this heating method over the usual methods (hot water, electric heater, etc.) are, first, volume heating of the plug (owing to deep penetration of the electromagnetic radiation), i.e., heating is much more rapid and uniform in volume, and, second, the absence of a heat-transfer agent, which makes control of the heating process easy and adaptable.In order to achieve maximum effectiveness (in velocity and maximum depth of melting), it is necessary to choose correctly the radiation frequency, which determines the absorption factor a and the related depth of electromagnetic radiation penetration 1 = 1/a. If the factor a is too small (a very great depth of penetration l), a considerable part of radiation power goes through the plug or is distributed over a great length and is dissipated through the pipe walls without providing the required heating. When the factor a is too large (a very small depth l), a large amount of the power is absorbed in the layers of the plug substance that are the nearest to the radiator. This causes overheating of the layers and intense energy dissipation through the corresponding sections of the lateral wall. In both cases, heating is not effective, and the depth of melting is small. Consequently, there are optimum values of e for which the greatest depth and rate of melting are achieved (for given plug dimensions and conditions of heat exchange). Finding of these optimum values is the aim of the paper.In addition, for some substances in a certain frequency range the factor o~ depends significantly (in a resonant way) on temperature, and this can be used to increase the effectiveness of heating. If the radiation frequency is chosen correctly, heating can be realized in the "thermM wave" regime, and its rate can be substantially increased. Moreover, using the nonlinear function v~ (T), we can obtain a temperature wave moving in the opposite direction: from the remote end of the plug to the radiation source, i.e., an effect which is impossible...
