A mathematical model of the conjugate heat transfer of the well was developed subject to phase transitions and drilling fluid circulation during the drilling. Calculations were carried out for the permafrost thaw process around a well while drilling using by solutions with different ethylene glycol contents. It was established the main regularities of conjugate thermohydraulic processes during the drilling of permafrost subject to thawing and solution circulation. It was shown the addition of ethylene glycol leads to a decrease of the heat transfer coefficient and the quantity of heat entering the well, which in turn leads to a significant slowdown in the thawing permafrost process.