Nonlinear analysis of coupled temperature-seepage problem of warm oil pipe in permafrost regions of Northeast China

This study investigated the influence of an underground warm oil pipe on the stability of the permafrost foundation in Northeast China on the basis of a coupled mathematical model of heat transfer and seepage and the finite element method. The thawing cycles around a non-insulated oil pipe and around an oil pipe packaged with insulations of three different thicknesses were analyzed. The results show that in the case of the non-insulated pipe, the maximum thawing depth under the pipe exceeded 8 m after 30 years of operation. Further, the maximum thawing depth decreased significantly after the pipe was insulated. The thawing cycle of the permafrost foundation expanded and shrank alternately between the warm and cold seasons. The range of thermal influence of the warm oil pipe on the upper active layer was much smaller than that on the lower permafrost foundation in the vertical direction. Among the different insulation thicknesses examined (5 cm, 8 cm, and 10 cm), the 8-cm-thick insulation was found to be sufficient to keep the permafrost foundation stable when the oil temperature was maintained at 15 °C. Insulation of the underground warm oil pipe can help maintain the stability of the permafrost and reduce the disturbance of the permafrost environment. •The influence of warm oil pipe on permafrost foundation was investigated.•A model of temperature field coupled with phase change and seepage is presented.•Warm oil pipe resulted in large thawing cycle in the permafrost foundation.•Proper pipe insulation can keep the permafrost foundation stable.