Permafrost degradation induced by warm-oil pipelines and analytical results of thermosyphon-based thawing mitigation

The China–Russia Crude Oil Pipeline (CRCOP) has been in operation for more than ten years, and its oil temperature has been increasing annually. Problems with ground surface subsidence and pipeline settlement were found in geological investigations along the CRCOP, indicating the risk of pipeline instability. In this study, a system was established to monitor pipeline–permafrost interactions along the CRCOP. It was found that the seasonal thawing depth (STD) of a borehole 2 m away from the horizontal line of the CRCOP reached about 11 m in 2022. Based on the on-site measured boundary, a laboratory experiment was conducted to study the evolution of the thermal regime, and to investigate the cooling effect of thermosyphons. The results indicated the consistent existence of a thaw bulb surrounding the pipeline, which was open in warm seasons but remained closed in cold seasons and expanded in three directions at different speeds. Thermosyphoning erased the thaw bulb and altered the thermal evolution of the permafrost, with a gradually decreasing STD. The results of this research can serve as a reference for thermal regime assessments of the CRCOP and thaw settlement mitigation along the CRCOP, as well as for other counterparts across the world.