Numerical analysis on hydrothermal process around oil pipeline in permafrost regions of Qinghai-Tibet Plateau

• Published in: Heat and mass transfer Vol. 59; no. 4; pp. 763 - 778
• Main Authors: Lan, Tianli, Luo, Xiaoxiao, Ma, Qinguo
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.04.2023; Springer Nature B.V
• Subjects: Degradation; Engineering; Engineering Thermodynamics; Freeze thaw cycles; Geotemperature; Heat and Mass Transfer; Heat exchange; Industrial Chemistry/Chemical Engineering; Mathematical models; Mechanical properties; Numerical analysis; Original Article; Permafrost; Petroleum pipelines; Physical properties; Pipelines; Soil mechanics; Soil properties; Soil stability; Soil water; Stability analysis; Temperature effects; Thermodynamics; Unsaturated soils
• ISSN: 0947-7411; 1432-1181
• DOI: 10.1007/s00231-022-03299-8

Heat exchange between the oil pipeline and the permafrost leads to the geotemperature redistribution and permafrost degradation, threatening the pipeline stability. The water redistribution during freeze–thaw cycles affects the physical and mechanical properties of soil and induces heat convection. However, the hydro-thermal process of unsaturated soil around pipeline in permafrost regions still lacks comprehensive analysis. For this problem, a numerical hydro-thermo-vapor coupling model fully considering the contribution of vaporous water to water redistribution and the thermal effect of water migration in unsaturated soil was established, and the soil water and temperature distributions were analyzed. The results show that: (1) The proposed model is feasible to simulate the hydro-thermal process of soil during freezing process. (2) Oil pipeline significantly degrades underlying permafrost. The thermal effect of water migration deepens the permafrost table and aggravates the permafrost degradation. (3) Soil water not only accumulates near the permafrost table, but also migrates toward the pipeline bottom in the form of vaporous water. The influence of pipeline on permafrost is underestimated only from the aspect of temperature. The water redistribution should also be considered to evaluate the pipeline stability. (4) Insulation layer can effectively maintain the thermal state of permafrost. Water accumulation on the pipeline side will lead to soil slide downward, which is a potential threat to pipeline stability.