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Numerical analysis of temperature fields around the buried arctic gas pipe-line in permafrost regions

Li Xinze (State Key Laboratory of Frozen Soils Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China + College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China + Sinopec Petroleum Engineering Co., Dongying, China)
Jin Huijun (State Key Laboratory of Frozen Soils Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China + College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China + School of Civil Engineering, Northeast-China Observatory and Research-Station of Permafrost Geo-Environment-Ministry of Education, Institute of Cold-Regions Engineering, Science and Technology, Northeast Forestry University, Harbin, China), hjjin@lzb.ac.cn
Wei Yanjing (State Key Laboratory of Frozen Soils Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China + College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China)
Wen Zhi (State Key Laboratory of Frozen Soils Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China + College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China)
Li Yan (State Key Laboratory of Frozen Soils Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China + College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China)
Li Xinyu (School of Civil Engineering, Harbin Institute of Technology, Harbin, China)

Based on one planned arctic natural gas pipe-line engineering which will cross continuous, discontinuous, sporadic and non-permafrost areas from north to south, with different pipe-line temperatures set, a thermal model of the interac-tion between pipe-line and permafrost is established to investigate the influence of pipe-lines on the freezing and thawing of frozen soil around pipe-line and thermal stability of permafrost. The results show that different pipe-line temperatures influ¬ence the permafrost table greatly. Especially in discontinuous permafrost areas the permafrost table is influenced in both positive temperature and negative tempera¬ture. The warm gas pipe-line of 5℃ could decrease the value of permafrost table about 1 to 3 times pipe diameter and aggravate the degradation of permafrost around pipe-line; –1℃ and –5℃ chilled gas pipe-line can effectively improve the permafrost table and maintain the temperature stability of frozen soil, but the temperature of soils below pipe-line of –5℃ decreases obviously, which may lead to frost heave hazards. In terms of thermal stability around pipe-line, it is advised that transporting temperature of –1℃ is adopted in continuous permafrost area; in discontinuous permafrost area pipe-line could operate above freezing in the summer months with the station discharge temperature trending the ambient air temperature, but the discharge temperature must be maintained as –1℃ through¬out the winter months; in seasonal freezing soil area chilled pipe-line may cause frost heave, therefore, pipe-line should run in positive temperature without extra temperature cooling control.

Keywords: natural gas pipe-line, coupled thermal-hydraulic modeling, pipe-soil heat exchange, numerical simulation, permafrost, chilled transporting processes