Abstract
The freezing-thawing processes of the soil around the buried oil and gas pipelines in permafrost regions due to the effect of the pipe and atmospheric environment may bring about dangers to the pipelines as frost heave and thaw settlement occur and go on, and then the buried pipes may face huge challenges for safe operation. To analyze the thermal effect of the buried pipe on the surrounding soil, a two-dimensional computational model of the soil temperature fields was established based on the process of the heat transfer with phase change in the soil. The temperature fields and the thaw characteristics of the soil around the operating pipeline in permafrost regions were studied using numerical methods via the software FLUENT in this paper. The developments of the maximum thawed cylinders and corresponding thaw depths under the pipeline within operation life cycle were predicted and analyzed for various medium temperatures, water contents of soils, insulation layer thicknesses and imposed boundary conditions by climatic warming. In addition, the maximum thaw settlement of the soil under the pipeline in 5 typical permafrost areas along the Russia — China oil pipeline (the section in China) within operation life cycle was calculated. The medium temperatures were assumed to be constant and sinusoidal. The results indicated that the maximum thaw depths and thawed cylinders around the pipeline in permafrost regions enlarged with time elapse and the decrease in water content of the soils under the same boundary conditions. The maximum thaw depths and thawed cylinders increased with the increase of medium temperatures after the same operation time. The insulation layer weakened heat exchange between the pipeline and the surrounding soils and thus reduced the development of the thawed cylinders effectively during the early operation period. This research may provide an effective method for engineering application, and the results may provide references for predicting the thaw settlement of the soil and pipeline in permafrost regions.
