Study on the water-heat coupled phenomena in thawing frozen soil around a buried oil pipeline

Buried pipelines are one of the most economical and efficient methods for long distance transportation of crude oils, but when a pipeline goes through the cold regions, it may suffer serious threats caused by the freezing and thawing problems of frozen soil. In this study, the water-heat coupled problem of frozen soil around buried hot oil pipeline in cold regions is systematically studied by means of numerical simulation. The temperature field, water content field and unfrozen water migration of frozen soil under different pipeline operation periods are obtained by pure heat conduction model and water-heat coupled model respectively to illustrate the influence of water content field on temperature distribution of frozen soil and oil temperature along the pipeline. It can be concluded from the simulation results that it is the coupled interactions of temperature distribution and water migration that determine the ultimate status of transport phenomena in frozen soil. The most obvious water migration occurs in the soil area close to the buried oil pipeline where there is the largest gradient of temperature. And the change of thermal properties caused by the water migration turns out to be one of the most important factors affecting the temperature field of frozen soil.