Numerical Simulation For Couplings Of Water, Temperature And Stress Fields Of Underground Oil Pipeline In Cold Region

At present, underground pipelines engineering constructed by China and Russia, Kazakhstan have been completed. The petroleum and natural gas pipelines all go through permafrost regions in northeastern China. The pipeline from desert-river to Daqing is in the permafrost regions. The soil frost heaving and thaw have already affected the safety of the pipeline engineering. This paper is depending on Chinese Petroleum Corporation Funded Project"Oil pipelines optimization and operation safety technology". Based on the heat transfer, percolation mechanics and frost heaving mechanics theory, the thermal physical parameters under different conditions in seasonal frozen soil were systematically studied. The relation of the temperature field and water field was deeply analyzed. The frost heaving and thaw deformation of the underground oil pipeline caused by permafrost temperature, moisture and the stress and strain field couplings was stated. Main research results are as follows:Numerical calculation for economic buried depth of oil and gas pipelines in cold region based on temperature field equationConsidered the initial soil temperature cyclical changes, the different average surface temperature and soil freeze conditions, the unsteady temperature field equation of underground oil pipeline soil was established. The temperature fields of underground pipeline in Daqing are calculated by using finite element method. The trend of temperature fields for a variety of buried depth was studied, and the more appropriate buried depth of pipelines was calculated. Not considering the soil freezing and non-frozen state effect on natural temperature, when the pipeline operation management analyzed. Numerical calculation for soil temperature field of underground pipeline considering effects of moisture in cold region Aimed to frozen and melted soil in the frozen soil area, and considering the latent heat of phase change and water movement, the frozen soil temperature field around underground pipeline is numerically calculated. The results show that the latent heat of phase change and water movement has certain effects on the soil temperature field. These factors should be considered in calculations.Numerical calculation for water and heat couplings of marsh developmental soil around underground pipelines in cold regionThe soil water and heat couplings mathematics model were established as porous medium. Based on the finite volume theory, the conservation of mass, momentum and energy conservation equations were put forward. The temperature field of marsh developmental frozen soil, the thaw curve and migration velocity vector diagram were numerically simulated in a period of time. The permafrost and thawing process were affected by temperature and moisture transfer. The relation of underground pipelines different insulation layer thickness and permafrost thawing process was studied. The influence of soil porosity and permeability was analyzed.Numerical simulation for couplings of water, temperature and stress fields of underground oil pipeline in cold regionThe mechanism of frozen soil frost heaving and thaw was analyzed. The mathematics model of couplings of water, temperature and stress fields was established in cold region. The model was discreted and calculated by finite elements method. The temperature, moisture and frost heaving stress and strain fields influented by the soil surface air temperature were numerically calculated during a period of time. The soil freezing displacement was studied. Soil deformation and frost heaving have close relationship with water ice transformation temperature. Based on the pipeline's bending deformation, the stress and strain was calculated. Whether the stress destruction will happen was determined.