Scholarly record

COMPUTER SIMULATION OF OIL AND GAS FLOW LINE STRESS-STRAIN BEHAVIOR

Peter Burkov

Abstract

Flow lines are one of the key elements of oil field facilities as they ensure safe transport of raw multiphase mixtures of gas, oil and water from reservoir to reception facilities. The growth of oil extraction in Russia makes the issue of developing new deposits and maintaining high production of oil and gas from existing ones particularly important. Therefore, maintenance of flow lines in service is of great significance. Most of Russia?s oil production originates in West Siberia . The territory is characterized with considerable annual and daily fluctuations of temperature, high precipitation, and vast wetlands. A specific challenge is to maintain underground sections of pipeline constructed under severe climatic conditions. Pipeline failures and accidents operated under harsh climatic conditions are primarily induced by bending deformation accompanied with soil-pipe-fluid (gas) displacements. To prevent accidents that could be caused by excessive bending deformations, it is essential to analyze the impact of climatic conditions, soils, and operation parameters, as well as to reveal the most potentially dangerous pipeline sections. To detect the most dangerous sections, alongside with various technical tools and equipment, pipeline strength and stability are calculated. The following regulative documents that prescribe the procedure of underground pipeline strength calculation SNiP (construction rules and regulations) 2.05.06-85* ?Transmission pipelines? (section 8.25), set of rules 34-116-97 ?Instruction on oil and gas flow line design, construction, and repair? (section 8.1) state the requirements for simulating soil-pipe interaction. The search for new methods to calculate strain-stress behavior of underground pipelines is of particular importance as due to the great length of pipeline the increase in pipe wall thickness at least by 1 mm leads to significant overspend. It is worth noting that soil is not the only source of external load, but also serves as an environment where pipe deformations occur. At the same time, these documents do not explain the calculation procedure itself. The remaining time (RT) is estimated as the time over which defects accumulate until ultimate limit state is reached. As a rule, the procedure of RT calculation is not detailed. The calculations are done on the basis of formulas used for estimating facility life time according to the deterministic and probabilistic schemes. When using deterministic methods, the fixed data on fracture toughness, loads on pipelines and pipe defects are considered. The remaining time is predicted on the basis of safety coefficients (fracture resistance) and survivability. RT is defined as a moment when hypothetical cracks or cracks existing in the pipeline are in compliance with the safety requirements for the damaged system based on the criteria of fracture mechanics and survivability. To perform probability calculations, the reliability theory which rests on the statistic.

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