Mechanical Coupling Analysis Of Pipe-in-pipe System In Typical Sea Condition

With the increasing demand of oil resource,oil development in deep sea has already become hot technology at home and abroad.Due to complex and terrible characteristics of marine environment,compared with operation on land,working under sea could be more difficult.Pipe-in-pipe system,which is made up by the riser and coiled tubing,is one of the most important devices to link the wellhead and platform on the sea.As the depth of water increases,force analysis will become more complex,and injection and failure problems will be more highlighted.In this case,it is necessary to study behavior characteristics of Pipe-in-pipe system systematically.Considering the difficulty and complexity of coupling model establishment,this article divides the establishing process into three parts: fixed boundary model,floating boundary model and model in ocean loads.Using infinitesimal method to model in each step,simplifying the model by Intermediate difference method,and finally solving the model by iterative scheme set up by Newton-Raphson method.At the same time,a vertical bench has been built up,not only experimental results but also simulation results observed by ABAQUS have been used to prove the accuracy of the model.Practicability of the model is also confirmed by practical examples.Based on research above,some factors such as outer diameter of coiled tubing,water depth,platform migration,friction coefficient has be studied to figure out the effect on axis load transmission efficiency.Deformation and bending moment of the riser are also studied to form appropriate work window about air and tidal velocity,which offers reference to practical operation to some degree.