Mechanical Analysis And Design Of Drilling Riser Under Ice Load

Drilling riser is an important structure in the process of safe exploitation,production and transportation of oil and gas.As global oil and gas demand increases,the development of oil and gas gradually going to Arctic waters,the service environment of the riser becomes more stringent,and the consequences are usually very serious once the drilling riser are damaged.For drilling operations in polar ice areas,the effect of ice load on the riser is much greater than that of other loads.Therefore,it is necessary to strengthen the mechanical properties and anti-icing design of the riser system under ice load.In this paper,the mechanical response of the drilling riser under ice load and the rapid release of the riser are studied.Finally,the preliminary discussion on the anti-icing design of the riser is carried out.The main research contents are as follows:(1)For the impact between single-floating ice and drilling riser,the material experiment of the steel strip and the PE used in MSFP and collision experiment between MSFP and ice were designed.The stress-strain curves of the steel strip and PE were obtained through material experiments.For the overall model experiment,the analysis of four groups of working conditions under pure current and wave current at 40cm and 50cm water depths was performed.Each group of working conditions is selected for research with different current velocity and wave height,the changes of the strain in the collision area and the top tension of the riser are discussed and analyzed.The finite element model was first established by Abaqus finite element software.The finite element analysis of pure current conditions at two water depths were carried out.Errors of the top tension between finite element model and experiment are within 10%,which verifies the correctness of the finite element model.Finally,the relevant parameter analysis was performed,which include the effects of ice speed,ice thickness and water depth.(2)For the impact between crushed ice and drilling riser,A discrete element modeling method is proposed to analyze the impact of crushed ice and riser.Compared with the previous method of simulating ice load directly in finite element,it is more accurate and reliable.The ice force of the riser during the collision increases with the increase of ice thickness,riser size,and sea ice density.(3)A drift theoretical analysis method is proposed,the theoretical analysis results and the overall analysis results of orcaflex finite element are mutually confirmed,and the results fit well.The critical time of each warning ring obtained in the finite element analysis can be used to guide the engineering practice.(4)For the anti-ice design scheme of the riser system,a literature survey and preliminary discussion are carried out.Different shape of the riser can have different form of collision damage,thereby reducing the response of the riser system;and adding a layer of armor at a certain height outside the riser can effectively protect the riser.