Ultra Deepwater Top Tensioned Drilling Riser Structure And VIV Fatigue Analysis

Energy is the motivity of our society, and petroleum is one kind of energy usually be used now. But the oil output on land is less and less during these years, we have to go to the ocean to strive for it. By exploring, it is found that it is rich in oil and gas in our south sea, but for the water depth and the limitation of the drilling equipments of China, we don't have the ability to exploit it. So the development of deepwater and ultra deepwater drilling equipments is urgent. Mainly, this thesis is focused on the study of drilling riser which is the most important tool in deepwater drilling.Firstly, the mechanic property and VIV fatigue mechanism of the top tensioned drilling riser were illustrated based on the introduction of the development and research status of drilling riser. And the introduction of the ocean environment condition as well as the calculation methods of the current load was done which was the preparation for the following strength calculation.Secondly, the strength calculation of the ultra deepwater top tensioned drilling riser was done by using the non-linear finite element analysis software ABAQUS. The working condition were operational condition and hang-off condition, the sea condition was 10-year winter storm, and the currents were 1-year bottom current plus 1-year eddy current, 10-year eddy current and 100-year eddy current respectively. And by calculation, it was obvious that the strength of the operational condition couldn't meet the requirements of the standards as well as the hang-off condition, but through model modification, the economical and reasonable drilling riser configuration of the hang-off condition was got. Also in this part, the operability envelop of the drilling platform was defined.Thirdly, on VIV fatigue analysis, the comparison of the VIV frequency was conducted by using ABAQUS, VIV fatigue analysis software Shear7 and the theoretical calculation method refer to the reference. The best way to get the VIV frequency was obtained and applied to the calculation of the VIV fatigue life of the drilling riser. From the calculation, it was got that the fatigue life of the hang-off condition might be ignored and that of the operational condition was very short because the current speeds were very large and the riser was vulnerable.Finally, the relationship study of the drilling platform operability envelop to the top tension ratio of the drilling riser system was carried out. The top tension ratio was changed from 1.1 to 1.4 to see the changing rule of the operability envelop.From the strength analysis study in this paper, it tells us that the drilling riser of deepwater and ultra deepwater can be damaged easily. And on different working conditions, the riser should be treated differently. The operational condition is the worst working condition, and the riser should be carefully used.The strength analysis study in this thesis is an academic and practical basic to the offshore drilling equipment study, and the applicable value of this thesis is evident.